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1.  The coumarin scopoletin potentiates acetylcholine release from synaptosomes, amplifies hippocampal long-term potentiation and ameliorates anticholinergic- and age-impaired memory 
Neuroscience  2011;197(1):280-292.
In a previous study the simple, naturally derived coumarin scopoletin (SCT) was identified as an inhibitor of acetylcholinesterase (AChE), using a pharmacophore-based virtual screening approach. In this study the potential of SCT as procholinergic and cognition-enhancing therapeutic was investigated in a more detailed way, using different experimental approaches like measuring newly synthesized acetylcholine (ACh) in synaptosomes, long-term potentiation (LTP) experiments in hippocampal slices, and behavior studies. SCT enhanced the K+-stimulated release of ACh from rat frontal cortex synaptosomes, showing a bell-shaped dose effect curve (Emax: 4 μM). This effect was blocked by the nicotinic ACh receptor (nAChR) antagonists mecamylamine (MEC) and dihydro-β-erythroidine (DHE). The nAChR agonist (and AChE inhibitor) galantamine induced a similar increase in ACh release (Emax: 1 μM). SCT potentiated LTP in hippocampal slices of rat brain. The high-frequency stimulation (HFS)-induced, N-methyl-D-aspartate (NMDA) receptor dependent LTP of field excitatory postsynaptic potentials at CA3-CA1 synapses was greatly enhanced by pre-HFS application of SCT (4 μM for 4 min). This effect was mimicked by nicotine (2 μM) and abolished by MEC, suggesting an effect on nAChRs. SCT did not restore the total inhibition of LTP by NMDA receptor antagonist d, l-2-amino-5-phosphonopentanoic acid (AP-5). SCT (2 μg, i.c.v.) increased T-maze alternation and ameliorated novel object recognition of mice with scopolamine-induced cholinergic deficit. It also reduced age-associated deficits in object memory of 15–18-month-old mice (2 mg/kg sc). Our findings suggest that SCT possesses memory-improving properties, which are based on its direct nAChR agonistic activity. Therefore, SCT might be able to rescue impaired cholinergic functions by enhancing nAChR-mediated release of neurotransmitters and promoting neural plasticity in hippocampus.
Highlights
▶The coumarin scopoletin has been described as AChE inhibitor. ▶Now we show it exerts promising procognitive properties via nAChRs. ▶It enhances release of ACh and potentiates hippocampal LTP. ▶It improves novel object recognition and T-maze alternation in scopolamine-amnestic mice and ameliorates object memory in age-impaired mice.
doi:10.1016/j.neuroscience.2011.09.006
PMCID: PMC3212650  PMID: 21945033
ACh release; long-term potentiation; hippocampus slice; nicotinic acetylcholine receptor; T-maze; object recognition; ACh, acetylcholine; AChE, acetylcholinesterase; AD, Alzheimer's dementia; AP-5, d,l-2-amino-5-phosphonopentanoic acid; CSF, cerebrospinal fluid; DHE, dihydro-β-erythroidine; DMSO, dimethyl sulfoxide; fEPSPs, field excitatory postsynaptic potentials; HFS, high-frequency stimulation; LTP, long-term potentiation; MAO, monoamino oxidase; MEC, mecamylamine; nAChR, nicotinic acetylcholine receptor; NMDA, N-methyl-D-aspartate; SCOP, scopolamine; SCT, scopoletin
2.  ATP-Citrate Lyase Is Required for Production of Cytosolic Acetyl Coenzyme A and Development in Aspergillus nidulans▿ 
Eukaryotic Cell  2010;9(7):1039-1048.
Acetyl coenzyme A (CoA) is a central metabolite in carbon and energy metabolism and in the biosynthesis of cellular molecules. A source of cytoplasmic acetyl-CoA is essential for the production of fatty acids and sterols and for protein acetylation, including histone acetylation in the nucleus. In Saccharomyces cerevisiae and Candida albicans acetyl-CoA is produced from acetate by cytoplasmic acetyl-CoA synthetase, while in plants and animals acetyl-CoA is derived from citrate via ATP-citrate lyase. In the filamentous ascomycete Aspergillus nidulans, tandem divergently transcribed genes (aclA and aclB) encode the subunits of ATP-citrate lyase, and we have deleted these genes. Growth is greatly diminished on carbon sources that do not result in cytoplasmic acetyl-CoA, such as glucose and proline, while growth is not affected on carbon sources that result in the production of cytoplasmic acetyl-CoA, such as acetate and ethanol. Addition of acetate restores growth on glucose or proline, and this is dependent on facA, which encodes cytoplasmic acetyl-CoA synthetase, but not on the regulatory gene facB. Transcription of aclA and aclB is repressed by growth on acetate or ethanol. Loss of ATP-citrate lyase results in severe developmental effects, with the production of asexual spores (conidia) being greatly reduced and a complete absence of sexual development. This is in contrast to Sordaria macrospora, in which fruiting body formation is initiated but maturation is defective in an ATP-citrate lyase mutant. Addition of acetate does not repair these defects, indicating a specific requirement for high levels of cytoplasmic acetyl-CoA during differentiation. Complementation in heterokaryons between aclA and aclB deletions for all phenotypes indicates that the tandem gene arrangement is not essential.
doi:10.1128/EC.00080-10
PMCID: PMC2901662  PMID: 20495057
3.  Effects of lowering extracellular and cytosolic pH on calcium fluxes, cytosolic calcium levels, and transmitter release in presynaptic nerve terminals isolated from rat brain 
The Journal of General Physiology  1988;91(2):305-315.
We examined the effects of extracellular and intracellular pH changes on the influx of radioactive 45Ca, the concentration of ionized Ca (pCai) as monitored with the Ca-sensitive fluorescent indicator fura-2, and the efflux of dopamine in presynaptic nerve endings (synaptosomes) isolated from rat brain corpora striata and preloaded with [3H]dopamine. Cytosolic pH (pHi) was monitored by loading the synaptosomes with the H+-sensitive fluorescent indicator 2',7'- bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) (see Nachshen, D. A., and P. Drapeau, 1988, Journal of General Physiology, 91:289-303). An abrupt decrease of the pH of the external medium, from 7.4 to 5.5, produced a slow decrease of pHi (over a 5-min period) from an initial value of 7.2 to a steady state level of approximately 5.8. When 20 mM acetate was present in acidic media, pHi dropped as fast as could be measured (within 2 s) to a level similar to that reached (more slowly) in the absence of acetate. It was therefore possible to lower pHi over short time periods to different levels depending on whether or not acetate was present upon extracellular acidification. Extracellular acidification to pH 5.5 (in the absence of acetate) had no significant effect on pCai and dopamine release over a 30-s period (pHi = 6.4). Acidification in the presence of acetate lowered pHi to 5.8 without affecting pCai, but dopamine efflux increased approximately 20-fold. This increase in basal dopamine release was also observed in the absence of extracellular Ca. Thus, intraterminal, but not extracellular, acidification could stimulate the efflux of dopamine in a Ca-independent manner. The high Q10 (3.6) of acid-stimulated dopamine efflux in the presence of nomifensine (which blocks the dopamine carrier) was consistent with an activation of vesicular dopamine release by H+. When synaptosomes were both depolarized for 2 s in high- K (77.5 mM) solutions and acidified (in the absence of acetate), there was a parallel block of 45Ca entry and evoked dopamine release (50% block at pH 6.0 with 0.2 mM external Ca). When acetate was included in the acidic media to further reduce pHi, Ca entry remained blocked, but evoked dopamine release was increased. Therefore, extracellular, but not cytosolic, acidification inhibited the release of dopamine by blocking voltage-gated Ca channels. The stimulation by cytosolic acidification of both basal and evoked dopamine release suggests that vesicular release in resting and depolarized synaptosomes was directly activated by cytoplasmic H+.
