Neuropeptides in Alzheimer type dementia

gamma-Aminobutyric acid-containing basal forebrain neurons innervate inhibitory interneurons in the neocortex

The basal forebrain-neocortex pathway--involved in higher cognitive processing, selective attention, and arousal--is considered one of the functionally most important ascending subcortical projections. The mechanism by which this relatively sparse subcortical pathway can control neuronal activity patterns in the entire cortical mantle is still unknown. The present study in the cat provides evidence that gamma-aminobutyric acid-containing basal forebrain neurons participate in the neocortical projection and establish multiple synaptic connections with gamma-aminobutyric acid-releasing interneurons containing somatostatin or parvalbumin. We propose that a mechanism by which the numerically small ascending pathways can exert a powerful global effect in the neocortex is by the selective innervation of gamma-aminobutyric acid-releasing interneurons, which, in turn, control the activity of large populations of pyramidal cells through their extensive axon arborizations. Finally, these results demonstrate a direct anatomical link between two cell populations implicated in Alzheimer disease pathology: basal forebrain neurons and cortical somatostatin cells.

Parvalbumin immunoreactive neurons in normal human temporal neocortex and in patients with Alzheimer's disease

Parvalbumin-immunoreactive (PARV-ir) neurons were studied in the temporal neocortex of 4 normal subjects and in 7 patients with Alzheimer's disease (AD) whose brains were removed from the skull between 1 and 4 h after death and immediately fixed by perfusion through the carotid arteries to minimize pitfalls related to delayed tissue processing. Freezing microtome sections were immunostained free-floating for PARV using a well characterized monoclonal antibody diluted at 1:5000 and the peroxidase-antiperoxidase method. PARV-ir cells predominated in layers III, IV and V and were classified as bitufted cells and small, medium and large multipolar neurons according to their dendritic arbors. Immunoreactive cell processes surrounding the soma of neighbouring cells and immunoreactive vertical strings of buttons were consistent, respectively, with terminal axons of basket cells and chandelier neurons. The number of PARV-ir cells in the superior (T1), middle (T2) and inferior (T3) temporal gyri was variable from one case to another in both normal and pathological cases. Only 1 of 7 patients with AD had significantly reduced numbers of PARV-ir neurons, thus suggesting that PARV-ir cells in the neocortex are relatively resistant to degeneration in Alzheimer's disease.

Recent advances in the neurochemical pathology of Alzheimer's disease. Studies of neuropeptides, cholinergic function and Alzheimer's disease-associated protein

Our findings from three postmortem tissue studies in Alzheimer's disease (AD) are presented. We investigated (1) alterations in somatostatin (SRIF) and corticotropin-releasing factor (CRF) in AD; (2) regulatory changes in presynaptic cholinergic function in AD; and (3) use of Alzheimer's disease-associated protein (ADAP) as a diagnostic test for AD in postmortem tissue. Taken together, these findings reveal marked reductions in SRIF and CRF concentrations in many cerebrocortical areas in AD, a marked up-regulation of cholinergic neuronal activity in surviving cholinergic neurons in AD, and excellent specificity and sensitivity for the use of the ADAP assay as a diagnostic test for AD in postmortem tissue.

Asymmetric increase in substance P immunoreactivity in the rat and guinea pig substantia nigra after unilateral neocortical ablation

Substance P was visualized in the rat and the guinea pig basal ganglia, mesencephalon and spinal cord after surgical unilateral cortical ablation. An increased density in substance P-like immunoreactive patterns in the substantia nigra was observed ipsilaterally to the lesioned hemisphere. These results, together with previous observations in cases of Alzheimer's disease presenting with asymmetric cortical atrophy, suggest an influence of the corticostriatal pathway on substance P-like immunoreactivity in these subcortical structures. Finally, these experiments proved to be a reliable animal model for the study of the effects of neocortical lesions on the neuropeptidergic innervation of certain subcortical regions.

The basal forebrain cholinergic system: efferent and afferent connectivity and long-term effects of lesions

The first part of this article deals with several aspects of efferents and afferents of the rat basal forebrain cholinergic system (BFChS) studied with anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L). PHA-L tracing of the BFChS efferents revealed topographically differentiated axonal trajectories and patterns of presynaptic endings to the neocortex, mesocortex, olfactory nuclei and hippocampus. Combining this method with second immunolabeling, we identified the muscarinic cholinoceptive neurons in the neocortex and the somatostatinergic neurons in the hippocampus as being directly innervated by the magnocellular basal nucleus and the medial septum, respectively. The prefrontal cortex was identified as a source of afferent input to the basal forebrain cholinergic neurons. This projection also exhibits a topographic organization, which shows a reciprocal relationship with the BFChS efferents to the cortex. The second part of this article describes the anatomical changes of cortical cholinergic and some other neurotransmitter systems after long-term cholinergic denervation in the aged rat cortex. The spared cholinergic projection in the largely denervated areas shows abundant malformations, which are similar in appearance to the anatomical alterations of the surviving cholinergic fibers in dementia of the Alzheimer type (AD). Hypertrophic changes also occur in the serotonergic system. The neuropeptide-Y- and somatostatin-containing cortical systems respond with an increment of their axonal densities, in contrast to the decline of these peptides in AD. Although transsynaptic effects are mediated by long-term cholinergic lesions, they do not support the hypothesis that the cholinergic deficiency is a primary event in the pathophysiology of AD.

