Loss Of Cholinergic Fibers Research Articles

Ovariectomy-induced hormone deprivation aggravates Aβ1-42 deposition in the basolateral amygdala and cholinergic fiber loss in the cortex but not cognitive behavioral symptoms in a triple transgenic mouse model of Alzheimer's disease.

Alzheimer’s disease is the most common type of dementia, being highly prevalent in elderly women. The advanced progression may be due to decreased hormone synthesis during post-menopause as estradiol and progesterone both have neuroprotective potentials. We aimed to confirm that female hormone depletion aggravates the progression of dementia in a triple transgenic mouse model of Alzheimer’s disease (3xTg-AD). As pathological hallmarks are known to appear in 6-month-old animals, we expected to see disease-like changes in the 4-month-old 3xTg-AD mice only after hormone depletion. Three-month-old female 3xTg-AD mice were compared with their age-matched controls. As a menopause model, ovaries were removed (OVX or Sham surgery). After 1-month recovery, the body composition of the animals was measured by an MRI scan. The cognitive and anxiety parameters were evaluated by different behavioral tests, modeling different aspects (Y-maze, Morris water maze, open-field, social discrimination, elevated plus maze, light–dark box, fox odor, operant conditioning, and conditioned fear test). At the end of the experiment, uterus was collected, amyloid-β accumulation, and the cholinergic system in the brain was examined by immunohistochemistry. The uterus weight decreased, and the body weight increased significantly in the OVX animals. The MRI data showed that the body weight change can be due to fat accumulation. Moreover, OVX increased anxiety in control, but decreased in 3xTg-AD animals, the later genotype being more anxious by default based on the anxiety z-score. In general, 3xTg-AD mice moved less. In relation to cognition, neither the 3xTg-AD genotype nor OVX surgery impaired learning and memory in general. Despite no progression of dementia-like behavior after OVX, at the histological level, OVX aggravated the amyloid-β plaque deposition in the basolateral amygdala and induced early cholinergic neuronal fiber loss in the somatosensory cortex of the transgenic animals. We confirmed that OVX induced menopausal symptoms. Removal of the sexual steroids aggravated the appearance of AD-related alterations in the brain without significantly affecting the behavior. Thus, the OVX in young, 3-month-old 3xTg-AD mice might be a suitable model for testing the effect of new treatment options on structural changes; however, to reveal any beneficial effect on behavior, a later time point might be needed.

The effects of astaxanthin treatment on a rat model of Alzheimer’s disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder characterized by memory loss and dementia, could be a consequence of the abnormalities of cortical milieu, such as oxidative stress, inflammation, and/or accompanied with the aggregation of β-amyloid. The majority of AD patients are sporadic, late-onset AD, which predominantly occurs over 65 years of age. Our results revealed that the ferrous amyloid buthionine (FAB)-infused sporadic AD-like model showed deficits in spatial learning and memory and with apparent loss of choline acetyltransferase (ChAT) expression in medial septal (MS) nucleus. In hippocampal CA1 region, the loss of pyramidal neurons was accompanied with cholinergic fiber loss and neuroinflammatory responses including glial reaction and enhanced expression of inducible nitric oxide synthase (iNOS). Surviving hippocampal CA1 pyramidal neurons showed the reduction of dendritic spines as well. Astaxanthin (ATX), a potent antioxidant, reported to improve the outcome of oxidative-stress-related diseases. The ATX treatment in FAB-infused rats decreased neuroinflammation and restored the ChAT + fibers in hippocampal CA1 region and the ChAT expression in MS nucleus. It also partly recovered the spine loss on hippocampal CA1 pyramidal neurons and ameliorated the behavioral deficits in AD-like rats. From these data, we believed that the ATX can be a potential option for slowing the progression of Alzheimer's disease.

Elevated Levels of miR-144-3p Induce Cholinergic Degeneration by Impairing the Maturation of NGF in Alzheimer's Disease.

