David M. Bowen

Alzheimer's disease: Correlation of cortical choline acetyltransferase activity with the severity of dementia and histological abnormalities☆

We have examined the choline acetyltransferase [CAT] activity in autopsy samples of frontal and temporal lobe cortex from 47 patients (31 with Alzheimers disease, 4 with dementia due to cerebrovascular disease and 12 undemented controls) and compared it with the severity of dementia during life and with the numbers of argyrophilic plaques and neurofibrillary tangles in the corresponding areas of cortex in the contralateral cerebral hemisphere. CAT activity was significantly reduced, most severely in the temporal lobe, in patients with Alzheimers disease but not in patients with a cerebrovascular cause for their dementia, and CAT activity showed no significant reduction with age in the undemented control patients. In the patients with Alzheimers disease the reduction in CAT activity was significantly correlated with the severity of dementia and with the numbers of neurofibrillary tangles, but not argyrophilic plaques, present in the corresponding contralateral cortex.

Biochemical assessment of serotonergic and cholinergic dysfunction and cerebral atrophy in Alzheimer's disease.

Abstract: Markers of serotonin synapses in entire temporal lobe and frontal and temporal neocortex were examined for changes in Alzheimers disease by use of both neurosurgical and autopsy samples. Uptake of [3H]sero‐tonin, binding of [3H]imipramine, and content of indola‐mines were all significantly reduced, indicating that serotonin nerve terminals are affected. Binding of [3H]serotonin was also reduced, whereas that of [3H]qui‐nuclidinyl benzilate, [3H]muscimol, and [3H]dihydroal‐prenolol were unaltered. When the Alzheimers samples were subdivided according to age, the reduction in [3H]serotonin binding was a feature of only autopsy samples from younger patients. In contrast, presynaptic cholinergic activity was reduced in all groups of Alzheimers samples, including neurosurgical specimens. Five markers, thought to reflect cerebral atrophy, cytoplasm, nerve cell membrane, and neuronal perikarya were measured in the entire temporal lobe. In Alzheimers disease the reductions (mean 25%, range 20–35%) were thought to be too large to be due only to loss of structures associated with the presumed cholinergic perikarya in the basal forebrain and monoamine neurones in the brain stem.

Presynaptic Cholinergic Dysfunction in Patients with Dementia

Abstract: Indices of presynaptic cholinergic nerve endings were assayed in neocortical biopsy samples from patients with presenile dementia. For those patients in whom Alzheimers disease was histologically confirmed, [14C]acetylcholine synthesis, choline acetyltransferase activity and choline uptake were all found to be markedly reduced (at least 40%) below mean control values. The changes occurred in samples from both the frontal and temporal lobes and for [14C]acetylcholine synthesis the decrease was similar under conditions of high and low neuronal activity (as assessed by incubations in 31 mM and 5 mM K+ respectively). Samples from other demented patients, in whom the histological features of Alzheimers disease were not detected, produced values for all three biochemical parameters which were similar to controls. For the total group of patients with presenile dementia there were correlations between values for the three markers of presynaptic cholinergic nerve endings suggestive of a loss of functional activity at these sites in Alzheimers disease.

Accelerated ageing or selective neuronal loss as an important cause of dementia

Extensive biochemical analysis of whole temporal lobe from cases of dementia and controls suggests that Alzheimers disease is a primary degenerative nerve-cell disorder and not the result of accelerated ageing. There is selective loss of neocortical cholinergic neurones. Transmitter systems apart from the cholinergic system appears to be affected, but to a lesser extent, and there are no significant changes in the caudate nucleus. The change in cholinergic neurones has been confirmed in biopsy samples.

Presynaptic Serotonergic Dysfunction in Patients with Alzheimer's Disease

Abstract: Indices of presynaptic serotonergic nerve endings were assayed in neocortical biopsy samples from patients with histologically verified Alzheimers disease. The concentrations of 5‐hydroxytryptamine (serotonin) and 5‐hydroxyindoleacetic acid, serotonin uptake, and K+‐stimulated release of endogenous serotonin were all found to be reduced below control values. Changes occurred in samples from both the frontal and temporal lobes, but they were most severe (at least a 55% reduction) in the temporal lobe. This is indicative of substantial serotonergic denervation. Values for serotonergic markers in Alzheimers disease samples did not show correlations with rating of the severity of dementia, indices of cholinergic innervation, or senile plaque and cortical pyramidal neurone loss. However, neuronbrillary tangle count and an index of glucose oxidation (both probably reflecting pyramidal cells) correlated with the concentration of 5‐hydroxyindoleacetic acid.

Choline acetyltransferase activity and histopathology of frontal neocortex from biopsies of demented patients.

Cortical biopsies were taken from the frontal lobe of 25 patients with presenile dementia. Choline acetyltransferase (ChAT) activity, and in some specimens the high affinity uptake of choline, was used to estimate loss of cholinergic nerve terminals. Of the 15 samples with varying degrees of histological evidence of Alzheimers disease (AD) 14 were from clinically suspected examples of the disease. There was significant loss of ChAT in 10 of the 15 compared with control and the mean activity was also highly significantly reduced (to 41% of control). The deficit was found in patients examined within a year of onset of symptoms. In 6 biopsies from clinically suspected cases of AD without diagnostic histological features there was loss of activity in only one, subsequently shown to have Jakob-Creutzfeldt disease. The remaining samples were two of vascular dementia (no loss of ChAT), one probable disorder of white matter (no loss of activity) and one undiagnosed disorder (with loss of ChAT activity). Thus most patients without histologically demonstrated AD had no evidence of a presynaptic cholinergic defect. It was concluded that suspected cases of AD particularly suitable for putative cholinergic therapy were those with an onset of the disease at 55 to 65 and an absence of family history.

