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

Antibodies to viral antigens, xenoantigens, and autoantigens in Alzheimer's disease

Sera from 19 patients with Alzheimer's disease (AD) and 21 control subjects were studied by immunofluorescence and enzyme immunoassay for antibody activity against various viruses and 12 self- and non-self-antigens. Total IgG mean level was significantly higher in the AD group; the IgG level was above 15 g/L in 52.8% of AD patients versus 14.3% of control subjects. Antiviral antibody titers showed no significant differences except for antibodies to herpes simplex virus-1, which were increased in control group. In contrast, autoantibodies were more frequently found in AD patients, and the prevalence of antibodies to spectrin, peroxidase, and thyroglobulin was significantly increased. Thus, in our series, autoimmune but not antiviral responses were heightened in at least 42% of AD patients (versus 9% of the control group) suggesting the existence of two subpopulations in the AD group.

Quantitation of catecholamine neurons in the locus coeruleus in human brains of normal young and older adults and in depression

A quantitative study of the morphology and distribution of norepinephrinergic neurons in the human locus coeruleus (LC) is given for normal young and older adult brain. Norepinephrine (NE)-producing neurons are identified by immunocytochemistry of two NE biosynthetic enzymes, tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), visualized by the peroxidase-antiperoxidase and immunogold-silver-staining methods. TH and DBH immunoreactions yield equivalent results. Both immunocytochemical visualization methods allow detailed analysis of neuronal morphology. The neurons of the human LC fall into four classes: large multipolar neurons with round or multiangular somata, large elliptical "bipolar" neurons, small multipolar neurons, and small ovoid "bipolar" neurons. Though most of the neurons contain neuromelanin pigment, some larger neurons lack pigmentation. Dendritic arborization of all neurons is extensive. Computer-assisted quantitative measurements of the parameters somatic size, dendritic arbor length, surface area, and volume are given. Somatic areas of LC neurons of all four classes are decreased in older adult brain, but dendritic arborization is equally extensive as in the younger. The rostrocaudal length of the LC is approximately 15 mm, and no age-dependent decrease is observed. Computer-assisted mapping of immunoreactive neurons and three-dimensional reconstruction allow division of the LC into rostral, middle, and caudal parts with characteristic distribution of neurons. Small neurons predominate in all parts, but the relative contribution of larger cells decreases in a rostrocaudal direction. A cell loss of 27-37% occurs in older adult brains and to 55% in the brain of a chronically depressed patient without dementia. Cell loss is highest in the rostral part, lower in the middle, and absent in the caudal part, and more small cells are lost than larger ones.

Noradrenergic innervation of human pineal gland: abnormalities in aging and Alzheimer's disease

Using previously characterized polyclonal antibody directed against dopamine beta-hydroxylase (DBH), immunoreactive fibers were demonstrable in pineals of 6 controls of various ages and of 3 individuals with Alzheimer's disease (AD). Abnormal, swollen axons were present in pineals from aged individuals and from individuals with AD. The pathology of noradrenergic axons in a structure innervated by the superior cervical ganglion suggests that peripheral noradrenergic systems may be affected in aging and in AD.

Noradrenaline depletion protects cholinergic neurons in rat hippocampus against AF64A-induced damage

The role of the noradrenergic system in the cholinotoxicity of ethylcholine aziridinium ion (AF64A) was studied in rats. Male Sprague-Dawley rats were treated with the noradrenergic neurotoxin DSP-4 (N-(2-chloroethyl)-n-ethyl-2-bromobenzylamine; 50 mg/kg i.p.) in the presence of the serotonin uptake inhibitor fluoxetine, 14 days prior to bilateral intracerebroventricular injection of AF64A (2 nmol/lateral ventricle). In rats in which noradrenaline (NA) was depleted by 94%, the loss of acetylcholine (ACh) in hippocampus induced by AF64A was significantly attenuated (p less than 0.02). However, when there was only a partial depletion of NA (50% reduction), the AF64A-induced loss of ACh was a pronounced as in rats with intact noradrenergic function. These findings indicate that the noradrenergic lesion has to be complete before a protective effect is apparent. Moreover, they imply that noradrenergic input is involved in AF64A-induced cholinergic damage in the hippocampus.

