Daily scheduled feeding is a potent time cue that elicits anticipatory
activity in rodents. This food-anticipatory activity (FAA) is controlled by a
food-entrainable oscillator (FEO) that is distinct from light-entrained
oscillators of the suprachiasmatic nucleus (SCN). Circadian rhythms within the
SCN depend on transcription-translation feedback loops in which CLOCK protein is
a key positive regulator. The Clock gene is expressed in
rhythmic tissues throughout the brain and periphery, implicating its widespread
involvement in the functioning of circadian oscillators. To examine whether
CLOCK protein is also necessary for the FEO, the effect of daily food
restriction was studied in homozygous Clock mutant
(Clk/Clk) mice. The results show that
Clk/Clk mutant mice exhibit FAA, even when their circadian
wheel-running behavior is arrhythmic. As in wild-type controls, FAA in
Clk/Clk mutants persists after temporal feeding cues are
removed for several cycles, indicating that the FEO is a circadian timer. This
is the first demonstration that the Clock gene is not necessary
for the expression of a circadian, food-entrained behavior and suggests that the
FEO is mediated by a molecular mechanism distinct from that of the SCN.
food-anticipatory activity; feeding; entrainment; clock genes; suprachiasmatic nucleus
Diabetes increases the risk of stroke and contributes to poor clinical outcomes in this patient population. Myogenic tone of the cerebral vasculature, including basilar arteries, plays a key role in controlling cerebral blood flow. Increased myogenic tone is ameliorated with ET receptor antagonism in Type 1 diabetes. However, the role of ET-1 and its receptors in cerebrovascular dysfunction in Type-2 diabetes, a common comorbidity in stroke patients, remains poorly elucidated. Therefore, we hypothesized that 1) cerebrovascular dysfunction occurs in the Goto-Kakizaki (GK) model of Type-2 diabetes, and 2) pharmacological antagonism of ETA receptors ameliorates while ETB receptor blockade augments vascular dysfunction. GK or control rats were treated with antagonists to either ETA (Atrasentan, 5mg/kg/d) or ETB (A-192621, 15 or 30 mg/kg/d) receptors for four weeks and vascular function of basilar arteries was assessed using a wire myograph. GK rats exhibited increased sensitivity to ET-1. ETA receptor antagonism caused a rightward shift indicating decreased sensitivity in diabetes while it increased sensitivity to ET-1 in control rats. Endothelium-dependent relaxation was impaired in diabetes. ETA receptor blockade restored relaxation to control values in the GK animals with no significant effect in Wistars and ETB blockade with 30 mg/kg/d A-192621 caused paradoxical constriction in diabetes. These studies demonstrate that cerebrovascular dysfunction occurs and may contribute to altered regulation of myogenic tone and cerebral blood flow in diabetes. While ETA receptors mediate vascular dysfunction, ETB receptors display differential effects. These results underscore the importance of ETA/ETB receptor balance and interactions in cerebrovascular dysfunction in diabetes.
There has been scant evidence for a phase-shifting effect of melatonin in shift-work or jet-lag protocols. This study tested whether melatonin can facilitate phase shifts in a simulated night-work protocol. Subjects (n = 32) slept in the afternoons/evenings before night work (a 7-h advance of the sleep schedule). They took melatonin (0.5 mg or 3.0 mg) or placebo before the first four of eight afternoon/evening sleep episodes at a time when melatonin has been shown to phase advance the circadian clock. Melatonin produced larger phase advances than placebo in the circadian rhythms of melatonin and temperature. Average phase advances (±SD) of the dim light melatonin onset were 1.7 ± 1.2 h (placebo), 3.0 ± 1.1 h (0.5 mg), and 3.9 ± 0.5 h (3.0 mg). A measure of circadian adaptation, shifting the temperature minimum enough to occur within afternoon/evening sleep, showed that only subjects given melatonin achieved this goal (73% with 3.0 mg, 56% with 0.5 mg, and 0% with placebo). Melatonin could be used to promote adaptation to night work and jet travel.
body temperature; jet lag; sleep; sleepiness; shift work; work-schedule tolerance; humans; constant routine
Endogenous endothelin-1-dependent (ET-1) tone in coronary arteries depends on the balance between ETA and ETB receptor-mediated effects and on parameters such as receptor distribution and endothelial integrity. Numerous studies highlight the striking functional interactions that exist between nitric oxide (NO) and ET-1 in the regulation of vascular tone. Many of the cardiovascular complications associated with cardiovascular risk factors and aging are initially attributable, at least in part, to endothelial dysfunction characterized by a dysregulation between NO and ET-1. The contribution of the imbalance between smooth muscle ETA/B and endothelial ETB receptors to this process is poorly understood. An increased contribution of ET-1 that is associated with a proportional decrease in that of NO accompanies the development of coronary endothelial dysfunction, coronary vasospasm, and atherosclerosis. These data form the basis for the rationale of testing therapeutic approaches counteracting ET-1-induced cardiovascular dysfunction. It remains to be determined whether the beneficial role of endothelial ETB receptors declines with age and risk factors for cardiovascular diseases, revealing smooth muscle ETB receptors with proconstricting and proinflammatory activities.