PMCID: PMC2216128  PMID: 3373181
4.  Enzymic analysis of the crabtree effect in glucose-limited chemostat cultures of Saccharomyces cerevisiae. 
The physiology of Saccharomyces cerevisiae CBS 8066 was studied in glucose-limited chemostat cultures. Below a dilution rate of 0.30 h-1 glucose was completely respired, and biomass and CO2 were the only products formed. Above this dilution rate acetate and pyruvate appeared in the culture fluid, accompanied by disproportional increases in the rates of oxygen consumption and carbon dioxide production. This enhanced respiratory activity was accompanied by a drop in cell yield from 0.50 to 0.47 g (dry weight) g of glucose-1. At a dilution rate of 0.38 h-1 the culture reached its maximal oxidation capacity of 12 mmol of O2 g (dry weight)-1 h-1. A further increase in the dilution rate resulted in aerobic alcoholic fermentation in addition to respiration, accompanied by an additional decrease in cell yield from 0.47 to 0.16 g (dry weight) g of glucose-1. Since the high respiratory activity of the yeast at intermediary dilution rates would allow for full respiratory metabolism of glucose up to dilution rates close to mumax, we conclude that the occurrence of alcoholic fermentation is not primarily due to a limited respiratory capacity. Rather, organic acids produced by the organism may have an uncoupling effect on its respiration. As a result the respiratory activity is enhanced and reaches its maximum at a dilution rate of 0.38 h-1. An attempt was made to interpret the dilution rate-dependent formation of ethanol and acetate in glucose-limited chemostat cultures of S. cerevisiae CBS 8066 as an effect of overflow metabolism at the pyruvate level. Therefore, the activities of pyruvate decarboxylase, NAD+- and NADP+-dependent acetaldehyde dehydrogenases, acetyl coenzyme A (acetyl-CoA) synthetase, and alcohol dehydrogenase were determined in extracts of cells grown at various dilution rates. From the enzyme profiles, substrate affinities, and calculated intracellular pyruvate concentrations, the following conclusions were drawn with respect to product formation of cells growing under glucose limitation. (i) Pyruvate decarboxylase, the key enzyme of alcoholic fermentation, probably already is operative under conditions in which alcoholic fermentation is absent. The acetaldehyde produced by the enzyme is then oxidized via acetaldehyde dehydrogenases and acetyl-CoA synthetase. The acetyl-CoA thus formed is further oxidized in the mitochondria. (ii) Acetate formation results from insufficient activity of acetyl-CoA synthetase, required for the complete oxidation of acetate. Ethanol formation results from insufficient activity of acetaldehyde dehydrogenases.(ABSTRACT TRUNCATED AT 400 WORDS)
PMCID: PMC184133  PMID: 2566299
5.  Presynaptic Nicotinic α7 and Non-α7 Receptors Stimulate Endogenous GABA Release from Rat Hippocampal Synaptosomes through Two Mechanisms of Action 
PLoS ONE  2011;6(2):e16911.
Background
Although converging evidence has suggested that nicotinic acetylcholine receptors (nAChR) play a role in the modulation of GABA release in rat hippocampus, the specific involvement of different nAChR subtypes at presynaptic level is still a matter of debate. In the present work we investigated, using selective α7 and α4β2 nAChR agonists, the presence of different nAChR subtypes on hippocampal GABA nerve endings to assess to what extent and through which mechanisms they stimulate endogenous GABA release.
Methodology/Findings
All agonists elicited GABA overflow. Choline (Ch)-evoked GABA overflow was dependent to external Ca2+, but unaltered in the presence of Cd2+, tetrodotoxin (TTX), dihydro-β-erythroidine (DHβE) and 1-(4,4-Diphenyl-3-butenyl)-3-piperidinecarboxylic acid hydrochloride SKF 89976A. The effect of Ch was blocked by methyllycaconitine (MLA), α-bungarotoxin (α-BTX), dantrolene, thapsigargin and xestospongin C, suggesting that GABA release might be triggered by Ca2+ entry into synaptosomes through the α7 nAChR channel with the involvement of calcium from intracellular stores. Additionally, 5-Iodo-A-85380 dihydrochloride (5IA85380) elicited GABA overflow, which was Ca2+ dependent, blocked by Cd2+, and significantly inhibited by TTX and DHβE, but unaffected by MLA, SKF 89976A, thapsigargin and xestospongin C and dantrolene. These findings confirm the involvement of α4β2 nAChR in 5IA85380-induced GABA release that seems to occur following membrane depolarization and opening calcium channels.
Conclusions/Significance
Rat hippocampal synaptosomes possess both α7 and α4β2 nAChR subtypes, which can modulate GABA release via two distinct mechanisms of action. The finding that GABA release evoked by the mixture of sub-maximal concentration of 5IA85380 plus sub-threshold concentrations of Ch was significantly larger than that elicited by the sum of the effects of the two agonists is compatible with the possibility that they coexist on the same nerve terminals. These findings would provide the basis for possible selective pharmacological strategies to treat neuronal disorders that involve the dysfunction of hippocampal cholinergic system.
doi:10.1371/journal.pone.0016911
PMCID: PMC3034729  PMID: 21346795
6.  The α5 neuronal nicotinic acetylcholine receptor subunits plays an important role in the sedative effects of ethanol but does not modulate consumption in mice 
Background
Alcohol use disorders (AUDs) are a major public health problem, and the few treatment options available to those seeking treatment offer only modest success rates. There remains a need to identify novel targets for the treatment of AUDs. The neuronal nicotinic acetylcholine receptors (nAChRs) represent a potential therapeutic target in the brain, as recent human genetic studies have implicated gene variants in the α5 nAChR subunit as high risk factors for developing alcohol dependence.
Methods
Here, we evaluate the role of α5* nAChR for ethanol-mediated behaviors using male α5+/+ and α5−/− mice. We characterized the effect of hypnotic doses of ethanol and investigated drinking behavior using an adapted Drinking-in-the Dark (DID) paradigm that has been shown to induce high ethanol consumption in mice.
Results
We found the α5 subunit to be critical in mediating the sedative effects of ethanol. The α5−/− mice showed slower recovery from ethanol-induced sleep, as measured by loss of righting reflex. Additionally the α5−/− mice showed enhanced impairment to ethanol-induced ataxia. We found the initial sensitivity to ethanol and ethanol metabolism to be similar in both α5+/+ and α5−/− mice. Hence the enhanced sedation is likely due to a difference in the acute tolerance of ethanol in α5−/− mice. However the α5 subunit did not play a role in ethanol consumption for ethanol concentrations ranging from 5% to 30% using the DID paradigm. Additionally, varenicline was effective in reducing ethanol intake in α5−/− mice.
Conclusion
Together, our data suggest that the α5 nAChR subunit is important for the sedative effects of ethanol but does not play a role in ethanol consumption in male mice. Varenicline can be a treatment option even when there is loss of function of the α5 nAChR subunit.
doi:10.1111/acer.12009
PMCID: PMC3901849  PMID: 23164049
α5 nAChR; ethanol; mice; varenicline
7.  Role of Acetyl Coenzyme A Synthesis and Breakdown in Alternative Carbon Source Utilization in Candida albicans▿  
Eukaryotic Cell  2008;7(10):1733-1741.
