Topographical distribution of neurochemical changes in Alzheimer's disease

Combined study of cerebral glucose metabolism and [11C]methionine accumulation in probable Alzheimer's disease using positron emission tomography

There is a characteristic decrease in glucose metabolism in associative frontal and temporo-parietal cortices of patients suffering from Alzheimer's disease (AD). The decrease in metabolism might result from local neuronal loss or from a decrease of synaptic activity. We measured in vivo [11C]methionine accumulation into proteins with positron emission tomography (PET) to assess cortical tissue loss in AD. Both global regional activity and compartmental analysis were used to express [11C]methionine accumulation into brain tissue. Glucose metabolism was measures with [18F]fluorodeoxyglucose and autoradiographic method. Combined studies were performed in 10 patients with probable AD, compared to age-matched healthy volunteers. There was a significant 45% decrease of temporo-parietal glucose metabolism in patients with AD, and frontal metabolism was lowered in most patients. Temporo-parietal metabolism correlated to dementia severity. [11C]methionine incorporation into temporo-parietal and frontal cortices was not significantly decreased in AD. There was no correlation with clinical symptoms. Data suggest that regional tissue loss, assessed by the decrease of [11C]methionine accumulation, is not sufficient to explain cortical glucose hypometabolism, which reflects, rather, reduced synaptic connectivity.

The neurochemistry of Alzheimer type, vascular type and mixed type dementias compared

We present the results of a meta-analysis of neurochemical changes in human post mortem brains of Alzheimer type (AD), vascular type (VD) and mixed type (MF) dementias, and matched controls based on 275 articles published between January 1980 and February 1994. Severity of degeneration between the different neurochemical systems is as follows, although ranking is difficult with regard to limited numbers of investigations in some neurochemical systems: Cholinergic system > serotonergic system > excitatory amino acids > GABAergic system > energy metabolism > NA > oxidative stress parameters > neuropeptides > DA. But, within a neurochemical system, degeneration is not evenly distributed. Spared parameters, e.g. muscarinic receptors and MAO-B, allow to make some suggestions for future therapeutic strategies.

Expression of the protooncogene bcl-2 in Alzheimer's disease brain

To investigate the role of the apopotosis-related protooncogene bcl-2 in Alzheimer's disease (AD), we compared levels of its protein product, designated Bcl-2, in AD and nondemented (ND) age-matched control neocortical samples. The 26 kD Bcl-2 protein is increased in expression by more than three-fold in AD compared to ND samples as detected by immunoblots. Immunohistochemical analyses give similar results. In AD patients Bcl-2 immunoreactivity is dense and profuse and appears to occur on reactive astrocytes, whereas Bcl-2 immunoreactivity of astrocytes in ND patients is light and sparse. Staining of both gray and white matter is observed but is most prominent in the latter. Increased expression of Bcl-2 by astrocytes may partially underlie their resistance to loss in AD. By contrast, neuronal Bcl-2 immunoreactivity is more sparse and equivocal, perhaps reflecting the vulnerability of this cell type to apoptotic mechanisms in AD. High levels of Bcl-2 in glial cells may aid in cell survival of reactive astrocytes resulting in either beneficial or deleterious effects on neuronal viability.

Free D-serine in post-mortem brains and spinal cords of individuals with and without neuropsychiatric diseases

We have measured the concentrations of free D-serine post-mortem in the prefrontal cortex, parietal cortex, cerebellum and spinal cord from individuals with and without (controls) neuropsychiatric diseases using high-performance liquid chromatography with fluorometric detection. The levels of D-serine were found to be high in the prefrontal and parietal cortex (around 100 nmol/g wet weight) and very low in the cerebellum and spinal cord (below 10 nmol/g wet weight). The uneven distribution of the D-amino acid in the human central nervous system (CNS) resembles that observed in rodents, suggesting that, as shown in the rat CNS, the regional variation of D-serine content in the human brain might also be closely correlated with those of the N-methyl-D-aspartate (NMDA) type excitatory amino acid receptor. In the prefrontal cortex, the gray and white matter had a similar concentration of D-serine. These findings, together with the selective action of D-serine at the NMDA-related glycine site and the non-neurogenic nature of extracellular D-serine release, add further support to the view that D-serine could be an intrinsic modulator of the NMDA receptor liberated from certain glial cells in the mammalian brain. Despite the anti-psychotogen activity of D-serine in the rat, there were no statistically significant differences between the D-serine contents in the prefrontal or parietal cortex of controls and those of patients with schizophrenia or dementia of the Alzheimer type.

Improving the Clinical Recognition of Very Mild Dementia Using Multiple Levels of Assessment

Neuropsychological test batteries alone are often unable to differentiate very mild dementia from both normal aging and mild dementia of the Alzheimer type (DAT). The authors hypothesized that some of the difficulties of neuropsychological tests in the identification of very mild dementia could be overcome by the inclusion of additional levels of assessment (activities of daily living, psychopathology, and subjective complaints). Three groups (very mild dementia, mild-to-moderate DAT, and healthy control subjects) of community-dwelling older persons were assessed on cognitive and noncognitive variables. Results indicated that noncognitive variables improved prediction of group assignment. For accurate identification of all patients with very mild dementia, in addition to neuropsychological variables, subjective complaints of impaired orientation and disturbances of apperception were necessary and sufficient.