Clonidine prevents transient loss of noradrenaline in response to cholinergic hypofunction induced by ethylcholine aziridinium (AF64A)

Intracerebroventricular injection of ethylcholine aziridinium (AF64A) (2 nmol/ventricle) induced a considerable decrease in the level of acetylcholine (ACh) in hippocampus (from 21.14 +/- 0.84 to 10.04 +/- 0.59 pmol/mg of tissue; p less than 0.001) 4 days after application. The reduction of cholinergic function was accompanied by a decrease in the level of noradrenaline (NA) (from 1.96 +/- 0.08 to 1.41 +/- 0.06 pmol/mg of tissue; p less than 0.001). Two days after administration of AF64A (1 or 2 nmol/ventricle), the dose-dependent decrease in NA level was associated with an increase in the level of its major metabolite, 3-methoxy-4-hydroxyphenylglycol (MHPG), resulting in a considerable increase in the MHPG/NA molar ratio (from 0.84 +/- 0.06 to 1.62 +/- 0.17; p less than 0.002). Chronic treatment of AF64A-injected rats with clonidine (0.02-0.2 mg/kg, i.p., every 8-12 h) had no significant effect on the loss of ACh content, whereas the decrease in NA content in hippocampus was completely prevented. Clonidine induced aggressive behavior in the AF64A-treated rats, in contrast to sedation in vehicle-injected rats. The response to clonidine under these experimental conditions and the increased MHPG/NA molar ratio in response to AF64A suggest that the transient loss of NA content following AF64A administration results from increased NA release. The increased noradrenergic activity in hippocampus may be linked to the reduction of tonic inhibitory cholinergic input. These results are discussed in relation to possible implications for senile dementia of the Alzheimer type.

The neurobiology of Alzheimer's disease

The defining histological characteristics of Alzheimer's disease (AD) are neurofibrillary tangles and neuritic plaques, although neither is pathognomonic for this disorder. The distribution of AD histopathology suggests selective neuronal vulnerability, with specific cell populations affected within discrete regions of the cerebral hemispheres and within certain subcortical and brain-stem nuclear areas. At the ultrastructural level, tangles and plaque neurites contain paired helical filaments whose composition is unknown but may include altered cytoskeletal elements. Amyloid, deposited in plaque cores and often focally present within the cerebral vasculature, contains a polypeptide ("beta-protein," or "beta-amyloid") encoded by a chromosome 21 gene. At least in occasional families, AD has been linked to a separate chromosome 21 locus, but different underlying genetic factors may operate in other cases. Inorganic substances, including aluminum and silicon, are reported to co-localize within tangle-bearing neurons and plaque cores. Specific environmental agents have not been confirmed to be pathogenetically important, however, but may eventually prove to exert a permissive, facilitatory, or even causative role in many AD patients.

Noradrenergic systems in human cerebellum

Thin, beaded axons, immunostained with antisera to human dopamine beta-hydroxylase (DBH), were present in all layers of the anterior vermis of human cerebellum. This plexus appears similar to that described in rodents and provides information complementary to receptor autoradiographic studies that show significant noradrenergic innervation of mammalian cerebellum. Moreover, in two aged controls, we demonstrated abnormal, swollen, tortuous axons not visualized in young controls.

Substance P and somatostatin coexist within neuritic plaques: implications for the pathogenesis of Alzheimer's disease

In recent years the present authors and others have sought to determine the neurochemical composition of the dilated neuronal processes found within neuritic plaques of patients with Alzheimer's disease. To date a number of neurotransmitter and neuropeptide systems have been observed within different plaques, yet at present it is unclear whether individual human plaques contain more than one transmitter substance. In the present study a highly sensitive dual-immunolabeling procedure was employed and it was demonstrated that substance P and somatostatin-immunoreactive profiles coexist within single senile plaques of patients with Alzheimer's disease. Coexistence of somatostatin and substance P immunoreactivity within plaques was observed in the hippocampus and amygdala but not in the neocortex, although the latter region contained plaques within which somatostatin and substance P existed alone. The frequency with which we observed one or more neuropeptide within plaques was relatively low and in fact most plaques contained neither substance P nor somatostatin immunoreactivity. In addition, a large number of swollen peptidergic processes were observed outside of plaques. The significance of these observations with respect to the pathogenesis of Alzheimer's disease is discussed.

Chronic oral physostigmine without lecithin improves memory in Alzheimer's disease

Sixteen patients with early Alzheimer's disease (AD) completed a 3-month outpatient double-blind parallel trial of oral physostigmine versus placebo. Ten subjects received drug; six received placebo. After a dose-titration phase, each patient was placed on his or her best dose of drug or placebo. Subjects were evaluated with both memory and nonmemory tasks. Seven of the ten drug-treated patients, but none of the six placebo-treated patients, demonstrated improvement on a selective reminding task, a test of verbal memory. Family members reported improvement in six of ten drug-treated patients and none of six placebo-treated individuals. There was a trend toward greater improvement with increasing drug dose. There was no improvement on the nonmemory tests administered. The data indicate that oral physostigmine improves memory but not other areas of cognition.

