Selective neuronal degeneration with concomitant changes in neurotransmitter systems are features of both normal ageing and Alzheimer's disease. There are, however, important neurochemical differences in cerebral cortex. Choline acetyltransferase declines with age in frontal cortex in contrast to the prominent change in the temporal cortex in Alzheimer's disease. The loss of somatostatin, and the recently reported reciprocal change in corticotropin-releasing factor and receptors are not seen with ageing. However, age itself may have an important influence on the neurochemical deficits in Alzheimer's disease which are restricted in the older patients. The problems of post-mortem studies in the analysis of ageing and possible approaches to this are discussed.

Multiple neurotransmitter systems are affected in senile dementia of the Alzheimer's type (SDAT). Among them, acetylcholine has been most studied. It is now well accepted that the activity of the enzyme, choline acetyltransferase (ChAT) is much decreased in various brain regions including the frontal and temporal cortices, hippocampus and nucleus basalis of Meynert (nbm) in SDAT. Cortical M2-muscarinic and nicotinic cholinergic receptors are also decreased but only in a certain proportion (30-40%) of SDAT patients. For other systems, it appears that cortical serotonin (5-HT)-type 2 receptor binding sites are decreased in SDAT. This diminution in 5-HT2 receptors correlates well with the decreased levels of somatostatin-like immunoreactive materials found in the cortex of SDAT patients. Cortical somatostatin receptor binding sites are decreased in about one third of SDAT patients. Finally, neuropeptide Y and neuropeptide Y receptor binding sites are distributed in areas enriched in cholinergic cell bodies and nerve fiber terminals and it would be of interest to determine possible involvement of this peptide in SDAT. Thus, it appears that multi-drug clinical trials should be considered for the treatment of SDAT.

The local cerebral metabolic rate for glucose (LCMRgl) was determined by positron emission tomography (PET) using the 18F-fluorodeoxyglucose method in a series of Alzheimer patients and normal controls. The LCMRgl declined in the cerebral cortex with age, but the decrement was significantly greater in the clinically diagnosed Alzheimer's cases. Comparison of PET and psychological data indicated that, as the disease progressed clinically, the reduction in cortical LCMRgl and the number of cortical regions involved also increased. Variable regions of cortex were involved in the early stages but the temporal, parietal and frontal regions were most typically affected. One case coming to autopsy showed that the severity of the LCMRgl decline paralleled loss of neurons in the cortex and their replacement with astroglia.

A case of Pick's disease coming to autopsy had shown a different and highly characteristic pattern of cortical metabolic defect. In this case also a poor metabolic rate was associated with extensive gliosis.

Acetylcholinesterase (AChE) staining of the cerebral cortex in elderly normals and Alzheimer's disease cases with a new, highly sensitive method showed that in Alzheimer's disease there was an extensive loss of AChE-positive fibers with senile plaques frequently incorporating AChE-positive fiber debris. AChE staining of the substantia innominata area, where the cells giving rise to these neocortical fibers are presumably located, also showed evidence of degenerating cells and fibers.

Deficiencies in cholinergic nerve function have been clearly documented in patients with Alzheimer's disease. The lack of this neurotransmitter may be responsible for early memory loss in patients with the disease. Choline mustard Az ion has been used in our laboratory to produce cholinergic hypofunction in rat brain. Injections of the compound into the medial septal nucleus and dorsal hippocampus produced tissue lesions. The lesions were dose and time-dependent. Lesions produced in the medial septum resulted in transmitter depression in the hippocampus. These results suggest non-specific tissue damage because 5-HT levels were lower than normal. Other strategies for getting choline mustard Az ion into rat brain are being investigated to circumvent the apparent ability of this compound and other nitrogen mustard analogs of choline to produce non-specific tissue damage when injected directly into brain tissue.

Cholinergic receptors (muscarinic subtypes M1 and M2, and putative nicotinic binding) have been examined in the hippocampus obtained at autopsy from a variety of patients with cognitive disorders (Alzheimer's, Parkinson's, and Huntington's diseases, Down's Syndrome and alcoholic dementia) and compared with neurologically normal controls and cases of Motor Neuron disease. In all of the disorders associated with a pre-synaptic cortical cholinergic deficit reflected by an extensive loss of choline acetyltransferase (Alzheimer's disease, Parkinson's disease and Down's Syndrome) there was a substantial reduction in the binding of (3H) nicotine to the nicotinic receptor. By contrast reductions in both muscarinic subtypes (M1 and M2) were apparent to only a moderate extent in Alzheimer's disease, whereas in Parkinson's disease binding was significantly increased (apparently not in relation to anti-cholinergic drug treatment) in the non-demented but not demented cases. A further abnormality detected in Alzheimer's disease but not the other disorders investigated was a decrease in an endogenous inhibitor of nicotinic binding, the identity of which is as yet unknown but which may be a candidate for a possible endogenous modulator of the nicotinic receptor. These observations suggest that in Alzheimer's disease not only muscarinic but also nicotinic receptor function should be considered in relation both to future therapeutic strategies and, in the search for a clinical marker which might be of diagnostic value, to potential probes of the cortical cholinergic system.