Acetyl coenzyme A (acetyl-CoA) is the central intermediate of the pathways required to metabolize nonfermentable carbon sources. Three such pathways, i.e., gluconeogenesis, the glyoxylate cycle, and β-oxidation, are required for full virulence in the fungal pathogen Candida albicans. These processes are compartmentalized in the cytosol, mitochondria, and peroxosomes, necessitating transport of intermediates across intracellular membranes. Acetyl-CoA is trafficked in the form of acetate by the carnitine shuttle, and we hypothesized that the enzymes that convert acetyl-CoA to/from acetate, i.e., acetyl-CoA hydrolase (ACH1) and acetyl-CoA synthetase (ACS1 and ACS2), would regulate alternative carbon utilization and virulence. We show that C. albicans strains depleted for ACS2 are unviable in the presence of most carbon sources, including glucose, acetate, and ethanol; these strains metabolize only fatty acids and glycerol, a substantially more severe phenotype than that of Saccharomyces cerevisiae acs2 mutants. In contrast, deletion of ACS1 confers no phenotype, though it is highly induced in the presence of fatty acids, perhaps explaining why acs2 mutants can utilize fatty acids. Strains lacking ACH1 have a mild growth defect on some carbon sources but are fully virulent in a mouse model of disseminated candidiasis. Both ACH1 and ACS2 complement mutations in their S. cerevisiae homolog. Together, these results show that acetyl-CoA metabolism and transport are critical for growth of C. albicans on a wide variety of nutrients. Furthermore, the phenotypic differences between mutations in these highly conserved genes in S. cerevisiae and C. albicans support recent findings that significant functional divergence exists even in fundamental metabolic pathways between these related yeasts.
doi:10.1128/EC.00253-08
PMCID: PMC2568070  PMID: 18689527
8.  Cholinergic Modulation of Locomotion and Striatal Dopamine Release is Mediated by α6α4* Nicotinic Acetylcholine Receptors 
The Journal of Neuroscience  2010;30(29):9877-9889.
Dopamine (DA) release in striatum is governed by firing rates of midbrain DA neurons, striatal cholinergic tone, and nicotinic ACh receptors (nAChRs) on DA presynaptic terminals. DA neurons selectively express α6* nAChRs, which show high ACh and nicotine sensitivity. To help identify nAChR subtypes that control DA transmission, we studied transgenic mice expressing hypersensitive α6L9′S* receptors. α6L9′S mice are hyperactive, travel greater distance, exhibit increased ambulatory behaviors such as walking, turning, and rearing, and show decreased pausing, hanging, drinking, and grooming. These effects were mediated by α6α4* pentamers, as α6L9′S mice lacking α4 subunits displayed essentially normal behavior. In α6L9′S mice, receptor numbers are normal, but loss of α4 subunits leads to fewer and less sensitive α6* receptors. Gain-of-function nicotine-stimulated DA release from striatal synaptosomes requires α4 subunits, implicating α6α4β2* nAChRs in α6L9′S mouse behaviors. In brain slices, we applied electrochemical measurements to study control of DA release by α6L9′S nAChRs. Burst stimulation of DA fibers elicited increased DA release relative to single action potentials selectively in α6L9′S, but not WT or α4KO/α6L9′S, mice. Thus, increased nAChR activity, like decreased activity, leads to enhanced extracellular DA release during phasic firing. Bursts may directly enhance DA release from α6L9′S presynaptic terminals, as there was no difference in striatal DA receptor numbers or DA transporter levels or function in vitro. These results implicate α6α4β2* nAChRs in cholinergic control of DA transmission, and strongly suggest that these receptors are candidate drug targets for disorders involving the DA system.
doi:10.1523/JNEUROSCI.2056-10.2010
PMCID: PMC3390922  PMID: 20660270
nicotinic; nicotine; dopamine; striatum; nucleus accumbens; midbrain; substantia nigra; ventral tegmental area; addiction; Parkinson's disease; hyperactivity; acetylcholine; cholinergic; locomotion; motor; reward
9.  Brain cholinergic impairment in liver failure 
Brain  2008;131(11):2946-2956.
The cholinergic system is involved in specific behavioural responses and cognitive processes. Here, we examined potential alterations in the brain levels of key cholinergic enzymes in cirrhotic patients and animal models with liver failure. An increase (∼30%) in the activity of the acetylcholine-hydrolyzing enzyme, acetylcholinesterase (AChE) is observed in the brain cortex from patients deceased from hepatic coma, while the activity of the acetylcholine-synthesizing enzyme, choline acetyltransferase, remains unaffected. In agreement with the human data, AChE activity in brain cortical extracts of bile duct ligated (BDL) rats was increased (∼20%) compared to controls. A hyperammonemic diet did not result in any further increase of AChE levels in the BDL model, and no change was observed in hyperammonemic diet rats without liver disease. Portacaval shunted rats which display increased levels of cerebral ammonia did not show any brain cholinergic abnormalities, confirming that high ammonia levels do not play a role in brain AChE changes. A selective increase of tetrameric AChE, the major AChE species involved in hydrolysis of acetylcholine in the brain, was detected in both cirrhotic humans and BDL rats. Histological examination of BDL and non-ligated rat brains shows that the subcellular localization of both AChE and choline acetyltransferase, and thus the accessibility to their substrates, appears unaltered by the pathological condition. The BDL-induced increase in AChE activity was not parallelled by an increase in mRNA levels. Increased AChE in BDL cirrhotic rats leads to a pronounced decrease (∼50–60%) in the levels of acetylcholine. Finally, we demonstrate that the AChE inhibitor rivastigmine is able to improve memory deficits in BDL rats. One week treatment with rivastigmine (0.6 mg/kg; once a day, orally, for a week) resulted in a 25% of inhibition in the enzymatic activity of AChE with no change in protein composition, as assessed by sucrose density gradient fractionation and western blotting analysis. In conclusion, this study is the first direct evidence of a cholinergic imbalance in the brain as a consequence of liver failure and points to the possible role of the cholinergic system in the pathogenesis of hepatic encephalopathy.