Brain and CSF somatostatin concentrations in patients with psychiatric or neurological illness. An overview

Somatostatin was originally isolated as a 14-amino-acid peptide from the ovine hypothalamus. The peptide has a widespread regional distribution within the central and peripheral nervous systems, as well as in peripheral organs. Preservation of the chemical structure over a wide range of vertebral species indicates important functional roles of the peptide. Recent results about the role of somatostatin and related peptides in different psychiatric (depression, schizophrenia, Alzheimer's disease) and neurological (Huntington's disease, multiple sclerosis, Parkinson's disease) diseases, and the effects on the hypothalamic-pituitary-adrenal axis are summarized. Also, the influence of some psychotropic drugs (halo-peridol, carbamazepine) on somatostatin levels in cerebrospinal fluid is discussed.

Evidence for retrograde degeneration of epinephrine neurons in Alzheimer's disease

Alzheimer's disease (AD) is associated with a progressive loss of locus ceruleus neurons. These noradrenergic neurons receive a major afferent projection from epinephrine neurons in epinephrine cell groups in the brainstem. The epinephrine neurons have a specific enzymatic marker, phenylethanolamine N-methyltransferase (PNMT), which allows them to be identified chemically and immunohistochemically. We have previously reported a decrease in PNMT in brains of patients with AD. We now report that the decrease in PNMT activity in projections to the locus ceruleus is not due to the loss of epinephrine neurons, although up to 33% of these neurons are atrophic. The decrease in presynaptic PNMT does, however, correlate with the loss of postsynaptic locus ceruleus neurons in brains from AD patients. The percentage of degenerating neurons in the epinephrine nuclei also correlates significantly with the amount of loss of locus ceruleus neurons in AD. In addition, there is a 55% decrease in mitogen activity, a nonspecific measure of growth or maintenance factors, in dialysed locus ceruleus extracts from the AD patients compared to those from control subjects. The mitogen activity in the locus ceruleus was significantly correlated with PNMT activity and with the density of locus ceruleus neurons in all cases examined. These findings provide evidence for the hypothesis that retrograde degeneration is a mechanism of neuronal degeneration in AD and suggest that trophic factors may play a role in this process.

The differential involvement of subcortical nuclei in senile dementia of Alzheimer's type

Cell counts have been performed on cholinergic subcortical nuclei, dorsal raphe nucleus, and locus caeruleus from up to 18 cases of Alzheimer's disease and 10 age-matched control subjects. In general, the extent of cell loss in these structures was similar. In the basal nucleus the anteromedial subdivision was the least, and the posterior subdivision the most affected. A subgroup of demented subjects with Alzheimer's disease had a relatively preserved basal nucleus, and frontal lobe (CAT) choline acetyltransferase activities similar to those in control subjects, but significantly more neuronal loss in the locus caeruleus.

Innervation of human hippocampus by noradrenergic systems: normal anatomy and structural abnormalities in aging and in Alzheimer's disease

Immunocytochemical studies, using an antibody directed against human dopamine beta-hydroxylase, identified an extensive plexus of noradrenergic axons/terminals in normal human hippocampus. In hippocampi of individuals with Alzheimer's disease, the density of noradrenergic innervation was reduced and abnormal noradrenergic axons, which exhibited multifocal enlargements, were present in the neuropil. Some of these neurites were clustered around deposits of amyloid (senile plaques), and these abnormalities were most common in CA3-4, a region normally showing a relatively high density of noradrenergic terminals. This investigation provides direct evidence for structural abnormalities of noradrenergic axons/nerve terminals in hippocampi of individuals with Alzheimer's disease.

A post-mortem study of noradrenergic, serotonergic and GABAergic neurons in Alzheimer's disease

Involvement of noradrenergic, serotonergic and GABAergic neurons in Alzheimer's disease/senile dementia of Alzheimer type (AD/SDAT) was studied in 20 histologically confirmed AD/SDAT cases by comparing these with 14 control patients. Concentrations of noradrenaline (NA) were decreased significantly in the frontal cortex, temporal cortex, hippocampus and putamen in AD/SDAT. Serotonin (5-HT) levels were significantly lowered in the hippocampal cortex, hippocampus, caudate nucleus and putamen and the concentrations of 5-HIAA, a metabolite of 5-HT, were reduced in 3 cortical areas, thalamus and putamen in patients with AD/SDAT. Furthermore, 5-HIAA/5-HT ratios were in general slightly lower in AD/SDAT reaching significance in the temporal and hippocampal cortex. Glutamic acid decarboxylase (GAD) enzyme activity was not changed significantly in AD/SDAT although patients without evidence of premortem hypoxia and hypovolemia showed a consistent trend for increased GAD activity in the thalamus, striatum and substantia nigra. These findings further confirm the involvement of NA and 5-HT neuronal systems in AD/SDAT. The damage of 5-HT neurons seemed to be more generalized and more severe than that of NA neurons. The possible clinical relevance of these findings is briefly discussed and the need for critical evaluations of the behavioral effects related to these abnormalities described in patients with AD/SDAT is emphasized.