Cholinergic degeneration is one of the key pathological hallmarks of Alzheimer’s disease (AD), a condition that is characterized by synaptic disorders and memory impairments. Nerve growth factor (NGF) is secreted in brain regions that receive projections from the basal forebrain cholinergic neurons. The trophic effects of NGF rely on the appropriate maturation of NGF from its precursor, proNGF. The ratio of proNGF/NGF is known to be increased in patients with AD; however, the mechanisms that underlie this observation have yet to be elucidated. Here, we demonstrated that levels of miR-144-3p are increased in the hippocampi and the medial prefrontal cortex of an APP/PS1 mouse model of AD. These mice also exhibited cholinergic degeneration (including the loss of cholinergic fibers, the repression of choline acetyltransferase (ChAT) activity, the reduction of cholinergic neurons, and an increased number of dystrophic neurites) and synaptic/memory deficits. The elevated expression of miR-144-3p specifically targets the mRNA of tissue plasminogen activator (tPA) and reduces the expression of tPA, thus resulting in the abnormal maturation of NGF. The administration of miR-144-3p fully replicated the cholinergic degeneration and synaptic/memory deficits observed in the APP/PS1 mice. The injection of an antagomir of miR-144-3p into the hippocampi partially rescued cholinergic degeneration and synaptic/memory impairments by restoring the levels of tPA protein and by correcting the ratio of proNGF/NGF. Collectively, our research revealed potential mechanisms for the disturbance of NGF maturation and cholinergic degeneration in AD and identified a potential therapeutic target for AD.

Immunization with Small Amyloid-β-derived Cyclopeptide Conjugates Diminishes Amyloid-β-Induced Neurodegeneration in Mice.

Background: Soluble oligomeric (misfolded) species of amyloid-β (Aβ) are the main mediators of toxicity in Alzheimer’s disease (AD). These oligomers subsequently form aggregates of insoluble fibrils that precipitate as extracellular and perivascular plaques in the brain. Active immunization against Aβ is a promising disease modifying strategy. However, eliciting an immune response against Aβ in general may interfere with its biological function and was shown to cause unwanted side-effects. Therefore, we have developed a novel experimental vaccine based on conformational neo-epitopes that are exposed in the misfolded oligomeric Aβ, inducing a specific antibody response.Objective: Here we investigate the protective effects of the experimental vaccine against oligomeric Aβ1-42-induced neuronal fiber loss in vivo.Methods: C57BL/6 mice were immunized or mock-immunized. Antibody responses were measured by enzyme-linked immunosorbent assay. Next, mice received a stereotactic injection of oligomeric Aβ1-42 into the nucleus basalis of Meynert (NBM) on one side of the brain (lesion side), and scrambled Aβ1-42 peptide in the contralateral NBM (control side). The densities of choline acetyltransferase-stained cholinergic fibers origination from the NBM were measured in the parietal neocortex postmortem. The percentage of fiber loss in the lesion side was determined relative to the control side of the brain.Results: Immunized responders (79%) showed 23% less cholinergic fiber loss (p = 0.01) relative to mock-immunized mice. Moreover, fiber loss in immunized responders correlated negatively with the measured antibody responses (R2 = 0.29, p = 0.02).Conclusion: These results may provide a lead towards a (prophylactic) vaccine to prevent or at least attenuate (early onset) AD symptoms.

Postlesion Estradiol Treatment Increases Cortical Cholinergic Innervations via Estrogen Receptor-α Dependent Nonclassical Estrogen Signaling in Vivo

17β-Estradiol (E2) treatment exerts rapid, nonclassical actions via intracellular signal transduction system in basal forebrain cholinergic (BFC) neurons in vivo. Here we examined the effect of E2 treatment on lesioned BFC neurons in ovariectomized mice and the role of E2-induced nonclassical action in this treatment. Mice given an N-methyl-d-aspartic acid (NMDA) injection into the substantia innominata-nucleus basalis magnocellularis complex (SI-NBM) exhibited cholinergic cell loss in the SI-NBM and ipsilateral cholinergic fiber loss in the cortex. A single injection of E2 after NMDA lesion did not have an effect on cholinergic cell loss in the SI-NBM, but it restored the ipsilateral cholinergic fiber density in the cortex in a time- and dose-dependent manner. The most effective cholinergic fiber restoration was observed with 33 ng/g E2 treatment at 1 h after NMDA lesion. The E2-induced cholinergic fiber restoration was absent in neuron-specific estrogen receptor-α knockout mice in vivo. Selective activation of nonclassical estrogen signaling in vivo by estren induced E2-like restorative actions. Selective blockade of the MAPK or protein kinase A pathway in vivo prevented E2's ability to restore cholinergic fiber loss. Finally, studies in intact female mice revealed an E2-induced restorative effect that was similar to that of E2-treated ovariectomized mice. These observations demonstrate that a single E2 treatment restores the BFC fiber loss in the cortex, regardless of endogenous E2 levels. They also reveal the critical role of nonclassical estrogen signaling via estrogen receptor-α and protein kinase A-MAPK pathways in E2-induced restorative action in the cholinergic system in vivo.

