Alzheimer's disease and Down's syndrome

Increased cortical synaptic activation of TrkB and downstream signaling markers in a mouse model of Down Syndrome

Down Syndrome (DS), trisomy 21, is characterized by synaptic abnormalities and cognitive deficits throughout the lifespan and with development of Alzheimer's disease (AD) neuropathology and progressive cognitive decline in adults. Synaptic abnormalities are also present in the Ts65Dn mouse model of DS, but which synapses are affected and the mechanisms underlying synaptic dysfunction are unknown. Here we show marked increases in the levels and activation status of TrkB and associated signaling proteins in cortical synapses in Ts65Dn mice. Proteomic analysis at the single synapse level of resolution using array tomography (AT) uncovered increased colocalization of activated TrkB with signaling endosome related proteins, and demonstrated increased TrkB signaling. The extent of increases in TrkB signaling differed in each of the cortical layers examined and with respect to the type of synapse, with the most marked increases seen in inhibitory synapses. These findings are evidence of markedly abnormal TrkB-mediated signaling in synapses. They raise the possibility that dysregulated TrkB signaling contributes to synaptic dysfunction and cognitive deficits in DS.

Similar deficits of central histaminergic system in patients with Down syndrome and Alzheimer disease

In order to study whether Alzheimer-like neuropathological changes involve the central histaminergic system we measured the concentration of histamine, its precursor histidine as well as the activity of histidine decarboxylase (HDC) and histamine-N-methyl-transferase (HMT) in frontal cortex of aging Down syndrome (DS) patients, Alzheimer patients and control individuals. The study populations were also investigated for choline acetyltransferase (ChAT) activity, since reduced ChAT activity is an established biochemical hallmark in DS and Alzheimer disease (AD). HDC and ChAT activity were reduced in brains of both DS and Alzheimer patients versus control patients. Additionally, we observed a significant decrease of histamine levels in the DS group. Histamine levels in AD brains tended to be decreased. Histidine concentrations and HMT activities were comparable between the three groups. Thus, our results for the first time show histaminergic deficits in brains of patients with DS resembling the neurochemical pattern in AD. Neuropathological changes may be responsible for similar neurochemical alterations of the histaminergic system in both dementing disorders.

Excitatory amino acids and monoamines in parahippocampal gyrus and frontal cortical pole of adults with Down syndrome

Aspartate (ASP), glutamate (GLU), noradrenaline (NA), dopamine (DA) and its acidic metabolites DOPAC and HVA, serotonin (5-HT) and its metabolite 5-HIAA were simultaneously investigated in post-mortem tissue samples from right parahippocampal gyrus (temporal cortex) and frontal cortical pole (frontal cortex) of adults with Down syndrome (DS), and of neurologically healthy controls by use of high performance liquid chromatography (HPLC). In parahippocampal gyrus, ASP, GLU, NA, DOPAC and 5-HT levels were significantly decreased in patients with DS, compared to levels found in control subjects (approximately 50%). No significant changes were observed in frontal pole. ASP and GLU levels were significantly lower in parahippocampal gyrus than in frontal pole of DS, a regional distribution that could not be observed in control subjects. In conclusion, the results of this study suggest that the temporal cortex would be more affected than the frontal cortex in adult patients with DS, a finding in line with reports showing a marked hypometabolism and extensive cell loss in temporal cortex of DS, and with those showing that parahippocampal gyrus abnormality may correlate with the extent of mental retardation affecting this type of patients.

Olfactory function in young adolescents with Down's syndrome

Decreased ability to smell is present in adults with Down's syndrome, many of whom are known to have brain pathology analogous to that seen in Alzheimer's disease. Because olfactory loss is well documented in Alzheimer's disease, the question arises whether young adolescents with Down's syndrome, who have no clear Alzheimer's disease-like neuropathology, also exhibit olfactory dysfunction. To consider this issue, standardised tests of odour discrimination and identification were administered to 20 young adolescents with Down's syndrome (mean age (SD) 13.89 (1.98) years) and their test scores were compared with 20 mentally retarded and 20 non-mentally retarded control subjects matched to the patients with Down's syndrome on the basis of cognitive ability. No significant differences in olfactory function were found among the three study groups. These findings, along with those from studies of olfactory function in older patients with Down's syndrome, suggest that Down's syndrome related olfactory dysfunction occurs only at ages when Alzheimer's disease-like pathology is present.