doi:10.1093/brain/awn209
PMCID: PMC2577805  PMID: 18772221
cirrhosis; hepatic encephalopathy; cerebral cortex; acetylcholinesterase; acetylcholine
10.  PROTEASOME INHIBITOR TREATMENT REDUCED FATTY ACID, TRIACYLGLYCEROL AND CHOLESTEROL SYNTHESIS 
In the present study, the beneficial effects of proteasome inhibitor treatment in reducing ethanol-induced steatosis were investigated. A microarray analysis was performed on the liver of rats injected with PS-341 (Bortezomib, Velcade®), and the results showed that proteasome inhibitor treatment significantly reduced the mRNA expression of SREBP-1c, and the downstream lipogenic enzymes, such as fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), which catalyzes the carboxylation of acetyl-CoA to malonyl-CoA, the rate-limiting step in fatty acid synthesis. ELOVL6, which is responsible for fatty acids long chain elongation, was also significantly down regulated by proteasome inhibitor treatment. Moreover, PS-341 administration significantly reduced the expression of acyl-glycerol-3-phosphate acyltransferase (AGPAT), and diacylglycerol acyltransferase (DGAT), enzyme involved in triacylglycerol (TAG) synthesis. Finally, PS-341 was found to down regulate the enzymes 3-hydroxy-3-methylglutaryl-CoenzymeA synthase (HMG-CoA synthase) that is responsible for cholesterol synthesis. Proteasome inhibitor was also found to play a role in intestinal lipid adsorption because apolipoproteins A (apoA-I, apoAII, apoA-IV and ApoCIII) were down regulated by proteasome inhibitor treatment, especially ApoA-II that is known to be a marker of alcohol consumption. Proteasome inhibitor treatment also decreased apobec-1 complementation factor (ACF) leading to lower level of editing and production of ApoB protein. Moreover apolipoprotein C-III, a major component of chylomicrons was significantly down regulated. However, lipoprotein lipase (Lpl) and High density lipoprotein binding protein (Hdlbp) mRNA levels were increased by proteasome inhibitor treatment. These results suggested that proteasome inhibitor treatment could be used to reduce the alcohol-enhanced lipogenesis and alcohol-induced liver steatosis. A morphologic analysis, performed on the liver of rats fed ethanol for one month and treated with PS-341, showed that proteasome inhibitor treatment significantly decreased ethanol-induced liver steatosis. SREBP-1c, FAS and ACC were increased by ethanol feeding alone, but were significantly decreased when proteasome inhibitor was administered to rats fed ethanol. Our results also show that both mRNA and protein levels of these lipogenic enzymes, up regulated by ethanol, were then down regulated when proteasome inhibitor was administered to rats fed ethanol. It was also confirmed that alcohol feeding caused an increase in AGPAT and DGAT, which was prevented by proteasome inhibitor treatment of the animal fed ethanol. Chronic alcohol feeding did not affect the gene expression of HMG-CoA synthase. However, PS341 administration significantly reduced the HMG-CoA synthase mRNA levels, confirming the results obtained with the microarray analysis. C/EBP transcription factors alpha (CCAAT/enhancer-binding protein alpha) has been shown to positively regulate SREBP-1c mRNA expression, thus regulating lipogenesis. Proteasome inhibition caused a decrease in C/EBP alpha mRNA expression, indicating that C/EBP down regulation may be the mechanism by which proteasome inhibitor treatment reduced lipogenesis. In conclusion, our results indicate that proteasome activity is not only involved in down regulating fatty acid synthesis and triacylglycerol synthesis, but also cholesterol synthesis and intestinal lipid adsorption. Proteasome inhibitor, administrated at a non-toxic low dose, played a beneficial role in reducing lipogenesis caused by chronic ethanol feeding and these beneficial effects are obtained because of the specificity and reversibility of the proteasome inhibitor used.
doi:10.1016/j.yexmp.2012.03.006
PMCID: PMC4197193  PMID: 22445925
Fatty acid; Triacylglycerol and Cholesterol Synthesis; Proteasome inhibitor
11.  A role for α4(non-α6)* nicotinic acetylcholine receptors in motor behavior 
Neuropharmacology  2013;73:19-30.
Nicotinic acetylcholine receptors (nAChRs) containing either the α4 and/or α6 subunit are robustly expressed in dopaminergic nerve terminals in dorsal striatum where they are hypothesized to modulate dopamine (DA) release via acetylcholine (ACh) stimulation from cholinergic interneurons. However, pharmacological blockade of nAChRs or genetic deletion of individual nAChR subunits, including α4 and α6, in mice, yields little effect on motor behavior. Based on the putative role of nAChRs containing the α4 subunit in modulation of DA in dorsal striatum, we hypothesized that mice expressing a single point mutation in the α4 nAChR subunit, Leu9′Ala, that renders nAChRs hypersensitive to agonist, would exhibit exaggerated differences in motor behavior compared to WT mice. To gain insight into these differences, we challenged WT and Leu9′Ala mice with the α4β2 nAChR antagonist dihydro-β-erythroidine (DHβE). Interestingly, in Leu9′Ala mice, DHβE elicited a robust, reversible motor impairment characterized by hypolocomotion, akinesia, catalepsy, clasping, and tremor; whereas the antagonist had little effect in WT mice at all doses tested. Pre-injection of nicotine (0.1 mg/kg) blocked DHβE-induced motor impairment in Leu9′Ala mice confirming that the phenotype was mediated by antagonism of nAChRs. In addition, SKF 82958 (1 mg/kg) and amphetamine (5 mg/kg) prevented the motor phenotype. DHβE significantly activated more neurons within striatum and substantia nigra pars reticulata in Leu9′Ala mice compared to WT animals, suggesting activation of the indirect motor pathway as the circuit underlying motor dysfunction. ACh evoked DA release from Leu9′Ala striatal synaptosomes revealed agonist hypersensitivity only at α4(non-α6)* nAChRs. Similarly, α6 nAChR subunit deletion in an α4 hypersensitive nAChR (Leu9′Ala/α6KO) background had little effect on the DHβE-induced phenotype, suggesting an α4(non-α6)* nAChR-dependent mechanism. Together, these data indicate that α4(non-α6)* nAChR have an impact on motor output and may be potential molecular targets for treatment of disorders associated with motor impairment.
doi:10.1016/j.neuropharm.2013.05.001
PMCID: PMC3784255  PMID: 23688922
nicotinic acetylcholine receptor; motor behavior; basal ganglia; dopamine
12.  Metabolomics and mass isotopomer analysis as a strategy for pathway discovery: Pyrrolyl and cyclopentenyl derivatives of the pro-drug of abuse, levulinate 
Chemical research in toxicology  2012;26(2):213-220.
We recently reported that levulinate (4-ketopentanoate) is converted in the liver to 4-hydroxypentanoate, a drug of abuse, and that the formation of 4-hydroxypentanoate is stimulated by ethanol oxidation. We also identified 3 parallel β-oxidation pathways by which levulinate and 4-hydroxypentanoate are catabolized to propionyl-CoA and acetyl-CoA. We now report that levulinate forms three seven-carbon cyclical CoA esters by processes starting with the elongation of levulinyl-CoA by acetyl-CoA to 3,6-diketoheptanoyl-CoA. The latter gamma-diketo CoA ester undergoes two parallel cyclization processes. One process yields a mixture of tautomers, i.e., cyclopentenyl- and cyclopentadienyl-acyl-CoAs. The second cyclization process yields a methyl-pyrrolyl-acetyl-CoA containing a nitrogen atom derived from the epsilon nitrogen of lysine, but without carbons from lysine. The cyclic CoA esters were identified in rat livers perfused with levulinate, and in livers and brains from rats gavaged with calcium levulinate ± ethanol. Lastly, 3,6-diketoheptanoyl-CoA, like 2,5-diketohexane, pyrrolates free lysine and, presumably, lysine residues from proteins. This may represent a new pathway for protein pyrrolation. The cyclic CoA esters and related pyrrolation processes may play a role in the toxic effects of 4-hydroxypentanoate.
doi:10.1021/tx3003643
PMCID: PMC3997259  PMID: 23171137
gamma diketones; CoA esters; lysine; pyrrolation; 4-hydroxypentanoate
13.  Immunophilin regulation of neurotransmitter release. 
Molecular Medicine  1996;2(3):325-333.