A correlation study of CSF neuropeptides in Alzheimer's and Parkinson's disease

The concentrations of somatostatin (SRIF), vasoactive intestinal polypeptide (VIP), beta-endorphin (beta-EP), adrenocorticotropin (ACTH) and corticotropin-releasing factor (CRF) immunoreactivity were measured in cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD), patients with Parkinson's disease (PD) and controls. In order to study the mechanisms that regulate peptide levels in CSF and peptide interactions, correlations between CSF peptides were determined. Within all patient groups a number of significant correlations were shown to exist between CSF peptides. The correlations were apparently not coincidental, since there was no such relation between the concentrations of CSF peptides and CSF protein content. Neither age, sex, severity of dementia nor the presence of extrapyramidal signs could explain the number of significant correlations. These results indicate, that the correlations found between CSF peptides may be due to common regulatory mechanisms or general physiological behaviour of peptides in the CSF.

Hypothalamic monoamines and neuropeptides in dementia

The concentrations of monoamines and various neuropeptides were determined in the hypothalamus of brains from patients with Alzheimer's disease and vascular dementia (n = 26) and compared with control values (n = 21). Decreased concentrations of 5-hydroxyindoleacetic acid (P less than 0.05) and homovanillic acid (P less than 0.01) were found, and increased arginine vasopressin- (P less than 0.01), galanin- (P less than 0.05) and somatostatin- (P less than 0.01) like immunoreactivity. It is proposed that this disequilibrium may be important for certain circadian symptoms, e.g. the changes in sleep/wake rhythms that are rather often observed in dementia.

A selective loss of somatostatin in the hippocampus of patients with temporal lobe epilepsy

Although neuropeptides have been demonstrated to be hippocampal neuromodulators in laboratory animals, their role in human hippocampal physiology or pathophysiology remains to be defined. The concentrations of somatostatin, cholecystokinin octapeptide, vasoactive intestinal polypeptide, and dynorphin A 1-17 were determined in hippocampal tissue resected from patients with cryptogenic temporal lobe epilepsy, a common seizure disorder originating in or near the hippocampus. Control tissue was obtained from cadavera or epilepsy patients in whom the hippocampus was removed during the resection of temporal lobe tumors. Peptide determinations were performed on extracts of punch biopsy specimens taken from six different hippocampal regions. A significant decrease in immunoreactive somatostatin concentration was identified in the dentate gyrus and in region cornu ammonis 4 of cryptogenic temporal lobe epilepsy specimens. No significant changes were present in any other hippocampal region or in the levels of other peptides. In situ hybridization studies performed on cryostat sections from similar patients confirmed a marked loss of neurons expressing the somatostatin gene, which was restricted to the dentate hilus. The density of specific 125I-somatostatin binding to cryostat sections, as determined by semiquantitative in vitro autoradiography, was significantly increased in the dentate gyrus of the cryptogenic epilepsy patients, compared with tumor control specimens. We conclude that a loss of somatostatin-producing interneurons with an upregulation of dentate somatostatin receptors is a specific and characteristic element in the pathophysiology of human cryptogenic temporal lobe epilepsy.

Neocortical concentrations of neuropeptides in senile dementia of the Alzheimer and Lewy body type: comparison with Parkinson's disease and severity correlations

Corticotropin releasing hormone (CRH), somatostatin (SRIF), and arginine vasopressin (AVP) concentrations were estimated using radioimmunoassay in the temporal and occipital cortices in postmortem brain from patients clinically and neuropathologically diagnosed as senile dementia of the Lewy body type (SDLT), senile dementia of the Alzheimer type (SDAT), and Parkinson's disease (PD) and from neurologically normal controls. The concentration of temporal and occipital neocortical CRH was diminished in both SDAT and SDLT compared to control values, whereas SRIF was reduced only in temporal cortex in both these conditions. In contrast, the concentrations of both CRH and SRIF were unaltered in PD. The concentrations of AVP in SDLT, SDAT, and PD were similar to those found in the control groups. The decrement in SRIF, but not CRH, was found to be correlated with some indices of severity of illness in SDAT; a similar but nonsignificant trend for SRIF was observed in SDLT.

