Neuropathological and biochemical observations on the noradrenergic system in Alzheimer's disease

Evidence for cholinergic neurites in senile plaques

In the neocortices and amygdalae of young and aged macaques, cholinergic axons were identified by means of a monoclonal antibody to bovine choline acetyltransferase. Many fine, linear, immunoreactive profiles were seen in these animals. In the older animals, some cholinergic axons showed multifocal enlargements along their course. In some instances, neurites with choline acetyltransferase immunoreactivity were associated with deposits of amyloid (visualized with thioflavin T fluorescence). The appearance of these amyloid-associated abnormal cholinergic processes was similar to that of neurites in senile plaques, as shown by conventional silver impregnation techniques. Cholinergic systems thus give rise to some of the neurites within senile plaques.

Dopamine-beta-hydroxylase and acetylcholinesterase activities of cerebrospinal fluid in Alzheimer's disease

Recent neurochemical studies have indicated that in Alzheimer's disease there is disturbance of the cholinergic metabolism of the brain. Defects in other transmitter systems have also been suggested. As a marker of noradrenergic metabolism of the central nervous system, we measured dopamine-beta-hydroxylase (EC. 1.14.17.1) activity in cerebrospinal fluid (CSF) from 60 Alzheimer patients and 20 controls of the same age and sex. Dopamine-beta-hydroxylase activities of the CSF from Alzheimer patients did not differ significantly from those for the controls. The dopamine-beta-hydroxylase activities were not correlated with severity of dementia. As reported previously, the activity of a cholinergic marker, acetylcholinesterase (EC 3.1.1.7), was reduced in the CSF of Alzheimer patients. Interestingly, dopamine-beta-hydroxylase activities were correlated with acetylcholinesterase activities both in Alzheimer patients and control group.

Monoamine metabolite concentrations in lumbar cerebrospinal fluid of patients with histologically verified Alzheimer's dementia

Concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxy indoleacetic acid (5-HIAA) and homovanillic acid (HVA) were determined in lumbar cerebrospinal fluid (CSF) from control subjects and patients of both presenile and senile age with histologically verified Alzheimer's dementia. CSF HVA increased with age in control but not in Alzheimer patients. HVA and 5-HIAA in the CSF of presenile Alzheimer patients was lower than that of age matched control subjects.

Studies on neurotransmitter receptor systems in neocortex and hippocampus in senile dementia of the Alzheimer-type

Ligand binding to alpha 1-, alpha 2- and beta-adrenergic, serotonin, benzodiazepine and GABA receptors was studied in neocortex and hippocampus of controls and patients with senile dementia of the Alzheimer-type. A selective loss of serotonergic binding sites characterised as a loss of both S1 and S2 sites was observed. The reduction in serotonin receptors did not correlate with a clinical assessment of the degree of dementia, or with the extent of Alzheimer-type neuropathological change.

Alzheimer's presenile dementia, senile dementia of Alzheimer type and Down's syndrome in middle age form an age related continuum of pathological changes

A loss of nerve cells from the nucleus basalis of Meynert and the locus caeruleus together with a reduction in nucleolar volume in surviving cells was measured in twenty-two patients with Alzheimer's disease who ranged in age from 48-92 years, and in six patients over 50 years of age with Down's syndrome who also showed extensive formation of senile plaques and neurofibrillary tangles within their cerebral cortex. When compared with age matched controls the severity of these changes was greatest in the younger patients with Alzheimer's disease, but this fell with age such that by 90 years the level of change in Alzheimer's disease approached that in old age alone. There were only slight differences in the extent of these pathological changes in those patients with Down's syndrome when compared with others of similar age with Alzheimer's disease. It is concluded that the presenile dementia of Alzheimer's disease, the senile dementia of Alzheimer type and Down's syndrome in middle age all form an age-related continuum of pathological change.

