Nucleus basalis neuronal loss, neuritic plaques and choline acetyltransferase activity in advanced Alzheimer's disease

Quantitation and three-dimensional reconstruction of Ch4 nucleus in the human basal forebrain

The basal nucleus of Meynert, incorporating the Ch4 group of cholinergic neurons, was examined in six patients with no signs of neurological abnormalities. The ages of the patients ranged from 20 to 80 years. Despite a number of descriptions of these neurons, few age-related studies have been dedicated to the analysis of the entire anteroposterior extent of the nucleus. Staining with cresyl violet and acetylcholinesterase histochemistry, alone or in combination, was used to identify the cytoarchitectural organization of the Ch4. Computer-assisted morphometry was used for three-dimensional visualization and quantitation. The three-dimensional computer reconstructions revealed a continuous ribbon of neurons with a highly variable density. Four distinct subregions could be clearly identified in all cases by their cytoarchitecture and cellular morphology, although these subgroups were different to those previously described. There were no quantitative differences between the hemispheres in volume, density or cell number of the Ch4, although equivalent levels varied in area and density. The measures were similar in all cases with the exception of the case aged 80 years old. The data demonstrate individual variability in three dimensions and confirm previous studies that found only a mild decline of the Ch4 in old age.

Levomepromazine receptor binding profile in human brain--implications for treatment-resistant schizophrenia

The receptor binding profile of levomepromazine (LMP) in human brain was compared with that of clozapine (CLOZ) and chlorpromazine (CPZ). LMP showed significantly greater binding affinity for both alpha-1 and serotonin-2 binding sites than either CLOZ or CPZ, and significantly greater binding to alpha-2 sites than CPZ. A potent pharmacological effect at these receptor sites may explain the beneficial effect of LMP on psychotic symptoms and akathisia in treatment-resistant schizophrenia recently described in 2 open studies. LMP requires further appraisal as a potentially useful neuroleptic in the management of treatment-resistant schizophrenia.

Interactions between the effects of basal forebrain lesions and chronic treatment with MDL 26,479 on learning and markers of cholinergic transmission

The effects of ibotenic acid-induced basal forebrain lesions and treatment with the triazole MDL 26,479 on the acquisition of an operant visual conditional discrimination task and on [3H]hemicholinium-3 and [3H]vesamicol binding were examined. Lesioned animals required more training sessions to acquire the stimulus-response rules of this task. They also showed longer response latencies throughout the experiment. The effects of the treatment with MDL 26,479 (5 mg/kg; i.p. 60 min before each training session) interacted with the effects of the lesion, producing a decrease in the number of sessions required to perform above chance-level in lesioned but not in control animals. MDL 26,479 did not seem to produce immediate performance effects but interacted with the learning process. The lesions destroyed the cell bodies in the area of the substantia innominata, basal nucleus of Meynert, and the globus pallidus. The number of frontocortical cholinergic terminals as primarily indicated by hemicholinium-3 binding was reduced in lesioned animals; however, another measure of cholinergic terminals, vesamicol binding, was unchanged. Behavioral performance of animals correlated significantly with hemicholinium binding in the frontal cortex of the right hemisphere. The fact that the lesion delayed but did not block the acquisition of the task may have been a result of compensatory mechanisms in remaining cholinergic terminals as indicated by stable vesamicol binding. These data allow assumptions about the conditions for the demonstration of beneficial behavioral effects of MDL 26,479. They also suggest that the long-term effects of basal forebrain lesions on cortical cholinergic transmission remain unsettled.

Improvement of ischemic myocardial dysfunction by nisoldipine in relation to its coronary vasodilating action

We examined the cardioprotective effect of nisoldipine against myocardial dysfunction during ischemia and reperfusion in comparison with those of diltiazem and nifedipine in rabbit hearts perfused at constant pressure. These calcium antagonists were administered to the hearts before 60 min of ischemia. They inhibited the increase of end-diastolic pressure during ischemia in a dose-dependent manner. Diltiazem at 1.0 microM, nifedipine at 3.0 microM and nisoldipine at 0.01 microM produced the maximal cardioprotective effect. Nisoldipine had a beneficial effect with less negative inotropic effect than those of diltiazem and nifedipine and it produced a significant increase of coronary flow during reperfusion. When the vascular component was eliminated under constant flow perfusion, nisoldipine also showed the cardioprotective effect. Nisoldipine did not produce any beneficial effect without the inhibition of the increase in end-diastolic pressure during ischemia nor did it do so without the increase of reperfusion flow. Therefore, the nisoldipine-increased coronary flow during reperfusion as well as the inhibition of ischemic contracture by nisoldipine seems to play a crucial role in improving the myocardial dysfunction of ischemic-reperfused hearts.