Non-classical actions of cholinesterases: role in cellular differentiation, tumorigenesis and Alzheimer's disease

The cholinesterases are members of the serine hydrolase family, which utilize a serine residue at the active site. Acetylcholinesterase (AChE) is distinguished from butyrylcholinesterase (BChE) by its greater specificity for hydrolysing acetylcholine. The function of AChE at cholinergic synapses is to terminate cholinergic neurotransmission. However, AChE is expressed in tissues that are not directly innervated by cholinergic nerves. AChE and BChE are found in several types of haematopoietic cells. Transient expression of AChE in the brain during embryogenesis suggests that AChE may function in the regulation of neurite outgrowth. Overexpression of cholinesterases has also been correlated with tumorigenesis and abnormal megakaryocytopoiesis. Acetylcholine has been shown to influence cell proliferation and neurite outgrowth through nicotinic and muscarinic receptor-mediated mechanisms and thus, that the expression of AChE and BChE at non-synaptic sites may be associated with a cholinergic function. However, structural homologies between cholinesterases and adhesion proteins indicate that cholinesterases could also function as cell-cell or cell-substrate adhesion molecules. Abnormal expression of AChE and BChE has been detected around the amyloid plaques and neurofibrillary tangles in the brains of patients with Alzheimer's disease. The function of the cholinesterases in these regions of the Alzheimer brain is unknown, but this function is probably unrelated to cholinergic neurotransmission. The presence of abnormal cholinesterase expression in the Alzheimer brain has implications for the pathogenesis of Alzheimer's disease and for therapeutic strategies using cholinesterase inhibitors.

Immunohistochemical analysis of the basal forebrain in Alzheimer's disease

An immunohistochemical analysis utilizing antibodies to glial fibrillary acid protein (GFAP), microglia, beta-amyloid, amyloid P-component, neurofibrillary tangles (NFT), and microtubule associated protein-tau (MAP-tau) was performed on the cholinergic basal forebrain in Alzheimer's disease (AD). This severely compromised system, which includes the nucleus basalis of Meynert, is largely responsible for the massive loss of cortical and subcortical cholinergic innervation in the diseased state. Our study juxtaposes the basal forebrain immunohistopathology to the hippocampus, amygdala, and entorhinal cortex in AD. Key findings include a progressive degeneration of these cholinergic neurons characterized by the formation of immunoreactively atypical NFT, the loss of intraneuronal lipofuscin, a lack of senile plaque and beta-amyloid deposition within the basal forebrain, and end-stage gliosis without residual extracellular NFT. These structural and compositional differences suggest a unique pathogenesis of the basal forebrain separate from other cortical regions in AD.

Hippocampal pyramidal cell response to 6-hydroxydopamine lesions of the rat ventral tegmental area

The occurrence of neurofibrillary tangles (NFT) in the perforant pathway in association with dopaminergic cell loss in the ventral tegmental area (VTA) in human mesolimbic dementia, raises the possibility that denervation is a cause of NFT formation. This was tested in the rat by lesioning dopaminergic neurons which project to the hippocampus from the ventral tegmental area by means of stereotaxic injections of 6-hydroxydopamine. This resulted in the appearance of immunoreactivity to the paired helical filament protein plus an increase of tau and MAP-2 proteins in pyramidal neurons of CA-1 and CA-2. These neuronal responses to dopaminergic denervation are consistent with a precursor stage to NFT development.

Senile dementia: a threshold phenomenon of normal aging? A contribution to the functional reserve hypothesis of the brain

Neurochemical investigations with normal aging brains show that in the first 70 years of life no major changes of the glycolytic pathway can be observed. Only in the following decades does a significant decrease of brain metabolic turnover occur. Changes in nerve cell size, one of the most relevant parameters in evaluating a diffuse nerve cell atrophy, appear in the brain cortex not earlier than between 85 and 94 years of age; a 21% nerve cell shrinkage is the mean. The results demonstrate that a significant decrease in turnover of the glycolytic pathway is followed by a significant but moderate shrinkage of the nerve cells after a delay of 10-15 years. Similar investigations in brains from senile demented subjects demonstrate that the change in glycolytic turnover is much more a quantitative than a qualitative phenomenon. In comparison with age-matched controls a decrease in glycolytic turnover of more than 60% is observed. Morphometric investigations of the nerve cell sizes in the brain cortex of senile demented subjects showed a decrease of 45-55% when compared with age-matched controls. When normal aging is compared with senile dementia it seems that old age dementia is a threshold phenomenon which starts if the glycolytic turnover drops below 50% of its value in young healthy adults. Physiological aging, however, stays within the range of the reserve capacity of normal brain performance. In conclusion, it seems that the exhaustion of the functional reserve capacity may shift an aging brain into a dementia syndrome.

