Abnormal Tau proteins in progressive supranuclear palsy. Similarities and differences with the neurofibrillary degeneration of the Alzheimer type

We have previously shown that abnormal Tau species are produced during the neurofibrillary degeneration of the Alzheimer type. These abnormal Tau proteins consist of a characteristic triplet named Tau 55, Tau 64 and Tau 69 which are constantly found in Alzheimer's disease (AD) and Downs syndrome brain regions with tangles. To determine if abnormal Tau species are also produced in other neurodegenerative conditions where intraneuronal filamentous Tau aggregates are observed, we have undertaken an immuno-blot study of brain homogenates from patients with progressive supranuclear palsy (PSP), a neurological disorder characterized by the presence of tangles in subcortical and cortical brain areas. We show here that abnormal Tau species are produced in PSP but that they are different from those in AD. Indeed, although Tau 64 and 69 were present in PSP brain homogenates, possibly as the result of an abnormal phosphorylation as in AD, they were detected in smaller amounts (three times lower) than in AD. In addition Tau 55 was undetected by the immunological tools, such as the absorbed anti-PHF antisera, which specifically label the abnormal Tau proteins. Also the two-dimensional analysis revealed different isoelectric properties. Our results suggest that the production of abnormal Tau species is a very important event during all types of neurofibrillary degeneration. The differences in the pathological Tau-variant profile that were observed between PSP and AD possibly reflect different etiopathogenetic pathways and might explain the formation of different types of filamentous Tau aggregates.

Absence of aluminium in Alzheimer's disease brain tissue: electron microprobe and ion microprobe studies

Brain tissue from the frontal cortex and hippocampal formation, taken at autopsy or biopsy from 7 patients with Alzheimer's disease, was studied by two methods of microanalysis. One case of Down's syndrome was also studied. Electron probe microanalysis of the frontal cortex and Ammon's horn of the hippocampus showed no aluminium in the various cell organelles, especially in the lysosomes, although some aluminium was found in a few contaminating dusts. Ion microscopy, a method of extremely high sensitivity, also showed the absence of an aluminium signal.

Infarction in the anterior rostral cerebellum (the territory of the lateral branch of the superior cerebellar artery)

We report 9 patients with an isolated infarct of the anterior part of the rostral cerebellum, ie, the territory of the lateral branch of the superior cerebellar artery. Clinicoanatomic correlations are based on CT, MRI, or both in 8 patients and on pathologic data in the ninth. The main clinical features were ipsilateral dysmetria and axial lateropulsion, dysarthria, and unsteadiness. In 1 patient, the clinical presentation mimicked a lacunar stroke (dysarthria and clumsy hand syndrome). There were no edematous cerebellar infarcts with signs of brainstem compression, and all patients spontaneously improved without significant sequellae. Angiography in 2 patients and pathologic examination of arteries in 1 patient disclosed no occlusion in the vertebrobasilar system. Six patients had a cardiac source of emboli. In conclusion, infarcts of the anterior part of the rostral cerebellum can be regarded as a benign condition in which there is, frequently, a cardiac source of emboli.

Axonal growth and glial migration from co-cultured hippocampal and septal slices into fibrin-fibronectin-containing matrix of peripheral regeneration chambers: a light and electron microscope study

In order to investigate whether a fibrin-fibronectin-containing matrix of a peripheral regeneration chamber could promote the growth of central nervous system neurons, hippocampal and septal slices were co-cultured in the presence of this acellular substrate. In introducing the peripheral matrix into a 2-mm-long tube between hippocampal and septal slices, a spatio-temporal sequence of cell migration and axonal growth was described by light and electron microscopy. Axons were able to elongate directly into the flocculent material constituting the matrix and a possible neurite-promoting activity was implicated in this process as axonal growth was not detected in direct contact with rat plasma coagulated with calcium, or chicken plasma coagulated with thrombin, used as control matrices. However, in the 3 different substrates tested, astrocytes were able to migrate and dilated astroglial processes containing intermediate filaments were detected. Axonal processes were observed growing on the glial cell surface. GFAP-positive phagocytic cells, that could be of the same origin as astrocytes, were involved in matrix removing. Neuronal growth and glial migration arose from hippocampal and septum slices and acetylcholinesterase-containing fibers were seen in the bridging structure suggesting that cholinergic axons were able to progress to the hippocampal slice. This technique appeared to provide a model in which axonal growth and cell migration can be studied 'in vitro' in a 3-dimensional environment.