Substance P-like immunoreactive neurons are depleted in Alzheimer's disease cerebral cortex

We studied the morphology and distribution of substance P-like immunoreactive elements in normal and Alzheimer's disease brain with a monoclonal anti-substance P antibody. Bands of prominent terminal-like staining were found in the dentate gyrus of normal brain. Multipolar substance P-immunoreactive neurons were seen in dentate polymorphic layer and CA4 and prominent fiber staining was present in the CA fields of the hippocampus and adjacent allocortex. Reactive perikarya, concentrated in deep cortex and infracortical white matter, were found in all isocortical regions. Greatest density was in frontal and parietal association cortex; lowest in visual cortex. Fiber density was generally greatest in layers I and II. In Alzheimer's disease, staining intensity was reduced in the dentate gyrus. Hilar neurons were unaffected but other CA field neurons were distorted with pruned dendritic trees. Isocortical perikarya and fibers were significantly depleted and distorted in all regions. Globular deposits consisting of distorted neurites or dissolving perikarya were frequently seen. Double staining methods showed that the vast majority of isocortical, but not hippocampal, substance P-like immunoreactive neurons are nicotinamide adenine dinucleotide phosphate diaphorase-positive. Despite the modest quantitative depletion of substance P in Alzheimer's disease cortex as measured by radioimmunoassay compared to somatostatin, there is a significant depletion of substance P-like immunoreactive perikarya. This disparity may be due to persistence of afferent projections which make a major contribution to substance P concentrations in cerebral cortex or to the high substance P content of dystrophic fibers in Alzheimer's disease cortex.

Reduction of neurotensin immunoreactivity in the amygdala in Alzheimer's disease

The density of neurotensin immunoreactivity (NT-IR) was dramatically decreased in 6 of 12 amygdaloid nuclear subregions in patients with Alzheimer's disease (AD) compared to age-matched normals. Diminution of NT-IR was most pronounced in amygdaloid regions containing the greatest number of senile plaques. This contrasts to our previous findings of little, if any, loss of substance P or somatostatin immunoreactivity within these same regions. The present findings corroborate biochemical reports of a decrease in NT-IR in the AD amygdala and suggest that this peptide may be selectively affected relative to other neuropeptides.

Neurotensin innervation of the human cerebral cortex: lack of colocalization with catecholamines

We have localized neurotensin (NT) with immunocytochemical methods in the normal human cerebral cortex. Extensive areas of the frontal cortex, the hippocampal formation, and selected areas of the parietal, temporal and occipital lobes, were examined using post-mortem brain tissue. The peptidergic innervation was characteristically restricted to the limbic belt and to the dorsally contiguous regions. NT-labeled perikarya were found throughout the subiculum, including its dorsal supra-callosal continuation. NT terminal plexuses were particularly abundant in layers I-VI of the anterior cingulate cortex, in layer I of area 32 and of medical areas 9, 8, 6 and in layers II-III of area 29, of the presubiculum and entorhinal cortex. Elsewhere, NT fibers were scarce being more frequent in layer I. This regional and laminar pattern differed significantly from that of tyrosine hydroxylase (TH), which was used to label catecholaminergic axons, and preferentially the dopaminergic ones. Even in zones where TH and NT innervations were abundant, such as the anterior cingulate cortex or area 32, double-labeling procedures disclosed no colocalized fibers. The lack of NT-TH colocalization in human, contrasts with previous findings in the rodent cortex, where a contingent of the DA cortical afferents contains NT. The DA mesocortical neuronal population, labeled by TH antisera, thus seems to change its chemical phenotype, by losing the expression of an associated peptidergic neurotransmitter; this could be related to the predominant extension in the ascent of the phylogenetic scale of the non-colocalized, type of cortical DA innervation which is also found in rodents. The possible origins of the cortical, non-dopaminergic NT innervation in human are discussed: thalamo-cortical, subiculo-cortical or intrinsic. Such cortical NT innervation could be very important in limbic circuitry as a regulatory peptide in affective processes and could be involved in the physiology of pain and memory.

Cortical concentrations of corticotropin-releasing hormone and its receptor in Alzheimer type dementia and major depression

Corticotropin-releasing hormone-immunoreactivity (CRH-IR) and CRH receptors (binding capacity and affinity) were measured in postmortem cortical areas from depressed subjects, two groups of senile dementia of the Alzheimer type (SDAT), and age-, sex-, and postmortem-delay-matched controls. No difference in CRH-IR and CRH receptor status between depressed subjects and controls was noted. CRH-IR was decreased in all cortical areas in SDAT, with a corresponding increase in CRH receptor binding capacity (with no change in affinity) in occipital cortex. No effects of postmortem delay were seen. It is suggested that the increase in CRH receptor numbers in SDAT is related to the degree of distribution of pathological involvement in specific regions.