Brain N-acetyl-L-aspartic acid in Alzheimer's disease: a proton magnetic resonance spectroscopy study

This study was performed in order to measure changes in brain N-acetyl-L-aspartic acid (NAA) in post-mortem brain tissue in Alzheimer's disease (AD) in comparison to normal control subjects using the technique of magnetic resonance spectroscopy. Brain tissue was obtained at autopsy and frozen until use, from seven patients diagnosed according to current research criteria for AD and 7 control subjects. Detailed clinical evaluations were available for all the dementia cases. Representative brain samples were obtained from three neocortical regions and a limbic region (parahippocampal gyrus) in white and grey matter. NAA was quantified on perchloric acid extracts using proton nuclear magnetic resonance (NMR) spectroscopy. Regional NAA did not vary significantly with age. In AD, reductions were present in the grey matter of the neocortex but not in the white matter. Within the parahippocampal gyrus there were reductions in both tissue types; only cortical levels correlated with clinical scales of dementia severity. A pattern of increasing correlation was observed between dementia severity as measured by the mini mental state examination during life and NAA levels from brain areas of increasing pathological predilection in AD. These post-mortem studies show reductions in brain NAA in AD which correlate with dementia severity during life and which support the use of future in vivo NAA spectroscopic images in the evaluation of AD patients.

beta-Amyloid precursor protein isoforms show correlations with neurones but not with glia of demented subjects

Post-mortem cerebral cortex from 15 demented patients was specially collected to minimise autolysis and two membrane fractions and one soluble fraction were quantitatively examined for the major species of beta-amyloid precursor protein (APP) of high apparent molecular mass (> or = 80 kDa) together with the major mRNA species encoding APP isoforms. The number of pyramidal neurones and astrocytes, putative biochemical indices of interneurones and pyramidal neurones, and choline acetyl transferase activity were also determined. Multiple regression analysis has been used to investigate intercorrelations of APP species with biochemical and morphometric measures, free of any effects of confounding demographic variables. Subjects with Alzheimer's disease showed a loss of cholinergic activity and D-aspartate uptake compared with patients with other causes of dementia. The major finding of the study is that measures of neurones rather than astrocytes most closely correlate with the concentration of APP. Pyramidal cell numbers were positively correlated with mRNA for APP695. APP in the soluble fraction showed a negative correlation with pyramidal cell numbers and cholinergic activity. These results indicate that neurones within the cerebral cortex are the major source of APP, and that secretion of APP is dependent upon cortical pyramidal neuronal activity and cholinergic activity.

Brain angiotensin receptor subtypes in the control of physiological and behavioral responses

This review summarizes emerging evidence that supports the notion of a separate brain renin-angiotensin system (RAS) complete with the necessary precursors and enzymes for the formation and degradation of biologically active forms of angiotensins, and several binding subtypes that may mediate their diverse functions. Of these subtypes the most is known about the AT1 site which preferentially binds angiotensin II (AII) and angiotensin III (AIII). The AT1 site appears to mediate the classic angiotensin responses concerned with body water balance and the maintenance of blood pressure. Less is known about the AT2 site which also binds AII and AIII and may play a role in vascular growth. Recently, an AT3 site was discovered in cultured neoblastoma cells, and an AT4 site which preferentially binds AII(3-8), a fragment of AII now referred to as angiotensin IV (AIV). The AT4 site has been implicated in memory acquisition and retrieval, and the regulation of blood flow. In addition to the more well-studied functions of the brain RAS, we review additional less well investigated responses including regulation of cellular function, the modulation of sensory and motor systems, long term potentiation, and stress related mechanisms. Although the receptor subtypes responsible for mediating these physiologies and behaviors have not been definitively identified research efforts are ongoing. We also suggest potential contributions by the RAS to clinically relevant syndromes such as dysfunctions in the regulation of blood flow and ischemia, changes in cognitive affect and memory in clinical depressed and Alzheimer's patients, and angiotensin's contribution to alcohol consumption.

The release and uptake of excitatory amino acids in rat brain: effect of aging and oxidative stress

The excitatory amino acids (EAAs) L-aspartate and L-glutamate constitute the major neurotransmitters in the mammalian brain. This study established the influence of aging and oxidative stress on the release and uptake of EAAs. The high affinity uptake of D-[3H]aspartate in synaptosomal fractions of the neostriatum, hippocampus, and neocortex was not significantly different in Fisher 344/Norwegian Brown hybrid rats aged 3, 12, 24, and 37 months. Similarly, the K(+)-evoked efflux of endogenous aspartate and glutamate from neocortical minislices was also unaffected by age. To examine the possibility that EAA nerve terminals become more vulnerable to oxidative stress with age, the influence of an inhibitor of the electron transport chain (sodium cyanide) on EAA uptake and release was determined. Although cyanide inhibited D-[3H]aspartate uptake and potentiated the potassium-evoked efflux of aspartate and glutamate in a Ca(2+)-independent fashion, neither of these changes were influenced by age. Thus, the functional integrity of EAA nerve terminals and their vulnerability to oxidative stress are both preserved in normal aging. The potency of cyanide to inhibit D-[3H]aspartate uptake did, however, display regional variability: hippocampus > neocortex > neostriatum (IC50 = 1.2 +/- 0.2 mM, 1.9 +/- 0.1 mM and 2.7 +/- 0.2 mM, respectively), suggesting that EAA nerve terminals in the hippocampus may be selectively vulnerable to oxidative stress.

An aspect of Alzheimer neuropathology after suicide transport damage

Concentrations of APP-like immunoreactivity have been determined by western blotting in a soluble fraction and two membrane fractions of brain cortex from demented patients (14 with Alzheimer's disease and 8 with other diagnoses). The concentration of APP in the soluble fraction correlated with the number of pyramidal neurones but not astrocytes or indices of interneurones. Experimental lesions in rats and quantitative autoradiography were used to investigate the cellular localisation of receptors. Lesions were produced by intrastriatal or intracortical injections of volkensin to destroy corticofugal and corticortical pyramidal neurons respectively. Volkensin treatment caused significant loss of pyramidal neurones which was accompanied by reduced binding to muscarinic cholinergic m1 receptors. [3H] 8-OH-DPAT (serotonin 1A receptors) binding was reduced only following intrastriatal volkensin. Results from the human and rat investigations are discussed in terms of the biology of cortical pyramidal neurones and drugs for the treatment of Alzheimer's disease.