Gami-Chunghyuldan ameliorates memory impairment and neurodegeneration induced by intrahippocampal Aβ1–42 oligomer injection

Soluble oligomeric forms of amyloid beta (AβO) are regarded as a main cause of synaptic and cognitive dysfunction in Alzheimer’s disease (AD) and have been a primary target in the development of drug treatments for AD. The present study utilized a mouse model of AD induced by intrahippocampal injection of AβO (10μM) to investigate the effects of Gami-Chunghyuldan (GCD), a standardized multi-herbal medicinal formula, on the presentation of memory deficits and neurohistological pathogenesis. GCD (10 and 50mg/kg/day, 5days, p.o.) improved AβO-induced memory impairment as well as reduced neuronal cell death, astrogliosis, and microgliosis in the hippocampus. In addition, GCD prevented AβO-triggered synaptic disruption and cholinergic fiber loss. These results suggest that GCD may be useful in the prevention and treatment of AD.

Expression and regulation of the two cyclooxygenase isoforms in rhesus macaque brain during lentivirus infection: differentiation of reversible inflammatory and irreversible neuronal sequelae

The regulation of cyclooxygenase type-1 and type-2 (COX-1, COX-2), key enzymes in the conversion of arachidonic acid to prostanoids and mediators of inflammation, was investigated in the brain of simian immunodeficiency virus (SIV)-infected rhesus macaques. COX-1 and COX-2 were constitutively expressed in hippocampal and cortical neurons. COX-1 was additionally found to be expressed in cholinergic basal forebrain neurons (septum, diagonal band of Broca and nucleus basalis of Meynert). This expression was highly species-specific, as COX-1 was coexpressed with specific cholinergic markers choline acetyl transeferase, vesicular acetyl choline transporter (VAChT) and high affinity choline transporter in these neurons, in both the rhesus macaque and human, but was absent from basal forebrain cholinergic neurons in rat, mouse and guinea pig brain. COX-1 immunoreactivity was decreased more than 50% in cholinergic projection neurons of the basal forebrain in AIDS-diseased monkeys. Decreased COX-1 expression was accompanied by a decrease of VAChT-positive fibers and terminals in parietal and frontal cortex, and hippocampus. Additionally, COX-1 and COX-2 were downregulated in frontal cortex neurons in AIDS. Nonneuronally, only COX-1 was expressed constitutively in microglia and endothelial cells, and was not changed in early SIV infection. Late stage of disease was characterized by upregulation of COX-1 in scattered microglia/macrophages, macrophage nodules and multinucleated giant cells. Endothelial COX-1 expression was unchanged during SIV infection. In AIDS-symptomatic monkey brains COX-2 was induced focally in nodule and syncytium forming macrophages and in endothelial cells in areas of viral burden and inflammatory cell infiltrates. Treatment with the antiretroviral brain-permeant 6-chloro-2',3'-dideoxyguanosine (6-Cl-ddG) substantially reduced focal expression of COX-1 and COX-2 in AIDS, but diffuse COX-1 microgliosis was not. 6-Cl-ddG did not decrease COX-1 immunoreactivity in cortical and cholinergic basal forebrain neurons and cortical cholinergic fiber loss. We conclude that COX-1 coexpression is a feature of the cholinergic basal forebrain telecephalic projection system specific to primates, and may be important in primate-specific functions of this system, and in the cholinergic dysregulation that accompanies primate lentiviral encephalitis. Nonneuronal COX-2 induction is associated with reversible overt inflammatory events to areas of active viral replication. Treatment with cyclooxygenase-inhibitors and central cholinomimetica might be beneficial beside highly active antiretroviral therapy in immunodeficiency virus-induced encephalopathy and encephalitis.