PMID: 20237301 CAMSID: cams2990
vascular tone; inflammation; shear stress; coronary blood flow
The Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an outbred strain of Long Evans Tokushima Otsuka rat (LETO) that lacks CCK-1 receptor expression, is hyperphagic and develops obesity and type-2 diabetes. The present study sought to assess how OLETF rats alter intake, preference, and conditioned preference of palatable solutions after acute food deprivation. Our results show that after 24 hr chow restriction LETO rats increase both sucrose intake and two-bottle sucrose preference relative to their free-fed baseline, whereas OLETF rats do not increase sucrose intake (0.3M or 1.0M sucrose) or preference (1.0M vs. 0.3M sucrose) when food-deprived. In contrast, OLETF rats exhibit a higher conditioned flavor preference when sucrose is used as unconditioned stimulus (US) relative to LETO rats, whether overnight food-restricted (81% vs. 71% for OLETF and LETO rats, respectively) or free-fed (82% vs. 54% for OLETF and LETO rats, respectively) on test. When a non-caloric saccharin solution is used as US, OLETF rats show a higher preference for the saccharin-associated flavor relative to LETO rats when non-deprived (76% vs. 58% for OLETF and LETO rats, respectively), however neither strain shows differential conditioned flavor preference for saccharin in the deprivation state on test. These findings suggest that OLETF rats fail to integrate post-absorptive and orosensory effects of sucrose in a conditioning setting to influence intake. Thus, it appears that OLETF rats form preferences for sucrose based largely on orosensory and hedonic properties of the solution, rather than caloric value.
food intake; CCK-1 receptor; hyperphagia; diet-induced obesity; palatability
The contribution of the organum vasculosum laminae terminalis (OVLT) in mediating central hyperosmolality-induced increases of sympathetic nerve activity (SNA) and arterial blood pressure (ABP) was assessed in anesthetized rats. Solutions of graded NaCl concentration (150, 375, and 750 mM) were injected (150 μl) into the forebrain vascular supply via an internal carotid artery (ICA). Time-control experiments (n = 6) established that ICA NaCl injections produced short-latency, transient increases of renal SNA (RSNA) and mean ABP (MAP) (P < 0.05– 0.001). Responses were graded, highly reproducible, and unaltered by systemic blockade of vasopressin V1 receptors (n = 4). In subsequent studies, stimulus-triggered averaging of RSNA was used to accurately locate the OVLT. Involvement of OVLT in responses to ICA NaCl was assessed by recording RSNA and MAP responses before and 15 min after electrolytic lesion of the OVLT (n = 6). Before lesion, NaCl injections increased RSNA and MAP (P < 0.05– 0.001), similar to time control experiments. After lesion, RSNA responses were significantly reduced (P < 0.05– 0.001), but MAP responses were unaltered. To exclude a role for fibers of passage, the inhibitory GABA-A receptor agonist muscimol was microinjected into the OVLT (50 pmol in 50 nl) (n = 6). Before muscimol, hypertonic NaCl increased RSNA, lumbar SNA (LSNA), and MAP (P < 0.05– 0.001). After muscimol, both RSNA and LSNA were significantly reduced in response to 375 and 750 mM NaCl (P < 0.05). MAP responses were again unaffected. Injections of vehicle (saline) into OVLT (n = 6) and muscimol lateral to OVLT (n = 5) each failed to alter responses to ICA NaCl. We conclude that OVLT neurons contribute to sympathoexcitation by central hyperosmolality.
sympathetic nerve discharge; body fluid homeostasis; blood pressure; osmolality
There has been considerable interest in the use of creatine (Cr) supplementation to treat neurological disorders. However, in contrast to muscle physiology, there are relatively few studies of creatine supplementation in the brain. In this report, we use high-field MR 31P and 1H spectroscopic imaging of human brain with a 7-day protocol of oral Cr supplementation to examine its effects on cerebral energetics (phosphocreatine, PCr; ATP) and mitochondrial metabolism (N-acetyl aspartate, NAA; and Cr). We find an increased ratio of PCr/ATP (day 0, 0.80 ± 0.10; day 7, 0.85 ± 09), with this change largely due to decreased ATP, from 2.7 ± 0.3 mM to 2.5 ± 0.3 mM. The ratio of NAA/Cr also decreased (day 0, 1.32 ± 0.17; day 7 1.18 ± 0.13), primarily from increased Cr (9.6 ± 1.9 to 10.1 ± 2.0 mM). The Cr-induced changes significantly correlated with the basal state, with the fractional increase in PCr/ATP negatively correlating with the basal PCr/ATP value (R = −0.74, P < 0.001). As NAA is a measure of mitochondrial function, there was also a significant negative correlation between basal NAA concentrations with the fractional change in PCr and ATP. Thus healthy human brain energetics is malleable and shifts with 7 days of Cr supplementation, with the regions of initially low PCr showing the largest increments in PCr. Overall, Cr supplementation appears to improve high-energy phosphate turnover in healthy brain and can result in either a decrease or an increase in high-energy phosphate concentrations.