BACKGROUND: The immunophilins are proteins that mediate actions of immunosuppressant drugs such as FK506 and cyclosporin A by binding to calcineurin, inhibiting its phosphatase activity, and increasing the phosphorylation level of transcription factors required for interleukin 2 formation. Though concentrations in the brain greatly exceed levels in immune tissues, no function has been previously established for nervous system immunophilins. Nitric oxide (NO) has been implicated in neurotransmitter release. FK506 appears to inhibit NO production by maintaining NO synthase in a highly phosphorylated and thereby inactivated state. Accordingly, we examined effects of FK506 and cyclosporin A on neurotransmitter release in PC12 cells treated with nerve growth factor (NGF) and in rat brain striatal synaptosomes. MATERIALS AND METHODS: We monitored effects of immunophilin ligands on [3H]-neurotransmitter release from PC12 cells differentiated with NGF. Rat brain striatal synaptosomes were loaded with radiolabeled transmitters and treated with FK506 or cyclosporin A prior to initiating neurotransmitter release with N-methyl-D-aspartate (NMDA) or potassium depolarization. Striatal synaptosomes were also loaded with 32P-orthophosphate and treated with FK506. 32P-labeled synaptic vesicle proteins were isolated from these synaptosomes in an attempt to relate specific FK506-dependent phosphorylation of vesicle proteins with the effects of FK506 on neurotransmitter release. Identification of proteins targetted by FK506 was made by immunoblot analysis and immunoprecipitation. RESULTS: Low nanomolar concentrations of the immunosuppressant drugs FK506 and cyclosporin A (CsA) inhibit transmitter release from PC-12 cells and from NMDA-stimulated brain synaptosomes. By contrast, the immunosuppressants augment depolarization-induced transmitter release from synaptosomes. Synapsin I, a synaptic vesicle phosphoprotein, displays enhanced phosphorylation in the presence of FK506. CONCLUSIONS: Inhibition of transmitter release in PC-12 cells and NMDA-treated synaptosomes by immunosuppressants may reflect augmented phosphorylation of NO synthase, reducing its catalytic activity. This fits with the requirement of NO for transmitter release in PC12 cells and NMDA-treated synaptosomes. Stimulation by immunosuppressants of transmitter release in potassium depolarized synaptosomes may result from augmented phosphorylation of synapsin I, whose phosphorylation is known to facilitate transmitter release. Thus, immunophilins may modulate release of numerous neurotransmitters both by influencing NO formation and the phosphorylation state of synaptic vesicle-associated proteins.
Images
PMCID: PMC2230146  PMID: 8784785
14.  Evidence that parathyroid hormone-mediated calcium transport in rat brain synaptosomes is independent of cyclic adenosine monophosphate. 
Journal of Clinical Investigation  1988;81(4):982-988.
In vivo PTH administration to rats resulted in increased brain synaptosomal Ca++ transport, while parathyroidectomy (PTX) resulted in decreased transport. To determine the mechanism of action of PTH on Ca++ transport in rat brain synaptosomes, we performed transport studies by the Na-Ca exchanger and also measured cAMP generation in synaptosomes from PTX rats. Ca++ transport was studied after in vivo additions of either bovine (b)PTH, cAMP, or forskolin, and adenylate cyclase activity was assessed after additions of either bPTH, forskolin, sodium fluoride (NaF), or isoproterenol. In the presence of 1-34 bPTH [10(-7) M], Ca++ uptake was significantly increased by 55% (P less than 0.001) above control, while 3-34 bPTH [10(-7) M] had no effect on uptake. Both 8br,cAMP [10(-6) M] and dibut,cAMP [10(-6) M] also significantly increased (P less than 0.001) Ca++ uptake above control by 63 and 44%, respectively. Similarly, forskolin [10(-5) M], the adenylate cyclase activator, increased Ca++ uptake by 41%. We next evaluated Ca++ efflux, and found that 1-34 bPTH [10(-7) M], 1-84 bPTH [10(-7) M], and forskolin [10(-5) M] also increased Ca++ efflux by 50, 73, and 120%, respectively, above control. Since Ca++ transport was increased by either PTH, cAMP, or forskolin, we decided to determine if PTH action on Ca++ transport in synaptosomes was dependent on cAMP. This was investigated by measuring cAMP production during the conversion of 32P-ATP to 32P-cAMP in the presence of an ATP regenerating system (30 micrograms creatine phosphokinase, 10 mM creatine phosphate), and the cyclic nucleotide phosphodiesterase inhibitor (1 mM IBMX). Whereas forskolin [10(-4) M] and NaF [100 mM] significantly increased (P less than 0.001) adenylate cyclase activity in synaptosomes by eight- and fourfold, respectively, neither 1-34 bPTH nor 1-84 bPTH increased synaptosomal cyclase activity. However, in canine renal cortical plasma membranes (CRCPM), we observed significant increases in cAMP production with either forskolin, NaF, or PTH. Finally, to determine if synaptosomes contain an intact adenylate cyclase system, we measured cAMP production in the presence of the beta adrenergic agent, isoproterenol. Isoproterenol significantly increased adenylate cyclase activity in both synaptosomes (90%) and CRCPM (50%). These data suggest that although there is an intact adenylate cyclase system in rat brain synaptosomes, PTH-stimulated calcium transport in synaptosomes appears to be independent of this system.
PMCID: PMC329621  PMID: 2832450
15.  Regulatory and metabolic rewiring during laboratory evolution of ethanol tolerance in E. coli 
We have designed an experimental/computational framework for studying complex phenotypes in bacteria.Our framework relies on whole-genome fitness profiling coupled with a module-level analysis to discover pathways that directly affect fitness.As a proof-of-principle, we studied ethanol tolerance in Escherichia coli and we identified key pathways that contribute to this phenotype.We then validated our findings through genetic manipulations, gene-expression profiling, metabolite-level measurements, and stable-isotope labeling.
Elucidating the genetic basis of complex phenotypes remains a fundamental challenge in biology. We have developed a systematic framework for comprehensive genetic analysis of microbial phenotypes. Our approach combines the power of fitness profiling (Girgis et al, 2007; Amini et al, 2009) with the sensitivity of module-level analysis (Goodarzi et al, 2009a) to identify key genetic modules that directly affect a phenotype under study. We applied our technology to ethanol tolerance, a complex phenotype with broad industrial relevance. Ethanol affects a variety of cellular components and pathways, including but not limited to membrane integrity (Dombek and Ingram, 1984), enzyme activities (Millar et al, 1982), and proton flux (D'Amore et al, 1990). Given the diversity of targets, the emergence of ethanol tolerance requires modifications to multiple pathway (D'Amore and Stewart, 1987).
To reveal the genetic basis of ethanol tolerance in Escherichia coli, we used two high-coverage mutant libraries (a transposon library and an overexpression library) to assess the fitness consequences of single-locus perturbations. Each cell in our transposon library contains a random transposon insertion in its genome (Girgis et al, 2007); whereas the cells in the overexpression library carry 1–3 kb genomic fragments cloned into a cloning vector (Amini et al, 2009). We grew these libraries under mild (4% v/v) and harsh (5.5% v/v) ethanol concentrations. On growth, the abundance of each transposon insertion or overexpression mutant changes as a function of its fitness, a process that can be monitored through parallel genetic footprinting and microarray hybridization (Figure 1A). This results in a global fitness profile, where the contribution of each genetic locus to ethanol tolerance can be quantified in parallel. However, in the context of ethanol tolerance and other complex phenotypes, single-locus perturbations typically result in modest changes in fitness. Although these small differences can be amplified through multiple rounds of selection, the number of generations is limited as spontaneous beneficial mutations emerge in the population and cause strong biases in the resulting fitness profiles. To boost our analytical power without introducing these biases in the data, we used a module-level computational method to discover the pathways and components that are strongly associated with the data as opposed to focusing on the genes individually (Goodarzi et al, 2009a). Genes function in the context of pathways and modules and module-level analyses increase statistical power through combining information from multiple genes functioning as part of a given pathway (Subramanian et al, 2005).