Subtypes and differential laminar distributions of beta A4 deposits in Alzheimer's disease: relationship with the intellectual status of 26 cases

beta A4 immunoreactivity was studied in temporal neocortex, area 22, of 26 cases with graded intellectual status. Sampling was performed in psychometrically assessed women over 75 years, either intellectually normal or affected by senile dementia of Alzheimer type of various degrees of severity. beta A4 antibodies labelled various types of beta A4 deposits in 22/26 cases: (1) small, stellate deposits; (2) diffuse deposits, (3) primitive, (4) classic and (5) compact, or burn-out, plaques. The densities of the stellate deposits, primitive and classic plaques were always positively linked with the severity of the intellectual status, whereas those of the diffuse deposits were not. This was due to a single case with normal mental status and numerous beta A4 deposits. Densities of stellate and diffuse deposits were higher in layers I, III and IV, whereas densities of primitive, classic, and neuritic plaques observed with Bodian's technique were higher in layers II and III. Topographical distribution of each subtype did not vary as a function of the severity of the intellectual status. These data suggest that deposits of beta A4 protein appear a necessary but not a sufficient condition for inducing neuritic plaque formation, in the neocortex as in other brain areas. beta A4 proteins could accumulate either as diffuse deposits, which do not cause an intellectual deficit, or as dense deposits, associated with argyrophilic neurites, i.e., classic neuritic plaques, highly correlated to the intellectual impairment. This evolution could depend on factors which are laminarily distributed in the neocortex.

Leuko-araiosis

Leuko-araiosis is an unspecific radiologic sign, seen with CT scan or with MRI. It can be found as well in normal elderly persons as in pathological conditions. For the sake of clarity, CT scan and MRI images have to be distinguished. CT leuko-araiosis is linked with vascular risk factors and with age. The situation is more complex for MRI leuko-araiosis (likely on account of the higher sensitivity of MRI). Some images (caps and rims), frequently seen in normal, even young, individuals, are more frequent in aging. On the contrary, abnormal images at a distance from the ventricle are more difficult to interpret. Some of them are due to pathological well defined conditions (small infarcts, Binswanger's disease, cysts, plaques). Others may be secondary to remote pathologies (such as infarcts). Others are due to little specific conditions, such as perivascular dilatations ('état criblé' due to brain vasogenic edema, or to brain atrophy whatever its cause, and more frequently seen in the elderly). Other changes, such as incomplete infarction or myelin pallor with gliosis, have been described. At last, in some cases, no clearcut pathological lesion could be found. Leuko-araiosis may be present in primary degenerative dementia of the Alzheimer type, but it is neither necessary nor sufficient to establish the diagnosis of Alzheimer's disease, and it does not seem more frequent than in elderly controls. The mechanism of leuko-araiosis in Alzheimer's disease is likely multifactorial (for example, cerebral atrophy, amyloid angiopathy, associated hypertensive arteriolosclerosis could be involved). The relationship between leuko-araiosis, myelin pallor and white matter atrophy is poorly understood, and remains to be studied.

Glial fibrillary acidic protein and beta A4 protein deposits in temporal lobe of aging brain and senile dementia of the Alzheimer type: relation with the cognitive state and with quantitative studies of senile plaques and neurofibrillary tangles

The aim of this study was to compare brain glial fibrillary acidic protein (GFAP) levels to the modifications of cognitive functions (Blessed test score [BTS]), the density of the main neuropathological lesions (senile plaques [SP] and neurofibrillary tangles [NFT]), and the density of the two main subtypes of beta A4 deposits (classic plaques and diffuse deposits) in a series of patients with normal aging and senile dementia of the Alzheimer type of various degrees of severity. GFAP levels (enzyme-linked immunosorbent assay [ELISA] technique) and the densities of changes were measured in the temporal lobe of 12 women over 75 years of age. Under these conditions, the ELISA assay could determine GFAP in brain homogenates (aqueous-Triton buffer soluble extract) in a range from 2.5 ng to 600 ng per assay. Least affected patients (with a BTS of 19 and over) all ranged below 60 micrograms/mg protein. Most affected patients (with a BTS under 6) ranged above 150 micrograms/mg protein. However, interindividual variations were wide. A significant correlation between the BTS and the amount of GFAP could be found only when using the non parametric test of Spearman. There was a significant positive correlation between the amount of GFAP and the density of 1) SP, 2) NFT both revealed by Bodian's silver stain, and 3) classic beta A4 plaques shown by immunocytochemistry. On the contrary, no correlation was observed with diffuse beta A4 deposits. One case with very large amounts of diffuse beta A4 deposits without SP or NFT showed no associated GFAP reactivity. This suggests that GFAP production is a critical event in the formation of classic SP.