high-energy phosphates; brain; N-acetyl aspartate; metabolism
In this study the hypothesis was tested that chronic infusion of ANG II attenuates acute volume expansion (VE)-induced inhibition of renal sympathetic nerve activity (SNA). Rats received intravenous infusion of either vehicle or ANG II (12 ng·kg−1 ·min−1) for 7 days. ANG II-infused animals displayed an increased contribution of SNA to the maintenance of mean arterial pressure (MAP) as indicated by ganglionic blockade, which produced a significantly (P < 0.01) greater decrease in MAP (75 ± 3 mmHg) than was observed in vehicle-infused (47 ± 8 mmHg) controls. Rats were then anesthetized, and changes in MAP, mean right atrial pressure (MRAP), heart rate (HR), and renal SNA were recorded in response to right atrial infusion of isotonic saline (20% estimated blood volume in 5 min). Baseline MAP, HR, and hematocrit were not different between groups. Likewise, MAP was unchanged by acute VE in vehicle-infused animals, whereas VE induced a significant bradycardia (P < 0.05) and increase in MRAP (P < 0.05). MAP, MRAP, and HR responses to VE were not statistically different between animals infused with vehicle vs. ANG II. In contrast, VE significantly (P < 0.001) reduced renal SNA by 33.5 ± 8% in vehicle-infused animals but was without effect on renal SNA in those infused chronically with ANG II. Acutely administered losartan (3 mg/kg iv) restored VEinduced inhibition of renal SNA (P < 0.001) in rats chronically infused with ANG II. In contrast, this treatment had no effect in the vehicle-infused group. Therefore, it appears that chronic infusion of ANG II can attenuate VE-induced renal sympathoinhibition through a mechanism requiring AT1 receptor activation. The attenuated sympathoinhibitory response to VE in ANG II-infused animals remained after arterial barodenervation and systemic vasopressin V1 receptor antagonism and appeared to depend on ANG II being chronically increased because ANG II given acutely had no effect on VE-induced renal sympathoinhibition.
sympathetic nerve activity; cardiopulmonary reflex; body fluid balance; arterial baroreceptor reflex
Melanin-concentrating hormone (MCH) and neuropeptide Y (NPY) are orexigenic peptides found in hypothalamic neurons that project throughout the forebrain and hindbrain. The effects of fourth ventricle (4V) infusions of NPY (5 μg) and MCH (5 μg) on licking for water, 4 mM saccharin, and sucrose (0.1 and 1.0 M) solutions were compared to identify the contributions of each peptide to hindbrain-stimulated feeding. NPY increased mean meal size only for the sucrose solutions, suggesting that caloric feedback or taste quality is pertinent to the orexigenic effect; MCH infusions under identical testing conditions failed to produce increases for any tastant. A second experiment also observed no intake or licking effects after MCH doses up to 15 μg, supporting the conclusion that MCH-induced orexigenic responses require forebrain stimulation. A third experiment compared the 4V NPY results with those obtained after NPY infusions (5 μg) into the third ventricle (3V). In contrast to the effects observed after the 3V NPY injections and previously reported forebrain intracerebroventricular (ICV) NPY infusion studies, 4V NPY failed to increase meal frequency for any taste solution or ingestion rate in the early phases of the sucrose meals. Overall, 4V NPY responses were limited to intrameal behavioral processes, whereas forebrain ICV NPY stimulation elicited both consummatory and appetitive responses. The dissociation between MCH and NPY effects observed for 4V injections is consistent with reports that forebrain ICV injections of MCH and NPY produced nearly dichotomous effects on the pattern of licking microstructure, and, collectively, the results indicate that the two peptides have separate sites of feeding action in the brain.
taste; feeding; microstructure; intake
M3 muscarinic receptors mediate cholinergic-induced contraction in most smooth muscles. However, in the denervated rat bladder, M2 receptors participate in contraction because M3-selective antagonists [para-fluoro-hexahydro-sila-diphenidol (p-F-HHSiD) and 4-DAMP] have low affinities. However, the affinity of the M2-selective antagonist methoctramine in the denervated bladder is consistent with M3 receptor mediating contraction. It is possible that two pathways interact to mediate contraction: one mediated by the M2 receptor and one by the M3 receptor. To determine whether an interaction exists, the inhibitory potencies of combinations of methoctramine and p-F-HHSiD for reversing cholinergic contractions were measured. In normal bladders, all combinations gave additive effects. In denervated bladders, synergistic effects were seen with the 10:1 and 1:1 (methoctramine:p-F-HHSiD wt/wt) combinations. After application of the sarcoplasmic reticulum ATPase inhibitor thapsigargin to normal tissue, the 10:1 and 1:1 ratios became synergistic, mimicking denervated tissue. Thus in normal bladders both M2 and M3 receptors can induce contraction. In the denervated bladder, the M2 and the M3 receptors interact in a facilitatory manner to mediate contraction.