Laminar distribution of neuron degeneration in posterior cingulate cortex in Alzheimer's disease

The laminar distribution of neuron losses in posterior cingulate cortex were evaluated in 25 clinically and neuropathologically diagnosed cases of dementia of the Alzheimer type (DAT). The layer of maximal neuron loss in area 23a for each DAT case was determined by comparison with mean neuron densities for each layer of 17 neurologically intact control cases. The DAT cases were separated into five classes: class 1, 12% of all DAT cases, no or less than 40% neuron loss in any layer; class 2, 24%, maximal neuron losses in layers II or III; class 3, 28%, losses mainly in layer IV; class 4, 12%, losses mainly in layers V or VI; class 5, 24%, severe losses in all layers. An analysis of large and small neurons showed that in class 2 there was an equal loss of both in layer IIIa--b, in class 3 mostly small neurons were lost in layer IV, in class 4 mostly large neurons were lost in layers III, IV and V, while in class 5 there was no selectivity. The age of disease onset and length of the disease were the same for all classes, although classes 4 and 5 tended to have an earlier onset. No measures of thioflavin S-stained neuritic plaque (NP) or neurofibrillary tangle (NFT) density discriminated among these classes. In 64% of all DAT cases there was a progressive shift in NFT from ventral area 30 where most were in layer II to areas 23a--b where there was a balance between those in superficial and deep layers to dorsal area 23c where most were in layers V and VI.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatostatin in neurodegenerative illnesses

Somatostatin may play a role in several neurodegenerative diseases. Somatostatin concentrations are depleted in cerebral cortex in both Alzheimer's disease and in the dementia that accompanies Parkinson's disease. Somatostatin neurons in both illnesses are markedly dystrophic and may be reduced in number. In Huntington's disease, somatostatin concentrations are increased in the basal ganglia, as is the density of somatostatin neurons. The precise role of somatostatin changes in the pathophysiology of these illnesses requires further study.

Neuropeptides and Alzheimer's disease

Because of their putative roles as neurotransmitters, neuromodulators, and neuroregulators in the central nervous system, neuropeptides have been the focus of considerable research over the past two decades. There is evidence that alterations in the synaptic availability of particular neuropeptides occur in certain neuropsychiatric disorders, such as schizophrenia and affective disorders. Alzheimer's disease is the most common neurodegenerative disorder, affecting a sizable proportion of our aging population. Alzheimer's disease is characterized by the presence of neurofibrillary tangles and senile plaques in the central nervous system. Postmortem studies have provided evidence that several neuropeptide-containing neurons are pathologically altered in this disorder. The purpose of this article is to describe recent advances in neuropeptide biology with a focus on the role of neuropeptides in the pathogenesis of Alzheimer's disease.

Distribution of 125I-neurotensin binding sites in human forebrain: comparison with the localization of acetylcholinesterase

The distribution of 125I-neurotensin binding sites was compared with that of acetylcholinesterase reactivity in the human basal forebrain by using combined light microscopic radioautography/histochemistry. High 125I-neurotensin binding densities were observed in the bed nucleus of the stria terminalis, islands of Calleja, claustrum, olfactory tubercle, and central nucleus of the amygdala; lower levels were seen in the caudate, putamen, medial septum, diagonal band nucleus, and nucleus basalis of Meynert. Adjacent sections processed for cholinesterase histochemistry demonstrated a regional overlap between the distribution of labeled neurotensin binding sites and that of intense acetylcholinesterase staining in all of the above regions, except in the bed nucleus of the stria terminalis, claustrum, and central amygdaloid nucleus, where dense 125I-neurotensin labeling was detected over areas containing only weak to moderate cholinesterase staining. At higher magnification, 125I-neurotensin-labeled binding sites in the islands of Calleja, supraoptic nucleus of the hypothalamus, medial septum, diagonal band nucleus, and nucleus basalis of Meynert were selectively associated with neuronal perikarya found to be cholinesterase-positive in adjacent sections. Moderate 125I-neurotensin binding was also apparent over the cholinesterase-reactive neuropil of these latter three regions. These data suggest that neurotensin (NT) may directly influence the activity of magnocellular cholinergic neurons in the human basal forebrain, and may be involved in the physiopathology of dementing disorders such as Alzheimer's disease, in which these neurons have been shown to be affected.

Somatostatin depresses GABA receptor-mediated inhibition in the rat dorsolateral septal nucleus

The effect of somatostatin-14 (SS-14) on gamma-aminobutyric acid (GABA)-mediated inhibitory neurotransmission in the dorsolateral septal nucleus (DLSN) was investigated using a submerged slice preparation and intracellular recording techniques. Somatostatin-14 applied by superfusion or by pressure ejection from micropipettes predominantly inhibited the intracellularly recorded fast inhibitory postsynaptic potential (fIPSP) and late hyperpolarizing potential (LHP) elicited by focal electrical stimulation of the DLSN. The decreases in LHP and fIPSP amplitude occurred at low concentrations of peptide, in the absence of appreciable changes in the passive-membrane properties of postsynaptic neurons, and outlasted the membrane hyperpolarizing effect produced by SS-14 at higher concentrations. The ability of SS-14 to modulate postsynaptic GABA receptor responses underlying the fIPSP and LHP were investigated by applying baclofen, a selective GABAB receptor agonist, and isoguvacine, a selective GABAA receptor agonist, by pressure ejection. Hyperpolarizing responses to GABAA and GABAB receptor stimulation were significantly decreased during superfusion of SS-14. Tetrodotoxin applied by superfusion blocked electrically evoked synaptic potentials but not the depressant effect of SS-14 on baclofen- or isoguvacine-induced hyperpolarization. Facilitation of the fIPSP or LHP by SS-14 also occurred but less frequently and consistently than the depressant action. Excitatory postsynaptic potentials and membrane response to NMDA or quisqualate appeared unaltered by bath-applied SS-14. These findings suggest a novel postsynaptic action of SS-14 leading to depression of synaptic responses mediated by GABAA and GABAB receptors. Synaptically released SS-14 in the DLSN may participate in modulation of feedforward and/or feedback inhibitory mechanisms coordinating DLSN function in the septo-hippocampal system.