Constant neurofibrillary changes in the neocortex in progressive supranuclear palsy. Basic differences with Alzheimer's disease and aging

Neocortical neurofibrillary tangles (NFT) revealed by Bodian technique and anti-tau immunolabelling were seen in 5/5 cases of progressive supranuclear palsy (PSP) aged 58-76 years. These lesions differed from Alzheimer's disease or age-related changes: (1) they were most frequent in the precentral gyrus (Brodmann's area 4) whereas associative areas are predominantly lesioned in Alzheimer's disease; (2) they affected mainly large pyramidal neurons and small cells, relatively sparing the cell population selectively involved in Alzheimer's disease; (3) they predominated in layers V and VI of area 4, whereas NFT are most dense in layers III and V in Alzheimer's disease; (4) mature senile plaques (1/5 cases) and beta-amyloid diffuse deposits (3/5 cases), which usually precede or go together with NFT in Alzheimer's disease were rare or absent (2/5) in PSP. Neuropil threads and tufts of abnormal fibres were also seen. In addition, NFT and neuropil threads were found in the hippocampus. PSP is thus another example of abnormal storage of tau developing in the neocortex in the absence of beta-amyloid deposits. It might prove a useful model for the understanding of the mechanisms of localization and spreading of tau storage in the brain.

Arterial pathology in cerebellar infarction

We reviewed 88 pathologically proven cerebellar infarcts, examining the entire thoracocervical arterial system (including the spinal part of the vertebral artery, the intracranial arteries, and the heart) in all cases. For 50 infarcts, we found an arterial occlusion. The intracranial part of the vertebral artery was involved in 38 infarcts (76%), the basilar artery in 20 infarcts (40%), and a cerebellar artery in 12 infarcts (24%). Eight infarcts were due to bilateral distal vertebral artery occlusions. For the 50 infarcts, the cause of the occlusion was atherosclerosis in 28 (56%) and a cardiac embolism in 12 (24%). For the remaining 38 infarcts, we found no arterial occlusions on postmortem examination. Of these 38 infarcts, 26 (68%) were associated with a cardiac source of emboli. For the entire group of 88 infarcts, atherosclerosis was the cause in 31 (35%), while a cardiac embolism was proven or presumed in 38 (43%). Dissecting aneurysms, atherosclerotic artery-to-artery embolism, or hemodynamic mechanisms could have been responsible for a few infarcts. We conclude that cerebellar infarcts often arise from cardiogenic embolism.

Cerebellar infarction in the territory of the superior cerebellar artery: a clinicopathologic study of 33 cases

We reviewed the clinical and pathologic findings in 33 patients with infarcts in the territory of the superior cerebellar artery (SCA). The clinical manifestations included the rostral basilar artery syndrome (8); coma at onset, often with tetraplegia (11); cerebellar and vestibular signs (9, with delayed coma due to cerebellar swelling in 6); and, in only 1 patient, the "classic" syndrome of the SCA. Clinical features were overshadowed by an infarct in the territory of the middle cerebral artery in 3 other patients, and the diagnosis was made only at autopsy in a fourth. Pathologically, SCA infarcts occurred in isolation in 7 patients. The most striking finding was the high frequency of associated infarcts in the territory of the rostral part of the basilar artery (73%). One-third of patients also had an infarct in the territory of the posterior inferior cerebellar artery, sometimes associated with infarction of the anterior inferior cerebellar artery. Tonsillar herniation was observed in 15 patients, 8 of whom had no infarcts in other cerebellar territories. Occlusions occurred mainly in the distal basilar artery and distal vertebral artery. The infarcts were mostly caused by cardiac and artery-to-artery emboli.