urinary bladder; synergy; denervation; second messengers
Major pelvic ganglion electrocautery (MPGE) and spinal cord injury in the rat induce bladder hypertrophy and a change in muscarinic receptor subtypes mediating bladder contraction from predominantly M3 to a combination of M2 and M3. To determine whether this is a result of bladder hypertrophy or denervation, we studied the following groups: sham-operated controls, urinary diversion (DIV), MPGE together with urinary diversion (DIV-DEN), bilateral MPGE (DEN), bladder outlet obstruction (BOO), and MPG decentralization (MPG-DEC). The degree of bladder denervation was determined by the maximal carbachol response normalized to the response to electric field stimulation. Receptor subtype density was determined by immunoprecipitation. The affinity of subtype-selective muscarinic antagonists for inhibition of carbachol-induced contractions was used to determine the subtype-mediating contraction. DEN, MPG-DEC, and BOO bladders were hypertrophic whereas DIV bladders were atrophic compared with sham operated. Bladder contraction in sham-operated, DIV, and DIV-DEN was mediated by the M3 receptor subtype, whereas the M2 subtype participated in contraction in the DEN, MPG-DEC, and BOO groups. The hypertrophied bladders had an increase in total and M2 receptor density while all experimental groups showed a reduction in M3 receptor density. Thus bladder hypertrophy, independent from bladder denervation, causes a shift in the muscarinic receptor subtype mediating bladder contraction from M3 toward M2.
denervation; outlet obstruction; urinary diversion
Bladder muscle specimens from seven patients with neurogenic bladder dysfunction were analyzed to determine whether the muscarinic receptor subtype mediating contraction shifts from M3 to the M2 subtype as found in the denervated, hypertrophied rat bladder. Seven bladder specimens were analyzed from six female and one male patients. Six of the patients had traumatic cervical spinal cord injuries (C4–C7), and the other patient had an L1 congenital myelomeningocele. This was compared with results from bladder specimens obtained from eight organ transplant donors. The affinities of three subtype-selective muscarinic receptor antagonists for inhibition of carbachol-induced contractions were determined. The affinity of the M3 selective antagonists darifenacin or p-fluoro-hexahydrosiladifenadol (p-F-HHSiD) was determined in six of the seven spinal injury patient specimens. The affinity was consistent with M2-mediated contractions in four of these six specimens, intermediate between M2 and M3 in one specimen, and within the M3 range in one specimen. The other specimen, tested only with the M2 selective antagonist methoctramine, showed an M3 affinity. In the organ donors, the affinity of p-F-HHSiD was within the M2 range for six of seven specimens, whereas the affinity of darifenacin was within the M3 range for five of six and intermediate between M2 and M3 for the other specimen tested. The affinity of methoctramine in both organ donor specimens tested was within the M3 range. Whereas normal detrusor contractions are mediated by the M3 receptor subtype, in patients with neurogenic bladder dysfunction as well as certain organ transplant donors, contractions can be mediated by the M2 muscarinic receptor subtype.
spinal cord injury
The Otsuka Long Evans Tokushima Fatty (OLETF) rat lacking the CCK-1 receptor is hyperphagic, prefers palatable and high caloric meals, and gradually develops obesity and type-2 diabetes. To determine dopamine levels in this strain, we used in-vivo quantitative (no-net flux) microdialyis at three different ages representing non-diabetic (8 weeks), pre-diabetic (18 weeks), and diabetic (56 weeks) stages in OLETF and age-matched lean LETO controls. Results showed significantly elevated basal dopamine levels in the caudomedial nucleus accumbens of OLETF rats compared to LETO at younger ages (8 weeks: 20.10 ± 5.61 nM vs. 15.85 ± 5.63 nM; 18 weeks: 7.37 ± 3.71 nM vs. 4.75 ± 1.25 nM, Mean ± SD). In contrast, at 56 weeks of age, a profound decline in extracellular dopamine concentrations was seen in both strains with a tendency for a greater effect in OLETF rats (1.78 ± 0.40 nM vs. 2.39 ± 0.42 nM). Further, extracellular fraction, an index for reuptake, was higher in 56-week old OLETF compared to LETO (0.648 ± 0.049 vs. 0.526 ± 0.057). Potassium-stimulated dopamine efflux revealed an increased capacity of vesicular pool in OLETF rats compared to LETO across all age groups with an accentuated strain difference at 56 weeks. These findings demonstrate altered striatal dopamine functions (i.e. increased stimulated release and uptake) in obese OLETF rat. This could be due to the lack of functional CCK-1 receptors, or metabolic and hormonal factors associated with the development of obesity and insulin resistance, or both.