Changes in Na+,K(+)-ATPase, Ca2(+)-ATPase and some soluble enzymes related to energy metabolism in brains of patients with Alzheimer's disease

Hexokinase, lactate dehydrogenase, acylphosphatase, (Na+,K+)-ATPase and Ca2(+)-ATPase of selected areas from postmortem Alzheimer's disease brains were studied. Hexokinase and lactate dehydrogenase were significantly changed in all the examined subcortical nuclei. (Na+,K+)-ATPase activity was altered in several areas of Alzheimer's disease brains. No changes in Ca2(+)-ATPase and acylphosphatase were observed. The main alterations of the assayed enzymes were observed in subcortical areas but not in cortical areas of Alzheimer's disease brains.

A quantitative assessment of somatostatin-like and neuropeptide Y-like immunostained cells in the frontal and temporal cortex of patients with Alzheimer's disease

Immunocytochemical studies utilizing radioimmunoassay and morphological techniques have provided conflicting evidence for the involvement of somatostatin and neuropeptide Y in Alzheimer's disease (AD). However, previous investigators have not considered the effects of cortical atrophy in AD tissue on their findings. This study reports the numbers of somatostatin-like (SLI) and neuropeptide Y-like immunoreactive (NPYLI) neuronal perikarya and the length of SLI and NPYLI immunoreactive fibres, with appropriate corrections for atrophy in 6 control and 6 AD cases. There were significantly fewer SLI neurones in AD in layers II + III combined from the temporal cortex, and fewer NPYLI neurones in layers V + VI in both frontal and temporal cortices. Using a randomized method to quantify immunostained fibre length in the neuropil, an analysis of variance revealed no significant differences in the mean SLI or NPYLI fibre length per cortical strip between control and AD groups in frontal or temporal cortex. However, using a second measure of fibre length by tracing the fibres attached to consecutive immunostained perikarya, there were significant reductions in the AD brains in the mean fibre length per cell in layers V + VI for SLI in the temporal cortex, and for NPYLI in the frontal cortex. This reduction in fibre length per individual cell was presumably masked by the large variation in the fibre length found between cases using the randomized approach. It was concluded that in order to evaluate the involvement of these neuropeptides in AD from any measurements of concentration, it is essential to include some compensation for the extent of cortical atrophy that occurs with the disease.

Developmental expression of somatostatin in mouse brain. I. Immunocytochemical studies

The postnatal development of the distribution of somatostatin immunoreactive (SOMLI) neurons and fibers in the forebrain of the Balb/C mouse and their relationship to cholinergic afferents have been examined. SOMLI was first discernable in the hypothalamus on postnatal day (PND) 3 and increased gradually to reach adult levels by PND 30. In the limbic system, SOMLI is detectable at birth. In all other structures of the forebrain, SOMLI could be observed by PND 3 but the distribution, density and morphology of the immunoreactive neurons evolved over the following 2-3 weeks. In general, SOMLI cells and fibers increased for 1-3 weeks after their initial appearance and subsequently declined to achieve adult levels. The distribution pattern of SOMLI elements in adult mouse brain was similar to previous reports in rat with a few notable differences in thalamus, olfactory structures and, to a lesser degree, cortex and hippocampus. The temporal pattern of SOMLI expression in extrahypothalamus forebrain regions, during development, suggests a role of this peptide in differentiation and synapse formation. Such an hypothesis receives further support from neonatal lesions of the basal forebrain which resulted in transient cortical cholinergic deafferentation, a delay of cortical differentiation and a transient increase in the number of SOMLI cells in cortex.

Altered post-receptorial signal transduction mechanism under various stimulation in polymorphonuclear granulocytes of Alzheimer's disease

The cyclic nucleotide changes were studied under 10(-6) M isoproterenol (IP), 10(-6) M carbachol and 10(-8) M Met-enkephalin (Met-enk) stimulations in polymorphonuclear granulocytes (PMNLs) of middle-aged (aged 35-52 years) and elderly (aged 61-97 years) healthy subjects, as well as of patients with Alzheimer's disease (AD) (aged 58-65 years). From our results we can conclude that in the case of middle-aged healthy subjects only the IP caused a marked cAMP elevation while in elderly and AD all the applied substances stimulated the cAMP at different degrees. Concerning the cGMP levels in PMNLs, we observed a marked increase under carbachol and Met-enk stimulation, in middle-aged subjects, while in the elderly a weak change was obtained by carbachol. In AD practically no change of cGMP levels could be obtained. Thus, the main features of AD are a cAarP response to Met-enk and an abolition of a GarP response to carbachol. We can conclude that in PMNLs of elderly and patients with AD we assist to an altered post-receptorial signal transduction mechanism, which seems to be even more marked in the case of AD comparing to normal aging.