Basal Forebrain Cholinergic Input Is Not Essential for Lesion-Induced Plasticity in Mature Auditory Cortex

The putative role of the basal forebrain cholinergic system in mediating lesion-induced plasticity in topographic cortical representations was investigated. Cholinergic immunolesions were combined with unilateral restricted cochlear lesions in adult cats, demonstrating the consequence of cholinergic depletion on lesion-induced plasticity in primary auditory cortex (AI). Immunolesions almost eliminated the cholinergic input to AI, while cochlear lesions produced broad high-frequency hearing losses. The results demonstrate that the near elimination of cholinergic input does not disrupt reorganization of the tonotopic representation of the lesioned (contralateral) cochlea in AI and does not affect the normal representation of the unlesioned (ipsilateral) cochlea. It is concluded that cholinergic basal forebrain input to AI is not essential for the occurrence of lesion-induced plasticity in AI.

Cholinergic changes in the APP23 transgenic mouse model of cerebral amyloidosis.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.

Cholinergic Changes in the APP23 Transgenic Mouse Model of Cerebral Amyloidosis

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.

17β-Estradiol enhances cortical cholinergic innervation and preserves synaptic density following excitotoxic lesions to the rat nucleus basalis magnocellularis

Estradiol exerts beneficial effects on neurodegenerative disorders associated with the decline of cognitive performance. The present study was designed to further investigate the effect of 17β-estradiol on learning and memory, and to evaluate its neuroprotective action on cholinergic cells of the nucleus basalis magnocellularis, a neural substrate of cognitive performance. Female rats were ovariectomized at an age of 6 months. Three weeks later they received injections of either a mid-physiological dose of 17β-estradiol or vehicle (oil), every other day for 2 weeks. The effect of estradiol on cognitive performance was tested in two associative learning paradigms. In the two-way active shock avoidance task estradiol-replaced animals learned significantly faster, while in the passive shock avoidance test no differences were observed between the experimental groups. Subsequent unilateral infusion of N-methyl- D-aspartate in the nucleus basalis magnocellularis resulted in a significant loss of cholinergic neurons concomitant with the loss of their fibers invading the somatosensory cortex. Estradiol treatment did not affect the total number of choline-acetyltransferase-immunoreactive neurons and their coexpression of the p75 low-affinity neurotrophin receptor either contralateral or ipsilateral to the lesion. In contrast, cholinergic fiber densities in estradiol-treated animals were greater both in the contralateral and ipsilateral somatosensory cortices as was detected by quantitative choline-acetyltransferase and vesicular acetylcholine transporter immunocytochemistry. However, estradiol treatment did not affect the lesion-induced relative percentage loss of cholinergic fibers. A significant decline of synaptophysin immunoreactivity paralleled the cholinergic damage in the somatosensory cortex of oil-treated animals, whereas an almost complete preservation of synaptic density was determined in estradiol-treated rats. Our results indicate that estradiol treatment enhances the cortical cholinergic innervation but has no rescuing effect on cholinergic nerve cells in the basal forebrain against excitotoxic damage. Nevertheless, estradiol may restore or maintain synaptic density in the cerebral cortex following cholinergic fiber loss. This estradiol effect may outweigh the lack of cellular protection on cholinergic cells at the functional level.

Effect of physical training on the age-related changes of acetylcholinesterase-positive fibers in the hippocampal formation and parietal cortex in the C57BL/6J mouse