Heterogeneity and selectivity of the degeneration of cholinergic neurons in the basal forebrain of patients with Alzheimer's disease

Cholinergic neurons were studied by immunohistochemistry, with an antiserum against choline acetyltransferase (ChAT), in the basal forebrain (Ch1 to Ch4) of four patients with Alzheimer's disease (AD) and four control subjects. ChAT-positive cell bodies were mapped and counted in Ch1 (medial septal nucleus), Ch2 (vertical nucleus of the diagonal band), Ch3 (horizontal nucleus of the diagonal band) and Ch4 (nucleus basalis of Meynert). Compared to controls, the number of cholinergic neurons in AD patients was reduced by 50% on average. The interindividual variations in cholinergic cell loss were high, neuronal loss ranging from moderate (27%) to severe (63%). Despite the small number of brains studied, a significant correlation was found between the cholinergic cell loss and the degree of intellectual impairment. To determine the selectivity of cholinergic neuronal loss in the basal forebrain of AD patients, NPY-immunoreactive neurons were also investigated. The number of NPY-positive cell bodies was the same in controls and AD patients. The results (1) confirm cholinergic neuron degeneration in the basal forebrain in AD and the relative sparing of these neurons in some patients, (2) indicate that degeneration of cholinergic neurons in the basal forebrain contributes to intellectual decline, and (3) show that, in AD, such cholinergic cell loss is selective, since NPY-positive neurons are preserved in the basal forebrain.

Intermediary metabolism disturbance in AD/SDAT and its relation to molecular events

1. Early-onset dementia of Alzheimer type (EODAT; AD) and late-onset dementia of Alzheimer type (LODAT; SDAT) are heterogenous in origin. 2. A common superordinate pathobiochemical principle in the etiopathogenesis of both types of dementia is neuronal energy failure with subsequent abnormalities in cellular Ca2+ homeostasis and glucose-related amino acid metabolism. 3. These metabolic abnormalities are assumed to occur first at axodendritic terminals of the acetylcholinergic-glutamatergic circuit and to cause morphological damage at synaptic sites. 4. Metabolic stress and structural damage at synaptic sites may induce enhanced formation of APP and its cleavage product amyloid. 5. Energy-metabolism related abnormalities along with functional and structural changes at synaptic sites of the acetylcholinergic-glutamatergic circuit may precede the formation of amyloid in DAT brain.

Effects of propentofylline, a NGF synthesis stimulator, on alterations in muscarinic cholinergic receptors induced by basal forebrain lesion in rats

Basal forebrain (BF) lesions induced by ibotenic acid produced increases in the Bmax and Kd values of [3H]QNB binding sites in the frontal cortex, parietal cortex, and hippocampus. Twenty-eight-day successive administration of propentofylline (10 and 25 mg/kg, p.o.) significantly reduced the Kd values of [3H]QNB binding sites, to the levels of those in a sham group, in a dose-dependent manner. Moreover, propentofylline (25 mg/kg, p.o.) significantly reduced the Bmax value of [3H]QNB binding sites compared with that in a vehicle-treated BF-lesioned group. These results suggest that successive administration of propentofylline ameliorates changes in muscarinic cholinergic receptors through improving presynaptic cholinergic dysfunction.

Effects of nerve growth factor (NGF) in rats with basal forebrain lesions

Effects of nerve growth factor (NGF) on the basal forebrain (BF) lesion-induced amnesia in rats were investigated. When NGF infusion was begun immediately after the formation of BF lesions, NGF ameliorated amnesia in a water maze task and showed a tendency to increase choline acetyltransferase (CAT) activity in the fronto-parietal cortex. The amnesia and the decrease of CAT activity were not ameliorated when NGF infusion was begun 4 weeks after BF lesion formation. These observations suggest that NGF may act as a trophic and/or a protective factor on partially damaged cholinergic neurons and that the efficacy of NGF was influenced by the phase of neuronal damage.

Specificity of 192 IgG-saporin for NGF receptor-positive cholinergic basal forebrain neurons in the rat

A monoclonal antibody to the rat nerve growth factor (NGF) receptor, 192 IgG, accumulates bilaterally and specifically in cholinergic basal forebrain (CBF) cells following intraventricular injection. An immunotoxin composed of 192 IgG linked to saporin (192 IgG-saporin) has been shown to destroy cholinergic neurons in the basal forebrain. We sought to determine if intraventricular 192 IgG-saporin affected choline acetyltransferase (ChAT) enzyme activity in the CBF terminal projection fields. ChAT assays from 192 IgG-saporin-treated animals showed significant time-dependent decreases in ChAT activity in the neocortex, olfactory bulb and hippocampus, compared to PBS- or OKT1-saporin-injected controls. ChAT and tyrosine hydroxylase activity in the striatum was always unchanged by 192 IgG-saporin. ChAT immunohistochemistry was confirmative of major cell loss in the CBF, while other cholinergic nuclei appeared unremarkable. The data provide further evidence of the selectivity of 192 IgG-saporin in abolishing cholinergic, NGF receptor-positive CNS neurons.

Soluble and membrane-bound forms of brain acetylcholinesterase in Alzheimer's disease

In order to determine the effect of Alzheimer's disease on the relative distribution of soluble and membrane-bound molecular forms of acetylcholinesterase (AChE) in the brain, postmortem samples (delay interval less than 12 h) were obtained from parietal cortex (Brodmann area 40) and hippocampus as well as the areas containing their respective projection nuclei, i.e., substantia innominata and septal nucleus, in 9 patients with Alzheimer's disease (AD) and 4 normal controls. The monomer (G1), dimer (G2), and tetramer (G4) forms of AChE were examined. In AD compared to controls, significant changes occurred in area 40 and hippocampus but not in the areas containing projection nuclei, and included loss of mean total AChE activity, decrease in the relative percentage of membrane-bound G4, and increase in the relative percentage of soluble G1-G2. Percent of soluble G4 was unaffected in AD brain. In area 40 but not hippocampus a large increase in percent membrane-bound G1-G2 occurred. Thus, these results emphasize that the selective decrease in membrane-bound G4 accounts for the decrease in total G4 activity in AD brain.

