John R. Atack

Cerebrospinal fluid production is reduced in healthy aging

In order to study age-related differences in cerebrospinal fluid (CSF) production in humans, we measured the rate of CSF production in 7 young (age 21 to 36 years) and 7 elderly (age 67 to 84 years) healthy volunteers, using a modified Masserman method. In addition, we evaluated CSF protein gradients by collecting CSF in serial fractions up to the 30th ml and assaying for total protein concentration. The mean rate of CSF production was significantly less in the elderly than in the young subjects. Mean CSF total protein concentrations were higher in the elderly than in the young, and significant rostrocaudal protein gradients with similar slopes were present in both groups. However, there was no correlation between CSF production and CSF total protein concentrations or protein gradient slopes. Age-related reductions in CSF production, together with the ventricular dilatation that occurs with aging, should presumably result in reduced CSF turnover and therefore influence measured concentrations of lumbar CSF constituents.

Reductions in [3H]nicotinic acetylcholine binding in Alzheimer's disease and Parkinson's disease An autobiographic study

In Alzheimers disease (AD) and Parkinsons disease (PD), dysfunction in the basal forebrain cholinergic system is accompanied by a consistent loss of presynaptic cholinergic markers in cortex, but changes in cholinergic receptor binding sites are poorly understood. In the present study, we used receptor autoradiography to map the distribution of nicotinic [3H]acetylcholine binding sites in cortices of individuals with AD and PD and matched control subjects. In both diseases, a profound loss of nicotinic receptors occurs in all cortical layers, particularly the deepest layers.

CSF and serum concentrations of albumin and IgG in Alzheimer's disease.

Cerebrospinal fluid (CSF) and serum concentrations of albumin and immunoglobulin G (IgG) were measured in 31 patients with presumptive Alzheimers disease (AD) and in 14 healthy control subjects. The albumin and IgG quotients, and IgG index were calculated to evaluate the permeability of the blood-brain barrier and the intrathecal production of immunoglobulins. X-ray computerized tomography (CT) of the head was performed to investigate the relation between cerebral atrophy and CSF protein concentrations. The albumin and IgG quotients, and the IgG index did not differ significantly between the AD and control groups. Cerebral atrophy, as measured by CSF volume, was not related to CSF protein concentrations in either group. The results do not support the hypothesized roles of blood-brain barrier disruption or of immunologically-mediated injury of the central nervous system in the pathogenesis of AD.

Bilateral changes in neocortical [3H]pirenzepine and [3H]oxotremorine-M binding following unilateral lesions of the rat nucleus basalis magnocellularis: an autoradiographic study

Neocortical choline acetyltransferase (ChAT) activity and muscarinic [3H]pirenzepine, [3H]oxotremorine-M, [3H]N-methylscopolamine ([3H]NMS; both high- and low-affinity agonist (carbachol) sites) and nicotinic [3H]acetylcholine binding were assessed both ipsi- and contralaterally 1 week and 13 weeks after unilateral ibotenic acid lesions of the rat nucleus basalis magnocellularis (NBM). Ipsilateral ChAT activity was reduced to 49% of control values 1 week postlesion but by 13 weeks had recovered to 80% of control values. Contralateral ChAT activity did not change significantly at either 1 week or 13 weeks postlesion. At 1 week postlesion, [3H]oxotremorine-M binding was increased by 33% and 54% in ipsilateral and contralateral neocortex, respectively. By week 13, both ipsi- and contralateral [3H]oxotremorine-M binding had returned to normal but [3H]pirenzepine binding was significantly decreased by 31% and 39% in the ipsilateral and contralateral hemispheres, respectively. The binding of [3H]NMS and [3H]acetylcholine did not differ significantly from control values at either 1 week or 13 weeks postlesion. These data suggest that none of the cholinergic binding sites studied is preferentially localized presynaptically and that there may be interhemispheric regulation of neocortical cholinergic binding sites.

Cerebrospinal fluid monoamine markers are decreased in dementia of the Alzheimer type with extrapyramidal features

We measured monoamine metabolites and biopterin in the CSF of 37 patients with dementia of the Alzheimer type (DAT), with or without extrapyramidal signs, and in 14 age-matched healthy controls. Compared with concentrations in DAT and controls, the concentrations of homovanillic acid (HVA) and biopterin were significantly decreased in DAT with extrapyramidal signs (EDAT). CSF 3-methoxy-4-hydroxy-phenethyleneglycol and 5-hydroxyindoleacetic acid did not differ significantly among these groups. Age at onset of dementia was positively correlated with CSF HVA (r = 0.49, p < 0.05). The two dementia groups did not differ significantly in the extent of ventricular dilation as measured by quantitative CT, but EDAT patients had lower Mini-Mental State Examination scores than did DAT patients. When patients were matched for age and dementia severity, CSF HVA and biopterin concentrations remained significantly lower in EDAT than in DAT patients. These results indicate that EDAT patients form a distinct subgroup of DAT with evidence of central monoamine dysfunction.