We investigated the effect of a moderate amount of prolonged physical training initiated at 3 months of age on the age-related changes of the hippocampal and cortical cholinergic fibers. A total of 80 male C57BL/6J mice were divided into five groups which were trained (including adult and old trained, AT and OT), sedentary (adult and old sedentary, AS and OS) and young (Y). From 3 months old, the mice of the trained groups were treated with a voluntary running wheel for 1 h each day, 5 days per week. AT had been trained up to 13-month-old whereas OT up to 24 months old. At the same time, the mice of the sedentary groups were put in immobilized wheels. We set the criterion for effective training in the trained mice such that the heart-to-body weight ratio should be at least 2 S.D. above the mean in the age-matched groups. Using AChE histochemistry and stereology, the AChE-positive fibers were analyzed quantitatively in the molecular layers in CA1, CA3 and the dentate gyrus of the hippocampal formation, and in III, V layers in the motor and somatosensory cortex. Comparison of Y, AS and OS (3, 13 and 24 months of age) showed minimum AChE-positive fiber density in the hippocampal formation and the cortex in OS ( P<0.01). After 10 and 21 months of running, the AChE-positive fibers in all regions examined in the trained groups were significantly increased compared to their age-matched controls ( P<0.05 or 0.01). In the hippocampal formation, the increase was about 17% in AT and 23% in OT, whereas, in the cortex, it was 13% in AT and 22% in OT. These results indicated that a moderate amount of prolonged physical training could modify the age-related loss of cholinergic fibers in the hippocampal formation and cortex, furthermore the modified loss of cholinergic fibers might be associated with the regeneration of hippocampal and cortical cholinergic fibers stimulated by chronic running.

Relationship between plaques, tangles, and loss of cortical cholinergic fibers in Alzheimer disease.

Recent observations in our laboratory have indicated substantial and systematic regional variations in the loss of cortical cholinergic fibers in Alzheimer disease (AD). Previous attempts to study the relationship between cortical cholinergic loss and the density of cortical pathological lesions have resulted in conflicting findings. Furthermore, most reports have correlated density of plaques and tangles with the residual level of cholinergic innervation rather than its loss. The purpose of the present study was to determine the relationship between loss of cholinergic axons and density of tangles and beta-amyloid (Abeta) deposits in various cortical areas of AD brains. Abeta deposits and tangles were observed throughout the cerebral cortex. Quantitative analysis revealed almost no correlation between loss of cholinergic fibers and the density of Abeta deposits. Qualitative observations revealed similar results when cored and neuritic plaques were considered separately. By contrast, cholinergic fiber loss displayed a significant correlation with the density of tangles (r = 0.52-0.79). However, in a few areas, such as the cingulate cortex, tangle density appeared to be unrelated to the loss of cholinergic fibers. These results indicate that cortical cholinergic denervation in AD is related to cytoskeletal pathology. However, the lack of a perfect relationship with cytoskeletal pathology implicates additional factors in the cholinergic pathology of AD.

Disturbance of the cortical cholinergic innervation in Borna disease prior to encephalitis.

Rats experimentally infected with the highly neurotropic Borna disease virus (BDV) display a wide variety of dysfunction such as learning deficiencies and behavioral abnormalities. Prior to the onset of encephalitis alterations of one of the major cortical neurotransmitters, acetylcholine, were monitored immunohistochemically by light and electron microscopy of its synthesizing enzyme choline acetyltransferase (ChAT). We found a progressing decrease in the number of ChAT-positive fibers, starting with discrete changes at day 6 post infection (p.i.) and ending with a nearly complete loss of cholinergic fibers, especially in the hippocampus and neocortex, suggesting a massive disturbance of the cholinergic innervation by day 15 p.i.. The fiber pathways (e.g., fimbria-fornix) connecting the basal forebrain with these target areas in the cortex displayed axon spheroids which are often linked to axonal transport dysfunction. No evidence for significant cellular destruction was seen in the brain, including the cells of origin of these axons in the basal forebrain. We conclude that the motor, mood, learning and memory disabilities in BDV-infected rats are likely to result, in part, from cortical cholinergic denervation. The present study gives new insights into the pathogenesis of neurological disease caused by a noncytopathogenic virus.

Effect of corticosterone and adrenalectomy on NMDA-induced cholinergic cell death in rat magnocellular nucleus basalis.