Mapping of somatostatin receptor localization in rat brain: forebrain and diencephalon

Using quantitative in vitro receptor autoradiography, minute distributions of 125I-Tyr11-somatostatin (SS)-14 binding sites were investigated in the rat forebrain and diencephalon. In the cerebral cortex, there was a high density of receptors observed in layers V-VI and a low density in layers I-IV. The entorhinal cortex displayed the highest receptor density of the cerebral cortices. The olfactory system had a high SS receptor density. The anterior olfactory nucleus, nucleus of the lateral olfactory tract, medial habenular nucleus and the basolateral amygdaloid nucleus showed moderate densities. In the limbic system, the CA1 and subiculum regions had high receptor densities. More detailed observations revealed high receptor densities in the oriens, radiatum and lacunosum layers and a much lower density in the pyramidal cell layer. The caudate putamen and substantia nigra showed low receptor densities, while the claustrum displayed the highest density of receptors in the rat brain. These data were not consistent with those of previous studies using 125I-SS-28 and 125I-201-995, which had shown that the high receptor density area in the basolateral amygdaloid group was identified as the lateral amygdaloid nucleus, and that the pyramidal cell layer in the hippocampus showed high receptor densities.

Secretions of somatostatin and VIP in cultures of fetal rat neuroblasts increased by amino acids

Neuroblasts obtained from 17 day old rat embryos were incubated for 8 days, after which half of them were treated with 10(-6) M FACE (a mixture of amino acids high in glycine, alanine and aspartic acid), and the other half were left as controls. At the end of 20 days, levels of somatostatin (SRIF) were over 6,000 pg/plate in neuroblasts treated with FACE, versus 500 pg/plate in controls. At this time vasoactive intestinal peptide (VIP) levels were over 230 pg/plate in the FACE treated cultures, while their controls contained less than 150 pp/plate. Protein totals were similar (about 1,000 micrograms/plate) in all FACE treated cultures and controls, indicating that increases in SRIF and VIP were not determined by changes in cell population, but by their synthetic and/or secretory activities triggered by minute amounts of FACE. These results may be of interest in the understanding of Alzheimer's disease.

Peptides in the neocortex in Alzheimer's disease and ageing

Studies which have examined neuropeptides in Alzheimer's disease (AD) and normal ageing are reviewed. A marked specificity and selectivity is noted: most neuropeptides are normal, and the only two peptides consistently altered are somatostatin (SRIF) and corticotropin releasing hormone (CRH). Binding sites for CRH are increased in number in a reciprocal fashion to the reduction in CRH. These findings (1) provide evidence for selective vulnerability within the cortex in AD, (2) suggest that the primary site of pathology in AD may be cortical, and (3) indicate that the pathological process of AD is distinct from that of normal ageing.

Alzheimer's disease: theories of causation

There are many theories to explain the cause of Alzheimer's disease. None is mutually exclusive of the others, and it may be that all are correct. The only problem may be that we do not understand which is the primary cause and which are the secondary effects of the primary abnormality in the disease. It is almost certain that Alzheimer's disease, as we recognize it today, is heterogeneous. One has only to think of the early-onset and late-onset familial cases to realize that this is so. All of the theories have experimental evidence to support them, and all have generated experiments to substantiate them. Some of them have generated potential concepts for treatment, none of which at present have proved to be successful. When in the end the underlying etiology of the condition is discovered, it will be possible to fit all of the experimental observations into place. It appears at present that the most likely breakthroughs in our understanding will come from detailed sequencing of the paired helical filaments and from breakthroughs in the field of molecular genetics studying the gene for familial Alzheimer's disease.

Somatostatin hyperpolarizes neurons and inhibits spontaneous activity in the rat dorsolateral septal nucleus

Intracellular recordings were made from rat brain neurons in a submerged slice preparation containing the dorsolateral septal nucleus (DLSN). Somatostatin-14 (SS-14) was applied to these neurons by superfusing solutions containing known concentrations of the peptide or by pressure ejection from micropipettes. With either method of treatment, SS-14 produced membrane hyperpolarization and decreased membrane resistance in a concentration-dependent manner. The hyperpolarizing response to SS-14 occurred in virtually all neurons tested and appeared to result from a direct action on DLSN neurons mediated by an increased permeability to potassium ions. The SS-14-induced membrane hyperpolarization was not blocked by naloxone, bicuculline, tetrodotoxin, or calcium-free, high-magnesium superfusion media. In a small number of neurons, SS-14 application produced a membrane depolarization which did not exhibit clear concentration-dependence and was blocked by superfusion of calcium-free, high-magnesium media indicating an indirect action. These findings reveal that SS-14 is a potent inhibitor of DLSN neurons in vitro and provide the first evidence that receptors for this putative neurotransmitter are located on postsynaptic neurons in this nucleus. Synaptically released SS-14 may play an important role in the modulation of septohippocampal function.