Alterations in the activity of adenylate cyclase and high affinity GTPase in Alzheimer's disease

The aim of this study was to assess the effect of Alzheimer's disease has on the functional integrity of several signal transduction proteins. The relative levels of the G-protein alpha subunits Gs alpha-L, Gs alpha-S, Gi alpha-2 and G(o) alpha were measured by western blotting and found to be unchanged in membranes prepared from Alzheimer-diseased frontal cortex or hippocampus compared to control brains. However the activity of the G-protein associated enzyme, high affinity GTPase, was found to be reduced in the frontal cortex (reduced by 25%) and by a similar magnitude in the hippocampus (reduced by 27%) of Alzheimer subjects. The same membrane preparations were also assayed for the activity of adenylate cyclase. Basal enzyme activity was not significantly altered in Alzheimer diseased hippocampus, but was markedly reduced (by 45%) in the frontal cortex. The ability of fluoride and aluminium ions to stimulate adenylate cyclase was not significantly changed in either brain region. This suggests that G-proteins, especially Gs, are still able to interact with this enzyme. These results indicate that although the presence of Alzheimer's disease does not significantly alter G-protein levels, changes have taken place in the overall activity of these proteins. However this alteration does not affect their ability to stimulate adenylate cyclase activity.

Physostigmine ameliorates the delusions of Alzheimer's disease

Alzheimer's disease (AD) patients frequently manifest delusions, and the cholinergic deficiency of AD may contribute to this aspect of the psychopathology of the disorder. In a double-blind, crossover study involving two patients, we compared the antidelusional efficacy of physostigmine, an acetylcholinesterase inhibitor, with haloperidol, a widely used neuroleptic agent. Physostigmine ameliorated the delusions and produced fewer side effects. These preliminary observations suggest that the cholinergic deficiency contributes to the occurrence of delusions in AD and cholinergic therapy may have a role in the treatment of the delusional symptoms.

Serotonergic pathology is not widespread in Alzheimer patients without prominent aggressive symptoms

Behavioural symptoms of Alzheimer's disease, such as aggression, may determine the care patients required. Most postmortem neurochemical studies have been of institutionalized patients and conclusions drawn from these may not be valid for all patients. We have shown that serotonin 2 receptors are not lost from 12 of the 13 areas of cerebral cortex examined in the patients assessed to be free of aggressive symptoms. This has been interpreted as representing the relative preservation of cortical interneurones. In contrast choline acetyltransferase activity was reduced in all areas whereas serotonin content was reduced in only 2 of the 4 areas examined.

Cholinergic fiber loss occurs in the absence of synaptophysin depletion in Alzheimer's disease primary visual cortex

The significance of cholinergic degeneration in Alzheimer's disease (AD) depends, in part, on whether it is an early event, possibly integral to the progression of the disease, or a late event, occurring only as a secondary effect of cortical degeneration. We have been studying the primary visual cortex in AD cases, on the assumption that the disease process may be retarded in this relatively-spared area, thus providing a 'window' on early AD. In this work, we have quantified acetylcholinesterase fiber density and the density of an immunohistochemical reaction for synaptophysin as measures of cholinergic and total synaptic loss, respectively, in the primary visual cortex of AD and control cases. Cholinergic fibers were depleted to 15% of control values, while synaptophysin density was not significantly altered. Cholinergic degeneration thus appears to occur in the absence of generalized synaptic loss in this area.

A selective reduction of excitatory amino acids in cerebrospinal fluid of patients with Alzheimer type dementia compared with vascular dementia of the Binswanger type

We determined the concentrations of the putative transmitter amino acids in the cerebrospinal fluid of patients with Alzheimer type dementia (ATD) and vascular dementia of the Binswanger type (VDBT). In ATD, aspartate and glutamate concentrations were significantly and selectively reduced, while in VDBT, concentrations of aspartate, glutamate, gamma-aminobutyric acid (GABA) and many other amino acids were decreased non-selectively. In both ATD and VDBT, we found a tendency for all amino acids to increase with progression of the disease, and this reached statistical significance for some amino acids.

Reduced temporal lobe blood flow in Alzheimer's disease

We used single photon emission computed tomography with the blood flow tracer [123I]N-isopropyl-p-iodoamphetamine (IMP) to study regional cerebral blood flow (rCBF) in 50 mildly and moderately demented Alzheimer's disease (AD) patients to evaluate rCBF as a function of disease severity. Relative rCBF (normalized to occipital cortex) was significantly lower than controls in temporal cortex for both mildly and moderately demented patients. Similar numbers of patients in both groups demonstrated perfusion abnormalities in temporal neocortex. Parietal cortex was more variably involved with greater numbers of moderately than mildly demented patients showing perfusion abnormalities. Relative rCBF in dirsolateral frontal cortex was reduced only in the moderately demented patients. Disease severity, as measured by the Mini Mental Status Examination, was associated with relative rCBF only in dorsolateral frontal and parietal cortex. These results suggest that the temporal lobes are the first neocortical regions affected by AD and that other cortical areas become involved as the disease progresses.

Astroglia in Alzheimer's disease

Amyloid deposits are characteristic of Alzheimer's Disease (AD) and there is growing evidence that amyloid may play an important role in the genesis of this neurodegenerative disease. This review discusses data which suggests that reactive astrocytes and microglia may be a necessary concomitant with amyloid to produce the neuropathology which manifests as AD. Several hypotheses and supporting data for mechanisms by which reactive astrocytes may mediate this neuropathology are presented. These include the possibility that amyloid induces excitotoxicity by interferring with astrocytic glutamate uptake, the possibility that amyloid has this effect via an action on a tachykinin-related receptor and the possibility that proteoglycans released by astrocytes may facilitate the deposition of amyloid plaques. Both symptomatic treatment to enhance cognitive function and treatment to stop the progression of AD are needed. It is hoped that answers to some of the unique questions raised here may provide new insight into the etiology and treatment of AD.