The module-level analysis of the fitness scores from both libraries revealed a diverse set of pathways that have a direct function in ethanol tolerance. Some of these pathways, including heat-shock stress response and osmoregulation, are known modifiers of ethanol tolerance; whereas others such as acid-stress response and fimbrial structures are novel pathways. Among our findings was the important function of three regulatory proteins: FNR, ArcA, and CafA. Knocking out FNR/ArcA that upregulates aerobic respiration proteins and TCA cycle components results in a marked increase in ethanol tolerance. Similarly, knocking out CafA, a post-transcriptional regulator of alcohol dehydrogenase, is beneficial for tolerance. Given these observations, we hypothesized that selection for ethanol tolerance can result in higher ethanol degradation.
As a large fraction of discovered pathways belonged to central metabolism, we used metabolomics to evaluate our findings. To directly assess the metabolic consequences of adaptation to ethanol, we evolved ethanol-tolerant strains in minimal media plus glucose for ∼30 and 160 generations. We then compared the steady-state level of metabolites in these strains to that of the wild type (Figure 1B). In agreement with our fitness profiling results, we observed a significant increase in TCA cycle metabolites in one of our ethanol-tolerant strains. Higher concentrations of TCA cycle components along with a high free coenzyme A (CoA) to acetyl-coenzyme A (acetyl-CoA) ratio hinted at the capacity of this strain to metabolize ethanol. To test this hypothesis, we performed stable-isotope labeling on our ethanol-tolerant strain versus wild type. After growth on labeled ethanol, we measured the fraction of metabolites that were labeled at each timepoint (Figure 1B). Our results confirmed that the ethanol-tolerant strain has the capacity to consume ethanol through its conversion into acetyl-CoA and further assimilation in the TCA cycle.
By using a variety of systems-level approaches, we have been able to genetically dissect ethanol tolerance in E. coli. We have shown that fitness profiling, in combination with module-level analysis tools, can serve as a powerful approach for revealing the genetic basis of complex phenotypes. The fact that laboratory evolution ended up using the very modules that we discovered, highlights the biological and adaptive relevance of the proposed framework.
Understanding the genetic basis of adaptation is a central problem in biology. However, revealing the underlying molecular mechanisms has been challenging as changes in fitness may result from perturbations to many pathways, any of which may contribute relatively little. We have developed a combined experimental/computational framework to address this problem and used it to understand the genetic basis of ethanol tolerance in Escherichia coli. We used fitness profiling to measure the consequences of single-locus perturbations in the context of ethanol exposure. A module-level computational analysis was then used to reveal the organization of the contributing loci into cellular processes and regulatory pathways (e.g. osmoregulation and cell-wall biogenesis) whose modifications significantly affect ethanol tolerance. Strikingly, we discovered that a dominant component of adaptation involves metabolic rewiring that boosts intracellular ethanol degradation and assimilation. Through phenotypic and metabolomic analysis of laboratory-evolved ethanol-tolerant strains, we investigated naturally accessible pathways of ethanol tolerance. Remarkably, these laboratory-evolved strains, by and large, follow the same adaptive paths as inferred from our coarse-grained search of the fitness landscape.
doi:10.1038/msb.2010.33
PMCID: PMC2913397  PMID: 20531407
adaptation; ethanol tolerance; evolution; fitness profiling
16.  Genetic Changes To Optimize Carbon Partitioning between Ethanol and Biosynthesis in Ethanologenic Escherichia coli†  
Applied and Environmental Microbiology  2002;68(12):6263-6272.
The production of ethanol from xylose by ethanologenic Escherichia coli strain KO11 was improved by adding various medium supplements (acetate, pyruvate, and acetaldehyde) that prolonged the growth phase by increasing cell yield and volumetric productivity (approximately twofold). Although added pyruvate and acetaldehyde were rapidly metabolized, the benefit of these additives continued throughout fermentation. Both additives increased the levels of extracellular acetate through different mechanisms. Since acetate can be reversibly converted to acetyl coenzyme A (acetyl-CoA) by acetate kinase and phosphotransacetylase, the increase in cell yield caused by each of the three supplements is proposed to result from an increase in the pool of acetyl-CoA. A similar benefit was obtained by inactivation of acetate kinase (ackA), reducing the production of acetate (and ATP) and sparing acetyl-CoA for biosynthetic needs. Inactivation of native E. coli alcohol-aldehyde dehydrogenase (adhE), which uses acetyl-CoA as an electron acceptor, had no beneficial effect on growth, which was consistent with a minor role for this enzyme during ethanol production. Growth of KO11 on xylose appears to be limited by the partitioning of carbon skeletons into biosynthesis rather than the level of ATP. Changes in acetyl-CoA production and consumption provide a useful approach to modulate carbon partitioning. Together, these results demonstrate that xylose fermentation to ethanol can be improved in KO11 by redirecting small amounts of pyruvate away from fermentation products and into biosynthesis. Though negligible with respect to ethanol yield, these small changes in carbon partitioning reduced the time required to complete the fermentation of 9.1% xylose in 1% corn steep liquor medium from over 96 h to less than 72 h.
doi:10.1128/AEM.68.12.6263-6272.2002
PMCID: PMC134451  PMID: 12450851
17.  Failure of the Normal Ureagenic Response to Amino Acids in Organic Acid-loaded Rats 
Journal of Clinical Investigation  1980;66(3):484-492.
Propionic and methylmalonic acidemia are both known to be associated with hyperammonemia. Rats injected with 10 or 20 mmol/kg of propionate or 20 mmol/kg of methylmalonate, along with 1.5 g/kg of a mixture of amino acids, developed severe hyperammonemia, whereas rats administered the same dosages of acetate did not. In vitro, neither propionyl nor methylmalonyl CoA affected the activity of carbamyl phosphate synthetase I, ornithine transcarbamylase, nor the activation constant (KA) of carbamyl phosphate synthetase I for N-acetyl glutamate. Furthermore, rats injected with propionate showed no alteration of liver amino acid concentrations, which could explain impaired ureagenesis. Animals injected with methylmalonate showed an increase in both citrulline and aspartate, suggesting that argininosuccinic acid synthetase may also have been inhibited. Liver ATP levels were unchanged. Citrullinogenesis, measured in intact mitochondria from livers of injected animals, was reduced 20-25% by 20 mmol/kg of propionate or methylmalonate (compared with acetate). This effect was attributable to an impairment in the normal rise of liver N-acetyl glutamate content after amino acid injection. Thus, carbamyl phosphate synthetase I activation was reduced. Liver levels of acetyl CoA and free CoA were reduced. Levels of unidentified acyl CoA derivatives rose, presumably reflecting the accumulation of propionyl and methylmalonyl CoA. Thus, the principal mechanism for hyperammonemia induced by these acids is depletion of liver N-acetyl glutamate, which is in turn attributable to depletion of acetyl CoA and/or competitive inhibition by propionyl and methylmalonyl CoA of N-acetyl glutamate synthetase. Injection of methylmalonate may also have an additional inhibitory effect on argininosuccinic acid synthetase.
PMCID: PMC371676  PMID: 7400325
18.  Calcium transport abnormality in uremic rat brain synaptosomes. 
Journal of Clinical Investigation  1985;76(5):1789-1795.