A comparison of changes in the nucleus basalis and locus caeruleus in Alzheimer's disease

In 22 patients with Alzheimer's disease loss of neurons from the nucleus basalis of Meynert and locus caeruleus averaged 58% and 71% respectively with nucleolar volume being reduced by 30% in both. These changes were greater in those patients under 80 years of age and in such patients damage to the locus was more severe than that to the nucleus basalis. In older patients (over 80 years) changes were similar in extent in both regions.

Dementia--Alzheimer type

At least half of the patients who present with progressive decline in their memory, cognitive, and intellectual abilities will eventually be diagnosed as having Alzheimer's disease. The diagnosis is reached by clinical and ancillary evaluation and exclusion of all other causes of dementia. Recently, considerable advances have been made in our understanding of the neurobiologic features of Alzheimer's disease. Cortical neurons contain paired helical filaments with a very specific electron microscopic appearance. These filaments contain proteins with unusual properties. A severe decline in cholinergic activity in the cortex is related to a marked loss of cholinergic neurons in deep cerebral structures, such as the nucleus basalis of Meynert in the substantia innominata. No specific treatment is available for Alzheimer's disease. Patients and the relatives who take care of them require substantial help and assistance in coping with the disease.

Dementia in idiopathic Parkinson's disease. A neuropathological study of 32 cases

Neuronal loss was estimated semiquantitatively in the substantia nigra (SN) and locus coeruleus (LC), and by cell counts in the nucleus basalis of Meynert (NBM), in 32 patients with idiopathic Parkinson's disease (14 non-demented and 18 demented). The number of senile plaques (SP) and neurofibrillary tangles (NFT) was rated in four cortical areas. Neuronal loss in the SN seemed in dependent of mental impairment, while severe lesions of the LC were more frequent in demented patients. In the NBM, neuronal loss and Lewy bodies were observed in most cases (95%) and were associated with significant reductions of choline acetyltransferase (CAT) activity both in the NBM and the cortex (measurements available for 13 cases). This confirms that the cholinergic innominato-cortical pathway is damaged in Parkinson's disease and that the lesion is severer in subjects with dementia. SP and NFT were present in the cortex in 75% of the cases and significantly more numerous in demented patients. However, in 37% of the cases (six cases with dementia), the score for cortical changes was low and could be related to age. Cortical SP and NFT were not correlated to the degree of cell loss in LC and NBM, or to CAT activity in the cortex or NBM. Damage to coeruleo-cortical, innominato-cortical and intra-cortical neurones could each play a role in the appearance of dementia in Parkinsonism. The lesions in the different neuronal systems do not seem to evolve in parallel, but may be additive or potentiate one another in terms of functional expression. Also, the variety in extent and degree of lesions encountered in Parkinson's disease may offer a pathological substrate for the wide variety of mental symptoms described in this illness.

Neuropathology of the locus ceruleus: a semi-quantitative study

The locus ceruleus was studied in 86 brains of the elderly, with or without degenerative disease. Parkinson's disease, multiple system atrophy, progressive supranuclear palsy and senile dementia were among the diseases studied. Nerve cell loss, the appearance of neurofibrillary changes and Lewy bodies were examined semi-quantitatively. The number of nerve cells diminished in old age, especially over 90 years. The decrease of nerve cells was greater in cases with Lewy bodies. A marked loss of nerve cell was observed in multiple system atrophies, including Shy-Drager syndrome, olivopontocerebellar atrophy and striatonigral degeneration, and in some cases of Parkinson's disease and senile dementia. The number of nerve cells did not decrease in cases of progressive supranuclear palsy. Lewy bodies and neurofibrillary tangles appeared increasingly in old age. However, the incidence of both changes in the same neuron was rare, and in such cases their structures appeared not to be related.