Behavioral screening for cognition enhancers: from indiscriminate to valid testing: Part I

Preclinical efforts to detect and characterize potential cognition enhancers appear to have been dominated by a strategy of demonstrating a wide variety of apparently beneficial behavioral effects with little attention given to the specific psychological mechanisms underlying behavioral enhancement. In particular, the question of whether or not behavioral facilitation is based on relevant mnemonic mechanisms and is independent of the stimulus properties and/or the motivational and attentional components of a task is not often considered. As a result, an overwhelming number of compounds have failed to produce the clinical effects predicted for them on the basis of preclinical research. The available data suggest that a more successful approach requires deductive research strategies rather than the indiscriminate accumulation of apparently beneficial effects in a variety of behavioral tasks and animal models. The first step towards such an approach is a systematic and rigorous evaluation of the different aspects of validity for the models most frequently used in preclinical research. It is concluded that a combination of good construct validity and good face validity represents a necessary condition for screening tests with predictive validity, and that the most popular paradigms fail to fulfil these criteria. Future screening programs for cognition enhancers will probably be characterized by a depreciation of "fast and dirty tests" in favor of approaches focussing on the validity of the effects of potential cognition enhancers.

Long-term retention of implicitly acquired learning in patients with Alzheimer's disease

This study examined retention of procedural learning, using the serial reaction time (SRT) task, over a 1- or 2-week delay in Alzheimer's disease (AD) patients and elderly control (EC) subjects. The SRT task is a four-choice reaction-time task consisting of blocks of 100 trials. A 10-item repeating sequence was embedded in the first four blocks of trials in session one and the first two blocks of session two. Sequence-specific learning was assessed in session one by comparing reaction time (RT) in the fourth block with a repeating sequence to a fifth block in session one in which the stimuli were randomly arranged. After excluding subjects with deficient session one learning, there were eight AD patients and 14 EC subjects who showed robust sequence-specific learning in session one. In these subjects, retention of sequence-specific learning over the 1- to 2-week delay was examined. The AD patients and EC subjects showed an equivalent change in RT across sessions, and all the AD patients lacked any declarative knowledge of the repeating sequence within the task. Individually, two of the eight AD patients appeared to deviate substantially from the others and from the EC subjects in their excess slowing of RT across sessions. Since six AD patients did show retention similar to the EC subjects, it is concluded that at least some AD patients show normal retention of implicitly acquired knowledge over a long delay. Preserved retention in some of the AD patients implies that it is mediated by brain structures that are not affected by the Alzheimer neuropathological process.

Cerebral perfusion patterns in vascular dementia of Binswanger type compared with senile dementia of Alzheimer type: a SPECT study

Cerebral perfusion patterns in 18 cases with vascular dementia of Binswanger type (VDBT) (8 moderate and 10 severe cases) were compared with 25 cases with senile dementia of Alzheimer type (SDAT) (16 moderate and 9 severe cases) and 14 controls by single photon emission computed tomography using N-isopropyl-p-123I iodoamphetamine (IMP) as a tracer. The cerebral: cerebellar IMP uptake ratio (%) (CCR) was used as a measured of relative cerebral perfusion. The CCRs were about 85-90% in all areas in controls. Moderate VDBT patients showed a remarkable decrease of CCRs in the basal grey region (thalamus and basal ganglia) (right 79%, left 77%) and in the frontal area (right 79%, left 80%) (P less than 0.01). In severe VDBT patients a significant decrease of the CCR was noted in all regions (P less than 0.01). The decrease of mean CCRs in the hemispheres was significantly correlated with the severity of disease determined by psychometric testing. Patients with SDAT showed a significant decrease of the CCR in the parietal (right 71%, left 74%) and right temporal (78%) areas in the moderate stage (P less than 0.01), and further progression of dementia was associated with low perfusion areas extending to the the frontal areas (78%, P less than 0.01). These differences in the perfusion patterns and their changes with progression of the illnesses may be reflected in characteristic clinical features.

Possible roles of L-phosphoserine in the pathogenesis of Alzheimer's disease

L-Phosphoserine is a membrane metabolite that is elevated in Alzheimer's disease brain. This compound has close structural similarity to L-glutamate. Electrophysiological studies indicate that L-phosphoserine has an acute inhibitory effect, but a delayed excitatory action. A hypothesis is developed based on pharmacological and electrophysiological studies that suggest that the inhibition may be mediated through presynaptic inhibition of L-glutamate release or perhaps antagonism of postsynaptic kainic acid receptors. The mechanism of the delayed excitation may lie in the tendency of L-phosphoserine to mimic the action of L-2-amino-4-phosphonobutyric acid, a blocker of chloride- and calcium-sensitive L-glutamate transport. L-Phosphoserine has also been found to be a competitive antagonist at the N-methyl-D-aspartate recognition site and an antagonist of metabotropic receptor-mediated hydrolysis of inositol phospholipids. Because of these actions, there are several potentially important implications for the elevation of L-phosphoserine in Alzheimer's disease, including production memory impairment through presynaptic inhibition of L-glutamate release or blockade of postsynaptic N-methyl-D-aspartate receptors and/or blockade of certain L-glutamate transport sites resulting in increased L-glutamate levels in the synaptic cleft.

Effect of central cholinergic stimulation on regional cerebral blood flow in Alzheimer's disease

Patients with Alzheimer disease (AD) had reduced regional cerebral blood flow (rCBF) in the posterior parietotemporal region compared with controls, as determined with technetium-99m hexamethyl propyleneamine oxime and single photon emission tomography. Central cholinergic stimulation with physostigmine produced a focal increase in rCBF in the posterior parietotemporal region in the patients with AD but not in controls.