Large amounts of neocortical beta A4 deposits without neuritic plaques nor tangles in a psychometrically assessed, non-demented person

An 88-year-old mentally normal woman (Blessed test score = 27) had very large amounts (397/mm2) of deposits stained by anti-beta A4 serum in the first temporal gyrus. Senile plaques and neurofibrillary tangles were lacking on sections stained with the Bodian's silver method, with anti-tau and anti-paired helical filament (anti-PHF) antibodies. The following beta A4 deposits were found in decreasing order of frequency: diffuse (64.8%), stellate (24.4%), primitive (10.2%), classic (0.6%) plaques. Compact plaques were not observed. Diffuse deposits predominated in layers I, III and IV. On the contrary, the rare classic plaques were located in layers II and III. No amyloid angiopathy was seen with Congo red stain although beta A 4 deposits were seen in vessel walls with immunocytochemistry. These data indicate that severe diffuse beta A4 deposits in the neocortex do not induce dementia. They suggest that the development of senile plaques composed of beta A4 amyloid and of degenerating neurites is not related solely to the density of the diffuse beta A4 deposits. Nor does it depend on the regional susceptibility of the nervous tissue since beta A4 deposits were seen in highly vulnerable cortical areas. Some other, as yet unknown, factors seem necessary. In addition, determination of beta A4 level in the neocortex is not sufficient for the diagnosis of dementia of Alzheimer type.

Human immunodeficiency virus (HIV) leukoencephalopathy and the microcirculation

We studied the brains of three patients with acquired immune deficiency syndrome (AIDS), all of whom developed subacutely progressive dementia unassociated with opportunistic infection or neoplasm in the central nervous system. Computed tomographic (CT) scans of the head revealed cortical atrophy, ventricular dilation, and diffuse hypodensity of the centrum semiovale. On microscopic examination, the cerebral and cerebellar white matter in all cases showed diffuse and focal, angiocentric regions of myelin pallor, focal vacuolization, and extensive gliosis. Variable axonal loss and axonal spheroids were evident. The microvasculature showed striking changes, including mural thickening, increased cellularity, and enlargement and pleomorphism of endothelial cells with variable numbers of macrophages and multinucleated giant cells (MNGC), which often contained hemosiderin pigment. Human immunodeficiency virus type 1 (HIV-1) antigens were identified immunocytochemically within perivascular macrophages and MNGC and in some microglial cells. We suggest that the morphologic abnormalities of the microcirculation may be associated with an alteration of the blood-brain barrier. The increased vascular permeability could contribute to damage and loss of the white matter including both myelin and axons, and result in subcortical cerebral atrophy. The HIV-1 infected cells present in relation to the microvasculature may play a role in mediating the vascular injury.

Neuropathology of the acquired immunodeficiency syndrome

This review attempts to assess critically the literature on the neuropathology of acquired immunodeficiency syndrome in light of our experience with 172 patients with acquired immunodeficiency syndrome who underwent extensive postmortem examinations of the central and peripheral nervous systems. The neuropathologic manifestations of the disease can be divided into three categories: (1) primary or putative/indirect effects of the human immunodeficiency virus, (2) opportunistic infections, and (3) neoplasms. We discuss the known etiologic agents and postulated pathogenetic mechanisms responsible for the broad range of neurologic diseases observed in patients with acquired immunodeficiency syndrome.

Rating of the lesions in senile dementia of the Alzheimer type: concordance between laboratories. A European multicenter study under the auspices of EURAGE