The nucleus basalis of Meynert in neurological dementing disease: a review

The nucleus basalis of Meynert of the substantia innominata supplies the major cholinergic innervation of the cerebral cortex. Pathological alterations have been observed in the nucleus basalis of Meynert in several dementing neurological disorders. This paper is an overview of the work done by several researchers in their attempt to find the possible connections between pathology in the nucleus basalis of Meynert and the clinical symptomatology of dementia in several neurological diseases.

RS 86 in the treatment of Alzheimer's disease: cognitive and biological effects

Twelve patients who met Research Diagnostic Criteria for Alzheimer's disease (AD) completed a double-blind crossover study comparing oral RS 86, a long-acting and specific muscarinic agonist, with placebo. Cognitive and noncognitive effects were assessed with the Alzheimer's Disease Assessment Scale (ADAS). RS 86 was found to improve ADAS test scores consistently (both cognitive and noncognitive subscales) in seven patients, with a clinically obvious improvement in only two patients. RS 86 produced a significant increase in peak nocturnal cortisol levels, and this increase correlated with improvement on ADAS testing. Similarly, there was a 38% increase in amplitude of the P300 evoked potential with RS 86. The biological findings suggest that RS 86 was effective only to the extent that it enhanced central cholinergic activity.

Effect of cholinergic deficit induced by ethylcholine aziridinium on serotonergic parameters in rat brain

The consequence of loss of cholinergic input on the function of serotonergic neurons has been studied in rat brain after bilateral intracerebroventricular injections of various doses of the cholinotoxin ethylcholine aziridinium ion (1 to 5 nmoles/ventricle). This treatment resulted in a dose-dependent decrease in acetylcholine content in hippocampus, which occurred 2 days after injection and persisted during the 28 day observation period. The reduction in acetylcholine content ranged from 50.3 +/- 6.0% to 76.9 +/- 3.8% when compared to vehicle-injected rats. Other brain areas, including cortex, striatum and hypothalamus, showed only minor and transient changes in acetylcholine levels. Treatment with ethylcholine aziridinium was accompanied by a dose-dependent response of serotonergic neurons. The predominant reaction, which we observed in all areas studied, was an initial increase in 5-hydroxyindoleacetic acid content, a decrease in serotonin content, and consequently an increase in the molar ratio of metabolite/amine, indicating an increase in serotonin turnover. As with acetylcholine, the decrease in serotonin content was most pronounced in the hippocampus, ranged from 19.4 +/- 2.9% to 53.4 +/- 4.1%, and even persisted at 28 days after injection of 3 and 5 nmoles of the toxin/ventricle, although serotonin levels returned towards normal at that time point after injection of 1 or 2 nmoles of the toxin/ventricle. These data suggest that, in the rat, withdrawal of cholinergic input to the hippocampus might have a considerable impact on serotonergic function. This includes an initial increase in activity and, as cholinergic degeneration progresses, a decrease in serotonergic function. The most likely explanation for the serotonergic deficit is that it may reflect adaptation of these neurons to the withdrawal of cholinergic input. Such a phenomenon might help to increase our understanding of the events taking place in the brains of patients with Alzheimer's disease as the cholinergic system starts to degenerate.

Catecholaminergic neurones assessed ante-mortem in Alzheimer's disease

Indices of dopaminergic and noradrenergic varicosities were assayed in neocortical tissue obtained at diagnostic craniotomy from patients with Alzheimer's disease in the presenium. Dopaminergic markers (concentrations of dopamine, dihydroxyphenylacetic acid and homovanillic acid) were not significantly different from controls in either frontal or temporal cortex. In the frontal cortex, the release of endogenous dopamine and noradrenaline (in the presence of both resting and stimulating concentrations of potassium) was also unaffected whereas release of endogenous serotonin was significantly reduced. In the temporal cortex, noradrenergic markers (concentration of noradrenaline and uptake of radiolabelled noradrenaline) were significantly reduced, to at least 47% of mean control values. These deficits are interpreted as reflecting denervation and were present in patients examined only some two years after developing symptoms of dementia. The ratio of 3-methoxy-4-hydroxyphenylglycol to noradrenaline (a putative index of noradrenaline turnover) was elevated in the temporal cortex, suggesting increased activity of the remaining noradrenergic varicosities. Noradrenergic markers did not correlate with either clinical or histological indices of the severity of the disease which contrasts with presynaptic cholinergic and serotonergic markers.

Amine accumulation in Parkinson's disease and other disorders

Amine accumulation in the axons of degenerating, amine-containing neurones is a natural component of neurone death in many species, including man. While it is becoming increasingly clear that this phenomenon may have functional significance in animal models of Parkinson's Disease, its potential importance in the clinical syndrome has been pretermitted. There are several reasons for this. Failure to sample tissue which contains accumulated amines, the masking of accumulation by adjacent depleted tissues and the degradation of accumulated amines in post-mortem tissues from Parkinsonian brains could account for the low incidence of detection of accumulation in this disorder. Increased levels of amines have been detected in the brains of patients with other conditions including cerebral infarction, Alzheimer's Disease and Huntington's Chorea. These increases have been attributed previously to enhanced aminergic activity, rather than a stage in the degenerative process, as our hypothesis suggests. In addition to the potential importance of amine accumulation in the pathophysiology of various clinical syndromes, a more thorough investigation of this phenomenon in animal models would seem essential since they are used routinely to both describe the basic principles of dopamine function and to evaluate therapeutic possibilities in Parkinson's Disease.