Cerebrospinal fluid somatostatin in delirium

Cerebrospinal fluid somatostatin-like immunoreactivity (CSF SLI) was determined for 67 elderly patients who met the DSM-III criteria for delirium and for 19 age-matched controls. As a group, and also when subdivided according to the type of delirium, severity of cognitive decline or the type of central nervous system disease, the delirious patients showed significant reductions of SLI compared with the controls, together with a declining trend associated with increasing cognitive dysfunction. These findings are in accordance with previous observations that reduced CSF SLI is associated with diseases in which cognitive function is disturbed and they extend this finding to delirium.

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.

Long-term effects of cholinergic basal forebrain lesions on neuropeptide Y and somatostatin immunoreactivity in rat neocortex

The effect of cholinergic basal forebrain lesions on immunoreactivity to somatostatin (SOM-i) and neuropeptide-Y (NPY-i) was investigated in the rat parietal cortex, 16-18 months after multiple bilateral ibotenic acid injections in the nucleus basalis complex. As a result of the lesion, the cholinergic fiber density in the cortex decreased by 66% with a concurrent increase in SOM-i fibers by more than 50% and a 124% increase in NPY-i fiber innervation. The neuropeptidergic sprouting response on cholinergic denervation does not match the concurrent cholinergic and peptidergic decline in Alzheimer's disease and as such does not support the cholinergic lesion alone as an animal model for this neurodegenerative disorder.

Neuropeptides in Alzheimer's disease: a postmortem study

The concentration of 5 neuropeptides, neurotensin (NT), somatostatin (SRIF), corticotropin-releasing factor (CRF), bombesin and thyrotropin-releasing hormone (TRH) was measured in 3 cerebrocortical areas and several subcortical regions in post-mortem brains obtained from patients with histologically verified Alzheimer's disease and from controls without neurological or psychiatric disorders using sensitive and specific radioimmunoassay procedures. In Alzheimer's disease, reductions in the concentration of SRIF and CRF were observed in frontal and temporal cortex. In addition, in Alzheimer's disease, SRIF was also reduced in concentration in the hypothalamus, whereas CRF concentrations were reduced in the caudate nucleus. Neurotensin was reduced in concentration in the amygdala in Alzheimer's disease. No alterations in TRH or bombesin/gastrin-releasing peptide were found. These findings provide further evidence for the pathological involvement of certain neuropeptide-containing neurons in Alzheimer's disease.

Dystrophic peptidergic neurites in senile plaques of Alzheimer's disease hippocampus precede formation of paired helical filaments

The relationship between peptidergic dystrophic neurites and paired helical filament (PHF)-positive neurites in Alzheimer's disease (AD) senile plaques (SPs) was studied using combined fluorescence and bright-field optics. Cryostat sections of AD hippocampi were first stained with thioflavine-S and immunolabelled with antisera raised against different neuropeptides: somatostatin-28(1-12), somatostatin-14, neuropeptide Y, cholecystokinin (CCK) and substance P. Secondly, using the elution-restaining procedure, sections were immunolabelled with anti-tau/PHF. In immature SPs, clusters of abnormal, swollen neurites were found. The dystrophic, strongly peptidic-positive neurites contained fewer PHFs than the poorly positive ones. Cell bodies, exhibiting a peptidic content, could be found within SPs without any alteration. These results suggest the following sequence of events: an extracellular poisoning mechanism, perhaps the amyloid substance, first changes the structure of presynaptic endings and causes the formation of ballooning dystrophic neurites filled with their normal peptidic content. Subsequently, intracellular degradation occurs with formation of the PHFs. Then the other structures such as dendrites and perikarya are damaged by the same mechanism. Therefore, this phenomenon seems to precede any formation of PHFs in SPs.

Clonidine-induced growth hormone secretion in elderly patients with senile dementia of the Alzheimer type and major depressive disorder

This study was undertaken to assess the value of growth hormone (GH) response to clonidine as a tool in the differential diagnosis between depression and dementia. This response is known to be blunted in depression, and neurochemical changes observed in senile dementia of the Alzheimer type (SDAT) could lead to an up-regulation of GH secretion. No difference was observed between GH response in depressed and demented patients. Together with studies on GH basal secretion in Alzheimer's disease, this finding suggests that the final consequence of SDAT-related changes in an accentuation of the effects of aging on GH reactivity.

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

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

Trends in searching for new cognition enhancing drugs

1. The great interest for new drugs having cognition enhancing properties is highlighted, particularly for the treatment of dementia of Alzheimer type. 2. A short survey is given of the pharmacological models currently used to mimic cognitive impairment. 3. A systematic survey is given of the major cognition enhancing drugs and of the new compounds showing activity.