The present study demonstrates the effects of adrenalectomy and subcutaneously administered corticosterone on N-methyl-D-aspartate-induced neurodegeneration in the cholinergic magnocellular basal nucleus of the rat. NMDA was unilaterally injected into the nucleus basalis at different plasma corticosterone concentrations in adrenalectomized rats, in adrenalectomized animals with subcutaneously implanted cholesterol-corticosterone pellets containing 25% or 100% corticosterone, and in sham-adrenalectomized controls. The neurotoxic impact of the NMDA injection in the various experimental groups was assessed by the loss of cholinergic fibers stained with acetylcholinesterase histochemistry in the parietal neocortex. Reactive cortical astrocytes as a result of the treatments were detected by glial fibrillary acidic protein immunohistochemistry. Measurements of the densities of astrocytes and cholinergic fibers at the injected side of the brain were carried out by image analysis. Adrenalectomy significantly potentiated the NMDA-induced neurodegeneration by 50%, while chronic administration of corticosterone significantly attenuated the NMDA-neurotoxicity in a dose-dependent manner. Compared to the ADX group, 25% corticosterone application reduced the NMDA damage by 37%, whereas the 100% corticosterone pellet diminished NMDA neurotoxicity by 75%. Both ADX and ADX + corticosterone implantation enhanced the NMDA-induced GFAP immunoreactivity. The increase of GFAP immunoreactivity was most pronounced in the adrenalectomized rats supplied with the 100% corticosterone pellets. The results demonstrate that corticosterone exerts a potent neuroprotective effect on NMDA-induced neurotoxicity in the magnocellular nucleus basalis. The activated astroglia suggest that astrocytes may contribute to the beneficial effect of corticosterone in the neuroprotective mechanisms against excitotoxic neuronal injury.

Systematic regional variations in the loss of cortical cholinergic fibers in Alzheimer's disease.

The loss of cortical cholinergic fibers in Alzheimer's disease was investigated using choline acetyltransferase immunohistochemistry and acetylcholinesterase histochemistry. Within both the normal and Alzheimer's cerebral cortex, the two methods revealed an identical pattern of fiber staining. In the normal brain, cholinergic fiber density was highest in limbic and paralimbic cortical zones, intermediate in most sensory-motor and association zones, and lowest within the primary visual and visual association areas of the occipital lobe. In general, supragranular cortical layers contained a higher density of cholinergic fibers, and most of these were oriented vertically. In Alzheimer's disease, an overall 55% loss of cortical cholinergic fibers was detected. There was, however, marked regional variations in the extent of this loss in different cortical areas. Cortical areas within the temporal lobe, particularly the temporal association areas, displayed a dramatic loss of cholinergic fibers. By contrast, the anterior cingulate cortex, primary visual, primary somatosensory, and primary motor cortex displayed a relative preservation of cholinergic fibers. As a whole, greater loss of cholinergic fibers was detected in supragranular layers and in fibers oriented vertical to the cortical surface. These results indicate that cholinomimetic therapies are likely to have different effects on cholinergic transmission in various cortical areas. The precise mechanisms that lead to the regional variations in cortical cholinergic denervation in Alzheimer's disease remain to be elucidated.

Differential effects on spatial navigation of immunotoxin-induced cholinergic lesions of the medial septal area and nucleus basalis magnocellularis

The effects on anatomy and behavior of a ribosomal inactivating protein (saporin) coupled to a monoclonal antibody against the low-affinity NGF receptor (NGFr) were examined. In adult rats, NGFr is expressed predominantly in cholinergic neurons of the medial septal area (MSA), diagonal band nuclei, and nucleus basalis magnocellularis (nBM), but also in noncholinergic cerebellar Purkinje cells. Rats with immunotoxin injections to the MSA, nBM, and lateral ventricle were compared to controls on a spatial and cued reference memory task in the Morris maze. Toxin injections to the MSA slightly impaired the initial, but not asymptotic, phase of spatial navigation. Injections to the nBM impaired all phases of spatial navigation. Cued navigation, however, was not affected in either the MSA or nBM group. The ventricular injections severely affected spatial and cued navigation. Acetylcholinesterase (AChE) histochemistry and NGFr and choline acetyltransferase immunohistochemistry revealed a loss of (1) almost all NGFr-positive cholinergic neurons in the MSA and AChE fibers in hippocampus (MSA group); (2) almost all NGFr neurons in the nBM, some in the MSA, most AChE fibers in neocortex and some in the hippocampus (nBM group), and (3) almost all NGFr neurons in the MSA and nBM and their corresponding hippocampal and cortical AChE fibers (ventricular group). Cholinergic nBM projections to the amygdala were largely preserved in all groups. The amount of cholinergic fiber loss in the cortex correlated modestly, but significantly, with the severity of impairment of the asymptotic phase of performance of the spatial task. An unambiguous interpretation of the anatomical locus of behavioral deficits was not possible because of damage to cholinergic striatal interneurons (nBM group) and to noncholinergic cerebellar Purkinje cells (ventricular group). These data suggest that the cholinergic cortical system is critical to the performance of this spatial memory task. Cholinergic denervation of the hippocampus alone, however, is not sufficient to impair markedly performance of this task.