obesity; CCK-1 receptor; type-2 diabetes; overeating; no-net flux microdialysis
In vitro preparations of whole urinary bladders of neonatal rats exhibit prominent myogenic spontaneous contractions, the amplitude and frequency of which can be increased by muscarinic agonists. The muscarinic receptor subtype responsible for this facilitation was examined in the present experiments. Basal spontaneous contractions in bladders from 1- to 2-wk-old Sprague-Dawley rats were not affected by M2 or M3 receptor antagonists. However, administration of 0.5 μM physostigmine, an anticholinesterase agent that increases the levels of endogenous acetylcholine, or 50–100 nM carbachol, a cholinergic agonist at low concentrations, which did not cause tonic contractions, significantly augmented the frequency and amplitude of spontaneous contractions. Blockade of M2 receptors with 0.1 μM AF-DX 116 or 1 μM methoctramine or blockade of M3 receptors with 50 nM 4-diphenylacetoxy-N-methylpiperidine methiodide or 0.1 μM 4-diphenylacetoxy-N-(2-chloroethyl)piperidine hydrochloride (4-DAMP mustard) reversed the physostigmine and carbachol responses. M2 and M3 receptor blockade did not alter the facilitation of spontaneous contractions induced by 10 nM BAY K 8644, an L-type Ca2+ channel opener, or 0.1 μM iberiotoxin, a large-conductance Ca2+-activated K+ channel blocker. NS-1619 (30 μM), a large-conductance Ca2+-activated K+ channel opener, decreased carbachol-augmented spontaneous contractions. These results suggest that spontaneous contractions in the neonatal rat bladder are enhanced by activation of M2 and M3 receptors by endogenous acetylcholine released in the presence of an anticholinesterase agent or a cholinergic receptor agonist.
M2 receptors; M3 receptors; overactive bladder; detrusor overactivity
This study was conducted to examine reflex mechanisms that mediate urinary bladder and external urethral sphincter (EUS) coordination in urethane-anesthetized female Sprague-Dawley rats. We investigated the properties of EUS reflexes elicited by electrical stimulation of pelvic nerve afferent axons (pelvic-EUS reflex). The changes in the reflexes induced by bladder distension and administration of agonists or antagonists for glutamatergic or serotonergic receptors were examined. The reflexes consisted of an early response (ER, 18- to 22-ms latency) and a late, long-duration (>100-ms latency) response (LR), which consisted of bursts of activity at 20- to 160-ms interburst intervals. In a few experiments, a reflex with an intermediate (40- to 70-ms) latency was also identified. With the bladder empty, the ER, but not the LR, was detected in the majority of experiments. The LR was markedly enhanced when the bladder was distended. The ER remained, but the LR was abolished, after spinal cord transection at T8–T9. The ER and LR were significantly decreased 75 and 35%, respectively, by the N-methyl-d-aspartate receptor antagonist MK-801 (0.3 mg/kg iv), but only decreased 18 and 14%, respectively, by the α-amino-5-methylisoxazole-4-propionate receptor antagonist LY-215490 (3 mg/kg iv). The serotonin (5-HT1A) receptor agonist 8-hydroxy-2-(din-propylamino)-tetralin (1 mg/kg iv) enhanced spontaneous EUS activity and the pelvic-EUS reflex. WAY-100635 (0.1–1 mg/kg iv), a 5-HT1A antagonist, reversed the effect of 8-hydroxy-2-(di-n-propylamino)-tetralin and suppressed EUS activity and the pelvic-EUS reflex. These results indicate that glutamatergic and serotonergic mechanisms are important in the reflex pathways underlying bladder-sphincter coordination in rats.
pelvic nerve; bladder distension; bursting activity; spinal cord injury
Spontaneous bladder contractions (SBCs) in the neonatal rat urinary bladder change from a high-amplitude, low-frequency pattern to a low-amplitude, high-frequency pattern during the first 6 wk of life. Understanding the mechanism of this developmental change may provide insights into the causes of bladder overactivity in adults. In vitro whole bladder preparations from Sprague-Dawley rats were used to study the modulation of SBCs by calcium-activated potassium channels (KCa) and electrical field stimulation from 3 days to 6 wk of life. SBCs in 3-day-old bladders were unmasked by treatment with iberiotoxin (100 nM), an inhibitor of large conductance KCa (BK) channels, or apamin (100 nM), an inhibitor of small conductance KCa (SK) channels. Iberiotoxin significantly increased the magnitude of SBCs at 2–3 wk, whereas apamin was only effective at 6 wk. In 1–2 wk bladders, exposure to room temperature Krebs solution decreased SBCs. This decrease was reversed by activating intramural nerves with electrical field stimulation. The effect of electrical field stimulation was inhibited by atropine (1 µM), suramin (10 µM), or pretreatment with tetrodotoxin (1 µM) but was not reversed by tetrodotoxin applied after electrical field stimulation. BK-α mRNA increased threefold, and BK-α protein increased fivefold from 3 days to 6 wk. These data suggest that BK channels play an important role in the regulation of SBCs in the neonatal bladder and that both increased BK channel activity, as well as changes in smooth muscle sensitivity to locally released neurotransmitters contribute to the downregulation of SBCs during early postnatal development.