Distribution and relative density of p75 nerve growth factor receptors in the rat brain as a function of age and treatment with antibodies to nerve growth factor

It is clear that nerve growth factor (NGF) has a role in the central nervous system. In order to begin to determine the possible roles of NGF in the CNS, neonatal rats were given daily subcutaneous injections of antibodies to NGF (ANTI-NGF) beginning at birth for a period of one month. By utilizing the monoclonal antibody, 192-IgG, which recognizes the p75 NGF receptor (NGFR), and standard immunohistochemical techniques we have localized p75 NGFR in variously aged ANTI-NGF-treated animals and compared the anatomic localization and relative density of the p75 NGFR immunoreactive (p75 NGFR-I) regions to same age untreated and preimmune sera-treated littermates. We confirm previously reported localizations of p75 NGFR-I in the rat brain. In addition, we demonstrate that p75 NGFR-I levels of ANTI-NGF-treated rats found in the molecular, the granular and the Purkinje cell layers of the cerebellum, the vestibular nuclei, the spinal tract of V and the cochlear nuclei remain at lower concentrations compared to same-age control animals. We also demonstrate that p75 NGFR-I levels in the basal nucleus approaches background levels after ANTI-NGF treatment. We hypothesize that ANTI-NGF biologically inactivates NGF, which over a period of 30 days results in decreased p75 NGFR-I. These results are consistent with neuronal loss in these regions following ANTI-NGF treatment. Furthermore, the immunological methods used to produce the specific deficits in the present study may have broader implications with respect to usefulness as a method for determining the dependency of CNS neuronal populations for a putative neurotrophic factor and as a method for the development of models of neurodegenerative diseases.

Cholecystokinin protects cholinergic neurons against basal forebrain lesion

Alzheimer's Disease (AD) patients have a severe degeneration of cholinergic neurons in their cerebral cortices. Basal forebrain (BF)-lesioned rat is used as a model animal of a cholinergic deficit in the cerebral cortex. Cholinergic markers were decreased in the cerebral cortex of BF-lesioned rats. Intracerebroventricular continuous infusion of cholecystokinin octapeptide (CCK8) following BF lesion obviously preserved these cholinergic markers. These results suggest that CCK8 prevents the degeneration of cholinergic neurons in the cerebral cortex following BF lesion.

Identification and characterization of a large human brain gene whose expression is increased in Alzheimer disease

A cDNA clone that was isolated from a human substantia innominata cDNA library is described. By Northern hybridization analysis, a 15.5 kilobase (kb) transcript was identified by this clone in RNA samples from several brain regions, but not in RNA samples from white matter, liver or placenta. Hybridization to human genomic DNA revealed a pattern indicative of a single copy gene. DNA sequence analysis showed 3.0 kb of 3' untranslated region with no significant open reading frame. An additional cDNA clone, representing a section of an alternate form of this transcript, was isolated that contained an additional 1.5 kb at the 3' end. Using a nuclease protection assay, the expression of this gene was found to be increased by 30% in Alzheimer disease temporal cortex RNA samples compared to temporal cortex RNA samples from normal controls, but to be at equivalent levels in Alzheimer disease, as compared to normal control, substantia innominata RNA samples. This assay also showed that this gene was expressed at 3.5-fold higher levels in normal substantia innominata than in normal cerebellum. In situ hybridization analysis showed that the transcript could be detected in cerebellar neurons.

Alzheimer's disease: is the decrease of the cholinergic innervation of the hippocampus related to intrinsic hippocampal pathology?

Consistent findings in the hippocampi of patients with Alzheimer's disease are the presence of neurofibrillary tangles in pyramidal neurons and the loss of choline acetyltransferase activity due to degeneration of hippocampal cholinergic terminals. The present study sought to clarify, in the brains of five patients with Alzheimer's disease and four controls, whether the loss of cholinergic terminals in the hippocampal stratum pyramidale in Alzheimer's disease is related to degenerative changes in hippocampal pyramidal cells. A polyclonal antibody to human choline acetyltransferase was employed to visualize immunohistochemically cholinergic terminals. Hippocampal neurons were stained with Cresyl Violet, neurofibrillary tangles with thioflavin S and a monoclonal antibody against phosphorylated neurofilament (RT97). Quantification of the stained structures was performed in CA4, CA1 and the subiculum, on five sections selected from the entire anteroposterior extent of each hippocampus. In the group of Alzheimer patients, the densities of cholinergic terminals were homogeneously diminished in the three hippocampal subregions in comparison with the controls (32-33%). In contrast, a significant loss of pyramidal neurons was found only in CA1, and the density of neurofibrillary tangles was markedly increased only in CA1 and the subiculum in Alzheimer's disease. These findings suggest that there is no relationship between the loss of cholinergic terminals and the degeneration of pyramidal cells in the hippocampus of patients with Alzheimer's disease.