Characterisation of the glycine modulatory site of the N-methyl-D-aspartate receptor-ionophore complex in human brain

[3H]Glycine binding and glycine modulation of [3H]MK-801 binding have been used to study the glycine allosteric site associated with the N-methyl-D-aspartate receptor complex in postmortem human brain. The effect of glycine on [3H]MK-801 binding appeared sensitive to duration of terminal coma, and possibly postmortem delay. Thirty percent of the binding occurred in a subfraction of brain tissue and did not show enhancement by glycine and glutamic acid. [3H]Glycine binding to a subfraction free from this component was studied and showed high specific binding. KD and Bmax values showed considerable intersubject variability which did not appear to be due to demographic features or to tissue content of amino acids with an affinity for this site. The pharmacological characteristics of binding in this subfraction and a correlation between Bmax values and the maximal enhancement of [3H]MK-801 binding by glycine are consistent with [3H]glycine binding occurring to an N-methyl-D-aspartate receptor complex associated site. Further support for this is provided by a significantly lower Bmax value for [3H]glycine binding in subjects with Alzheimer's disease and reduced glycine enhancement of [3H]MK-801 binding. However, the effect of perimortem factors makes it difficult to confidently attribute this solely to a disease-related change in the receptor. The possible role of the glycine allosteric site in the treatment of neuropsychiatric disorders is discussed.

Procedural learning is impaired in Huntington's disease: evidence from the serial reaction time task

The purpose of the study was to test the hypothesis that Huntington's disease (HD) is associated with impairment of procedural learning. We identified 13 patients with mild to moderate HD whose manual performance was still sufficiently intact to assess learning on the serial reaction time (SRT) task. Twelve age-matched neurologically normal control subjects were studied as well. The SRT task was a four-choice reaction time task in which the stimuli followed a sequence (10 items in length) which repeated itself 10 times during each of the first four blocks of trials. During the fifth block of trials, the stimuli were random. Learning was manifested by a reduction in response latency over the first four blocks and an increase in response latency in the fifth (random) block. Learning in this task has been demonstrated in other amnesics of other etiologies. The HD patients were significantly impaired on sequence-specific learning, using the log-transformed reaction time data (P less than 0.004). In addition, in an individual-by-individual analysis, five of the HD patients and none of the control subjects failed to show sequence-specific learning, a difference in proportions that was significant (P less than 0.04). No feature of the standard cognitive or motor assessment of the HD patients was associated with efficacy of procedural learning. HD, including patients with mild disease, was associated with a deficit in procedural learning, consistent with the hypothesis that the striatum plays a critical role in supporting procedural learning.

Correlations of regional postmortem enzyme activities with premortem local glucose metabolic rates in Alzheimer's disease

Correlations were sought between local cerebral metabolic rates (LCMRs) for glucose in various regions of the cortex, determined in premortem PET scans, with the regional activities of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), beta-glucuronidase (Gluc, a probable index of reactive gliosis), and phosphate-activated glutaminase (PAG, a possible indice of the large pyramidal neurons) measured on postmortem tissue. Significant negative correlations between LCMRs and Gluc activities were found in 6 PET-scanned cases of Alzheimer disease (AD), and positive correlations of LCMRs with PAG were found in 5. By contrast, a positive correlation with ChAT and AChE was found in only 1. The results are consistent with the metabolic deficits in AD being primarily a reflection of local neuronal loss and gliosis. Similar data on two cases of Huntington's disease showed no significant correlations, while 1 patient with Parkinson dementia showed a significant (negative) correlation only with Gluc.

Enzyme activities in relation to pH and lactate in postmortem brain in Alzheimer-type and other dementias

Phosphate-activated glutaminase, glutamic acid decarboxylase, pyruvate dehydrogenase, succinic dehydrogenase, pH, and lactate were measured in frontal cortex and caudate nucleus of postmortem brains from cases of Alzheimer-type dementia (ATD), Down's syndrome, Huntington's disease, and one case of Pick's disease, as well as from sudden death and agonal controls. Lactate levels were higher and pH, phosphate-activated glutaminase, and glutamic acid decarboxylase levels were lower in the agonal controls than in the sudden death controls. Phosphate-activated glutaminase and glutamic acid decarboxylase were correlated with tissue pH and lactate, and also were reduced by in vitro acidification, suggesting that the low activities of these enzymes in agonal controls were related to decreased pH consequent upon lactate accumulation. Compared with control tissues at the same pH, phosphate-activated glutaminase and glutamic acid decarboxylase were unaltered in ATD and Down's frontal cortex and reduced in Huntington's caudate nucleus, and glutamic acid decarboxylase was reduced in Huntington's frontal cortex. These data suggest that GABAergic neurons are not affected in ATD and confirm the GABAergic defect in Huntington's disease. Pyruvate dehydrogenase and succinic dehydrogenase activities were the same in agonal controls and sudden death controls and were unaffected by acid pH and lactate in vitro, and pyruvate dehydrogenase was not correlated with pH or lactate. Reduced pyruvate dehydrogenase in frontal cortex of individual ATD, Down's, and Pick's cases, and in the caudate nucleus of Huntington's and Down's cases, was accompanied by gliosis/neuron loss. We conclude that decreased pyruvate dehydrogenase reflects neuronal loss.

A comparison of the working memory performances of young and aged mice combined with parallel measures of testing and drug-induced activations of septo-hippocampal and nbm-cortical cholinergic neurones

The spatial working memory performances of young (2 months) and aged (24-26 months) mice of the C57BL/6 strain were compared using a delayed nonmatching to place (DNMTP) protocol in an automated 8-arm radial maze. The aged mice were observed to exhibit a selective and interference-related memory deficit. Parallel neurochemical analysis of the activity of septo-hippocampal and nbm-cortical cholinergic neurones in vivo was conducted using measures of sodium-dependent high-affinity choline uptake. Results showed that whereas the level of cholinergic activity in both brain regions varied less than 10% between young and aged mice in quiet conditions (basal) the activation usually observed at 30-sec posttest (+20-25%) in young mice was greatly attenuated in the frontal cortex and almost totally absent in the hippocampus of aged mice. In view of these results a complementary experiment was carried out in order to test the intrinsic ability of septo-hippocampal cholinergic neurones to activate using acute injection of scopolamine (1 mg/kg IP 20 min) to both young and aged mice in quiet conditions. The drug injection resulted in a very large (+70%) increase in hippocampal high-affinity choline uptake and with amplitudes which did not vary significantly between young and aged subjects. These observations attest to a relatively well-preserved state of central cholinergic neurones and an intact capacity to activate normally when challenged pharmacologically in aged mice. The results strongly suggest that the loss of cholinergic activation and associated memory deficit in aged mice might rather be related to a hypofunction of phasically active transsynaptic processes which normally mediate the activation of these cholinergic pathways during memory testing.