large-conductance KCa channel; small-conductance KCa channel; cholinergic; purinergic
The primary goal was to test the hypothesis that agonist-induced corticotropin-releasing factor type 1 (CRF1) receptor phosphorylation is required for β-arrestins to translocate from cytosol to the cell membrane. We also sought to determine the relative importance to β-arrestin recruitment of motifs in the CRF1 receptor carboxyl terminus and third intracellular loop. β-Arrestin-2 translocated significantly more rapidly than β-arrestin-1 to agonist-activated membrane CRF1 receptors in multiple cell lines. Although CRF1 receptors internalized with agonist treatment, neither arrestin isoform trafficked with the receptor inside the cell, indicating that CRF1 receptor-arrestin complexes dissociate at or near the cell membrane. Both arrestin and clathrin-dependent mechanisms were involved in CRF1 receptor internalization. To investigate molecular determinants mediating the robust β-arrestin-2-CRF1 receptor interaction, mutagenesis was performed to remove potential G protein-coupled receptor kinase phosphorylation sites. Truncating the CRF1 receptor carboxyl terminus at serine-386 greatly reduced agonist-dependent phosphorylation but only partially impaired β-arrestin-2 recruitment. Removal of a serine/threonine cluster in the third intracellular loop also significantly reduced CRF1 receptor phosphorylation but did not alter β-arrestin-2 recruitment. Phosphorylation was abolished in a CRF1 receptor possessing both mutations. Surprisingly, this mutant still recruited β-arrestin-2. These mutations did not alter membrane expression or cAMP signaling of CRF1 receptors. Our data reveal the involvement of at least the following two distinct receptor regions in β-arrestin-2 recruitment: 1) a carboxyl-terminal motif in which serine/threonine residues must be phosphorylated and 2) an intracellular loop motif configured by agonist-induced changes in CRF1 receptor conformation. Deficient β-arrestin-2-CRF1 receptor interactions could contribute to the pathophysiology of affective disorders by inducing excessive CRF1 receptor signaling.
corticotropin-releasing factor; G protein-coupled receptor kinase; receptor phosphorylation; internalization; stress adaptation
Gut barrier dysfunction may occur in short bowel syndrome (SBS). We hypothesized that systemic exposure to flagellin and lipopolysaccharide (LPS) in SBS might regulate specific immune responses. We analyzed serial serum samples obtained from parenteral nutrition (PN)-dependent patients with SBS versus non-SBS control serum. Serum from 23 adult SBS patients was obtained at baseline and 4, 8, 12, 16, 20, and 24 wk in a trial of modified diet with or without growth hormone. Control serum was obtained from 48 healthy adults and 37 adults requiring PN during critical illness. Serum flagellin was detected by an ELISA recognizing an array of gram-negative flagellins, and LPS was detected by limulus assay. Serum flagellin- and LPS-specific immunoglobulin levels (IgM, IgA, and IgG) were determined by ELISA. Serum flagellin and LPS were undetectable in control subjects. In contrast, serum flagellin, LPS, or both were detected in 14 SBS patients (61%) during one or more time points [flagellin alone, 5/23 (22%); LPS alone, 6/23 (26%); or flagellin + LPS, 3/23 (13%)]. Flagellin-specific serum IgM, IgA, and IgG levels were markedly increased in SBS patients compared with both control populations and remained elevated during the 6-mo study period. LPS-specific IgA was significantly higher in SBS patients compared with healthy controls; LPS-specific IgM, IgA, and IgG levels each decreased over time in association with PN weaning. We conclude that adults with PN-dependent SBS are systemically exposed to flagellin and LPS, presumably from the gut lumen. This likely regulates innate and adaptive immune responses to these specific bacterial products.
parenteral nutrition; intestinal barrier function
Activation of esophageal mechanosensors excites neurons in and near the central nucleus of the solitary tract (NSTc). In turn, NSTc neurons coordinate the relaxation of the stomach [i.e., the receptive relaxation reflex (RRR)] by modulating the output of vagal efferent neurons of the dorsal motor nucleus of the vagus (DMN). The NSTc area contains neurons with diverse neurochemical phenotypes, including a large population of catecholaminergic and nitrergic neurons. The aim of the present study was to determine whether either one of these prominent neuronal phenotypes was involved in the RRR. Immunohistochemical techniques revealed that repetitive esophageal distension caused 53% of tyrosine hydroxylase-immunoreactive (TH-ir) neurons to colocalize c-Fos in the NSTc. No nitric oxide synthase (NOS)-ir neurons in the NSTc colocalized c-Fos in either distension or control conditions. Local brain stem application (2 ng) of α-adrenoreceptor antagonists (i.e., α1-prazosin or α2-yohimbine) significantly reduced the magnitude of the esophageal distension-induced gastric relaxation to ~55% of control conditions. The combination of yohimbine and prazosin reduced the magnitude of the reflex to ~27% of control. In contrast, pretreatment with either the NOS-inhibitor NG-nitro-L-arginine methyl ester or the β-adrenoceptor antagonist propranolol did not interfere with esophageal distension-induced gastric relaxation. Unilateral microinjections of the agonist norepinephrine (0.3 ng) directed at the DMN were sufficient to mimic the transient esophageal-gastric reflex. Our data suggest that noradrenergic, but not nitrergic, neurons of the NSTc play a prominent role in the modulation of the RRR through action on α1- and α2-adrenoreceptors. The finding that esophageal afferent stimulation alone is not sufficient to activate NOS-positive neurons in the NSTc suggests that these neurons may be strongly gated by other central nervous system inputs, perhaps related to the coordination of swallowing or emesis with respiration.