Deficits in the somatostatin SS1 receptor sub-type in frontal and temporal cortices in Alzheimer's disease

The aim of this study was to evaluate the possible differential alterations of somatostatin (SRIF) receptor sub-types in Alzheimer's disease (AD). Consequently the binding profile of cortical SRIF receptors were examined in normal and AD brains using non-selective ([125I]Tyr0, D-Trp8-SRIF14) and SS1 receptor sub-type-selective ([125I]SMS204-090) radioligands. Maximal binding capacities, but not affinities, were reduced for both ligands in the temporal cortex. In contrast, only the maximal binding capacity of [125I]SMS204-090 was significantly reduced (68%) in the frontal cortex; no alterations were detected using the non-selective probe. This reveals that while the maximal binding capacity of the SS1 receptor sub-type is altered in frontal and temporal cortices in AD, other putative cortical SRIF receptor classes (such as SS2 sites) are not as broadly affected. This could be of significance for eventual therapeutic approaches using SRIF-related analogues.

Comparative alterations of nicotinic and muscarinic binding sites in Alzheimer's and Parkinson's diseases

We have recently reported on the differential alterations of various cholinergic markers in cortical and subcortical regions in Alzheimer's disease (AD). The main purpose of the present study was to determine if cholinergic deficits observed in patients with AD are unique to this disorder or can be generalized to others such as idiopathic Parkinson's disease (PD) and PD with Alzheimer-type dementia (PD/AD). Muscarinic M1, M2, and nicotinic receptor binding parameters (KD and Bmax) were determined in various cortical and subcortical areas using selective radioligands ([3H]pirenzepine, [3H]AF-DX 116, and N[3H]methylcarbamylcholine). Choline acetyltransferase activity was also determined as a marker of the integrity of cholinergic innervation. Alterations of cholinergic markers are comparable in cortical areas in AD, PD, and PD/AD brains. In frontal and temporal cortices, as well as in the hippocampus, choline acetyltransferase activity and binding capacities of M2 and nicotinic binding sites are similarly decreased in these three disorders compared with age-matched control values. M1 receptor binding parameters are not significantly modified in cortical areas in patients with these disorders. In contrast, important differences between AD and PD brain tissues are found in subcortical areas such as the striatum and the thalamus. The density of M1 sites is significantly increased in striatal areas only in patients with AD, whereas densities of nicotinic sites are decreased in thalamus and striatum in PD and PD/AD, but not AD, brain tissues. The binding capacity of M2 sites is apparently unchanged in subcortical areas in all three disorders, although tendencies toward reductions are observed in the striatum of PD and PD/AD patients. Thus, although comparable alterations of various cholinergic markers are observed in cortical areas in the three neurological disorders investigated in the present study, important differences are seen in subcortical areas. This may be relevant to the respective etiological and clinical profiles of AD and PD.

Pathology of Parkinson's disease. Changes other than the nigrostriatal pathway

In Parkinson's disease (PD), in addition to degeneration of the nigrostriatal dopaminergic pathway, a variety of neuronal systems are involved, causing multiple neuromediator dysfunctions that account for the complex patterns of functional deficits. Degeneration affects the dopaminergic mesocorticolimbic system, the noradrenergic locus ceruleus (oral parts) and motor vagal nucleus, the serotonergic raphe nuclei, the cholinergic nucleus basalis of Meynert, pedunculopontine nucleus pars compacta, Westphal-Edinger nucleus, and many peptidergic brainstem nuclei. Cell losses in subcortical projection nuclei range from 30 to 90% of controls; they are more severe in depressed and demented PD patients. Most of the lesions are region-specific, affecting not all neurons containing a specific transmitter or harboring Lewy bodies. In contrast to Alzheimer's disease (AD), subcortical system lesions in Parkinson's disease appear not to be related to cortical pathology, suggesting independent or concomitant degeneration. The pathogenesis of multiple-system changes contributing to chemical pathology and clinical course of Parkinson's disease are unknown.

Staurosporine, a protein kinase inhibitor, attenuates basal forebrain-lesion-induced amnesia and cholinergic neuronal deficit

We have investigated whether administration of staurosporine, which has been reported to induce differentiation in the human neuroblastoma cell in vitro, attenuates amnesia induced by basal forebrain lesion in rats. Multiple dosage of staurosporine at the doses of 0.05 and 0.1 mg/kg (i.p.) attenuated the impaired performance of the water maze task. Moreover, staurosporine (0.1 mg/kg) reversed the decrease of choline acetyltransferase activity in the fronto-parietal cortex. These results suggest that staurosporine attenuates amnesia through reversal of deficits in cholinergic neurons induced by basal forebrain lesion, and that neurotrophic factor-like substances may open the way for novel therapeutic approaches to Alzheimer's disease.

Long-term administration of mouse nerve growth factor to adult rats with partial lesions of the cholinergic septohippocampal pathway

Nerve growth factor (NGF), a neurotrophic factor acting on cholinergic neurons of the basal forebrain, has been proposed as a treatment for Alzheimer's disease. Experimental support for its pharmacological use is derived from short-term studies showing that intraventricular administration of NGF during 2-4 weeks protects cholinergic cell bodies from lesion-induced degeneration, stimulates synthesis of choline acetyltransferase, and improves various behavioral impairments. To investigate the consequences of long-term NGF administration, we tested whether cholinergic cell bodies are protected from lesion-induced degeneration and whether cholinergic axons are stimulated to regrow into the denervated hippocampus following fimbrial transections. We found that intraventricular injections of NGF twice a week for 5 months to adult rats resulted in extended protection of cholinergic cell bodies from lesion-induced degeneration and did not produce obvious detrimental effects on the animals. NGF treatment mildly stimulated growth of cholinergic neurites within the 2-mm area directly adjacent to the fimbrial lesion but it failed to induce significant homotypic growth of cholinergic neurites into the deafferented hippocampus.