Distribution of biogenic amines and their catabolites in brains from patients with Alzheimer's disease

Norepinephrine, epinephrine, dopamine, serotonin and their major catabolites were measured in 17 regions of the left hemisphere of two brains obtained from two brothers with Alzheimer's disease with very early onset. The clinical diagnosis was confirmed by histological examination of the right hemispheres and brain stems. The quantitative data were compared with our values in normal brains. In the patient suffering from the less severe dementia, there was a severe reduction of the serotonin concentration in all examined neocortical areas and its concentration was even below the detection limit in the nucleus amygdalis, hippocampus, caudate nucleus, putamen, globus pallidus and substantia nigra. In the other patient, who suffered from a more pronounced dementia with myoclonus, the serotonin concentration was below the detection limit in all examined structures. In contrast with these findings, the noradrenergic, adrenergic and dopaminergic systems appeared to be relatively unaffected by the disease process. Focusing our attention on the nuclei wherein the monoamine transmitter systems originate, it appeared that neuronal losses and neurofibrillary tangles clearly predominated in the substantia grisea subependymalis, the nucleus centralis superior and the nucleus raphe dorsalis, origin of the main serotonergic system. The serotonin deficiency sheds light on possible mechanisms of myoclonus in Alzheimer's disease.

Decreased somatostatin-like immunoreactivity in cerebral cortex and cerebrospinal fluid in Alzheimer's disease

To investigate changes in the somatostatinergic neurons of patients with Alzheimer's disease (AD), we determined the somatostatin-like immunoreactivity (SLI) in post-mortem brain tissue of histopathologically confirmed AD patients and in CSF of probable AD patients (according to DSM III). The CSF values were then correlated with psychological test scores. In 6 AD patients the SLI values were decreased 42% (P less than 0.005) in the frontal cortex, 28% (P less than 0.05) in the temporal cortex and 42% (P less than 0.01) in the parietal cortex but not in the thalamus and putamen compared to 11 control patients. In some brain areas there were statistical correlations between SLI values and cholinergic markers, choline acetyltransferase and acetylcholine esterase activities, suggesting a relationship between these two neurotransmitter systems. In the CSF among 75 AD patients SLI was 35% lower (P less than 0.001) than in controls. Severely demented power (P less than 0.001) than in controls. Severely demented patients showed lower SLI values than moderately demented individuals, but this difference was not significant. There was a weak but statistically significant correlation between SLI values in CSF and neuropsychological test scores. This study further confirms the involvement of somatostatinergic neurons in AD and suggests that this involvement may be related to the progression of dementia symptoms.

Animal models of Alzheimer's disease: behavior, pharmacology, transplants

Physostigmine, oxotremorine, RS-86, and a combination of piracetam and lecithin, have all been studied in patients with Alzheimer's disease. Intravenous physostigmine produced a significant improvement in patients' ability to recognize words and particularly to distinguish words they had never seen before from words previously presented. A subgroup of Alzheimer's patients had a clinically meaningful improvement to treatment with oral physostigmine, with the degree of improvement correlating with the ability of oral physostigmine to increase the nocturnal secretion of cortisol. No statistically significant differences of piracetam or piracetam and lecithin, compared to placebo were noted, however, the ratio of red cell to plasma choline might be associated with treatment responsivity. The potential therapeutic efficacy of oxotremorine proved all but impossible to assess due to concomitant adverse effects, particularly dysphoria. Results with another cholinergic agonist, RS-86, will be reported. This drug appeared to be better tolerated than oxotremorine. Animals with a kianic acid induced cortical depletion of choline acetyltransferase were found to have a significant impairment in retention of a passive avoidance task, an abnormality that was readily reversible by physostigmine, oxotremorine and 4-amino-pyridine. Cysteamine, a depletor of somatostatin, also produced a comparable deficit.