Postmortem human brain samples were taken from non-neurological controls as well as demented subjects who died with Alzheimer's disease (AD), multi-infarct dementia (MID), or a combination of AD and MID dementia (MIXED). Choline acetyltransferase (Ch AT) activity was measured radiometrically using [ 1 -l4C]acetyl-coenzyme A as the substrate, muscarinic binding was assayed with [3H]quinuclidinyl benzilate, and the proportion of binding associated with high affinity agonist sites was measured by carbamylcholine displacement of the radioligand.

Relative to control, ChAT activity was significantly reduced (p ≤0.01) in samples taken from the temporal, frontal, and hippocampal areas of demented patients. A small elevation in Bmax was noted in the hippocampal endplate (p ≤0.01) (AD vs. control) and the H1-subiculum region (p ≤0.05) (AD vs. all other groups). In addition, the percentage of binding associated with high affinity agonist sites was greater in the frontal cortex of AD and MID samples (p≤0.05), compared with MIXED and control, and in the temporal cortex of the AD group compared with all other groups (p≤0.05). The results suggest a regionally specific upregulation of cerebral muscarinic receptors in dementia, especially in AD.

Recent research with computerized tomography (CT) and magnetic resonance imaging (MR) of the brain has revealed a type of tissue change for which no fitting term exists. The change appears as areas of decreased density on CT and changed signals of the white matter in MR images. Because neither a definite pathological change nor a specific clinical deficit has been linked with the CT and MR changes, a designation is required that limits itself to describing the changes themselves.

We propose “leuko-araiosis”. The Greek root leuko-, signifying “white”, has found wide usage in modern medical terminology: e.g. leucine, leukocyte, leukorrhoea. Also several precedents exist for its application to the white matter of the central nervous system: e.g. leukoencephalitis, leukomyelitis, leukotomy. Araios is an adjective meaning “rarefied”, and the suffix -osis converts the adjective to a noun meaning “rarefaction, diminution of density”, a word used in the Hippocratic Collection to describe a state of excessive porosity of the lung.

A descriptive term precludes premature presuppositions and encourages the search for causes.

In order to study possible metabolic derangements in Alzheimer's disease (AD), we performed phosphorus 31 nuclear magnetic resonance (31P NMR) spectroscopy on brain samples obtained at autopsy from 7 patients with AD and 9 control subjects. Aqueous solutions of brain tissue contained well-defined peaks of intermediate compounds in phospholipid metabolism, including the phosphomonoesters phosphocholine and phosphoethanolamine, and the phosphodiesters glycerophosphorylcholine and glycerophosphorylethanolamine. 3IP NMR spectra also displayed the inorganic phosphorus signal, which provides an index to the in vivo concentration of high-energy compounds.

We found evidence for altered phospholipid metabolism in that relative levels of phosphomonoesters were decreased, and phosphodiesters increased, in frontal and parietal regions of patients with AD compared to control subjects. The inorganic phosphorus resonance peaks were similar in AD and control subjects, suggesting that energy stores are not diminished in AD. These preliminary data are consistent with the hypothesis that abnormalities in phospholipid metabolism contribute to possible neuronal membrane dysfunction and impaired cholinergic neurotransmission in AD.

Evidence indicates that Alzheimer's disease (AD) causes functional disconnection of neocortical association areas. In mildly demented AD patients without measurable neocortically-mediated cognitive abnormalities, positron emission tomography demonstrates reduced parietal lobe glucose metabolism and left/right metabolic asymmetries in neocortical association areas. Similar metabolic abnormalities occur in moderately demented patients, but are accompanied by appropriate language and visuospatial discrepancies. Left/right metabolic asymmetries correspond with reduced numbers of partial correlations between metabolic rates in homologous right and left regions, and in the frontal and parietal cortices, indicating metabolic uncoupling among these regions. The affected association regions are those which demonstrate Alzheimer-type neuropathology post-mortem.