[3H]vesamicol binding in human brain cholinergic deficiency disorders

We measured the binding of the vesicular acetylcholine transport blocker [3H]vesamicol (2-[4-phenylpiperidino] cyclohexanol; AH-5183) to autopsied frontal cortex and amygdala of patients from 4 disorders having a marked brain cholinergic reduction, namely Alzheimer's disease, Parkinson's disease with dementia, dominantly inherited olivopontocerebellar atrophy and Down's syndrome. Although mean activity of the specific cholinergic marker enzyme choline acetyltransferase (ChAT) was markedly reduced by about 60% in frontal cortex in the 4 patient groups and by 80% or greater in amygdala of the Alzheimer's and Down's syndrome patients, [3H]vesamicol binding density was, on average, either normal or only slightly reduced as compared with the controls. This discrepancy suggests that in human brain [3H]vesamicol binding is either not preferentially localized to cholinergic nerve endings or, in these cholinergic deficiency syndromes, a substantial proportion of the vesamicol binding sites persist on cholinergic nerve terminals despite loss of ChAT activity.

Choline acetyltransferase activity and [3H]vesamicol binding in the temporal cortex of patients with Alzheimer's disease, Parkinson's disease, and rats with basal forebrain lesions

[3H]Vesamicol binding was characterized in human brain post mortem. The number of binding sites was then determined in parallel with choline acetyltransferase activity in the temporal cortex of patients with Alzheimer's disease, demented and non-demented patients with Parkinson's disease, and in the cerebral cortex of rats with quisqualic acid lesions of the nucleus basalis magnocellularis. Whereas choline acetyltransferase activity decreased in patients with Alzheimer's or Parkinson's disease indicating loss of cholinergic innervation, the number of binding sites for [3H]vesamicol was the same as or higher than in controls. Similar results were obtained with the lesioned rats. It is suggested that the increase in binding sites may reflect compensatory regulation of the spared neurons at the level of the synaptic vesicle.

NGF receptor gene expression is decreased in the nucleus basalis in Alzheimer's disease

Basal forebrain neuronal atrophy in Alzheimer's disease (AD) may be caused by a deficit in the NGF responsiveness of magnocellular cholinergic neurons which project to the cerebral cortex and hippocampal formation. We have used in situ hybridization to show that NGF-receptor (NGF-R) mRNA-positive neurons are lost within all divisions of the nucleus basalis of Meynert (Ch4 cell group) in AD patients as compared to normal aged controls. The posterior division of the nucleus basalis showed the largest decrease in NGF-R mRNA hybridization in the disease, with no overlap in neuronal number between AD cases and normal controls. Northern (RNA) blotting showed decreased levels of NGF-R mRNA in the nucleus basalis in the disease. No differences in the number of NGF-R mRNA-positive neurons between normal aged and AD patients were detected within the NGF-responsive cell groups of the medial septum (Ch1) and nucleus of the vertical limb of the diagonal band (Ch2). These results show that NGF-R gene expression is selectively reduced within basal forebrain neuronal populations which exhibit degenerative changes in AD.

The olfactory system and Alzheimer's disease

Alzheimer's disease (AD) is considered to be the number one health problem and seems to be reaching epidemic proportion in the USA. The cause of AD is not known, a reliable animal model of the disease has not been found and appropriate treatment of this dementia is wanting. The present review focuses on the possibility that a virus or exogenous toxic materials may gain access to the CNS using the olfactory mucosa as a portal of entry. Anterograde and retrograde transport of the virus/zeolites to olfactory forebrain regions, which receive primary and secondary projections from the main olfactory bulb (MOB) and which, in turn, project centrifugal axons to the MOB, may initiate cell degeneration at such loci. Pathological changes may, thus, be initially confined to projecting and intrinsic neurons localized in cortical and subcortical olfactory structures; arguments are advanced which favor the view that excitotoxic phenomena could be mainly responsible for the overall degenerative picture. Neurotoxic activity may follow infection by the virus itself, be facilitated by loss of GABAergic terminals in olfactory cortex, develop following repeated episodes of physiological long term potentiation (which unmasks NMDA receptors) or be due to excessive release, faculty re-uptake or altered glutamate receptor sensitivity. Furthermore, a reduction in central inhibitory inputs to the MOB might then result in disinhibition of mitral/tufted neurons and enhance the excitotoxic phenomena in the MOB projecting field. Within this context, and in line with recent studies, it is believed that pathology begins at cortical (mainly olfactory) regions, basal forebrain neurons being secondarily affected due to retrograde degeneration. In addition, failure to produce a critical level of neurotrophic factors by a damaged MOB and olfactory cortex, could adversely affect survival of basal cholinergic neurons which innervate both regions. Support for these hypothesis is provided, first, by recent reports on pathological findings in AD brains which seem to involve preferentially the olfactory and entorhinal cortices, the olfactory amygdala and the hippocampus, all of which receive primary or secondary projections from the MOB; secondly, by the presence of severe olfactory deficits in the early stages of the disease, mainly of a discriminatory nature, which points to a malfunction of central olfactory structures.