What contribution can the Hachinski ischemic scale make to the differential diagnosis between multi-infarct dementia and primary degenerative dementia?

Five research studies in which clinical diagnoses using the Hachinski Ischemic Scale (HIS) underwent neuropathological verification were analysed. These studies reveal that the HIS differentiates between multi-infarct dementia (MID) and dementia of the Alzheimer type (DAT) with only limited accuracy. To some extent, there are considerable differences between the studies as regards the methodology and the patient population. However, there are indications that some items of the ischemic scale clearly distinguish between MID and DAT, whereas others hardly do so or some do not distinguish at all between these two conditions. If the HIS is revised according to the present findings, it can become a more valid differential diagnostic instrument. Such a diagnostic instrument which may be applied without any other technical equipment is required today, since epidemiological data and demographic prognoses show that the prevalence of dementing illnesses will markedly increase in the future.

5 HT2 receptors in dementia of Alzheimer type: a quantitative autoradiographic study of frontal cortex and hippocampus

Using both quantitative autoradiography in sections and a homogenate preparation assay, the distribution and density of 3H-ketanserin binding to 5 HT2 receptors was examined in frontal cortex and the hippocampal region from six control subjects and seven subjects who had dementia of the Alzheimer type (DAT). There was no difference between control and DAT subjects in the levels of ketanserin binding in any region of the frontal cortex or hippocampus determined by quantitative autoradiography or in parallel experiments using homogenate preparations (e.g. left frontal cortex, layer III; controls, 34.4 +/- 1.6 pmol/g, DAT, 37.1 +/- 4.6 pmol/g). In all of the DAT brains there were abundant neuritic plaques (e.g. superficial layers of left frontal cortex; 35 +/- 7 plaques/mm2), and a marked reduction of choline acetyltransferase activity, (by 30-60% relative to controls), in both frontal cortex and the hippocampus. Thus, despite the presence of morphological abnormalities and a loss of cholinergic function, two classic features of DAT, 5 HT2 receptor binding was unaltered in this group of DAT brains compared to controls.

A quantitative study of the neurofibrillary tangles and the choline acetyltransferase activity in the cerebral cortex and the amygdala in Alzheimer's disease

A quantitative study has been made of the number of neurofibrillary tangles and of the choline acetyltransferase activity in several sites in the cerebral hemispheres of eight patients who had had Alzheimer's disease. The neurofibrillary tangles were maximal in structures in the medial temporal lobe (uncus, amygdala, hippocampus and parahippocampal gyrus), severe in the neocortex on the lateral surface of the temporal lobe, moderate in the "association cortex" of the parietal and frontal lobes and minimal in primary somatic and visual sensory areas. There was a significant decrease in choline acetyltransferase activity in almost all areas, and the means of the percentage decreases for the different groups of areas correlate well with the counts of the neurofibrillary tangles. These results support the hypothesis that the pathological process in Alzheimer's disease may spread along a sequence of corticocortical connections between the main sensory areas and the hippocampal formation. The disease process may also spread along the reciprocal connections between the amygdala and the neocortex because the numbers of tangles in different areas of the neocortex closely parallel the density of their connections and the amygdala.

Activating the damaged basal forebrain cholinergic system: tonic stimulation versus signal amplification

The hypothesis that the cognitive decline in senile dementia is related to the loss of cortical cholinergic afferent projections predicts that pharmacological manipulations of the remaining cholinergic neurons will have therapeutic effects. However, treatment with cholinesterase inhibitors or muscarinic agonists has been, for the most part, largely unproductive. These drugs seem to disrupt the normal patterning of cholinergic transmission and thus may block proper signal processing. An alternative pharmacological strategy which focuses on the amplification of presynaptic activity without disrupting the normal patterning of cholinergic transmission appears to be more promising. Such a strategy may make use of the normal GABAergic innervation of basal forebrain cholinergic neurons in general, and in particular of the inhibitory hyperinnervation of remaining cholinergic neurons which may develop under pathological conditions. Disinhibition of the GABAergic control of cholinergic activity is assumed to intensify presynaptic cortical cholinergic activity and to enhance cognitive processing. Although the extent to which compounds such as the benzodiazepine receptor antagonist beta-carboline ZK 93,426 act via the basal forebrain GABA-cholinergic link is not yet clear, the available data suggest that the beneficial behavioral effects of this compound established in animals and humans are based on indirect cholinomimetic mechanisms. It is proposed that an activation of residual basal forebrain cholinergic neurons can be achieved most physiologically via inhibitory modulation of afferent GABAergic transmission. This modulation may have a therapeutic value in treating behavioral syndromes associated with cortical cholinergic denervation.

Ante mortem cerebral amino acid concentrations indicate selective degeneration of glutamate-enriched neurons in Alzheimer's disease

There is little information about major constituents of the brain in Alzheimer's disease. In the case of amino acids most of the previous data are contradictory. These have been interpreted in an anatomic and neurotransmitter as well as a metabolic context. To help clarify this, the contents of 14 amino acids and ethanolamine were determined in samples of neocortex from diagnostic craniotomies of 15 demented patients (10 with Alzheimer's disease) and other neurosurgical procedures (57 patients, 18 with intractable depression). A comprehensive survey of the effects of possible complicating factors on the concentrations of amino acids showed that artefacts were few; this was in contrast to a post mortem series of brains (16 with Alzheimer's disease and 16 controls; six regions assayed). We have used the ante mortem data to provide the basis for an accurate comparison of amino acid values between Alzheimer and control samples. In Alzheimer's disease, the mean contents of many amino acids were slightly higher (sum of the increases of those significantly affected was 15 nmol/mg protein) whereas glutamate content alone was significantly reduced (by 16 nmol/mg protein). This was not a feature of depression or a group of patients with other dementias. Glutamate content of Alzheimer samples was related to pyramidal neuron density in cortical layer III. These alterations were detected relatively early during the course of Alzheimer's disease and are considered to be due to loss of corticocortical glutamatergic association pathways.