Cholinesterases during development of the avian nervous system

1. Long before onset of synaptogenesis in the chicken neural tube, the closely related enzymes butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) are expressed in a mutually exclusive manner. Accordingly, neuroblasts on the ventricular side of the neural tube transiently express BChE before they abruptly accumulate AChE while approaching the outer brain surface. 2. By exploiting AChE as a sensitive and early histochemical differentiation marker, we have demonstrated complex polycentric waves of differentiation spreading upon the cranial part of the chicken neural tube but a smooth rostrocaudal wave along the spinal cord. Shortly after expression of AChE, these cells extend long projecting neurites. In particular, segmented spinal motor axons originate from AChE-positive motoneurones; they navigate through a BChE-active zone within the rostral half of the sclerotomes before contacting BChE/AChE-positive myotome cells. At synaptogenetic stages, cholinesterases additionally are detectable in neurofibrillar laminae foreshadowing the establishment of cholinergic synapses. 3. In order to elucidate the functional significance of cholinesterases at early stages, we have investigated specific cholinesterase molecules and their mechanisms of action in vivo and in vitro. A developmental shift from the low molecular weight forms to the tetramers of both enzymes has been determined. In vitro, the addition of a selective BChE inhibitor leads to a reduction of AChE gene expression. Thus, in vivo and in vitro data suggest roles of cholinesterases in the regulation of cell proliferation and neurite growth. 4. Future research has to show whether neurogenetic functioning of cholinesterases can help to understand their reported alterations in neural tube defects, mental retardations, dementias and in some tumours.

Down's syndrome and Alzheimer's disease: dendritic spine counts in the hippocampus

Samples of the hippocampus of four patients with Down's syndrome [two men aged 35 and 36 years with no evidence of Alzheimer's disease (AD) and two patients aged 47 and 55 years with associated AD] were obtained at post mortem and processed according to the rapid Golgi method. A significant reduction in the number of dendritic spines (DS) was found in the apical (middle, distal and oblique segments) and basilar (thick and thin segments) dendritic arbors of CA1 and CA2-3 pyramidal neurons in patients with Down's syndrome and no AD when compared to age-matched controls. An additional decrease of DS in every segment occurred in Down's patients with associated AD when compared to age-matched controls and Down's patients with no AD. In Down's syndrome (either associated or not to AD) thin basilar dendrites were the most severely involved; in AD patients CA1 pyramids were more severely affected than pyramidal neurons of the CA2-3 subfield.

Reduced D-[3H]aspartate binding in Down's syndrome brains

The binding of D-[3H]aspartate to glutamate uptake sites was measured in post-mortem brains from subjects with Down's syndrome (DS) and age-matched controls. DS brains had substantially reduced D-[3H]aspartate binding in the frontal and temporal cortex, hippocampus and caudate nucleus. There was no correlation between the numbers of Alzheimer-like plaques and tangles or clinically-assessed dementia and D-[3H]aspartate binding in DS brains. The binding of [3H]N-(1-[2-thienyl]cyclohexyl)piperidine ([3H]TCP) to postsynaptic N-methyl-D-aspartate sites was normal in DS brains. This study suggests that the reduction in glutamate uptake sites in DS is more substantial and widespread than in Alzheimer's disease.

The substantia nigra and ventral tegmental area in Alzheimer's disease and Down's syndrome

Degenerative changes in the substantia nigra and ventral tegmental area were investigated in 104 cases of Alzheimer's disease and 13 cases of Down's syndrome. Frequencies of tangles in three groups of patients with Alzheimer's disease were 86%, 44% and 46% (54% overall) respectively. About half of those with tangles, but no Lewy bodies, had excess nigral cell loss, and 16% had moderate or severe neuronal fallout, but none had a Parkinsonian syndrome. Cases with nigral tangles were younger, tended to have more hippocampal and cortical tangles and plaques, and lower activities of cortical choline acetyltransferase. In most cases of Alzheimer's disease degeneration in nigral and tegmental areas was greater than controls, and tangles were evenly distributed. All the cases of Down's syndrome had tangles in the nigra and eight showed mild cell loss. Mild degenerative changes accompanied by tangles in the substantia nigra and ventral tegmental area are common in Alzheimer's disease, but severe cell loss is rare. When a Parkinsonian syndrome occurs in Alzheimer's disease it is likely to be due to Lewy body pathology.

Telencephalic cholinergic system of the New World monkey (Cebus apella): morphological and cytoarchitectonic assessment and analysis of the projection to the amygdala

While the cholinergic projection from the nucleus basalis to the cortical mantle has received considerable attention, a similar projection to the magnocellular basal nucleus of the amygdala has not been studied in such detail. The present study analyzed the cholinergic basal forebrain projection to the amygdala in the Cebus apella monkey by using combined tract-tracing and immunocytochemical techniques. As a foundation for this assessment, the morphological and cytoarchitectonic organization of the cholinergic telencephalic system of the New World C. apella monkey was examined by using choline acetyltransferase (ChAT) immunocytochemistry. Although there were minor differences, the telencephalic cholinergic system of Cebus monkeys is similar to that seen in Old World nonhuman primates. ChAT-immunoreactive neurons were observed throughout the Ch1-4 regions of the basal forebrain, with subdivisions of the Ch4 region similar to those previously described (Mesulam et al., '83a). Most cholinergic neurons were hyperchromic and magnocellular; however, some neurons were parvicellular. Like most species, cholinergic neurons were also observed throughout the striatum. However, unlike in rodents, cholinergic perikarya were not observed within the cortex or hippocampus. To analyze the cholinergic fiber projections from the basal forebrain to the amygdala, monkeys received an intraamygdaloid injection of the retrograde tracer horseradish peroxidase conjugated to wheat germ agglutinin. Retrogradely labeled neurons that colocalized ChAT or acetylcholinesterase (AChE) were found predominantly in the anterolateral portion of the CH4 region. Fewer double-labeled neurons were found in the anteromedial and intermediate portion of CH4 and in the CH3 region. Neurons that exhibited retrograde labeling were only occasionally discerned in the posterior portions of the CH4 region, in the medullary laminae of the globus pallidus, or lodged within the internal capsule. These data are discussed in terms of the putative role this cholinergic input might play in cognitive processing in primates.