Brain calcium is elevated in patients and laboratory animals with uremia. The significance of this finding is unclear. We evaluated calcium transport in brain of both normal and acutely uremic rats (blood urea nitrogen = 250 mg/dl) by performing studies in synaptosomes from rat brain cerebral cortex. Synaptosomes are vesicular presynaptic nerve endings from brain that contain mitochondria and are metabolically active. Two mechanisms of calcium transport were evaluated using radioactive 45Ca++ as a tracer. Both mechanisms were evaluated in the absence of exogenously administered parathyroid hormone (PTH). We first evaluated Na+-Ca++ exchange in vesicles that were loaded with NaCl in an external media containing 10 microM CaCl2. Both initial rates of calcium transport and equilibrium levels of calcium accumulation in synaptosomes prepared from uremic rats were significantly greater (P less than 0.005) than in normal. To assess calcium efflux, ATP-dependent calcium uptake (1 mM ATP) was studied in inverted plasma membrane vesicles loaded with KCl. In the uremic synaptosomes, a significant increase (P less than 0.005) in ATP-dependent calcium uptake was observed as compared with the normal. These studies show that (a) Calcium accumulation via the Na+-Ca++ exchanger is increased in synaptosomes prepared from uremic rat brain. (b) Calcium influx into inverted plasma membrane vesicles from uremic rats via the ATP-dependent calcium transport mechanism is increased when compared with normal. (c) The increased calcium accumulation in uremia by both Na+-Ca++ exchange and ATP-dependent calcium transport mechanism appears to be a result of increased synaptosomal membrane permeability to calcium. Both these abnormalities of calcium transport in uremia would tend to increase brain extracellular calcium in vivo. The defects observed in uremia do not appear to be readily reversible, and the relationship to PTH is presently unclear. These abnormalities may affect neurotransmission in the uremic state.
PMCID: PMC424209  PMID: 4056053
19.  Effects of soluble β-amyloid on the release of neurotransmitters from rat brain synaptosomes 
Contradictory results have been reported on the interaction of beta-amyloid (Aβ) with cholinergic receptors. The present paper investigates the modulatory effect of Aβ1-40 on the neurotransmitter release evoked by nicotinic (nAChRs) and muscarinic (mAChRs) receptors. Aβ1-40 inhibits both nicotinic and muscarinic-evoked [3H]DA overflow from rat nerve endings. Added to perfusion medium, Aβ1-40 is able to enter into synaptosomes; it exerts its inhibitory effect at extracellular sites when release is stimulated by nAChRs and intracellularly when release is evoked by mAChRs. Moreover, our data show that Aβ1-40 acts as non competitive antagonist of heteromeric α4β2* but not of α3β4* nAChRs which modulate [3H]NA overflow. Positive allosteric modulators of nAChRs counteract its inhibitory effect. It might be that compounds of this type could be useful to prevent, slow down the appearance or reverse the cognitive decline typical of the normal processes of brain aging.
doi:10.3389/fnagi.2014.00166
PMCID: PMC4098032  PMID: 25076904
beta-amyloid; dopamine release; nicotinic receptors; muscarinic receptors; Alzheimer’s disease
20.  Localized low level re-expression of high affinity mesolimbic nicotinic acetylcholine receptors restores nicotine-induced locomotion but not place conditioning 
Genes, brain, and behavior  2008;8(3):257-266.
High affinity, β2 subunit-containing (β2*) nAChRs are essential for nicotine reinforcement; however, these nAChRs are found on both GABA and dopaminergic (DA) neurons in the VTA, and also on terminals of glutamatergic and cholinergic neurons projecting from the pedunculopontine tegmental area and the laterodorsal tegmental nucleus. Thus, systemic nicotine administration stimulates many different neuronal subtypes in various brain nuclei. To identify neurons in which nAChRs must be expressed to mediate effects of systemic nicotine, we investigated responses in mice with low-level, localized expression of β2* nAChRs in the midbrain/VTA. Nicotine-induced GABA and DA release were partially rescued in striatal synaptosomes from transgenic mice as compared to tissue from β2 KO mice. Nicotine-induced locomotor activation, but not place preference, was rescued in mice with low-level VTA expression, suggesting that low-level expression of β2* nAChRs in DA neurons is not sufficient to support nicotine reward. In contrast to control mice, transgenic mice with low level β2* nAChR expression in the VTA showed no increase in overall levels of CREB but did show an increase in CREB phosphorylation in response to exposure to a nicotine-paired chamber. Thus, CREB activation in the absence of regulation of total CREB levels was not sufficient to support nicotine place preference in β2tr mice. This suggests that partial activation of high affinity nAChRs in VTA might block the rewarding effects of nicotine, providing a potential mechanism for the ability of nicotinic partial agonists to aid in smoking cessation.
doi:10.1111/j.1601-183X.2008.00468.x
PMCID: PMC2672109  PMID: 19077117
addiction; ventral tegmental area; place conditioning; locomotor activation; nicotinic acetylcholine receptors; mouse
21.  Diphenylhydantoin and potassium transport in isolated nerve terminals 
Journal of Clinical Investigation  1971;50(9):1977-1984.
The antiepileptic action of diphenylhydantoin (DPH) has been explained by two different theories: (a) that DPH stimulates the Na-K pump; (b) that DPH specifically blocks the passive translocation of sodium. Since electrophysiological experiments have recently suggested abnormal synaptic mechanisms as the basis for epileptogenic discharges, the action of DPH on K transport within synaptic terminals isolated from “normal” rat brain cortex was examined directly. A rapid filtration technique was used to assess in vitro potassium transport within synaptosomes. In vivo DPH did not significantly change endogenous K content within synaptosomes. With sodium (50 mM) and potassium (10 mM) concentrations optimal for Na-K pump activity, in vivo and in vitro DPH (10-4 M) had minimal or no effects on total K uptake. DPH stimulated potassium uptake within synaptosomes under two situations: (a) at high sodium (50-100 mM) and low potassium (less than 2 mM) concentrations; (b) when synaptosomes were incubated with ouabain (10-4 M) 50 mM Na and 10 mM K. In both situations, K was leaking out of synaptic terminals and the enhancement in net K uptake roughly corresponded to the ouabain inhibitable segment. In the absence of ouabain, the stimulatory effects of DPH were not observed when K was 2 mM or higher and when Na was 10 mM or lower. The stimulatory effects of in vitro DPH appeared over a range of concentrations from 10-4 to 10-10 M while single intraperitoneal injections of DPH had to be administered for 2 days before its effects were observed on synaptosomal K transport. The present data provided direct evidence for DPH stimulation of active potassium transport within synaptosomes under ionic conditions simulating the depolarized state. At other ionic conditions, DPH had inhibitory or no effects on K uptake. Although the results do not specify whether the effects of DPH on the Na-K pump are direct or indirect, they suggest that the action of DPH depends upon the state of the membrane and the specific ionic environment.
Images
PMCID: PMC292123  PMID: 4254679
22.  Acrylonitrile has Distinct Hormetic Effects on Acetyl-Cholinesterase Activity in Mouse Brain and Blood that are Modulated by Ethanol 
Dose-Response  2011;11(1):49-59.