Transmitter-replacement therapy in Alzheimer's disease using intracerebroventricular infusions of receptor agonists

Neurotransmitter replacement therapy in Alzheimer's Disease is currently being attempted using bethanechol chloride (Urecholine) infused intracerebroventricularly with an Infusaid continuous infusion pump. The rationale of this therapy is based on the severe cortical pre-synaptic cholinergic deficit in the presence of relatively normal post-synaptic muscarinic receptor density. Patients are selected on the basis of strict clinical criteria at a functional stage 4 or 5 of Reisberg. A cortical biopsy at the time of pump and catheter implantation confirms the diagnosis by histological and biochemical examination. Pre-operative, post-operative and serial mental status assessments combined with functional ADL assessments monitor changes in behavior. A 6 months double-blind treatment period is done in every patient, who is then free to continue if he has improved on active treatment. This specific study is part of a multi-centre trial. Other therapeutic trials using somatostatin analogs, such as Sandostatin, could then be done. The biological effects of the latter compound are being studied currently in adult Green Vervet monkeys, prior to its use in Alzheimer patients. Furthermore autoradiography of bethanechol and peptides labeled with 14C administered in these animals by intracerebroventricular infusion will allow a better knowledge of their pharmacological site of action.

Dementia in movement disorders

Of all the movement disorders, Huntington's disease has been most consistently associated with dementia, while it is only over the last decade that intellectual cognitive decline have been recognized as common features of Parkinson's disease. It is now known that the pathology in these two conditions reflects differential involvement of the striatum. The Huntington lesion is primarily in the caudate, while the Parkinson lesion preferentially affects the putamen. Both conditions have more diffuse pathology, and dementia may also occur in a wide range of other extrapyramidal diseases, such as progressive supranuclear palsy, the parkinsonism-dementia complex of Guam, and certain spinocerebellar degenerations. Clinicopathological correlations will be reviewed in these disorders of primarily subcortical pathology, and comparisons will be made with Alzheimer's disease, a disorder of predominantly cortical pathology.

Antemortem markers of Alzheimer's disease

This review examines various approaches to the development of antemortem markers of Alzheimer's disease. Among the procedures discussed are: neurochemical and histopathologic studies of the cholinergic system, concentrating on CSF and blood plasma; genetic studies; imaging and electrophysiological studies; and neuroendocrine studies.

Nerve growth factor and Alzheimer's disease

Alzheimer's disease is associated with a pronounced loss of the cholinergic neurons that form the ascending cholinergic projections of the basal forebrain. Even though the disease is also characterized by changes in other neuronal systems and by a high frequency of neuronal plaques and tangles, the cholinergic deficit seems to be a principal element responsible for the memory loss typical of Alzheimer's disease. This review summarizes findings in experimental animals which indicate that nerve growth factor (NGF), a well-characterized protein, acts as a neurotrophic factor for cholinergic neurons of the basal forebrain. NGF is present in the target areas of these cholinergic neurons and affects their survival, fiber growth, and expression of transmitter-specific enzymes. Furthermore, NGF is able to prevent the degeneration of cholinergic neurons in adult rats with experimental lesions mimicking the cholinergic deficit in Alzheimer's disease. These findings suggest that increasing the availability of NGF to human cholinergic cells might promote their survival in certain disease processes. Additional steps are discussed for establishing the possible involvement of NGF in the pathogenesis of Alzheimer's disease and the development of an effective therapy.

Somatostatin-28(1-12)-like immunoreactivity is reduced in Alzheimer's disease cerebral cortex

A deficiency in somatostatin is the most consistently described neurochemical alteration in Alzheimer's disease (AD) attributable to intrinsic cortical neurons. Somatostatin-28 (SOM-28), an N-terminal-extended form of somatostatin, can be cleaved to form somatostatin-28(1-12)(SOM-28(1-12) ) and somatostatin-14 (SOM-14). We have measured concentrations of SOM-28(1-12)-like immunoreactivity in 8 cortical regions from 12 patients with AD and 13 controls. Significant reductions (P less than 0.001) were found in all cortical regions examined with the largest decrease in temporal lobe. Reductions were significantly correlated with decreases in somatostatin-14-like immunoreactivity in the same regions. The similar reductions of two prosomatostatin-derived peptides in AD cerebral cortex supports the contention that decreased somatostatin immunoreactivity in AD is caused by a degeneration of somatostatin cortical neurons and terminals.

The concept of subcortical and cortical dementia: another look

The subcortical dementias such as progressive supranuclear palsy, Huntington's disease, and Parkinson's disease are said to be characterized by the presence of slowed mentation, apathy, and the absence of aphasia, agnosia, and apraxia, symptoms that are claimed to be more common in cortical dementias such as Alzheimer's disease. Conceptual problems (such as vagueness of terms and difficulties with symptom definition) and methodological problems (such as improper matching of comparison groups and inadequate assessment techniques) found in currently available studies require a reappraisal of this classification of dementias into cortical and subcortical forms. A review of recent clinical, neuropathological, and neurochemical studies offers little support for this classification system, although adequate systematic studies have not been performed.