Evidence of Glutamatergic Denervation and Possible Abnormal Metabolism in Alzheimer's Disease

Excitatory dicarboxylic amino acids previously have been ascribed several functions in the brain. Here their total concentration and proposed neurochemical markers of neurotransmitter function have been measured in brain from patients with Alzheimers disease (AD) and controls. Specimens were obtained antemortem (biopsy) approximately 3 years after emergence of symptoms and promptly (<3 h) postmortem some 10 years after onset. Early in the disease a slight elevation in aspartic acid concentration of cerebral cortex was observed in the patients with AD. A reduction in glutamic acid concentration of a similar magnitude was found. It is argued that this, together with a decrease in CSF glutamine content and lack of change in the phosphate‐activated brain glutaminase activity of tissue, reflects an early metabolic abnormality. Later in the disease evidence of glutamatergic neurone loss is provided by the finding that in many regions of the cerebral cortex the Na+‐dependent uptake of D‐[3H]aspartic acid was almost always lowest in AD subjects compared with control when assessed by a method designed to minimise artifacts and epiphenomena. Release of endogenous neuro‐transmitters from human brain tissue postmortem did not appear to have the characteristics of that from human tissue antemortem and rat brain.

Monoaminergic innervation of the frontal and temporal lobes in Alzheimer's disease

Seven markers of ascending (corticopetal) dopaminergic, noradrenergic and serotonergic neurones and choline acetyltransferase activity have been studied postmortem in frontal and temporal cortex from subjects with Alzheimers disease and compared with a matched group of controls. Dopaminergic neurones (concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid) were not deficient but some markers of the other neurones were affected. Noradrenaline and serotonin concentrations were reduced whereas the concentrations of their metabolites were either unaltered (5-hydroxyindoleacetic acid) or increased (3-methoxy-4-hydroxyphenylglycol). All deficits were most pronounced in the temporal cortex. Severely demented subjects had evidence of generalized neuronal loss, whereas those with moderate dementia showed significant loss of only choline acetyltransferase activity. In Alzheimer subjects, a significant relationship (inverse) was found between 5-hydroxyindoleacetic acid concentration and the number of neurofibrillary tangles.

Mitochondrial function in brain tissue in primary degenerative dementia

Previous in vitro and in vivo studies of the brain in Alzheimers disease indicated alterations in metabolism related to energy production although the relationships between these changes remains obscure. To help resolve this issue, in vitro oxygen uptake by homogenates of fresh samples of frontal neocortex from patients with dementia and neurosurgical controls has been examined as a measure of energy-related metabolism and mitochondrial function. Maximal respiratory rates (measured in the presence of an uncoupling agent) were similar for samples from 7 controls, 5 patients with Alzheimers disease and two patients diagnosed clinically as Picks disease, suggesting that there was little or no effect of these dementias on the maximal metabolic capacity of the tissue. However, under some conditions producing sub-maximal metabolic activity (which are of potentially greater physiological relevance) oxygen uptake rates were significantly elevated in the dementia group. The ratio of oxygen uptake rates in the presence and absence of ADP was significantly reduced (to 58% of control; P less than 0.02) for the dementia patients compared with controls, possibly indicative of partial mitochondrial uncoupling. These results indicate metabolic changes expressed in vitro which may be relevant to the pathogenesis of Alzheimers disease and some related dementias.

Biochemical Evidence of Selective Nerve Cell Changes in the Normal Ageing Human and Rat Brain

Abstract: Atrophy with ageing of human whole brain, entire temporal lobe, and caudate nucleus was assessed in autopsy specimens, by biochemical techniques. Only the caudate nucleus showed changes. Markers for several neurotransmitter systems were also examined for changes with age. In neocortex and temporal lobe of human brain, small decreases were detected in markers of cholinergic nerve terminals, whereas a large decrease (79%) occurred in the caudate nucleus. Findings were similar in striatum from 3–33‐month‐old rats. No change occurred in binding of [3H]quinuclidinyl benzilate by human samples. Markers of serotonergic terminals were also unchanged in human and rat brain. By contrast, binding of [3H]lysergic acid diethylamide and [3H]serotonin was decreased (32–81%) in human neocortex and temporal lobe, but not in caudate nucleus. A 43% loss of a marker of γ‐aminobutyrate terminals occurred in human neocortex, while [3H]muscimol binding increased (179%). No changes were detected in markers of catecholamine synapses in temporal lobe or rat striatum. Hence, with human ageing there appears to be a loss of markers of γ‐aminobutyrate neurones intrinsic to neocortex and acetylcholine cells intrinsic to the caudate nucleus, as well as a change in postsynaptic serotonin receptors in neocortex. These losses are accompanied by relative preservation of markers of ascending projections from basal forebrain and brain stem.