Strategies for the identification of novel brain specific genes affected in Alzheimer disease

The pathological changes that occur in Alzheimer disease (AD) brain lead to a large loss of various classes of neurons and the production of novel proteinaceous elements such as neuritic plaques and neurofibrillary tangles. For the neuronal loss to occur and these elements to arise, there must be a disturbance in the expression or regulation of genes that code for proteins required for normal cell maintenance, or perhaps even for the expression of genes unique to AD. We describe the construction of a cDNA library from the human substantia innominata and strategies for isolating genes that are expressed differentially between brain regions and which may be affected by AD. Some of the results obtained using these strategies and a preliminary description of a novel brain specific mRNA of 15.5kb, whose expression is increased in AD affected temporal cortex, are presented.

Non-Alzheimer-type pattern of brain cholineacetyltransferase reduction in dominantly inherited olivopontocerebellar atrophy

We recently reported reduced activity of the cholinergic marker enzyme cholineacetyltransferase (ChAT) in several brain regions of patients with dominantly inherited olivopontocerebellar atrophy (OPCA). To document the regional extent of these changes we performed a comprehensive examination of the behavior of ChAT throughout both cerebral cortical and subcortical brain areas in 5 patients from one large OPCA pedigree. As compared with the controls, mean ChAT activities in OPCA were reduced by 39 to 72% in all (n = 27) cerebral cortical areas examined and in several thalamic subdivisions, caudate head, globus pallidus, red nucleus, and medial olfactory area. In contradistinction to findings in Alzheimer's disease (AD), mean ChAT levels in OPCA amygdala and hippocampal subdivisions were either normal or only mildly reduced. The lack of severe disabling dementia in our OPCA patients compared with AD patients having a similar cortical cholinergic reduction could be explained by an absence of either a marked cholinergic loss in amygdala or hippocampus or significant loss of noncholinergic cerebral cortical and limbic neurons as occurs in AD brain. We suggest that this and other OPCA pedigrees having a cortical cholinergic reduction represent a unique model for the study of behavioral consequences of a more selective cerebral cortical cholinergic lesion rather than a limbic cholinergic lesion.

Nerve growth factor receptor immunoreactive profiles in the normal, aged human basal forebrain: colocalization with cholinergic neurons

A monoclonal antibody raised against the receptor for nerve growth factor (NGF) has been used to map the distribution of NGF receptor-containing profiles within the human basal forebrain of four male and three female elderly patients without neurologic or psychiatric illness. Immunohistochemically processed tissue reveals a continuum of NGF receptor-positive neurons located within the medial septum, vertical and horizontal limb nuclei of the diagonal band, and nucleus basalis. NGF receptor-containing neurons are also found within the bed nucleus of the stria terminalis, the anterior commissure, the internal capsule, and the internal and external medullary laminae of the globus pallidus. Virtually all (greater than 95%) NGF receptor-containing neurons colocalize with the specific cholinergic marker choline acetyltransferase (ChAT) or the nonspecific marker acetylcholinesterase (AChE). Conversely, a few cholinergic perikarya are found which are not NGF receptor positive (and vice versa). These findings demonstrate that human basal forebrain neurons on which NGF receptor immunoreactivity is detected are primarily cholinergic and analogous to the nonhuman primate Ch1-Ch4 subgroups of Mesulam et al. (J. Comp. Neurol., 214:170-197, '83). NGF receptor-containing fiber tracts are observed emanating from the medial septum and vertical limb nucleus of the diagonal band coursing medially within the fornix. Another fascicle originating mainly from the nucleus basalis and travelling within the external capsule enroute to the cortex is observed innervating all cortical layers. Comparison of NGF receptor- and ChAT-containing neurons reveals cholinergic perikarya within the striatal complex, whereas virtually no NGF receptor-containing neurons are found in these structures. An occasional displaced NGF receptor-containing neurons is seen in the ventrolateral portion of the putamen and the white matter underlying the nucleus accumbens. These data are discussed in terms of the relationship of NGF receptor- and ChAT-containing neurons within the basal forebrain and in terms of the possible functional significance of NGF in normal and diseased brain.

Intracerebral drug delivery in rats with lesion-induced memory deficits

Pharmacological treatments directed at increasing cortical acetylcholine activity in patients with Alzheimer's disease have largely been disappointing, perhaps because denervated areas of brain may not be exposed to adequate amounts of drug. A new method has been developed to enable localized intracerebral delivery of neurotransmitter substances using a polymeric drug delivery system. Microspheres of a polyanhydride sebacic acid copolymer were impregnated with bethanechol, an acetylcholinesterase-resistant cholinomimetic. Twenty rats received bilateral fimbria-fornix lesions, producing cholinergic denervation of the hippocampus and marked impairment in spatial memory. The animals were trained for 2 weeks to run after which they received bilateral intrahippocampal implants of saline (five rats), blank polymer (five rats), or bethanechol-impregnated polymer (10 rats). Following implantation, spatial memory was assessed by radial-maze performance testing for 40 days. Untreated lesioned rats showed persistently poor spatial memory, entering maze arms with near random frequency. Similarly, animals treated with saline and blank polymer did not improve after implantation. Rats treated with bethanechol-impregnated microspheres, however displayed significant improvement within 10 days after implantation; this improvement persisted for the duration of the experiment (p less than 0.05, Student's t-test). Histological analysis of regional acetylcholinesterase staining showed widespread loss of activity throughout the hippocampus bilaterally in all animals. The microsphere implants were visible within the hippocampus, with minimal reactive changes in surrounding brain. It is concluded that intracerebral polymeric drug delivery successfully reversed lesion-induced memory deficits, and has potential as a neurosurgical treatment method for Alzheimer's disease and other neurodegenerative disorders.