Circumscribed changes of the cerebral cortex in neuropsychiatric disorders of later life

The extent and distribution of biochemical abnormalities thought to reflect disorders of subpopulations of neurons have been determined in the cerebral cortex from brains of patients with Alzheimer-type dementia and depressive illness who died of natural causes. In dementia, loss of gray matter from areas of the parietal and temporal lobes is most obvious. In depression, these areas are not affected, but the pars opercularis and temporal pole are smaller than in controls. Results expressed per unit mass of total protein indicate selective reductions in both disorders of serotonin 2 recognition sites in all areas examined and of somatostatin content in only the temporal pole of the six areas examined. In dementia alone a selective loss was found of somatostatin content of the superior parietal lobule and of serotonin 1A sites and choline acetyltransferase activity in all areas examined. Results for depression expressed per entire area indicate additionally reduced somatostatin content and serotonin 1A sites in the pars opercularis and serotonin 1A sites in the temporal pole. These multiple analyses performed on each sample provide further support for a prominent disorder of pyramidal neurons in dementia as well as more evidence for alterations in cortical neurons in depression, either as a result of the disease itself or its treatment.

Tacrine, a drug with therapeutic potential for dementia: post-mortem biochemical evidence

A review of biochemical findings is presented which support the idea that Alzheimer's disease represents a condition for which tetrahydroaminoacridine (tacrine) may have a beneficial effect. There is evidence that clinical and histopathologic hallmarks of the disease relate to cholinergic and serotonergic dysfunction, with less obvious abnormalities in other neurotransmitters (aspartate, dopamine, gamma-aminobutyrate, glutamate, noradrenaline and somatostatin). Clinically relevant concentrations of tacrine may ameliorate the above presynaptic deficits without producing harmful (neurotoxic) effects of aspartate and glutamate. The disease seems to be associated with an early and clinically relevant degeneration of some neurons with cortical perikarya that release these amino acid transmitters. Studies are now required on the effect of tacrine on postulated harmful peptide-bond hydrolase activity within and around such cells.

Cortical glutaminase, beta-glucuronidase and glucose utilization in Alzheimer's disease

Large pyramidal neurons of rat and human neocortex stain immunohistochemically for phosphate-activated glutaminase (PAG). In a limited number of postmortem brains, we find large reductions in cortical PAG activity in Alzheimer's disease (AD). This finding is consistent with histological evidence that pyramidal neurons are affected in AD. The reductions are greater than those found in the same samples in choline acetyltransferase (ChAT) but the possible deleterious effects of coma and similar premortem factors on human PAG activity have yet to be assessed. The activity of beta-glucuronidase, a lysosomal enzyme which occurs in reactive astrocytes, is elevated in the same samples. Positron emission tomography (PET) studies, using 18F-fluorodeoxyglucose (FDG), have demonstrated significant deficiencies in glucose metabolism in the cortex in AD, with the parietal, temporal and some frontal areas being particularly affected. We found in serial scans of 13 AD cases, including one relatively young (44-46 year old) familial case, an exacerbation of the defect over time in most cases. We have found a negative correlation between the regional metabolic rates for glucose (LCMR(s] measured premortem and the beta-glucuronidase activities measured postmortem on a few AD cases that have come to autopsy. The correlations between LCMR(s) and PAG and ChAT activities tend to be positive. The results are consistent with previous suggestions that decreased LCMR(s) in AD reflect local neuronal loss and gliosis.

Is Alzheimer's disease an anterograde degeneration, originating in the brainstem, and disrupting metabolic and functional interactions between neurons and glial cells?

A novel hypothesis is suggested for the pathogenesis of Alzheimer's disease, i.e. that a degeneration of adrenergic neurons in locus coeruleus and/or of serotonergic neurons in the raphe nuclei leads to impairment in metabolic and functional interactions between neurons and astrocytes (in the cerebral cortex and hippocampus as well as in nucleus basalis magnocellularis), and that a resulting deficient supply of substrates and failing energy metabolism in both neurons and astrocytes causes neuronal cell death in these areas and thus interference with additional transmitter systems. The hypothesis is based on (1) the topographical distribution of ascending pathways from locus coeruleus and the raphe nuclei; (2) the peculiar termination of many of these fibres in varicosities, from which released transmitter molecules reach their targets by diffusion, rather than in genuine synapses, suggesting a partly non-neuronal target; (3) the effects of locus coeruleus lesions in experimental animals; (4) the emergence of new knowledge in cellular neurobiology, indicating profound metabolic and functional interactions between neurons and astrocytes; and (5) the effects of adrenergic and serotonergic agonists upon metabolism and function in rodent astrocytes and neurons. These compounds influence energy metabolism, membrane transport of potassium and production of growth factors in astrocytes, and glutamate release from glutamatergic neurons. They thus influence essential metabolic interactions between neurons and astrocytes, as well as neuronal-astrocytic interactions in potassium homeostasis at the cellular level. Obviously, neither the individual findings alone, nor their combination into a conceptual framework, prove the correctness of the hypothesis. However, they do provide a basis for further experimental work, using postmortem brain tissue from Alzheimer's patients and lesion studies in rodents, which can confirm or refute the hypothesis.