Sleep in the Down syndrome

Polysomnographic recordings were obtained for 10 Down syndrome (DS) children (6 males and 4 females, 9 months to 7 years old) and 16 age-matched normal controls. The present study was conducted to study the sleep characteristics of DS patients of this age group. The percentage of each sleep stage, rapid eye movements (REMs)/min, time intervals between REMs(I)/min, times of awakening in the middle of sleep, body movements (BMs) and twitch movements (TMs) were studied. I/min was divided into three frequencies: I less than 1 sec, l less than or equal to I less than 2 sec and I greater than or equal to 2 sec. Two of the 10 patients showed an increase in the percentage of REM sleep. In the group aged 1 to 5 years old, the REMs/min and I/min (I less than 1 sec) values were higher than those in normal controls (p less than 0.05). Many times of awakening in the middle of sleep (greater than or equal to 5 times and/or greater than or equal to 60 min) were observed in 4 cases. The frequency of BMs in total sleep was higher than that in controls (p less than 0.01). Five of the 10 cases showed an abnormal pattern as to the frequency of BMs during each sleep stage. The frequency of TMs was less than that in controls (total sleep and stage 1, p less than 0.05; stage REM, p less than 0.01). Seven of 9 cases showed an abnormal pattern as to the frequency of TMs during each sleep stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Dendrites, dementia and the Down syndrome

Findings from a Golgi study of the visual cortex in patients with the Down syndrome were compared with those from neurologically normal, age-matched control subjects. The dendritic atrophy seen in childhood continued into adulthood, with a marked decrease in dendritic branching, dendritic length, and spine frequency in elderly adults with the Down syndrome. Subject more than 30 years old occasionally had degenerating pyramidal neurons in the cerebral cortex and degenerated pyramidal neurons and aspiny stellate cells, particularly in the temporal cortex. These dendritic abnormalities may be related to mental retardation in children and early dementia in older adults who have the Down syndrome. The genetic and extrinsic factors may be important determinants of Alzheimer type dementia in the Down syndrome.

Loss of neurons in the rat basal forebrain cholinergic projection system after prolonged intake of ethanol

A reduction in the number of acetylcholinesterase (AChE)-positive neurons in the basal nucleus of Meynert complex (NbM, Ch 1 to Ch4) to 83% of control values was observed in rat after ethanol intake (20% v/v) for 12 weeks. Activity of choline acetyltransferase (ChAT) and AChE in the basal forebrain was simultaneously reduced to 74% and 81% and content of acetylcholine (ACh) to 56% of control values respectively. Neuronal loss showed a gradient over the rostro-caudal extension of the cholinergic projection system being most pronounced in the septal-diagonal band area and reaching 27% in the medial septum (Ch1). Number of AChE-positive neurons was insignificantly reduced in the pedunculopontine nucleus (Ch5) and unchanged in the laterodorsal tegmental gray of the periventricular area (Ch6). ACh content and activity of AChE was significantly reduced in target areas of the NbM such as cortex, hippocampus and amygdala, but changes were less pronounced than in the basal nucleus. The results indicate a neurotoxic effect of prolonged intake of ethanol on cholinergic neurons in the NbM leading to a partial cholinergic denervation of cortex, hippocampus and amygdala. Chronic intake of ethanol in rat is suggested to represent an animal model suitable to test the cholinergic hypothesis of geriatric memory dysfunction and to develop strategies for an amelioration of the impairment in memory and cognitive function in dementing disorders associated with a degeneration in the NbM such as postalcoholic dementia and Alzheimer's disease.

The pathological association between Down syndrome and Alzheimer disease

The neuropathology of Down syndrome (DS) at middle age is compared with that of Alzheimer disease (AD) at that age, through a review of the published literature and from the author's personal observations on brains from a series of patients of different ages with DS. It is noted that the pathological changes of DS at middle age (i.e. the form and distribution of senile plaques and neurofibrillary tangles, the pattern of involvement (atrophy) of neuronal systems) are qualitatively the same as those of AD at that age, though quantitative differences do occur and these may relate to biological or sociological variations inherent to the two parent populations. It is concluded that in pathological terms patients with DS at middle age do indeed have AD. Some ways in which a study of patients with DS can give insight into the nature and development of the pathological changes of AD are put forward and discussed.