Morphological and biochemical changes in the cholinergic and monoaminergic systems in Alzheimer-type dementia

The integrity of cholinergic and monoaminergic neuronal systems in Alzheimer-type dementia (ATD) was studied using a combination of morphological and biochemical procedures applied to samples from seven ATD brains and ten control brains. On morphological examination, the number of neurons was counted in the nucleus basalis of Meynert (nbM), the locus coeruleus (LC) and the nucleus centralis superior (NCS). Biochemically, the activities of choline acetyltransferase (ChAT) and the concentrations of noradrenaline (NA) and serotonin (5-hydroxytryptamine; 5-HT) were measured in the nbM, LC, NCS, frontal cortex, temporal cortex and occipital cortex. Compared with the controls, the mean number of neurons in the nbM and LC were significantly reduced in the ATD brains. The neuronal loss in the NCS in the ATD brains was not significant. The ChAT activities in all regions from the ATD brains had a tendency to be reduced. Marked reductions in the NA concentrations in the LC and 5-HT concentrations in the temporal and occipital cortices were found in the ATD brains. These findings suggest that various neurotransmitter systems, including cholinergic, noradrenergic and serotonergic systems, are affected in the ATD brains.

Alpha 2-adrenergic mechanisms in prefrontal cortex associated with cognitive decline in aged nonhuman primates

This study provides evidence that the alpha 2-adrenergic receptor agonist clonidine ameliorates the cognitive deficits exhibited by aged nonhuman primates through drug actions at alpha 2 receptors. Furthermore, pharmacological profiles in animals with lesions restricted to the dorsolateral prefrontal cortex indicate that this area may be the site of action for some of clonidine's beneficial effects. These results demonstrate that alpha-adrenergic systems contribute to cognitive function and suggest a new strategy for treating memory disorders in aged humans.

Neurobiological studies of transmitter systems in aging and in Alzheimer-type dementia

Dysfunction and death of specific neuronal systems are important processes occurring in aging and in Alzheimer's and in Parkinson's disease. The neuropathology and neurochemistry of some of the neuronal systems at risk in these settings are subjects of active research; the nature and consequences of these cellular pathologies have begun to be clarified. The availability of animal models (including aged monkeys, macaques with cholinergic deficiencies, and monkeys with MPTP-induced nigrostriatal pathology, all of which recapitulate certain features of human aging or disease) allow the opportunity to assess the efficacies of new pharmacotherapies, neural grafts, and trophic factors. These approaches can be monitored by behavioral testing and, in some instances, by in vivo imaging methods, which can in turn be correlated with morphologic and chemical analyses of brain. Demonstration of the efficacy of these procedures in nonhuman primates would have profound implications on the development of new therapies designed to alleviate the effects of aging and disease on the human brain.

Clinical studies of the cholinergic deficit in Alzheimer's disease. I. Neurochemical and neuroendocrine studies

Autopsy studies indicating that cholinergic neurons are selectively lost in patients with Alzheimer's disease (AD) and senile dementia of the Alzheimer type (SDAT) suggest that peripheral markers for central cholinergic activity would be useful in diagnosis. The present studies found that cerebrospinal fluid (CSF) concentrations of acetylcholine (ACh) correlated with the degree of cognitive impairment (r = .70) in a sample of carefully diagnosed patients with AD/SDAT, but metabolites of other neurotransmitters were not related to cognitive state; this suggests that CSF ACh may be a valid measure of cholinergic degeneration. Cortisol and growth hormone were measured in plasma samples drawn from patients and controls every 30 minutes from 2100 to 1100 hours the next day. Mean plasma cortisol concentrations were higher in patients with AD/SDAT than in controls and correlated inversely with CSF methoxy-hydroxyphenylglycol (MHPG) (r = .61) and positively with degree of cognitive impairment (r = +.53); as anticholinergic drugs suppress cortisol this finding indicates that cortisol dysregulation may be a marker for abnormalities in other neurotransmitter systems, particularly the noradrenergic system. Growth hormone secretion was not different in patients and controls but was positively correlated with CSF MHPG (r = +.63).

Catecholaminergic neurites in senile plaques in prefrontal cortex of aged nonhuman primates

Immunocytochemical studies, using a polyclonal antibody directed against tyrosine hydroxylase, identified catecholaminergic axons in prefrontal cortex of young and aged nonhuman primates. Aged monkeys, who showed cortical senile plaques in silver stains, had swollen tyrosine hydroxylase-immunoreactive axons in neocortex. Some of these abnormal processes were associated with deposits of amyloid (visualized by thioflavin-T fluorescence) and were similar in appearance to neurites demonstrated by silver impregnation methods. This study provides evidence for structural abnormalities in catecholaminergic axons/nerve terminals in the neocortices of aged primates.