The study reported was intended to compare the impressions and analyses of investigators from 11 different laboratories on 2 slides, each from 6 cases with varying quantities of neuropathological change of the type found in Alzheimer's disease and normal ageing. The material came from 6 selected female patients over 75 years of age all of whom had been examined in detail and assessed by the Blessed Test Score. Two were severely demented, 2 mildly demented and 2 were considered to be normal. Unstained paraffin-embedded slides were sent to the investigators, the choice of the staining techniques being left to each laboratory. A quantitative evaluation of the changes was requested in 2 specified areas of the hippocampus and in the first temporal gyrus. Subjective scores of severity and a final guess about the pre mortem intellectual status (demented or not) were asked. The 11 replies were analyzed. A total of 14 different staining techniques were used. Absolute values of density differed much from one investigator to another, for senile plaques as well as for neurofibrillary tangles. Statistical analysis showed that concordance might be improved by the use of corrective factors which would standardize the scales of measurement. The ranking of the slides in increasing order of severity was in good agreement for 9 out of 11 observers concerning the neurofibrillary tangles and 3 out of 9 observers concerning the senile plaques. The correlation between the intellectual status and the density of lesions was higher for neurofibrillary tangles than for senile plaques. The subjective scores were in better agreement for the severely affected cases than for the mildly affected ones. The lowest correlation with intellectual deficit was obtained with the quantitative scores which took into account only the senile plaques or only the hippocampal lesions. The highest correlation coefficients were obtained with the subjective scores. The observers guessed correctly the intellectual status of the 2 most affected cases and often disagreed for the intermediate and normal cases. Neuropathology is mandatory for the diagnosis of definite Alzheimer's disease. Quantitative assessment is useful in cases with few lesions and light dementia but the neuropathological diagnostic procedure has to be more strictly standardized before quantitative histopathological criteria can be reliably transferred from one laboratory to another, especially when mildly affected cases are involved. Concordance seems presently easier to obtain by ranking the lesions and the cases in increasing order of severity than by using quantitative values of density.(ABSTRACT TRUNCATED AT 400 WORDS)

Correlation between microscopical changes and Tau 64 and 69 biochemical detection in senile dementia of the Alzheimer type. Tau 64 and 69 are reliable markers of the neurofibrillary degeneration

We have recently reported that the immunoblot detection of two abnormally phosphorylated tau proteins, named Tau 64 and 69, in homogenates of cortical areas from patients with Alzheimer's disease (AD) was systematically associated with the presence of neurofibrillary tangles (NFT) and senile plaques (SP) in these areas. A blind study was performed to confirm that these proteins had a reliable diagnostic value and to study more precisely the correlation between Tau 64 and 69 and the presence of the characteristic lesions of AD. The density of NFT and of SP was evaluated on histological sections of gyrus supramarginalis from 17 patients with graded intellectual status. Immunodetection of Tau 64 and 69 was semiquantitatively evaluated by densitometry (reflectance mode) on immunoblots of homogenates of the same area on the contralateral hemisphere. The statistical analysis of results showed that Tau 64 and 69 were more strongly correlated with NFT than with SP. Moreover, semiquantitative evaluation of Tau 64 and 69 was correlated with the intellectual status (BTS score). Therefore, these pathological forms of tau proteins are reliable markers of the presence of NFT and SP in the neocortex and may be used as a diagnostic tool.

Does adrenal graft enhance recovery of dopaminergic neurons in Parkinson's disease?

A 54-year-old man with a 5-year history of Parkinson's disease was treated with and autograft of adrenal medulla into the right caudate nucleus and died 4 months after surgery. Postmortem examination revealed that the graft was necrotic. It consisted mainly of reticulin and collagen fibrosis without catecholaminergic cell bodies identified either by immunohistochemistry or by in situ hybridization with labeled human tyrosine hydroxylase (TH) cDNA probe. Sparse TH-immunoreactive fibers, which did not stain for dopamine-beta-hydroxylase (DBH), ran through the graft. In contrast, intense staining for these catecholaminergic markers was found in the untransplanted adrenal medulla. Densely packed TH-positive, DHB-negative fibers were found in a restricted zone of the host striatum at the periphery of the graft. This effect was selective since the density of other neurons was not modified. The present study describes an additional patient in whom adrenal medulla autotransplantation failed to improve the parkinsonian disability. It suggests, however, that adrenal medulla grafts may stimulate the sprouting of striatal dopaminergic fibers in a limited zone of the grafted striatum.

Alterations in myelinated fibres in the sciatic nerve of rats after constriction: possible relationships between the presence of abnormal small myelinated fibres and pain-related behaviour

Morphology or peripheral myelinated fibres was analyzed in rats exhibiting hyperalgesia and allodynia with mechanical and thermal stimuli, consecutive to a mononeuropathy induced by 4 loose ligatures around a sciatic nerve. This preliminary study was based on weeks 2-3 after surgery, the time of the maximum alterations of the pain-related behaviour. At this time, contrasting with a marked decrease of the large afferent fibres a consistent number of much less than 5 micron fibres was pointed out. In addition to their extremely short internodal length, the majority of these fibres had an abnormal g-ratio, thus an abnormal myelin sheath. It is suggested that this group of abnormal fibres might be related to the A delta fibres described in neuromas and involved in pain-related behaviours seen in the mononeuropathic rats.