Induction of cortical cholinergic hypofunction and memory retention deficits through intracortical AF64A infusions

Ethylcholine mustard aziridinium ion (AF64A), an irreversible inhibitor of high-affinity choline uptake on cholinergic nerve terminals, appears to selectively decrease presynaptic cholinergic markers after intracerebral injection. To restrict AF64A's action to cholinergic terminals within the frontoparietal (FP) cortex, the present study utilized multiple-site cortical infusions of the agent. Following an extensive histological analysis, a dose of 1 nmol AF64A/1 microliter was selected for determining AF64A's effects on acetylcholinesterase (AChE) staining, cortical cholinergic/non-cholinergic markers, and passive avoidance behavior. Adult rats given two infusions of AF64A into the right FP cortex had reduced AChE staining throughout 75% of the ipsilateral FP cortex at 10 days following infusion, thus suggesting an extensive cortical diffusion of the agent; minimal non-specific damage was seen (totalling only 4% of the ipsilateral FP cortex for both infusion sites) and no effects on AChE staining were observed in the striatum or hippocampus. Three weeks after bilateral AF64A infusions into the FP cortex (two injections on each side), significant frontal cortex deficits were observed in high-affinity choline uptake, acetylcholine synthesis, acetylcholine release, and hemicholinium-3 binding compared to vehicle-infused controls. However, choline acetyltransferase activity within the anterior cortex did not appear to be consistently affected by AF64A infusion. Cortical glutamic acid decarboxylase activity, as well as cortical monoaminergic markers, and neuropeptide levels were also unaffected. Moreover, animals that received bilateral AF64A infusions and were tested two weeks afterwards showed marked memory retention deficits during both the 24-h and 48-h postshock trials of passive avoidance testing. These results indicate that cortical AF64A infusion induces a specific, long-term cholinergic hypofunction of presynaptic markers within the cortex, resulting in a significant long-term memory impairment. Since the primary cholinergic innervation to the FP cortex, originating in the nucleus basalis of Meynert, appears to become dysfunctional (but not totally degenerative) in Alzheimer's disease, cortical AF64A infusions may closely reflect this cholinergic dysfunction by 'functionally' eliminating cortical cholinergic terminals.

Long-term neuropathological and neurochemical effects of nucleus basalis lesions in the rat

The long-term effects of excitotoxic lesions in the nucleus basalis magnocellularis of the rat were found to mimic several neuropathological and chemical changes associated with Alzheimer's disease. Neuritic plaque-like structures, neurofibrillary changes, and neuronal atrophy or loss were observed in the frontoparietal cortex, hippocampus, amygdala, and entorhinal cortex 14 months after the lesions were made. Cholinergic markers in neocortex were reduced, while catecholamine and indoleamine metabolism was largely unaffected at this time. Bilateral lesions of the nucleus basalis magnocellularis increased somatostatin and neuropeptide Y in the cortex of the rat by at least 138 and 284 percent, respectively, suggesting a functional interaction between cholinergic and peptidergic neurons that may differ from that in Alzheimer's disease.

Molecular genetics: applications to the clinical neurosciences

Application of molecular biology, by means of linkage analysis and DNA probes that demonstrate restriction fragment length polymorphisms (RFLPs), has resulted in the chromosomal localization of the genes responsible for a number of neurological disorders. Characterization of the structure and function of individual genes for these diseases is in an early stage, but information available indicates that the molecular mechanisms underlying phenotypic expression of neurological diseases encompass a wide range of genetic errors ranging from the most minor (a single-base pair mutation) to large chromosomal deletions. Linkage analysis can now be used for genetic counseling in several of these disorders.

Loss of neurones from cortical and subcortical areas in Down's syndrome patients at middle age. Quantitative comparisons with younger Down's patients and patients with Alzheimer's disease

Brains were examined after autopsy from 12 patients over 53 years of age with Down's syndrome (in whose brains plaques and tangles were numerous in many areas of cortex and subcortex), 3 patients under 53 years of age with Down's syndrome (in whose brains plaques and tangles were minimal or absent), 10 patients, of age range similar to the older Down's group but with Alzheimer's disease and 5 control patients of age range similar to the younger Down's group. The number of plaques and tangles in the hippocampus and their density within the temporal cortex, the thickness of the temporal cortex, the cross-sectional area of the hippocampus and the relative number and mean nucleolar volume of nerve cells in these cortical and in some subcortical areas were estimated and compared in each of the 4 groups. The relative loss of nerve cells and the decrease in mean nucleolar volume were calculated in percentage terms for the older Down's syndrome patients by reference to data from the younger Down's syndrome patients, whereas such losses in Alzheimer's disease were calculated by reference to the younger control patients. While in qualitative terms, all areas of brain found to be damaged in Alzheimer's disease were also damaged in Down's syndrome at middle age, quantitative differences emerged with the reductions in relative nerve cell number and mean nucleolar volume being significantly less in many areas in Down's syndrome. Conversely plaques and tangles were more numerous in the hippocampus in Down's syndrome though in the temporal cortex plaques were less numerous. It seems, therefore, that although the same pathological process is likely to operate in the two conditions, additional biological and mortality differences between Down's syndrome and the general population may account for the observed quantitative variations.