The neuropathology of Alzheimer's disease: a review with pathogenetic, aetiological and therapeutic considerations

The neuropathology of Alzheimer's disease is reviewed in this paper emphasizing the morphological and morphometric changes that occur in the disease and their relationship to age and ageing. From this, a new hypothesis of pathogenesis is presented which accounts for the pattern of neuronal damage in Alzheimer's disease. This is that the pathogenesis of Alzheimer's disease begins with a leakage of a neurotoxin through a defective cortical blood brain barrier. This incites development of the senile plaque and later, via a retrograde transport of the same (or different) factors, intracellular neurofibrillary tangle formation and death of neurones within areas of cortex affected by plaques and in subcortical areas such as nucleus basalis of Meynert, locus caeruleus and dorsal raphe nuclei, all of which project to these same areas of cortex. Evidence consistent with this hypothesis is presented and the aetiological and therapeutic implications are discussed.

A double-blind, placebo controlled trial of high-dose lecithin in Alzheimer's disease

The first long-term double-blind placebo controlled trial of high dose lecithin in senile dementia of the Alzheimer type is reported. Fifty one subjects were given 20-25 g/day of purified soya lecithin (containing 90% phosphatidyl plus lysophosphatidyl choline) for six months and followed up for at least a further six months. Plasma choline levels were monitored throughout the treatment period. There were no differences between the placebo group and the lecithin group but there was an improvement in a subgroup of relatively poor compliers. These were older and had intermediate levels of plasma choline. It is suggested that the effects of lecithin are complex but that there may be a "therapeutic window" for the effects of lecithin in the condition and that this may be more evident in older patients.

Substance P immunoreactivity within neuritic plaques

In the present immunocytochemical study we examined brain tissue of patients with Alzheimer's disease in order to determine the relationship of substance P (SP)-labeled processes to neuritic plaques. Swollen neuropeptidergic processes were consistently observed within a relatively small percentage of the plaques. These data provide a morphologic correlate to the biochemical finding that SP levels are reduced in the brain tissue of patients with Alzheimer's disease, and further indicate that Alzheimer's disease affects multiple neurotransmitter and neuropeptide systems.

CSF levels of neurotransmitters in Alzheimer-type dementia. Effects of ergoloid mesylate

The cerebrospinal fluid level of homovanilic acid (HVA), 5 hydroxyindolacetic acid (5HIAA) and 3 methoxy-4-hydroxy phenylglycol (MHPG) was determined twice at 12 to 15-day intervals in 23 patients with Alzheimer-type dementia (ATD). No correlation was found with the degree of dementia as assessed by psychometric testing. In most of the patients, the CSF levels of 5HIAA, MHPG and to a lesser extent HVA were found to be rather stable within a period of 2 weeks. The observation of a decrease in the concentration of HVA but not of 5HIAA or MHPG in 10 out of 12 patients treated with ergoloid mesylate may therefore be of interest in elucidating the mechanism of action of this drug in ATD.

Catecholamine topochemistry in human basal ganglia. Comparison between normal and Alzheimer brains

Analysis of catecholamine levels in postmortem human control and Alzheimer brains revealed lower mean concentrations of noradrenaline, but not dopamine, in nucleus caudatus, putamen and globus pallidus, but not in hippocampus, of the Alzheimer brains. Generally, noradrenaline levels were higher in the more posterior parts of nucleus caudatus and putamen in the control brains, whereas such gradients were absent in the Alzheimer brains.

Alterations in L-glutamate binding in Alzheimer's and Huntington's diseases

Brain sections from patients who had died with senile dementia of the Alzheimer's type (SDAT), Huntington's disease (HD), or no neurologic disease were studied by autoradiography to measure sodium-independent L-[3H]glutamate binding. In brain sections from SDAT patients, glutamate binding was normal in the caudate, putamen, and claustrum but was lower than normal in the cortex. The decreased cortical binding represented a reduction in numbers of binding sites, not a change in binding affinity, and appeared to be the result of a specific decrease in numbers of the low-affinity quisqualate binding site. No significant changes in cortical binding of other ligands were observed. In brains from Huntington's disease patients, glutamate binding was lower in the caudate and putamen than in the same regions of brains from control and SDAT patients but was normal in the cortex. It is possible that development of positron-emitting probes for glutamate receptors may permit diagnosis of SDAT in vivo by means of positron emission tomographic scanning.

Catecholamine neurons with Alzheimer's neurofibrillary changes and alteration of tyrosine hydroxylase. Immunohistochemical investigation of tyrosine hydroxylase

Immunohistochemistry with antisera against tyrosine hydroxylase was performed on neurons with Alzheimer's neurofibrillary changes in the substantia nigra and locus ceruleus. These specimens were obtained from brains with Alzheimer's disease, Pick's disease, progressive supranuclear palsy, Alzheimer's type parkinsonism, parkinsonism-dementia complex on Guam, and normal aging. Under these neurologic conditions the affected catecholamine neurons with Alzheimer's neurofibrillary changes were stained positively with antisera against tyrosine hydroxylase. The results suggested that in these neurons, Alzheimer's neurofibrillary changes seemed to develop independently before the reduction of tyrosine hydroxylase protein synthesis.