Catecholamines and cholinergic enzymes in pre-senile and senile Alzheimer-type dementia and Down's syndrome

Noradrenaline, dopamine, homovanillic acid (HVA), choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) levels were measured in post-mortem brains from 8 cases of pre-senile Alzheimer-type dementia (ATD), 5 cases of senile ATD, 4 cases of Down's syndrome aged 53-57 years, one 27-year-old case of Down's syndrome and 13 controls. In the controls, the concentration of noradrenaline in hypothalamus (P less than 0.05) and mamillary body (P less than 0.02) decreased with age. Compared with age-matched controls, noradrenaline levels in these areas were more markedly reduced in pre-senile ATD (P less than 0.01), the 53-57-year-old cases of Down's syndrome (P less than 0.001) and in the 27-year-old Down's, than in senile ATD (hypothalamus P less than 0.05, mamillary body, n.s.). Dopamine and HVA concentrations in caudate nucleus were unaltered in pre-senile or senile ATD but dopamine was decreased (P less than 0.01) in the older cases, although not in the 27-year-old case, of Down's syndrome. In the olfactory tubercle in ATD the level of HVA was unaltered but the activity of ChAT was decreased (P less than 0.01). ChAT activity was reduced in pre-senile ATD (P less than 0.001), the older Down's cases (P less than 0.01) but not the young Down's case, and senile ATD (P less than 0.001) in the temporal cortex and in pre-senile ATD (P less than 0.001) and the older Down's cases (P less than 0.001) but not senile ATD in the caudate nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Senile dementia of the Alzheimer type

The prevalence of severe dementia in the United States is about 1.3 million cases, of which at least 50 to 60% are of the Alzheimer type. Severe dementia of the Alzheimer type is found rarely in a clearly dominant pattern, although often one or more relatives are affected. Down's syndrome in adults is often associated with Alzheimer changes. The diagnosis is a clinicopathological one; there is a considerable error rate in the clinical diagnosis early in the course of the disease, especially in regard to dementia in depression. The differential diagnosis involves a great many disorders, including multi-infarct dementia, tumors, subdural hematomas, and others. Physiological aspects of Alzheimer's disease include a diffusely slow electroencephalogram, reduced cerebral blood flow, and particular patterns noted on positron emission tomographic scanning. The latter technique has also demonstrated that oxygen extraction is normal in Alzheimer's disease, thus excluding ischemia from possible pathogenetic factors. Morphological changes, that is, the presence of plaques and tangles, are widely distributed in neocortex, paleocortex, and many deep gray areas down through the pontine tegmentum, but largely exclude the basal ganglia, thalamus, and substantia nigra. Numerous plaques without neocortical tangles are found in many demented persons older than 75 years. A severe loss of large neocortical neurons is characteristic of the disease. The chemical nature of the paired helical filaments that make up the neurofibrillary tangle has not yet been ascertained. Neurons are markedly deficient in the basal forebrain nuclei, and this deficiency may account for the severe diminution of choline acetyltransferase and acetylcholine in the neocortex and paleocortex. Muscarinic cholinergic receptors are present in normal amounts. Norepinephrine is reduced in some cases, and somatostatin in most. Substance P is low in severe cases. The etiology of the disorder is unknown and the role of aluminum is disputed. Management of patients with Alzheimer's disease is difficult, and neuroleptics are to be used with great caution because of their side effects. Substrate therapy has not been effective; physostigmine improves memory but is not suitable for general use. Trophic factors, gangliosides, and aluminum chelation are being investigated for use in pharmacological intervention.

The locus coeruleus and its possible role in ageing and degenerative disease of the human central nervous system

The central noradrenergic pathways with the mammalian brain are principally based on that group of nerve cells within the reticular substance of the upper pons known as the locus coeruleus. The physiological role of these nerve cells appears to be one of maintaining homeostasis within the central nervous system, whatever adverse conditions prevail in the rest of the body, through governing the flow of blood through, and degree of water permeability of, the capillary bed. The extensive ramifications of these noradrenergic terminals mean that the atrophy and loss of nerve cells from locus coeruleus that occurs in old age, and especially so in degenerative diseases of the central nervous system such as Alzheimer's disease and other conditions, will have widespread repercussions for brain function. The chain of physiological disturbances set up as a result of this cell loss may mean a progressive failure of homeostasis within the brain, which in the extreme may culminate in that pattern of mental breakdown which is usually termed dementia.