Alzheimer-like neurotransmitter deficits in adult Down's syndrome brain tissue

Brain tissue taken at necropsy from five cases of Down's syndrome and six controls was analysed for changes in neurotransmitter markers. Concentrations of noradrenaline (NA), dopamine (DA) and its major metabolite homovanillic acid (HVA), 5-hydroxytryptamine (5HT) and its metabolite 5-hydroxyindoleacetic acid (5HIAA) were determined by means of HPLC, whilst choline acetyltransferase (ChAT) was measured by a radiochemical technique. Significant reductions in NA, 5HT and ChAT were found in most cortical and subcortical regions of the Down's syndrome tissue investigated. The neuropathological lesions were assessed using a fluorescent stain for neuritic plaques and neurofibrillary tangles. These were present to varying extents in every Down's syndrome case except the youngest but were not found in control tissue of comparable age. The results indicate profound transmitter deficits and neuropathological abnormalities in adult patients with Down's syndrome, which closely resemble those of Alzheimer's disease.

Molecular genetics of human chromosome 21

Chromosome 21 is the smallest autosome, comprising only about 1.9% of human DNA, but represents one of the most intensively studied regions of the genome. Much of the interest in chromosome 21 can be attributed to its association with Down's syndrome, a genetic disorder that afflicts one in every 700 to 1000 newborns. Although only 17 genes have been assigned to chromosome 21, a very large number of cloned DNA segments of unknown function have been isolated and regionally mapped. The majority of these segments detect restriction fragment length polymorphisms (RFLPs) and therefore represent useful genetic markers. Continued molecular genetic investigation of chromosome 21 will be central to elucidating molecular events leading to meiotic non-disjunction and consequent trisomy, the contribution of specific genes to the pathology of Down's syndrome, and the possible role of chromosome 21 in Alzheimer's disease and other as yet unmapped genetic defects.

Cerebrospinal fluid monoaminergic metabolites are elevated in adults with Down's syndrome

Under conditions of rest and a low monoamine diet, brain monoamine activity was examined in young (less than 35 years) and old (greater than 35 years) adults with Down's syndrome and in control subjects by measuring the cerebrospinal fluid (CSF) and plasma concentrations of the neurotransmitter norepinephrine, and of 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy 4-hydroxyphenylglycol (MHPG), the respective metabolites of the neurotransmitters serotonin, dopamine, and norepinephrine. There were no age-related differences in metabolite concentrations in either the Down's syndrome or control subjects. CSF concentrations of 5-HIAA, HVA, and norepinephrine were significantly higher in young subjects with Down's syndrome as compared with young controls, and CSF concentrations of 5-HIAA and norepinephrine were significantly higher, by twofold or more, in old subjects with Down's syndrome as compared with older controls. The results suggest that monoamine turnover and brain functional activity involving monoamines is elevated in Down's syndrome, and that the early neuropathological changes in the disorder are not associated with a monoamine deficit.

Isolated senile plaque cores in Alzheimer's disease and Down's syndrome show differences in morphology

Frontal and temporal cortical tissue from the brains of elderly cases of Down's syndrome was used to make preparations of neuronal cell bodies containing senile plaque cores. Polarisation microscopy revealed normal "classical" plaque cores, and also a high proportion of unusual "amorphous" plaque cores which we have not seen in Alzheimer's disease. These two forms were easily distinguished by electron microscopy. This suggests that late Down's syndrome may not be an exact model for Alzheimer's disease.

The neurobiologic consequences of Down syndrome

Trisomy of the whole or distal part of human chromosome 21 (HSA 21) (Ts21) results in Down Syndrome (DS), which is characterized in part by mental retardation and associated neurological abnormalities. Structural abnormalities observed frequently include reduced brain weight, decreased number and depth of sulci in the cerebral cortices, neuronal heterotopias, and reduced numbers of specific populations of neurons, such as granule cells, in the cerebral cortices. Abnormalities in the structure of cells, primarily of the dendrites, are observed in portions of the neuraxis, such as the hippocampus, cerebellum, and cerebral cortices. Functional abnormalities in membrane properties in peripheral structures and in neurotransmitter enzyme systems in both peripheral and central structures are observed also. Brains of DS individuals over the age of 40 exhibit the characteristic neuropathologic and neurochemical stigmata of Alzheimer's disease (AD). The cholinergic and noradrenergic systems appear to be particularly vulnerable. To elucidate the mechanisms responsible for these abnormalities, identification of the genes located in the distal part of HSA 21 and the systematic study of animal model systems with close genetic homology are essential.