The nucleus basalis of Meynert in parkinsonism-dementia of Guam: a morphometric study

The nucleus basalis of Meynert (nbM) was studied morphometrically in three Guamanians with parkinsonism-dementia (PD) and in two Guamanian and two non-Guamanian controls. Paraffin-embedded blocks of the nbM were serially sectioned (20 microns thick) at increments of 200 microns so that a total of 24 sections (eight each from the anterior, intermediate and posterior sectors of the nbM) were studied. The mean cell density was determined for each sector and the diameter of 50 neurons, randomly chosen in the region of apparent maximal density, was calculated. A decrease of the mean cell density, due to the loss of neurons with diameters larger than 20 microns, was found in the PD cases compared to the controls. Two PD patients exhibited striking neuronal loss (65-95%) with predominant involvement of the intermediate and posterior sectors, while the third case showed only minimal neuronal loss in these sectors (15-40%). In both Guamanian and non-Guamanian controls large neurons (diameters greater than or equal to 20 microns) exceeded small neurons while the reverse was true in all sectors of the nbM for the PD cases. These data, while confirming a previous study reporting neuronal loss in the nbM of PD patients, underline the importance of detailed morphometric analysis of the different sectors of the nbM to recognize those patients in whom lesions are not uniformly distributed.

Behavioral neuroanatomy of cholinergic innervation in the primate cerebral cortex

This brief review summarizes the anatomy and behavioral affiliations of cortical cholinergic innervation. A depletion of this innervation has been reported in a number of human neurodegenerative conditions (including Alzheimer's disease) and may contribute to the genesis of the associated behavioral disturbances.

Choline acetyltransferase-like immunoreactivity in the hippocampal formation of control subjects and patients with Alzheimer's disease

A qualitative and quantitative immunohistochemical study of cholinergic systems in the human hippocampal formation was performed with an antibody against choline acetyltransferase. Four control subjects and six patients with Alzheimer's disease, matched for age and post-mortem delay, were examined. Immunoreactive nerve fibres and terminals were visualized, but no cholinergic cell bodies were seen. The distribution of the fibres and terminals suggests that a major afferent cholinergic pathway enters the hippocampus dorsally via the fimbria-fornix, a minor input entering from the temporal lobe along the alvear path. The cholinergic innervation suffers some degenerative change in normal aged subjects, but decreases considerably in density in patients with Alzheimer's disease. The extent of the decrease differs somewhat among the subregions of the hippocampus, but is homogeneously distributed within each subregion, and throughout the rostrocaudal extent of the structure. Compensatory sprouting in reaction to denervation was not detected.

The differential involvement of subcortical nuclei in senile dementia of Alzheimer's type

Cell counts have been performed on cholinergic subcortical nuclei, dorsal raphe nucleus, and locus caeruleus from up to 18 cases of Alzheimer's disease and 10 age-matched control subjects. In general, the extent of cell loss in these structures was similar. In the basal nucleus the anteromedial subdivision was the least, and the posterior subdivision the most affected. A subgroup of demented subjects with Alzheimer's disease had a relatively preserved basal nucleus, and frontal lobe (CAT) choline acetyltransferase activities similar to those in control subjects, but significantly more neuronal loss in the locus caeruleus.

Differential alteration of various cholinergic markers in cortical and subcortical regions of human brain in Alzheimer's disease

The main objective of the present study was to determine whether cholinergic markers (choline acetyltransferase activity and nicotinic and muscarinic receptors) are altered in Alzheimer's disease. Choline acetyltransferase activity in Alzheimer's brains was markedly reduced in various cortical areas, in the hippocampus, and in the nucleus basalis of Meynert. The maximal density of nicotinic sites, measured using the novel nicotinic radioligand N-[3H]methylcarbamylcholine, was decreased in cortical areas and hippocampus but not in subcortical regions. M1 muscarinic cholinergic receptor sites were assessed using [3H]pirenzepine as a selective ligand; [3H]pirenzepine binding parameters were not altered in most cortical and subcortical structures, although the density of sites was modestly increased in the hippocampus and striatum. Finally, M2-like muscarinic sites were studied using [3H]-acetylcholine, under muscarinic conditions. In contrast to M1 muscarinic sites, the maximal density of M2-like muscarinic sites was markedly reduced in all cortical areas and hippocampus but was not altered in subcortical structures. These findings reveal an apparently selective alteration in the densities of putative nicotinic and muscarinic M2, but not M1, receptor sites in cortical areas and in the hippocampus in Alzheimer's disease.