vagus; brain stem; c-Fos
We have shown recently that cholecystokinin octapeptide (CCK-8s) increases glutamate release from nerve terminals onto neurons of the nucleus tractus solitarius pars centralis (cNTS). The effects of CCK on gastrointestinal-related functions have, however, been attributed almost exclusively to its paracrine action on vagal afferent fibers. Because it has been reported that systemic or perivagal capsaicin pretreatment abolishes the effects of CCK, the aim of the present work was to investigate the response of cNTS neurons to CCK-8s in vagally deafferented rats. In surgically deafferented rats, intraperitoneal administration of 1 or 3 μg/kg CCK-8s increased c-Fos expression in cNTS neurons (139 and 251% of control, respectively), suggesting that CCK-8s’ effects are partially independent of vagal afferent fibers. Using whole cell patch-clamp techniques in thin brain stem slices, we observed that CCK-8s increased the frequency of spontaneous and miniature excitatory postsynaptic currents in 43% of the cNTS neurons via a presynaptic mechanism. In slices from deafferented rats, the percentage of cNTS neurons receiving glutamatergic inputs responding to CCK-8s decreased by ~50%, further suggesting that central terminals of vagal afferent fibers are not the sole site for the action of CCK-8s in the brain stem. Taken together, our data suggest that the sites of action of CCK-8s include the brain stem, and in cNTS, the actions of CCK-8s are not restricted to vagal central terminals but that nonvagal synapses are also involved.
brain stem; electrophysiology; c-fos
Coordination of the urinary bladder and the external urethral sphincter (EUS) is controlled by descending projections from the pons, and is also subject to modulation by segmental afferents. We quantified the effects on the micturition reflex of sensory inputs from genital afferents, traveling in the penile component of the somatic pudendal nerve, by electrical stimulation of the dorsal nerve of the penis (DNP) in α-chloralose anesthetized male cats. Depending on the frequency of stimulation (range 1–40 Hz), activation of penile afferents either inhibited contractions of the bladder and promoted urine storage or activated the bladder and produced micturition. Stimulation of the DNP at 5–10 Hz inhibited distension evoked contractions and increased the maximum bladder capacity before incontinence. Conversely, stimulation at 33 and 40 Hz augmented distension evoked contractions. When the bladder was filled above a threshold volume (70% of the volume necessary for distension evoked contractions), stimulation at 20–40 Hz activated de novo the micturition reflex and elicited detrusor contractions that increased voiding efficiency compared to distension evoked voiding. Electrical stimulation of the DNP with a cuff electrode or percutaneous wire electrode produced similar results. The ability to evoke detrusor contractions by activation of the DNP was preserved following acute spinal transection. These results demonstrate a clear role of genital afferents in modulating the micturition reflex and suggest the DNP as a potential target for functional restoration of bladder control using electrical stimulation.
electrical stimulation; spinal cord injury; dorsal nerve of the penis; frequency-dependence
It has long been known that the esophageal distension produced by swallowing elicits a powerful proximal gastric relaxation. Gastroinhibitory control by the esophagus involves neural pathways from esophageal distension-sensitive neurons in the nucleus tractus solitarius centralis (cNTS) with connections to virtually all levels of the dorsal motor nucleus of the vagus (DMV). We have shown recently that cNTS responses are excitatory and primarily involve tyrosine hydroxylase-immunoreactive cells, whereas the DMV response involves both an α1 excitatory and an α2 inhibitory response. In the present study, using an esophageal balloon distension to evoke gastric relaxation (esophageal-gastric reflex, EGR), we investigated the peripheral pharmacological basis responsible for this reflex. Systemic administration of atropine methyl nitrate reduced the amplitude of the gastric relaxation to 52.0 ± 4.4% of the original EGR, whereas NG-nitro-L-arginine methyl ester (L-NAME) reduced it to 26.3 ± 7.2% of the original EGR. Concomitant administration of atropine methyl nitrate and L-NAME reduced the amplitude of the gastric relaxation to 4.0 ± 2.5% of control. This reduction in the amplitude of induced EGR is quite comparable (4.3 ± 2.6%) to that seen when the animal was pretreated with the nicotinic ganglionic blocker hexamethonium. In the presence of bethanechol, the amplitude of the esophageal distension-induced gastric relaxation was increased to 177.0 ± 10.0% of control; administration of L-NAME reduced this amplitude to 19.9 ± 9.5%. Our data provide a clear demonstration that the gastroinhibitory control by the esophagus is mediated via a dual vagal innervation consisting of inhibitory nitrergic and excitatory cholinergic transmission.