Reduced glycine stimulation of [3H]MK-801 binding in Alzheimer's disease

The novel N-methyl-D-aspartate receptor channel ligand (+)-[3H]5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine maleate ([3H]MK-801) has been utilized to label this receptor in human brain tissue. Characteristics of [3H]MK-801 binding to well-washed membranes from 17 control subjects and 16 patients with Alzheimer's disease were determined in frontal, parietal, and temporal cerebral cortex and cerebellar cortex. In control tissue the pharmacological specificity of the binding of this substance is entirely consistent with the profile previously reported for rat brain. Binding could be stimulated by the addition of glutamic acid to the incubation medium; addition of glycine produced further enhancement which was not prevented by strychnine. The specificity of the effects of these and other amino acids on the binding was the same as in the rat. In Alzheimer's disease significantly less binding was observed in the frontal cortex under glutamate- and glycine-stimulated conditions. This appears to be associated with a reduced affinity of the site whereas the pharmacological specificity of the site remained unchanged. The effect did not appear to be due to differences in mode of death between Alzheimer's disease and control subjects and is unlikely to be related to factors for which the groups were matched. In contrast, binding was not altered in the absence of added amino acids and presence of glutamate alone. These results imply that in the cerebral cortex the agonist site and a site in the cation channel of the receptor are not selectively altered, but that their coupling to a strychnine-insensitive glycine recognition site is impaired.

Neurotrophic agents may exacerbate the pathologic cascade of Alzheimer's disease

The thesis is advanced that Alzheimer's disease is triggered by alterations in the regulatory mechanisms governing the patterns of cytoskeletal protein expression in structurally plastic neurons in the mature nervous system. As a consequence, polypeptide species acting to stabilize the cytoskeleton are preferentially affected, and neuronal architecture becomes increasingly determined by proteins involved in labile structural states. A cascade of interdigitating pathologies is then postulated to develop characterized by nerve terminal aberrancies, subsequent extrusion of atypical polypeptide species and their conjugates, reactive gliosis, abnormal neuronal growth, and degeneration. Within this context, growth factors promote and accelerate the pathologic cascade. Based on this model, a treatment strategy is suggested that the most effective management of Alzheimer's disease, particularly during earlier stages, is to delay its projected normal onset and to control the aberrant neuronal growth that is a hallmark of the malady.

Brain amino acid concentrations and Ca2+-dependent release in intractable depression assessed antemortem

The concentrations of 3 putative neurotransmitters (glutamate, aspartate and gamma-aminobutyrate), 4 related amino acids and 5 non-transmitter-related amino acids have been measured in neurosurgical samples (frontal cortex) from patients with intractable depression and controls. In addition, the glutamate receptor agonist 2-amino-4-sulpho-butanoic acid (homocysteic acid) has been identified in human brain and measured in these samples. There were no changes in the concentrations of amino acids in depressed patients compared to control with the exception of aspartic and homocysteic acids which were elevated in a sub-group of patients with depression compared to control. The Ca2+-dependent release (K+-stimulated) of putative neurotransmitters has been demonstrated for the first time from brain tissue of depressed patients. Glutamate release was unaltered from the control value. Aspartate values showed unexplained variability but it's release and that of gamma-aminobutyrate were elevated in some depressed subjects. These results do not support the hypothesis of reduced amino acid function in depressive illness.

Subpopulations of somatostatin 28-immunoreactive neurons display different vulnerability in senile dementia of the Alzheimer type

We tested whether the vulnerability of somatostatin (SST) neurons in senile dementia of the Alzheimer type (SDAT) depended upon their co-localization with neuropeptide Y (NPY). Density estimates of SST28- and NPY-immunoreactive neurons and percentage of double-labeled SST-NPY neurons were obtained in the cortex (areas 9 and 25) and the bed nucleus of stria terminalis (BST), in 6 SDAT and 5 control cases. Counts of senile plaques (SP) and neurofibrillary tangles (NFT) were done on thioflavin S stains. In both cortical areas, a decrease in the density of SST28-IR neurons was found in SDAT cases (-60% in area 25 and -80% in area 9), whereas density of NPY-IR neurons was unchanged. Accordingly, the proportion of single-labeled SST neurons decreased; this decrease was significantly correlated with SP (r = -0.89, P less than 0.001). We conclude that single SST-IR neurons, in cortical layers II-III, and V, are preferentially lost relative to co-localized SST-NPY neurons. In the BST, no significant reduction of SST-IR, NPY-IR neurons nor of the percentage of single labeled SST neurons was found, despite the presence of SP. Thus one subpopulation of SST neurons, defined by associated neurochemical characters (not co-localized with NPY nor with NADPH diaphorase) and by topography (cortical layers III and V) appears to be particularly vulnerable in SDAT. The potential importance of their position in neural circuitry is emphasized.

Loss of glycine-dependent radioligand binding to the N-methyl-D-aspartate-phencyclidine receptor complex in patients with Alzheimer's disease

Well washed membranes have been prepared from samples of cerebral cortex of control subjects and patients with Alzheimer's disease, obtained both at post mortem and by neurosurgical procedures earlier in the course of the disease. Binding to these membranes of two radioligands for the N-methyl-D-aspartate-phencyclidine receptor complex has been determined in the presence and absence of glycine. Glycine increased the binding in both control and Alzheimer tissue samples. At one concentration of radioligand, in the presence of glycine there was less binding to post-mortem samples, which Scatchard analysis showed was associated with a 36% loss of sites. In rare neurosurgical samples, there was also a loss of binding of radioligand which suggests that the effect is not due to post-mortem artefacts or epiphenomena. These new results may have implications for the symptomatic and preventative treatment of Alzheimer's disease.

Possible neurotransmitter basis of behavioral changes in Alzheimer's disease

Serotonin, 5-hydroxyindoleacetic acid, and homovanillic acid concentrations have been determined in 10 areas of the cerebral cortex from 17 subjects with Alzheimer's disease and 18 control subjects. The dopamine metabolite was not reduced in any area, whereas both indoleamines were reduced in the superior frontal, inferior temporal, and fusiform gyri, and the temporal pole. These areas and areas of the parietal cortex, where there were no changes in concentration, have not previously been reported on. We argue that the large loss of indoleamines from the frontal lobe (to 50-63% of control values) is rather unexpected based on other biochemical measurements and may relate to behavioral changes.