Cell loss in the locus coeruleus in senile dementia of Alzheimer type

Changes of biogenic amines and their metabolites in postmortem brains from patients with Alzheimer-type dementia

Noradrenaline (NA), 3,4-dihydroxyphenylethylamine (dopamine, DA), 5-hydroxytryptamine (serotonin, 5-HT), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in 22 regions of postmortem brains from four histologically verified cases with Alzheimer-type dementia (ATD) and nine histologically normal controls. Compared with the controls, concentrations of 5-HT and 5-HIAA in the ATD brains were significantly reduced in nine regions (superior frontal gyrus, insula, cingulate gyrus, amygdala, putamen, medial and lateral segments of globus pallidus, substantia nigra, lateral nucleus of thalamus) and in eight regions (amygdala, substantia innominata, caudate, putamen, medial and lateral segments of globus pallidus, medial and lateral nuclei of thalamus), respectively. NA concentrations of the ATD brains were significantly reduced in six regions (cingulate gyrus, substantia innominata, putamen, hypothalamus, medial nucleus of thalamus, raphe area). In contrast, significant reductions of DA and HVA concentrations in the ATD brains were found only in putamen and amygdala, respectively. The 5-HIAA/5-HT ratio in the ATD brains decreased significantly in locus coeruleus, while the HVA/DA ratio increased significantly in putamen and medial segment of globus pallidus. These findings suggest that the serotonergic and noradrenergic systems are affected, while the dopaminergic system is relatively unaffected in ATD brains.

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.

Genetics, ageing and dementia

The contribution of genetic differences to variation in ageing and the relationship of ageing to certain types of dementia are discussed. Neuropathological changes commonly found in the ageing brain are present in more severe form in Alzheimer-type dementia, Down's syndrome, multi-infarct dementia, and a substantial number of patients with Parkinson's disease. An increased frequency of ageing-associated changes outside the brain have been reported in Alzheimer-type dementia, Down's syndrome, and multi-infarct dementia, although the evidence is generally meagre and in many cases requires further corroboration. Genetic studies of Alzheimer-type dementia support the existence of heterogeneity on the basis of family history and age of onset; early onset is associated with greater genetic risk and severity of abnormality. The increasing evidence of an association between DNA damage, premature ageing, and neuronal cell loss may provide insights into the aetiology of these and other forms of dementia.

Stability of neuronal number in the human nucleus basalis of Meynert with age

Numbers of neurons in the nucleus basalis of Meynert were estimated in seventeen non-demented patients who died of chronic hepatic or cardiopulmonary disease. Neurons were counted at the site of maximal neuronal density (SMND). This site was chosen by reviewing serial sections around the decussation of the anterior commissure and appeared to be comparable in different individuals. No correlation between numbers of neurons and age could be found. It appears that no uniform neuronal loss occurs in the nucleus basalis with age. Taken together with biochemical studies of cerebral cortical choline acetyltransferase activity, these findings suggest that there is no overall change in cholinergic input to cerebral cortex with age.

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.

Neurochemical basis of dementia in Parkinson's disease

According to their mental status, patients with Parkinson's disease can be subdivided into three groups: (1) mentally normal patients; (2) patients with severe cognitive impairment and Alzheimer-type brain pathology (neuritic plaques, neurofibrillary tangles, granulovacuolar changes); and (3) demented patients without any evidence of Alzheimer changes. Neurochemically, irrespective of the presence or absence of Alzheimer-type brain pathology, demented Parkinson patients seem to have the same disturbance of cortical cholinergic neuron function as patients with Alzheimer-type dementia (Alzheimer's disease), namely, reduced levels of cortical acetylcholine esterase and choline acetyltransferase activity. At present, the question whether the "cortical cholinergic deficiency" is the only (or sufficient) neurochemical basis for the cognitive impairment in Parkinson patients with dementia cannot be answered with certainty; the additional role of other neurotransmitter changes known to occur in the Parkinson brain, especially loss of cortical, hippocampal and subcortical noradrenaline and/or dopamine cannot be ruled out.