Improvement of 8-arm maze performance in aged Fischer 344 rats with 3,4-diaminopyridine

Short-term memory of a spatial task by male Fischer 344 rats at 3, 12, and 24 months of age was examined in a radial 8-arm maze. Performance by 24 month old rats was significantly poorer than that of 3 or 12 month old rats. 3,4-Diaminopyridine (1000 pmole/kg), a compound that stimulates acetylcholine release, significantly improved 8-arm maze performance by 24 month old rats. Thus, an age-related deficit in short-term memory for a spatial task can be ameliorated by a compound that stimulates acetylcholine release.

Monoamine metabolism in senile dementia of Alzheimer type

Monoamine metabolism in senile dementia of the Alzheimer-type (SDAT) was assessed by measuring the concentrations of the dopamine metabolite HVA, the noradrenaline metabolite MHPG and serotonin metabolite 5-hydroxy-3-indoleacetic acid (5-HIAA) in post-mortem brains of SDAT patients, a group of control subjects and a group of chronically depressed patients. Concentrations of MHPG and 5-HIAA were significantly reduced in hippocampus and cortical regions of the SDAT group. These changes did not correlate with clinical assessments of the degree of dementia or neuropathological assessment of the degree of Alzheimer-type changes in the SDAT group. It is suggested that changes in monoamine metabolite concentrations are not primarily involved in the pathogenesis of SDAT, and may be secondary to the well established cholinergic deficits.

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

Markers of serotonin synapses in entire temporal lobe and frontal and temporal neocortex were examined for changes in Alzheimer's disease by use of both neurosurgical and autopsy samples. Uptake of [3H]serotonin, binding of [3H]imipramine, and content of indolamines were all significantly reduced, indicating that serotonin nerve terminals are affected. Binding of [3H]serotonin was also reduced, whereas that of [3H]quinuclidinyl benzilate, [3H]muscimol, and [3H]dihydroalprenolol were unaltered. When the Alzheimer's 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 Alzheimer's 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 Alzheimer's 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.

The neurochemistry of Alzheimer's disease and senile dementia

At this time we seem to be on the verge of opening two new fields of research on Alzheimer's disease. To treat the symptoms of this condition, an understanding of the factors regulating acetylcholine synthesis will be very important. Because of the vast amount of work on this neurotransmitter over the last 30 years, rapid progress in this area should be made. However, to truely conquer Alzheimer's disease, we need to learn what it is that attacks and apparently destroys the cholinergic neurons. While this second point may take a little more time to unravel, the work will be both exciting and very worth while.

Neurotransmitter deficits in Alzheimer's disease: criteria for significance

A series of histopathologic, morphologic, and pharmacologic criteria are proposed to establish the significance of neurochemical deficits in Alzheimer's disease. The underlying pathogenic biochemistry of a better understood neurotransmitter-deficiency syndrome, Parkinson's disease, validates these criteria. The major neurotransmitter systems are evaluated against these guidelines. Only the cholinergic system fulfills all the criteria. Noradrenergic mechanisms are also implicated. Subsequent neurochemical abnormalities found in the brains of patients with Alzheimer's disease can be evaluated against these criteria.

Pathological changes in the nucleus of Meynert in Alzheimer's and Parkinson's diseases

Combined neuropathological and neurochemical assessment of the nucleus of Meynert in senile dementia of Alzheimer type (SDAT) have demonstrated that the cholinergic biochemical activity, choline acetyltransferase, is more extensively reduced in the nucleus (over 90%) than the loss of putative cholinergic perikarya (35%). Acetylcholinesterase histochemical activity was however substantially retained in individual neurones in the nucleus although virtually absent from the neocortex in SDAT. These abnormalities are consistent with a primary degeneration of cholinergic axons projecting to the cortex and secondary loss of perikarya from the subcortical nucleus. In contrast, preliminary observations on cases of Parkinson's disease suggest that the neuronal loss from the nucleus of Meynert may be greater in this disease than in SDAT, and previous studies have not consistently demonstrated a reduction in cortical choline acetyltransferase activities in Parkinson's disease. These observations, together with major differences in the neuropathology of the nucleus in SDAT and Parkinson's disease (neurofibrillary tangle and Lewy body formation, respectively) suggest that the involvement of the cholinergic system may differ in the two disease processes.