Acrylonitrile(AN) is a neurotoxin both in animals and humans, but its effects on acetylcholinesterase (AChE) activity remain controversial. This study aimed to determine the dose-response effects of AN on AChE activity and the modulatory role of ethanol pre-treatment. A total of 144 Kunming mice were randomly divided into 18 groups: nine groups received 5% ethanol in their drinking water, and the remaining nine groups received regular tap water. One week later, both the ethanol and tap water only groups were given an intraperitoneal injection of AN at the following doses: 0 (control), 0.156, 0.3125, 0.625, 1.25, 2.5, 5, 10 or 20 mg AN/kg body weight. AChE activity was determined on whole blood and brain 24 h later. Blood AChE activity was higher in AN-injected mice than in controls at all doses. AChE activity in blood increased in a dose-dependent manner, peaking at 0.156 mg/kg, after which a gradual decrease ensued, displaying a β-typed dose-response relationship. In contrast, brain AChE activity, following a single AN injection, was consistently lower than in control mice, and continued to fall up to a dose of 0.313 mg/kg, and thereafter increased gradually with higher doses. Mice receiving a 20 mg/kg dose of AN exhibited AChE brain activity indistinguishable from that of control mice, demonstrating a typical U-typed dose-response relationship. The activity of AChE in the blood and brain of the AN + ethanol-treated groups displayed a shift to the right, and the magnitude of the decrease in AChE activity induced by AN was attenuated relative to the AN-only group. These results suggest that AN affects AChE activity in both mouse blood and brain in a hormetic manner. Pretreatment with ethanol modifies the effect of AN on AChE, indicating that parent AN has a more prominent role than its metabolites in modulating enzyme activity.
doi:10.2203/dose-response.11-030.Yuanqing
PMCID: PMC3578454  PMID: 23550232
acrylonitrile; acetylcholinesterase; biphasic effects; hormesis
23.  Metabolic Control of the Circulation 
Journal of Clinical Investigation  1978;62(5):1029-1038.
Chloralose-anesthetized dogs were infused intravenously with either Tris-acetate or Tris-pyruvate at 0.0375, 0.075, and 0.15 mmol/kg per min successively, each for 20 min. Acetate infusion increased cardiac output, left ventricular dP/dt and dP/dt/P, and coronary blood flow, while pyruvate infusion did not. Infusions of either substance increased arterial blood and skeletal muscle concentrations of citrate and malate, but only acetate infusion increased the tissue AMP content and decreased the ATP:AMP ratio. The increase in cardiac output produced by acetate was accompanied by an increase in total body oxygen consumption and a decrease in the difference between arterial and mixed venous blood oxygen.
Myocardial oxygen consumption increased during acetate infusion, but the decrease in myocardial oxygen extraction and the increase in coronary sinus blood oxygen saturation suggest that an active coronary vasodilation which was not a result of the increased cardiac work, occurred. The concentration of hypoxanthine in the coronary sinus and the content of myocardial adenosine increased, which suggests that the increase in coronary blood flow was caused by the vasodilator action of adenosine released from the myocardium, and that adenosine production is not necessarily tied to PO2.
These systemic and coronary hemodynamic changes also occurred when acetate (0.075 mmol/kg per min) was infused into conscious dogs. Acetate infusion also increased blood flow to the gastrointestinal tract, kidneys, intercostal muscle, and diaphragm. These changes were not affected by propranolol pretreatment, but were abolished by pretreatment with fluoroacetate which reduced acetate oxidation.
These results suggest that the circulatory stimulation produced by acetate was not caused by increases in tricarboxylic acid cycle intermediates. Instead, it was probably related to the increased cleavage of ATP to AMP that accompanies activation of acetate to acetyl CoA, and was not mediated via β-adrenergic receptors. It is speculated that hemodynamic changes may occur in patients who undergo hemodialysis with acetate-containing dialysate. Hemodynamic changes of ethanol may also be brought about by acetate, which is one of the intermediates that accumulates during ethanol metabolism.
PMCID: PMC371862  PMID: 568632
24.  Disruption of mesolimbic regulation of prefrontal cholinergic transmission in an animal model of schizophrenia and normalization by chronic clozapine treatment 
Abnormal mesolimbic control of cortical cholinergic activity has been hypothesized to contribute to the cognitive symptoms of schizophrenia. Stimulation of NMDA receptors in nucleus accumbens (NAC) increases acetylcholine (ACh) release in prefrontal cortex (PFC), an activation thought to contribute to attentional processing. Thus, the effects of intra-NAC perfusion of NMDA (250–400 μM) on ACh release in PFC were determined in rats receiving lesions of the ventral hippocampus (VH) as neonates (nVHLX), a neurodevelopmental model of schizophrenia, or as adults (aVHLX). NMDA elevated ACh release (100–150% of baseline) in adults sham-lesioned as neonates or in aVHLX rats. Adult nVHLX were unresponsive to NAC NMDA receptor stimulation. The inability of nVHLX to respond to NMDA emerged over development as a separate experiment demonstrated that evoked ACh release was normal prior to puberty (100–150% increase) yet, in these same nVHLX animals, absent after puberty. Amphetamine-evoked ACh release was assessed in nVHLX animals to exclude potential limitations in release capacity. Amphetamine produced greater increases in ACh release than in shams, indicating that nVHLX does not impair the capacity of cholinergic neurons to release ACh. Finally, the ability of 13 days of pretreatment with clozapine (1.25 mg/kg/day) to reinstate NMDA-evoked cortical ACh efflux was determined. Clozapine treatment normalized NMDA-evoked ACh release in nVHLX animals. These experiments reveal that mesolimbic regulation of cortical ACh release is disrupted in post-pubertal nVHLX rats and normalized by low-dose treatment of clozapine; supporting the usefulness of nVHLX animals for research on the neuronal mechanisms underlying the cognitive symptoms of schizophrenia.
doi:10.1038/npp.2009.105
PMCID: PMC2783192  PMID: 19693002
acetylcholine; hippocampus; prefrontal cortex; nucleus accumbens; basal forebrain; schizophrenia; clozapine
25.  Modulation of inflammatory cytokines and mitogen-activated protein kinases by acetate in primary astrocytes 
Acetate supplementation attenuates neuroglia activation in a rat model of neuroinflammation by a mechanism associated with an increase in brain acetyl-CoA, an alteration in histone acetylation, and reduction of interleukin (IL)-1β expression. We propose that reduced astroglial activation occurs by disrupting astrocyte-derived inflammatory signaling and cytokine release. Using primary astroglial cultures, we found that LPS (0–25 ng/ml, 4 hr) increased tumor necrosis factor (TNF-α) and IL-1β in a concentration-dependent manner, which was reduced by treatment with sodium acetate (12 mM). LPS did not alter H3K9 acetylation or IL-6 levels, whereas acetate treatment increased H3K9 acetylation by 2-fold and decreased basal levels of IL-6 by 2-fold. Acetate treatment attenuated the LPS-induced increase in TNF- mRNA, but did not reverse the mRNA levels of other pro-inflammatory cytokines. By contrast, LPS decreased TGF-β1 and IL-4 protein and TGF-β1 mRNA, all of which was reversed with acetate treatment. Further, we found that acetate treatment completely reversed LPS-induced phosphorylation of MAPK p38 and decreased basal levels of phosphorylated extracellular signal-regulated kinases1/2 (ERK1/2) by 2-fold. Acetate treatment also reversed LPS-elevated NF-κB p65, CCAAT/enhancer-binding protein beta protein levels, and reduced basal levels of phosphorylated NF-κB p65 at serine 536. These results suggest that acetate treatment has a net anti-inflammatory effect in LPS-stimulated astrocytes that is largely associated with a disruption in MAPK and NF-κB signaling.
doi:10.1007/s11481-012-9426-4
PMCID: PMC3587660  PMID: 23233245
MAPK; NF-κB; astrocyte; cytokines; acetate; inflammation

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