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.

Biological markers in mental disorders: post-mortem studies

Many neurotransmitters, related enzymes and receptors are stable post-mortem and can be measured in routine autopsy material. Comparison of brain tissue from control and disease cases can provide evidence of alterations in neurotransmitter systems in mental disorders. However, before attributing a difference in the neurochemical profile to the disease process itself, care has to be taken to exclude non-specific influences such as age, agonal state, drug therapy and post-mortem stability. Changes in a chemical marker can be used to assess the specificity of neuronal loss in degenerative disease but it may be impossible to distinguish such changes from alterations in turnover in surviving neurones. These problems are discussed with particular reference to post-mortem studies of schizophrenia and Alzheimer's disease.

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)

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.

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.

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.

Neurochemical insights into monoamine oxidase inhibitors, with special reference to deprenyl (selegiline)

Monoamine oxidase (MAO) is distributed in neurons and non-neuronal tissue in the human central nervous system. It occurs there as MAO type A and MAO type B. It is not, however, established where both types are located intra- and/or extra-neuronally. Recently, the use of selective MAO-B blockers has shown beneficial effects in the treatment of Parkinson's disease (PD). Knowledge about the locus of action of MAO inhibitors is therefore of great importance. Our findings indicate that MAO-B inhibitors like deprenyl act by blocking neuronal and extra-neuronal MAO-B. This demonstrates that in the early stages of PD the action of deprenyl improves dopamine neurotransmission and hormonal action, whereas in the advanced stages of the disease, when there is progressive loss of dopaminergic neurons accompanied by gliosis, the drug seems to exert beneficial effects via the hormonal route.

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.

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.

Pathological basis for neurotransmitter changes in Parkinson's disease

In eight patients with idiopathic Parkinson's disease, loss of nerve cells from the locus caeruleus, together with reductions in capacity for function in those of the dorsal motor vagus nucleus, the supraoptic and paraventricular nuclei of the hypothalamus and the nucleus basalis of Meynert in the substantia innominata are reported. These changes were more severe in three of these eight patients where mental impairment was present, though in none of these three was the number of senile plaques and neurofibrillary tangles or extent of granulovacuolar degeneration greater in the hippocampus and other cerebral cortical areas than would be expected for the age of the patient. Although these same three patients had received long term L-dopa, it seems that their pathology was related to the disease process and was not drug induced. It is possible therefore, that the dementia seen in some patients with Parkinson's disease is related to degeneration and failing function of noradrenergic and cholinergic neurotransmitter systems and not always associated with the coincidental acquisition of Alzheimer type lesions (Alzheimer's disease).

Serotonin nerve cells in Alzheimer's disease

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Accuracy of clinical diagnosis in primary degenerative dementia: correlation with neuropathological findings

Neuropathological features and causes of death are presented in 27 deceased patients belonging to a prospective series of 71 hospitalised patients with primary degenerative dementia. The clinical criteria for primary degenerative dementia used in the present study were accurate enough to exclude patients with multi-infarct dementia. At necropsy, 82% of the cases had neuropathological changes of Alzheimer's disease. The clinical features of patients with other neuropathological changes are described. The most common immediate cause of death was bronchopneumonia which accounted for 59% of deaths in Alzheimer's disease.