Cholinergic innervation of the amygdaloid complex in the human brain and its alterations in old age and Alzheimer's disease

The cholinergic innervation of the human amygdaloid complex was studied immunohistochemically with a choline acetyltransferase (ChAT) antibody in eight brains: five control and three with Alzheimer's disease (AD). All amygdaloid nuclei displayed ChAT-immunopositive axons and varicosities. The density of these axons reached levels that were higher than in any other part of the forebrain except for the striatum. The highest level of ChAT-immunopositive profiles was seen in the basolateral nucleus and the second highest in the lateral part of the central nucleus. The basomedial, accessory basal, and cortical nuclei, the amygdalohippocampal and cortico-amygdaloid transition areas, as well as the anterior amygdaloid area, showed a moderate density of ChAT-positive varicosities and fibers. The lateral nucleus displayed a relatively low density of cholinergic innervation, and there were only rare ChAT-positive fibers in the medial nucleus. Although the level of cholinergic innervation in the lateral nucleus was relatively lower than in many of the other amygdaloid nuclei, it was approximately equivalent to that of entorhinal cortex, a region that receives one of the heaviest cholinergic inputs in the cerebral cortex. The distribution of the cholinergic fibers as studied by ChAT immunohistochemistry was nearly identical to that observed with AChE histochemistry. Quantitative densitometry in control specimens showed that there was no decline of amygdaloid cholinergic input when middle-aged subjects were compared with senescent subjects. In AD there was a severe and regionally selective depletion of this innervation in the amygdaloid complex. The cortical, accessory basal, and lateral nuclei displayed the most severe loss of ChAT-positive profiles, whereas the basolateral, and especially the central, nuclei displayed relatively little change. There was no consistent relationship between the loss of cholinergic fibers and the density of amyloid plaques and neurofibrillary tangles in amygdaloid nuclei.

Cholinergic fiber loss occurs in the absence of synaptophysin depletion in Alzheimer's disease primary visual cortex

The significance of cholinergic degeneration in Alzheimer's disease (AD) depends, in part, on whether it is an early event, possibly integral to the progression of the disease, or a late event, occurring only as a secondary effect of cortical degeneration. We have been studying the primary visual cortex in AD cases, on the assumption that the disease process may be retarded in this relatively-spared area, thus providing a ‘window’ on early AD. In this work, we have quantified acetylcholinesterase fiber density and the density of an immunohistochemical reaction for synaptophysin as measures of cholinergic and total synaptic loss, respectively, in the primary visual cortex of AD and control cases. Cholinergic fibers were depleted to 15% of control values, while synaptophysin density was not significantly altered. Cholinergic degeneration thus appears to occur in the absence of generalized synaptic loss in this area.

Task-dependent memory loss and recovery following unilateral nucleus basalis lesion: behavioral and neurochemical correlation

We found that rats with unilateral AF64A lesions of the nucleus basalis of Meynert (nbM) showed significant impairment of active avoidance and Morris water maze learning. Impairment of active avoidance learning almost subsided within one month but impairment of Morris water maze learning persisted 5 months later. Two weeks after production of the lesion, choline acetyltransferase (ChAT) activity was reduced by 45% in the frontal cortex (FC), but not in the hippocampus or corpus striatum. The decreased ChAT activity in the FC gradually recovered, but it was still reduced by 20% even after 20 weeks. In contrast, ChAT activity on the contralateral side of the FC began to increase from 5 weeks onwards. Histological examination also indicated that loss of cholinergic fibers in the FC gradually recovered with time after induction of the lesion. The results from the present study suggest that specific learning (Morris water maze) tasks involve the cholinergic system and that recovery of cholinergic function (ChAT) may be related to plasticity of the contralateral FC.