Increased glutathione peroxidase activity in erythrocytes in patients with Alzheimer's disease/senile dementia of Alzheimer's type

Glutathione peroxidase (GSH-Px) activity in erythrocytes was studied in 9 patients with Alzheimer's disease/senile dementia of Alzheimer's type (AD/SDAT) of ages 34-64 years and compared with that in 16 healthy controls of ages 21-66 years. The median GSH-Px activity in erythrocytes from AD/SDAT patients was 408, mu kat/1 (range 338-500 mu kat/1) and that from healthy controls 348, mu kat/1 (range 258-439 mu kat). This difference was significant (p less than 0.005) Wilcoxon rank test. Since there are great clinical and pathological similarities between AD/SDAT and the dementia of Down's syndrome (DS) patients and since both these groups of patients have increased activity of the selenium-dependent enzyme GSH-Px, it is suggested that there could be a similar metabolic background of the dementia. Many findings in the oxidative metabolism of DS suggest increased oxidative damage with an elevation of the turnover of superoxides to peroxides within cells and with a secondary biochemical modification such as increase in tissual GSH-Px activity. A similar mechanism with elevated peroxidation within cells might be responsible for the present finding of increased GSH-Px activity in erythrocytes and for the development of dementia in AD/SDAT.

The nucleus basalis of Meynert

The nucleus basalis of Meynert has been studied extensively in the recent literature. Interest in this nucleus has resulted from the discovery that it is a major source of cortical cholinergic input and that there is neuronal loss in the nucleus basalis in some dementing illnesses. Consistent and severe involvement of the nucleus basalis of Meynert has been found in Alzheimer's disease and in the dementia accompanying Parkinson's disease. Occasional involvement is present in other dementing illnesses, such as progressive supranuclear palsy, Parkinsonism-Dementia complex of Guam, dementia pugilistica, Pick's disease, Korsakoff's syndrome, Down's Syndrome and Creutzfeldt-Jacob disease. Huntington's disease spares this nucleus. However, the role of the nucleus in cognitive function is as yet undetermined. Even its alteration with normal aging remains controversial. This review details the pathological studies of this region to date, with particular emphasis on the dementias. Its role in the dementias of Alzheimer's disease and Parkinson's disease is specifically addressed.

The nucleus basalis of Meynert in multi-infarct (vascular) dementia

The number and nucleolar volume of nerve cells within the nucleus basalis of Meynert were estimated in 10 patients with Alzheimer's disease, 12 with multi-infarct dementia, 9 with a mixed Alzheimer/multi-infarct dementia and in 10 age-matched controls. As reported previously in Alzheimer's disease, both the number and nucleolar volume of surviving cells was reduced, whereas in multi-infarct dementia no significant change in either measure was noted. In patients with Alzheimer's disease/multi-infarct dementia the loss of nerve cells and reduction in nucleolar volume varied greatly in severity from patient to patient according to the relative balance of Alzheimer and vascular type pathological changes present within each patient.

Senile plaques in cortex of aged normal monkeys

The density, type, and distributions of cortical senile plaques were determined in 6 aged rhesus monkeys. Plaque densities were highest in prefrontal and temporal cortices and lowest in occipital cortex. Neurite plaques contained many argentophilic neurites and little amyloid, mixed plaques had both neurites and amyloid, and amyloid plaques showed significant amounts of amyloid and fewer numbers of neurites. As total plaque density increased, there was a linear increase in the density of amyloid plaques, suggesting that plaques evolve from neurite, to mixed, to amyloid types.

Basal forebrain lesions produce a dissociation of trial-dependent and trial-independent memory performance

The behavioral effects of lesions in the basal forebrain (BF) of rats were evaluated using two tasks. The BF lesions included both the nucleus basalis magnocellularis (NBM) and the medial septal area (MSA). The first task was a Stone maze, which has 14 consecutive choice points and is a task of complex, trial-independent memory. BF lesions did not impair choice accuracy in this task. The second task was a win-shift spatial discrimination in a radial arm maze, which requires trial-dependent memory. BF lesions produced a significant decrease in choice accuracy in this task. These results demonstrate that BF lesions impair trial-dependent (working) memory but not trial-independent reference memory, and that task difficulty is not the sole factor determining whether BF lesions produce behavioral impairments.