Aging in the rat medial nucleus of the trapezoid body. I. Light microscopy

The medial nucleus of the trapezoid body (MTB), a cell group in the superior olivary complex, was examined in an age-graded series of rats for neuron loss, changes in the giant synaptic endings (chalices of Held) on MTB neurons, and accumulation of age pigment. Neuron counts were done on protargol-stained paraffin sections of MTBs from a series of 17 rats aged 2-3, 6, 18, and 24 months. Between 2-3 and 24 months a 34% decrease in the mean number of MTB neurons was observed. Significant loss (p less than 0.05) was first evident in the early portion of the life span, between 2-3 and 6 months. In thionin-stained sections, there was no change with aging in the proportions of three MTB neuron types: principal cells (approximately 82%), elongate cells (approximately 15%), and stellate cells (approximately 3%). In young adult rats, 25-26% of all MTB neurons were associated with identifiable chalices of Held in protargol stained sections. This ratio did not vary significantly with aging. Age pigment accumulation in the MTB was examined in 2 micrometers Araldite sections stained with toluidine blue. Age pigment deposits were larger and more numerous in the MTBs of old animals, but not as extensive as has been described previously in many other parts of the nervous system. This study is the first to report neuron loss in an animal brainstem nucleus.

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.

Nerve cell protein metabolism and degenerative disease

The mechanisms and organelles through which control of protein synthesis within healthy nerve cells is governed are discussed, and the ways in which expression of these biochemical pathways can be related to cell morphology are described. The volumes of the nucleus and nucleolus, and the amount of RNA within the cell body, are all interrelated and seem to be set at genetically predetermined levels which normally match the neurones basal needs for replacement proteins in respect of the size of its' projection field. However, in situations of (induced) hyperactivity or cell damage, or in others where disease may lower nerve cell activity, the protein requirements change, and it is noted that these morphological features also alter in a direction appropriate to the need for greater or lesser amounts of protein. How these alterations in protein synthesis can provide information as to both the basic pathology, or even the pathogenesis, of degenerative disease of the nervous system is illustrated by reference to Alzheimer's disease and motor neurone disease.

The noradrenergic system in Alzheimer and multi-infarct dementias

The number of melanin containing nerve cells of the locus coeruleus and vagus nucleus is reduced in Alzheimer's disease by 60% with decrease of 22% in the protein synthetic capability of remaining cells. These changes are matched by reductions in brain noradrenaline in eight regions, averaging 36%. In multi-infarct dementia, however, all three of these features are unchanged. These findings indicate that degeneration of central noradrenergic nerve cells is a specific aspect of the pathogenic process underlying Alzheimer's disease.

Parkinson's disease and Alzheimer's disease as disorders of the isodendritic core

Parkinson's disease and Alzheimer's disease may represent two parts of a spectrum of disease characterised by a primary loss of cells of the isodendritic core. Secondary cell loss from the striatum and cerebral cortex therefore occurs as a consequence of the loss of ascending projections from the isodendritic cells. The anatomy of this system should provide a unique opportunity for therapeutic intervention. Neurotransmitter replacement treatment may be provided either by enhancing transmitter release by any remaining neurones or by direct agonists. The wide dispersal of the isodendritic projection systems affected in Parkinson's and Alzheimer's disease and the possibility that they are tonically active create an opportunity for neurotransmitter replacement treatment. Animal studies should be able to show whether such treatment can delay secondary cell loss, and, together with human postmortem studies, whether the hypothesis that the primary lesion is a loss of isodendritic cells is correct.

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

Abnormalities of the noradrenergic system in Alzheimer's disease have been investigated by comparing quantitative histological and biochemical components of this transmitter system (locus coeruleus neuron counts and cortical dopamine beta-hydroxylase (DBH) activity, respectively) in a series of demented and non-demented cases. Cortical activities of the noradrenergic enzyme, DBH, did not correlate significantly with the number of locus coeruleus neurons, a finding which contrasts with the previous observations in animal brains of reductions in cortical DBH following locus coeruleus lesions. The extent of Alzheimer-type abnormalities, assessed from either morphological measures (mean plaque counts) or clinical measures (Mental Test Scores) of severity, was not significantly related to the cortical activity of DBH in the present series of cases, although non-significant trends were apparent. In contrast the activity of the cholinergic enzyme choline acetyltransferase did, as previously reported, correlate significantly with the extent of Alzheimer-type abnormalities, suggesting that abnormalities of the cholinergic system are more closely associated with specific aspects of the Alzheimer disease process than those of the noradrenergic system.