The locus coeruleus (LC) is a dense cluster of neurons that projects axons throughout the neuroaxis and is located in the rostral pontine tegmentum extending from the level of the inferior colliculus to the motor nucleus of the trigeminal nerve. LC neurons are lost in the course of several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. In this study, we used Nissl staining and tyrosine hydroxylase (TH) immunoreactivity to compare the human LC with that of closely related primate species, including great and lesser apes, and macaque monkeys. TH catalyzes the initial and rate-limiting step in catecholamine biosynthesis. The number of TH-immunoreactive (TH-ir) neurons was estimated in each species using stereologic methods. In the LC of humans, the mean total number of TH-ir neurons was significantly higher compared to the other primates. Because the total number of TH-ir neurons in the LC was highly correlated with the species mean volume of the medulla oblongata, cerebellum, and neocortical gray matter, we conclude that much of the observed phylogenetic variation can be explained by anatomical scaling. Notably, the total number of LC neurons in humans was most closely predicted by the nonhuman allometric scaling relationship relative to medulla size, whereas the number of LC neurons in humans was considerably lower than predicted according to neocortex and cerebellum volume.
Locus coeruleus; non-human primates; hominids; tyrosine hydroxylase; stereology
Amyloid-β protein (Aβ) accumulation is one of the major hallmarks of Alzheimer’s disease (AD) and plays a crucial role in its pathogenesis. Cellular models whereby amyloid precursor protein (APP) is highly expressed are commonly used to test the efficacy of novel neuroprotective compounds. In addition to Aβ, it is known that mutation in the protein presenilin contributes to early onset AD. Recently, a cellular neuroblastoma model where both APP and presenilin are expressed has become available. Since protective effects of nicotine against various neurotoxins have been observed, this study was designed to determine whether nicotine would also protect against cellular damage induced by APP or APP and presenilin. Wild type neuroblastoma (N2a) cell line, and those transfected with amyloid precursor protein (APP), and the combination of APP and presenilin were pretreated with various concentrations of nicotine and the survivability of the cells were determined by MTT assay. Nicotine dose dependently provided protection against cellular loss in all cell lines, with highest protection in the double transfected (44%) followed by single transfected (30%), and wild type (21%). The effects of nicotine in turn were blocked by mecamylamine, a non-selective nicotinic antagonist. These results suggest differential sensitivity of cell lines representing AD pathology to the protective effects of nicotine and provide further support of therapeutic potential of nicotinic agonists in at least a subtype of AD patients.
Nicotine; Neuroprotection; Beta Amyloid; APP; Presenilin; N2a Cells; Alzheimer’s Disease
Microscopic findings in Alzheimer’s disease (AD) at autopsy include a wide cortical distribution of beta amyloid (Aβ)-containing plaques and diminished numbers of pyramidal neurons in CA1 of hippocampus and tyrosine hydroxylase-positive (TH+) neurons in the locus coeruleus (LC). To better understand the neuropathology underlying cognitive decline in AD, we analyzed the AD-type neuropathology in brains of triple transgenic (3×Tg) mice harboring mutations for APPswe, PS1M146V, and tauP301L. Histochemical and immunohistochemical staining and computerized stereology were carried out in age-matched young, early middle age, and late middle age 3×Tg mice. The 3×Tg mice showed an intracellular Aβ deposition in subiculum and CA1 pyramidal neurons and an extracellular distribution of amyloid plaques specifically in the subiculum of hippocampal formation and in neocortical layer V. The 3×Tg mice also showed an age-related loss of TH+ neurons in LC, with a loss of 37% of these neurons at 15 months of age. There was no loss of CA1 neurons at any age examined. Reduced AD-type neuropathology in CA1 of 3×Tg mice suggests a possible neuroprotective role for high intracellular-to-extracellular ratios of insoluble Aβ deposits. Understanding the neurobiology of this apparent neuroprotection could lead to an improved understanding of age-related cognitive function in general, and the development of novel strategies for the therapeutic management of AD patients.