Noncollateral projections of basal forebrain neurons to frontal and parietal neocortex in primates

To test the hypothesis that axons of the basal forebrain cholinergic system collateralize to innervate widely separated areas of cortex, two distinct, retrogradely transported fluorescent dyes were injected into discrete neocortical regions of three macaques. In two monkeys, True Blue was injected into parietal cortex and Nuclear Yellow into frontal cortex; in a third monkey, placement of the dyes was reversed. Following these large (3-10 microliters total) injections, neurons single labeled with either Nuclear Yellow or True Blue were seen throughout most of the ipsilateral nucleus basalis of Meynert and nucleus of the diagonal band of Broca. Neurons projecting to either frontal or parietal cortex were most heavily concentrated in the anteromedial aspect of the basal forebrain. A small number of labeled neurons was also seen in the contralateral basal forebrain. Cells single labeled with either True Blue or Nuclear Yellow were frequently adjacent to one another, but in no case was a neuron labeled with both dyes. Thus, individual neurons of the basal forebrain complex do not appear to innervate both frontal and parietal lobes of monkeys. This finding is consistent with recent studies in rodents which suggest that basal forebrain neurons innervate relatively small, restricted cortical fields.

Alzheimer's disease: an emerging affliction of the aging population

Alzheimer's disease is one of several brain disorders under the broad category of dementia. It is a gradually debilitating illness with no known cure. The first symptom is usually a slowly increasing memory loss, beginning between 40 and 65 years of age. As the disease progresses, the brain begins to deteriorate more rapidly, until it literally stops functioning. Of great concern is the projection that the number of people who will have Alzheimer's disease will double by the year 2030 because of the rising elderly population. Treating this population will escalate from the current estimate in excess of $2.5 billion to more than $6 billion. Speculation toward the increasing costs in money and workforce has led to an accelerated program in search of a cure or at least a symptomatic therapy for this condition. One of the most promising research leads is the striking connection between Alzheimer's disease and Down's syndrome and certain cancers: --Virtually 100% of patients with Down's syndrome who survive past age 35 show the same mental deterioration and identical brain changes seen in patients with Alzheimer's disease, including the presence of plaque and neurofibrillary tangles.--The presence of a high percentage of Down's syndrome among relatives of patients with Alzheimer's disease. --A high incidence of certain types of syndrome and among relatives of people who have Alzheimer's disease, such as leukemia, lymphomas, Hodgkin's disease, and immune system disorders. The key to the intercorrections between Alzheimer's disease and Down's syndrome seems to be a genetic component related to chromosome 21.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of various cognition-enhancing drugs on in vitro rat hippocampal synaptosomal sodium dependent high affinity choline uptake

The purpose of the present study was to compare the effect of seven drugs, that have been reported to enhance cognitive functions, on rat hippocampal cholinergic neuronal activity. The latter was assessed by measuring the effects of the drugs on in vitro sodium-dependent high affinity choline uptake (HACU) into rat hippocampal synaptosomes 30 minutes after their in vivo administration. 3,4-Diaminopyridine (0.1 mg/kg IP), like pramiracetam (44 and 88 mg/kg IP), increased HACU with higher or lower doses being ineffective. Centrophenoxine (100 mg/kg IP) decreased HACU. Piracetam (100 and 500 mg/kg IP), aniracetam (10-200 mg/kg PO), lysine vasopressin (0.005-0.05 mg/kg IM) and 4-aminopyridine (0.01-3.0 mg/kg IP) were ineffective. The results indicate that 3,4-diaminopyridine and centrophenoxine, like pramiracetam may be increasing cognitive function in part by affecting hippocampal cholinergic neuronal activity. In addition, the findings indicate the usefulness of using in vitro HACU as a biochemical measurement to assess the potential effect of cognitive-enhancing drugs on cholinergic neuronal activity in vivo.

Expression of genes on human chromosome 21

Gene sequences were isolated from a lambda library containing inserts originating from human chromosome 21. One phage, CP21G1, had been selected on the basis of its lack of middle-repetitive sequences and its ability to hybridize with 32P-labeled cDNA synthesized from the cytoplasmic poly A+ RNA of cultured fibroblasts. Further experiments revealed that the human insert in this phage is unique-sequence DNA, maps to the long arm of chromosome 21, and is expressed in fibroblasts and T cells. A panel of 127 "unique-sequence" phage were also selected from the lambda library and were tested for hybridization to 32P-labeled cDNA synthesized from the cytoplasmic poly A+ RNA of CCRF-HSB-2, a T-blast leukemic line. Seventeen recombinants hybridized to the probe. One of these phages, CP8, contains a human unique-sequence DNA expressed in T cells and neuroblastoma cells. One phage (CP5) in the "unique-sequence" panel that had not hybridized to cDNA from T-cell RNA was found to carry a low-repeat sequence and to hybridize specifically to RNA from a neuroblastoma line. This phage appears to carry a brain-specific gene. Many of the genomic sequences related to the low-repeat sequence contained in CP5 map to the short arm of chromosome 21. The cloned genes described here represent new markers for the detailed mapping of human chromosome 21 and may prove valuable in studying tissue-specific gene regulation.