Distribution and some projections of cholinergic neurons in the brain of the common marmoset, Callithrix jacchus

The distribution of choline acetyltransferase-immunoreactive (ChAT-IR) neurons was studied in the brain of the common marmoset by using immunohistochemistry. ChAT-IR neurons were found in the medial septal nucleus, vertical and horizontal limb nuclei of the diagonal band, the nucleus basalis of Meynert, pedunculopontine nucleus and laterodorsal tegmental nucleus, and also in the striatum, habenula, and brainstem cranial nerve motor nuclei. The organization of ChAT-IR neurons in the basal forebrain, midbrain, and pons is consistent with the Ch1-Ch6 nomenclature introduced by Mesulam et al. ('83). The combination of the retrograde transport of HRP-WGA with ChAT immunohistochemistry revealed the distribution of neurons in the Ch4 cell group projecting to the dorsolateral prefrontal cortex. The activity of ChAT was highest in limbic cortical structures, such as the hippocampus, and lowest in association areas of the neocortex. Lesions at various loci in the basal forebrain resulted in differential patterns of ChAT loss in the cortex, which suggests some degree of topographical organization of Ch4 projections to the cortical mantle.

Developmental change in the nerve growth factor action from induction of choline acetyltransferase to promotion of cell survival in cultured basal forebrain cholinergic neurons from postnatal rats

Nerve growth factor (NGF), a well-characterized target-derived growth factor, has been postulated to promote neuronal differentiation and survival of the basal forebrain cholinergic neurons. In the present paper, we demonstrate that a developmental change in NGF action occurs in postnatal rat basal forebrain cholinergic neurons in culture. Firstly, NGF acts as maturation factor by increasing choline acetyltransferase (ChAT) activity and acts later as a survival factor. In dissociated cell cultures of septal neurons from early postnatal (P1-4) rats, ChAT activities were increased by the addition of NGF. That is, ChAT activities in P1 septal cells cultured for 7 days was increased 4-fold in the presence of NGF at a concentration of 100 ng/ml. However, the number of the acetylcholinesterase (AChE)-positive neurons was not significantly different between these groups. In contrast, septal neurons from P8 to P14 rats showed different responses to NGF. Although the P14 septal neurons in culture for 7 days without NGF lost about half of the ChAT activity during a 7-day cultivation, cells cultured with NGF retained the activity at the initial level. The number of AChE-positive neurons counted in cultures with NGF was much greater than the number without NGF. These results suggest that, during the early postnatal days, the action of NGF on the septal cholinergic neurons in culture changes from induction of ChAT activity to the promotion of cholinergic neuronal cell survival. During this developmental period in vivo, septal neurons are terminating their projections to the hippocampal formation. Similar NGF-regulated changes in cholinergic neurons were observed in cultured postnatal neurons from vertical limb of diagonal band. An analogy has been pointed out between the neuronal death of the basal forebrain cholinergic neurons and a similar neuronal death in senile dementia, especially Alzheimer's type. The work reported here might present a possibility that NGF could play a role in preventing the loss of the basal forebrain cholinergic neurons in this disease.

Topography of nerve cell loss from the locus caeruleus in middle aged persons with Down's syndrome

A topographical analysis of nerve cell loss from the locus caeruleus in middle aged patients with Down's syndrome (whose brains show the pathological changes of Alzheimer's disease), has shown that cell loss is confined to dorsal areas, being least most rostrally and greatest caudally. By contrast, there is no significant cell loss from ventral parts of the locus, at any point along its rostrocaudal length. Dorsally located neurones of the locus project to cerebral cortex; ventrally located neurones to non-cortical areas such as basal ganglia, cerebellum and spinal cord. These data suggest that the damage to nerve cells of the locus caeruleus in Down's syndrome at middle age, like that seen in Alzheimer's disease itself, relates to primary pathological events within the cortical projection fields of affected cells with perikaryal loss following on as a later change.

Quantitative changes in some subcortical nuclei in aging, Alzheimer's disease and Parkinson's disease

In normal aging, AD/SDAT and Parkinson's disease, the changes in subcortical neuronal systems are similar in quality and distribution, but highly variable in their intensity. Some correlations between the intensity and pattern of lesions in some subcortical nuclei with changes in cortical target areas in AD/SDAT suggest that age-related subcortical changes may represent a secondary phenomenon (antograde or retrograde degeneration) due to primary cortical damage. However, severe depletion of subcortical nuclei in both AD/SDAT and PD may also occur without considerable cortical pathology which is more compatible with a concomitant degeneration of both subcortical and intracortical neuronal systems.

Molecular biology and neurobiology of choline acetyltransferase

In the 45 years since the first description of choline acetyltransferase (ChAT; EC 2.3.1.6.), significant progress has been made in characterizing the molecular properties of this important neurotransmitter synthetic enzyme. We are now on the verge of understanding its genetic regulation and biological function(s). The Drosophila cDNA has been cloned, sequenced, and expressed in both a eucaryotic and a procaryotic system. The levels of ChAT specific mRNA have been determined during Drosophila development. Monoclonal and polyclonal antibodies have been produced to the enzyme from a variety of sources and used for biochemical and immunocytochemical studies. Two well characterized genetic systems have identified the ChAT gene and described a series of useful alleles. As a nervous system specific protein expressed only in the subset of neurons using acetylcholine as a neurotransmitter, ChAT is a good model for uncovering the processes and factors responsible for regulating genes involved in neurotransmitter phenotype selection and maintenance. Recent studies have described the purification of a cholinergic factor from muscle conditioned medium and indicated the potential importance of nerve growth factor (NGF) for regulating ChAT expression in the central nervous system. These factors, or ones remaining to be discovered, may be involved in the etiology or disease process of neurodegenerative nervous system disorders such as Alzheimer's disease.