Tyrosine hydroxylase-like immunoreactivity in senile plaques is not related to the density of tyrosine hydroxylase-positive fibers in patients with Alzheimer's disease

The numbers of silver-stained senile plaques and plaques containing tyrosine hydroxylase (TH)-like immunoreactivity were counted in the neocortex, amygdala and hippocampus of control subjects and patients with Alzheimer's disease, and compared with the density of TH-positive nerve fibers. The number of silver-stained senile plaques was lowest in the hippocampus and highest in the amygdala, and increased in all three structures in relation to the degree of dementia in the patients. A small proportion of plaques in the hippocampus of the most demented subjects and a large proportion of plaques in the amygdala were TH-positive. No TH-like immunoreactivity was found in plaques in the neocortex, although this structure contained almost as many silver-stained senile plaques and was as densely innervated by TH-positive fibers as the amygdala. The number of plaques containing TH-like immunoreactivity was, therefore, not proportional to the innervation of the structures by TH-positive fibers, nor to the total number of plaques in the structure, suggesting that the dissociation between the proportion of TH-positive plaques in the amygdala and neocortex may be due to differences in the populations of TH-positive fibers innervating the structures.

Cerebellar infarction in the territory of the anterior and inferior cerebellar artery. A clinicopathological study of 20 cases

Clinicopathological reports on infarction in the territory of the anterior inferior cerebellar artery (AICA) are rare. In the present series cerebellar infarcts involved only the AICA territory in 13 cases. They were bilateral in 3 cases. In these pontocerebellar infarcts the middle cerebellar peduncle was the core of the affected territory. It was seldom selectively affected. In a few cases, the infarction extended to the flocculus. Next most frequently involved was a thin band of tissue in the adjacent cerebellar white matter, comprising laterally the neighbouring cerebellar lobules. The largest infarcts extended to the anterior and inferior aspects of the cerebellum. In these cases, the posterior inferior cerebellar artery (PICA) was hypoplastic. In most infarcts, the inferolateral pontine territory was involved, the infarction sometimes extending up to the middle third of the lateral pons and down to the superior part of the lateral medulla. No brainstem compression or tonsillar herniation were observed with infarcts affecting the AICA territory alone. Clinically, involvement of several cranial nerves (facial palsy, multimodal trigeminal sensory impairment, deafness, sometimes with tinnitus, a vestibular syndrome, or lateral gaze palsy) was constant. Cerebellar signs and motor weakness occurred frequently. Contralateral pain and temperature sensory loss was present at times. Horner's syndrome or skew deviation was rare. Study of the arteries showed that arterial occlusion was mainly due to thrombosis superimposed on atheromatous stenosis. In 7 cases, the infarction also involved the PICA territory or the PICA and the superior cerebellar artery territories. These extensive infarcts were often associated with tonsillar herniation and massive paramedian brainstem infarction. The cases in which the territories of the three cerebellar arteries were affected presented in deep coma, together with tetraplegia in some patients. Those in which PICA and AICA territories were involved together presented with similar clinical features as in the cases in which only the AICA territory was involved.

Adult sphingomyelinase deficiency: report of 2 patients who initially presented with psychiatric disorders

We studied 2 unrelated adult patients under neuroleptic treatment who met all phenotypic and biochemical criteria for Niemann-Pick disease type B. In addition, they had chronic psychiatric disorders and low blood levels of HDL cholesterol. The marked and persistent deficiency of acid sphingomyelinase and the disturbance of sphingomyelin metabolism in skin fibroblast subcultures ruled out a pure drug-induced lipidosis. The association of Niemann-Pick disease type B with psychiatric disorders and with low levels of HDL cholesterol could be a chance association of 2 diseases, a new phenotype of Niemann-Pick type B, or the revelation by the neuroleptic treatment of a subclinical inborn sphingomyelinase deficiency.

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.