Locus coeruleus; Hippocampus; Alzheimer’s disease; Triple transgenic mice; Double transgenic mice
Preclinical as well as limited clinical studies indicate that ketamine, a non-competitive glutamate NMDA receptor antagonist, may exert a quick and prolonged antidepressant effect. It has been postulated that ketamine action is due to inhibition of NMDA and stimulation of AMPA receptors. Here, we sought to determine whether ketamine would exert antidepressant effects in Wistar-Kyoto (WKY) rats, a putative animal model of depression and whether this effect would be associated with changes in AMPA/NMDA receptor densities in the hippocampus. Adult female WKY rats and their control Wistar rats were subjected to acute and chronic ketamine doses and their locomotor activity (LMA) and immobility in the forced swim test (FST) were evaluated. Hippocampal AMPA and NMDA receptor densities were also measured following a chronic ketamine dose. Ketamine, both acutely (0.5–5.0 mg/kg ip) and chronically (0.5–2.5 mg/kg daily for 10 days) resulted in a dose-dependent and prolonged decrease in immobility in the FST in WKY rats only, suggesting an antidepressant-like effect in this model. Chronic treatment with an effective dose of ketamine also resulted in an increase in AMPA/NMDA receptor density ratio in the hippocampus of WKY rats. LMA was not affected by any ketamine treatment in either strain. These results indicate a rapid and lasting antidepressant-like effect of a low ketamine dose in WKY rat model of depression. Moreover, the increase in AMPA/NMDA receptor density in hippocampus could be a contributory factor to behavioral effects of ketamine. These findings suggest potential therapeutic benefit in simultaneous reduction of central NMDA and elevation of AMPA receptor function in treatment of depression.
Depression; Ketamine; NMDA Receptor; AMPA Receptor; Hippocampus; WKY Rats
Though the precise cause(s) of Alzheimer’s disease (AD) remain unknown, there is strong evidence that decreased clearance of β-amyloid (Aβ) from the brain can contribute to the disease. Therapeutic strategies to promote natural Aβ clearance mechanisms, such as the protein apolipoprotein-E (APOE), hold promise for the treatment of AD. The amount of APOE in the brain is regulated by nuclear receptors including retinoid X receptors (RXRs). Drugs that activate RXRs, including bexarotene, can increase APOE and ABCA1 production, and have been shown to decrease the Aβ burden and improve cognition in mouse models of Aβ amyloidosis. Although recent bexarotene studies failed to replicate the rapid clearance of Aβ from brains, behavioral and cognitive effects of this compound remain controversial.
In efforts to clarify these behavioral findings, mutant APP/PS1 mice were acutely dosed with bexarotene. While ABCA1 was upregulated in mutant APP/PS1 mice treated with bexarotene, this drug failed to attenuate Aβ plaques or cognitive deficits in these mice.
We recommend rigorous preclinical study to evaluate the mechanism and utility of such a compound for AD therapy.
Bexarotene; Alzheimer’s disease; Mouse model; RXR agonist; APOE; Cognition
Cells in the locus coeruleus (LC) constitute the sole source of norepinephrine (NE) in the brain and change their discharge rates according to vigilance state. In addition to its well established role in vigilance, NE affects synaptic plasticity in the postnatal critical period (CP) of development. One form of CP synaptic plasticity affected by NE results from monocular occlusion, which leads to physiological and cytoarchitectural alterations in central visual areas. Selective suppression of rapid eye movement sleep (REMS) in the CP kitten enhances the central effects of monocular occlusion. The mechanisms responsible for heightened cortical plasticity following REMS deprivation (REMSD) remain undetermined. One possible mediator of an increase in plasticity is continuous NE outflow, which presumably persists during extended periods of REMSD. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of NE and serves as a marker for NE-producing cells. We selectively suppressed REMS in kittens for 1 week during the CP. The number and size of LC cells expressing immunoreactivity to tyrosine hydroxylase (TH-ir) was assessed in age-matched REMS-deprived (RD)-, treatment–control (TXC)-, and home cage-reared (HCC) animals. Sleep amounts and slow wave activity (SWA) were also examined relative to baseline. Time spent in REMS during the study was lower in RD compared to TXC animals, and RD kittens increased SWA delta power in the latter half of the REMSD period. The estimated total number of TH-ir cells in LC was significantly lower in the RD than in the TXC kittens and numerically lower than in the HCC animals. The size of LC cells expressing TH-ir was greatest in the HCC group. HCC cells were significantly larger than TH-ir cells in the RD kittens. These data are consistent with presumed reduction in NE in forebrain areas, including visual cortex, caused by 1 week of REMSD.