Presynaptic cholinergic dysfunction in patients with dementia

Indices of presynaptic cholinergic nerve endings were assayed in neocortical biopsy samples from patients with presenile dementia. For those patients in whom Alzheimer's 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 Alzheimer's 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 Alzheimer's disease.

The abnormally aged brain. Its blood flow and oxidative metabolism. A review - part II

The most common brain disease in middle and old age is dementia. Primary dementias comprise degenerative (dementia of Alzheimer type, DAT) and cerebrovascular (dementia of vascular type, DVT) types. These dementia types differ in morphological, clinical, and pathobiochemical terms. In DAT, large amounts of neuritic plaques and neurofibrillary tangles or paired helical filaments, are present throughout the whole brain cortex, but particularly numerous in temporal areas. Here and in hippocampus, the presynaptic cholinergic system seems to be predominantly affected. In DVT, multiple small infarcts are scattered over brain cortex and white matter obviously due to disturbances in cerebral microcirculation. Dementia is closely related to disturbances in brain blood flow and oxidative metabolism. In the beginning of DAT, cerebral blood flow and CMR-oxygen are found to be in normal ranges, but CMR-glucose is reduced. In DVT, cerebral blood flow and CMR-oxygen are also within the normal range, but CMR-glucose is found to be abnormally increased. When dementia symptoms are well developed in DAT, the same relationship between circulation and metabolism are found. Well-developed DVT symptoms seem to be associated with changes in blood flow and metabolism similar to variations after ischemic/anoxic lesions. In the beginning of both dementia types, a close correlation exists between cerebral blood flow and CMR-oxygen, but there is a dissociation from CMR-glucose. In the further course of both dementia types, cerebral blood flow and metabolism run into a final common path of a low functional level. No distinction between the dementia types is possible. In general, severity of dementia symptoms are correlated to the deviation of cerebral blood flow and metabolism from normal. There is much evidence that dementia, i.e. abnormal cerebral aging is different from normal cerebral aging. Dementia is not a form of accelerated cerebral aging.

The cholinergic hypothesis of geriatric memory dysfunction

Biochemical, electrophysiological, and pharmacological evidence supporting a role for cholinergic dysfunction in age-related memory disturbances is critically reviewed. An attempt has been made to identify pseudoissues, resolve certain controversies, and clarify misconceptions that have occurred in the literature. Significant cholinergic dysfunctions occur in the aged and demented central nervous system, relationships between these changes and loss of memory exist, similar memory deficits can be artificially induced by blocking cholinergic mechanisms in young subjects, and under certain tightly controlled conditions reliable memory improvements in aged subjects can be achieved after cholinergic stimulation. Conventional attempts to reduce memory impairments in clinical trials hav not been therapeutically successful, however. Possible explanations for these disappointments are given and directions for future laboratory and clinical studies are suggested.

Somatostatin is not co-localized in cholinergic neurons innervating the rat cerebral cortex-hippocampal formation

The somatostatin content and choline acetyltransferase activity of the rat cerebral cortex and hippocampus were examined after lesions to the nucleus basalis, the fornix and the dorsal hippocampus. Lesions of the nucleus basalis caused reductions in cortical choline acetyltransferase activity but had no effect on the concentration of somatostatin. Fornix transection caused a reduction in choline acetyltransferase activity in the dorsal hippocampus, but again was without effect on the somatostatin content. Excitotoxin lesions of the dorsal hippocampus caused a 69% reduction in somatostatin concentration in this structure, with no reduction in choline acetyltransferase activity. The results indicate that somatostatin and choline acetyltransferase are in separate populations of neurons in the rat cerebral cortex and hippocampus.