receptive relaxation reflex; nonadrenergic; noncholinergic; vagovagal reflex
Glucocorticoids [e.g., corticosterone and dexamethasone (Dex)], when administered systemically, greatly increase water drinking elicited by angiotensin and sodium ingestion in response to mineralocorticoids [e.g., aldosterone and deoxycorticosterone acetate (DOCA)], possibly by acting in the brain. In addition, glucocorticoids exert powerful renal actions that could influence water and sodium ingestion by promoting their excretion. To test this, we determined water and sodium intakes, excretions, and balances during injections of Dex and DOCA and their coadministration (DOCA+Dex) at doses commonly employed to stimulate ingestion of water and sodium. In animals having only water to drink, Dex treatment greatly increased water and sodium excretion without affecting water intake, thereby producing negative water and sodium balances. Similar results were observed when Dex was administered together with DOCA. In animals having water and saline solution (0.3 M NaCl) to drink, Dex treatment increased water and sodium excretion, had minimal effects on water and sodium intakes, and was associated with negative water and sodium balances. DOCA treatment progressively increased sodium ingestion, and both water and sodium intakes exceeded their urinary excretion, resulting in positive water and sodium balances. The combination of DOCA+Dex stimulated rapid, large increases in sodium ingestion and positive sodium balances. However, water excretion outpaced total fluid intake, resulting in large, negative water balances. Plasma volume increased during DOCA treatment and did not change during treatment with Dex or DOCA+Dex. We conclude that increased urinary excretion, especially of water, during glucocorticoid treatment may explain the increased ingestion of water and sodium that occurs during coadministration with mineralocorticoids.
thirst; urine volume; dexamethasone; deoxycorticosterone acetate; food intake
We have investigated the effects of the reactive oxygen species (ROS) donors hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (t-BHP) on the intrinsic electrophysiological characteristics, ganglionic transmission and resting [Ca2+]i in neonate and adult rat intracardiac ganglion (ICG) neurons. Intracellular recordings were made using sharp microelectrodes filled with either 0.5 M KCl or Oregon Green 488 BAPTA-1, allowing recording of electrical properties and measurement of [Ca2+]i. H2O2 and t-BHP both hyperpolarized the resting membrane potential and reduced membrane resistance. In adult ICG neurons the hyperpolarizing action of H2O2 was reversed fully by Ba2+ and partially by tetraethylammonium, muscarine and linopiridine. H2O2 and t-BHP reduced the action potential afterhyperpolarization (AHP) amplitude, but had no impact on either overshoot or AHP duration. ROS donors evoked an increase in discharge adaptation to long depolarizing current pulses. H2O2 blocked ganglionic transmission in most ICG neurons, but did not alter nicotine-evoked depolarizations. By contrast, t-BHP had no significant action on ganglionic transmission. H2O2 and t-BHP increased resting intracellular Ca2+ levels to 1.6 (± 0.6, n=11, p<0.01) and 1.6 (± 0.3, n=8, p<0.001) respectively, of control value (1.0, ~ 60 nM). The ROS scavenger catalase prevented the actions of H2O2 and this protection extended beyond the period of application. Superoxide dismutase partially shielded against the action of H2O2, but this was limited to the period of application.
These data demonstrate that ROS decreases the excitability and ganglionic transmission of ICG neurons, attenuating parasympathetic control of the heart.
intracardiac ganglion neurons; synaptic transmission; Reactive Oxygen Species
We have investigated the effects of the reactive oxygen species (ROS) donors hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (t-BHP) on the intrinsic electrophysiological characteristics: ganglionic transmission and resting [Ca2+]i in neonate and adult rat intracardiac ganglion (ICG) neurons. Intracellular recordings were made using sharp microelectrodes filled with either 0.5 M KCl or Oregon Green 488 BAPTA-1, allowing recording of electrical properties and measurement of [Ca2+]i. H2O2 and t-BHP both hyperpolarized the resting membrane potential and reduced membrane resistance. In adult ICG neurons, the hyperpolarizing action of H2O2 was reversed fully by Ba2+ and partially by tetraethylammonium, muscarine, and linopirdine. H2O2 and t-BHP reduced the action potential afterhyperpolarization (AHP) amplitude but had no impact on either overshoot or AHP duration. ROS donors evoked an increase in discharge adaptation to long depolarizing current pulses. H2O2 blocked ganglionic transmission in most ICG neurons but did not alter nicotine-evoked depolarizations. By contrast, t-BHP had no significant action on ganglionic transmission. H2O2 and t-BHP increased resting intracellular Ca2+ levels to 1.6 ( ± 0.6, n = 11, P < 0.01) and 1.6 ( ± 0.3, n = 8, P < 0.001), respectively, of control value (1.0, ∼60 nM). The ROS scavenger catalase prevented the actions of H2O2, and this protection extended beyond the period of application. Superoxide dismutase partially shielded against the action of H2O2, but this was limited to the period of application. These data demonstrate that ROS decreases the excitability and ganglionic transmission of ICG neurons, attenuating parasympathetic control of the heart.
synaptic transmission; reactive oxygen species; intracellular calcium; intrinsic cardiac neuron; hydrogen peroxide