Evidence for a membrane lipid defect in Alzheimer disease.

We have previously shown that cells normally maintain their lipid metabolic pools at a critical composition, appropriate for spontaneous assembly of a stable membrane bilayer at their physiological temperature. When disease affects membrane lipids such that the new composition will only form a stable bilayer at a critical temperature (T*), which differs from the physiological value, membrane destabilization and hence cellular damage will necessarily ensue. We have previously tested this pathogenetic mechanism in metachromatic leukodystrophy, a disorder with a known primary lipid metabolic defect. In the present study, we found T* for cerebral cortex lipids from three Alzheimer disease (AD) patients ranged between 19 and 28 degrees C, independent of membrane protein composition. Control cortex lipids yielded a normal value for T* of 37 degrees C. Thus, one possible mechanism for neurodegeneration in AD is membrane destabilization secondary to a lipid compositional aberration, which shifts T* away from 37 degrees C. This lipid defect is brain region-specific as cerebellar lipids from the AD patients gave a normal value for T*. Studies aimed at delineating the nature of the biochemical anomaly are in progress.

Regional specificity of membrane instability in Alzheimer's disease brain ☆

We report an inherent tendency towards the destabilisation of cellular membranes in Alzheimers disease (AD) brain. This tendency is a natural consequence of abnormal membrane lipid composition, which has previously been documented in AD. Membrane destabilisation may contribute to AD pathogenesis in its own right and may also facilitate amyloid beta-protein deposition, which is potentially neurotoxic. The instability was found to co-localise selectively with areas of neurodegeneration in AD brain, thereby possibly accounting for the focal pathology observed in this disorder.

Selective elevation of c-myc transcript levels in the liver of the aging Fischer-344 rat

The expression of several proto-oncogenes involved in normal cell growth was examined as a function of age in male Fischer-344 rats aged 3, 6-9, 12 and 21-23 months. Northern blot analysis using RNA isolated from pooled livers or brains showed that the transcript levels of c-myc, but not c-sis or c-src-related genes, were markedly elevated in the liver with age. In contrast, there was no substantial change in transcript levels of any of these genes in aging brain. When c-myc expression was analyzed in livers from individual rats ranging in age from 4 to 22 months, a significant (p less than 0.01) 5-fold increase in c-myc transcript levels in relation to age was detected. The results indicate that expression of c-myc in rat liver is modulated during aging and more generally, that aging in rats is associated with organ-specific changes in the transcript levels of particular genes.

Regional analysis of rat brain proteins during senescence

Brains of male Fischer-344 rats aged 3-4 months and 28-30 months were dissected into 11 regions, and the patterns of brain proteins in these regions were analyzed using two dimensional gel electrophoresis in conjunction with a sensitive silver stain detection method. Several hundred abundant and moderately abundant brain proteins were detected in each region using this method. At 3-4 months, most proteins were present in approximately equal amounts in each of the 11 regions. On the whole, this distribution was maintained as a function of age. One protein of 21 kdal pI 5.1 was present in the cerebellum in greater amount than the other regions at both 3-4 months and 28-30 months. Two proteins, 44 kdal pI 5.4 and 47 kdal pI 5.2 were present at increased levels in the inferior colliculus of 28-30 month animals compared to 3-4 month animals. Of the abundant and moderately abundant brain proteins detected by this method, there were none which showed major decreases in levels as a function of age. These results provide support for the concept that the molecular mechanisms which result in differential gene expression in different regions of the young adult rat brain are operative and are maintained in the brains of senescent rats.

Carbamate analogues of (−)‐physostigmine: In vitro inhibition of acetyl‐ and butyrylcholinesterase

Reaction of (−)‐eseroline (1) with alkyl, aryl and aralkylisocyanates afforded a series of carbamate analogues of (−)‐physostigmine (2) which were assayed for inhibition of acetyl‐ and butyrylcholinesterase (AChE and BChE, respectively) in vitro. Included in this study were two N‐alkyl‐substituted carbamates 9 and 14 obtained from (−)‐eseroline (1) with dialkylcarbamoyl chlorides, and allophanates 12 and 13 obtained as by‐products in the reaction of 1 and benzylcarbamoyl eseroline (8) with benzyl isocyanate. Whereas none of the analogues studied was more potent than 2 against electric eel AChE, and carbamates 6, 7 and 8 were all more than 3 times more potent against human plasma BChE than 2.