norepinephrine; critical period; fast Fourier transforms; stereology; depression
The von Economo neurons (VENs) are large bipolar neurons located in fronto-insular cortex (FI) and anterior limbic area (LA) in great apes and humans but not in other primates. Our stereological counts of VENs in FI and LA show them to be more numerous in humans than in apes. In humans, small numbers of VENs appear the 36th week post conception, with numbers increasing during the first eight months after birth. There are significantly more VENs in the right hemisphere in postnatal brains; this may be related to asymmetries in the autonomic nervous system. VENs are also present in elephants and whales and may be a specialization related to very large brain size. The large size and simple dendritic structure of these projection neurons suggest that they rapidly send basic information from FI and LA to other parts of the brain, while slower neighboring pyramids send more detailed information. Selective destruction of VENs in early stages of fronto-temporal dementia implies that they are involved in empathy, social awareness, and self-control, consistent with evidence from functional imaging.
fronto-temporal dementia; autism; schizophrenia; empathy; disgust; self-awareness; hemispheric specialization
The observed high incidence of smoking amongst depressed individuals has led to the hypothesis of ‘self medication” with nicotine in some of these patients. The inbred Wistar-Kyoto (WKY) rats exhibit depressive-like characteristics as evidenced by exaggerated immobility in the forced swim test (FST). One aim of this study was to investigate whether nicotine may have an antidepressant-like effect in these animals. Moreover, because of human postmortem studies indicating a reduction of the hippocampus volume in depressed patients, it was of interest to determine whether such an anatomical anomaly may also be manifested in WKY rats and whether it would be affected by chronic nicotine treatment. Adult female WKY and their control Wistar rats were administered nicotine consecutively (0.2 mg/kg, ip, once or twice daily for 14 days) and their activity in an open field, as well as their immobility in FST were assessed either 15 min or 18 hr after the last injection. Another set of animals was treated twice daily with 0.2 mg/kg nicotine for 14 days and sacrificed on day 15 for stereological evaluation of the hippocampal volume. When tested 15 min after the last injection, once or twice daily nicotine exacerbated the immobility in the FST in WKY rats only. When tested 18 hr after the last injection, only twice daily nicotine treatment resulted in less immobility in the FST in WKY rats. Open field locomotor activity was not affected by any nicotine regimen. WKY rats had significantly less hippocampal volume (approximately 20%) than Wistar rats which was not altered by nicotine. These findings further validate the use of WKY rats as an animal model of human depression and signify the importance of inherent genetic differences in final behavioral outcome of nicotine.
WKY rats; Depression; Hippocampus; Nicotine; Forced Swim Test; Stereology
Murine models that mimic the neuropathology of Alzheimer’s disease (AD) have the potential to provide insight into the pathogenesis of the disease and lead to new strategies for the therapeutic management of afflicted patients. We used magnetic resonance imaging (MRI), design-based stereology, and high performance liquid chromatography (HPLC) to assess the age-related neuropathology in double transgenic mice that overexpress two AD-related proteins—amyloid precursor protein (APP) and presenilin 1 (PS1)—and age- and gender-matched wild-type (WT) controls. In mice ranging in age from 4–28 months, total volumes of the hippocampal formation (VHF) and whole brain (Vbrain) were quantified by the Cavalieri-point counting method on a systematic-random sample of coronal T2-weighted MRI images; the same stereological methods were used to quantify VHF and Vbrain after perfusion and histological processing. To assess changes in AD-type beta-amyloid (Aβ) plaques, sections from the hippocampal formation and amylgdaloid complex of mice aged 5, 12, and 15 months were stained by Congo Red histochemistry. In aged mice with large numbers of amyloid plaques, systematic-random samples of sections were stained by GFAP immunocytochemistry to assess gender and genotype effects on total numbers of astrocytes. In addition, levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and 5-HT metabolites were assayed by HPLC in fresh-frozen samples from neocortex, striatum, hippocampus, and brainstem. We confirmed age-related increases in amyloid plaques, beginning with a few plaques at 5 months of age and increasing densities by 12 and 15 months. At 15 months of age, there were robust genotype effects, but no gender effects, on GFAP-immunopositive astrocytes in the amygdaloid complex and hippocampus. There were no effects on monoamine levels in all brain regions examined, and no volume changes in hippocampal formation or whole brain as quantified on either neuroimages or tissue sections. Strong correlations were present between volume estimates from MRI images and histological sections, with about 85% reduction in mean VHF or mean Vbrain between MRI and processed histological sections. In summary, these findings show that the double transgenic expression of AD-type mutations is associated with age-related increases in amyloid plaques and astrocytosis; however, this model does not recapitulate the cortical atrophy or neurochemical changes that are characteristic of AD.
MRI; Alzheimer’s disease; Hippocampal formation; Amygdala; Unbiased stereology