Neurochemical characteristics of aluminum-induced neurofibrillary degeneration in rabbits

Aluminum-induced neurofibrillary degeneration in rabbits is known to affect particular populations of neurons. The neurotransmitter alterations which accompany aluminum neurofibrillary degeneration were examined in order to assess how closely they mimic those of Alzheimer's disease. There was a significant reduction in choline acetyltransferase activity in entorhinal cortex and hippocampus as well as significant reductions in cortical concentrations of serotonin and norepinephrine in the aluminum-treated rabbits. Significant reductions in glutamate, aspartate and taurine were found in frontoparietal and posterior parietal cortex. Concentrations of GABA were unchanged in cerebral cortex. Both substance P and cholecystokinin immunoreactivity were significantly reduced in entorhinal cortex but there were no significant changes in somatostatin, neuropeptide Y and vasoactive intestinal polypeptide. The five neuropeptides were unaffected in striatum, thalamus, cerebellum and brainstem. Neurochemical changes were found in the regions with the most neurofibrillary degeneration while regions with little or no neurofibrillary degeneration were unaffected. The reductions in choline acetyltransferase activity, serotinin and noradrenaline suggest that some neuronal populations preferentially affected in Alzheimer's disease are also affected by aluminum-induced neurofibrillary degeneration; however, the cortical somatostatin deficit which is a feature of Alzheimer's disease is not replicated in the aluminum model.

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

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

Cortical somatostatinergic system not affected in Alzheimer's and Parkinson's diseases

A reduction in the levels of somatostatin-like immunoreactivity (SLI) and somatostatin binding sites in the cerebral cortex has been previously reported to occur in Alzheimer's disease (AD) and Parkinson's disease with associated dementia. In the present study, the levels of both SLI and high affinity [3H]somatostatin binding sites have been measured in the frontal (Brodmann area 9) and temporal (Brodmann area 21) cortices in patients with presenile and senile Alzheimer's disease, and in mentally normal and cognitively impaired cases of Parkinson's disease. The results were compared with those obtained from a group of normal patients matched for age and postmortem delay. No significant changes in SLI or somatostatin binding in the frontal and temporal cortex were found between any of the disease groups. These results suggest that involvement of the somatostatinergic system in AD or Parkinson's disease is not a consistent or primary neurochemical feature of these diseases.

Visuospatial learning impairment following lesion of the cholinergic projection to the hippocampus

Ibotenic acid lesions of the vertical limb of the diagonal band of Broca (VDB) in marmosets produced significant depletions in choline acetyltransferase (ChAT) activity and a decrease in acetylcholinesterase (AChE) staining in the hippocampal formation and entorhinal cortex (to which the cholinergic neurones of the VDB project) but not in the neocortex or amygdala. Marmosets with VDB lesions were impaired on acquisition (but not retention) of repeated trial visuospatial tasks. This impairment was ameliorated by pretreatment with the cholinergic agonist pilocarpine indicating (a) that the learning impairment was a consequence of damage to the cholinergic system and (b) that the cholinergic projections exert a modulatory or enabling function on the target areas which can be substituted by a non-impulse-dependent drug action. Unlike marmosets with lesions of the basal nucleus of Meynert (NBM), VDB-lesioned animals were not impaired on learning repeated trial object discrimination and showed no change in general behaviour although they did become hypothermic and mesomorphic. These results are consistent with the suggestion that the hippocampus (perhaps in conjunction with the entorhinal cortex) is concerned primarily with memory for responses but not memory for reward and that lesions of the cholinergic system produce impairments equivalent to the effects of ablation of the terminal areas.

Regional distribution of vasoactive intestinal peptide in brains from normal and parkinsonian subjects

The distribution of vasoactive intestinal peptide (VIP) in the post-mortem human brain was determined by radioimmunoassay using a highly specific antiserum. The detection limit of the assay was 4 fmol/tube. The highest concentrations of VIP were found in the cerebral cortex, amygdala, hypothalamus and hippocampus. The lowest levels of peptide were detected in basal ganglia including caudate nucleus, external pallidum, putamen and substantia nigra. All dilution curves of acetic acid extracts from different brain areas were strictly parallel to the standard curve. Sephadex G-50 gel filtration of frontal cortex extract showed that VIP-like immunoreactivity (VIP-LI) eluted as a major peak comigrating with synthetic hVIP. Detailed mapping of VIP in the human cerebral cortex showed the existence of a rostro-caudal gradient of VIP-LI concentrations: the frontal cortex exhibited the highest VIP levels, the parietal and temporal cortex contained medium values and the occipital cortex contained the lowest VIP levels. The concentrations of VIP-LI were compared in various regions of the human brain from normal and parkinsonian subjects. No significant changes in VIP-LI levels occurred in the brains of patients dying with Parkinson's disease. No difference in VIP levels could be found either when the parkinsonian group was subdivided into nondemented and demented patients. These data indicate that VIP-containing neurons are not affected in parkinsonian patients. Our results also suggest that VIP neuronal systems are not involved in the course of dementing process in Parkinson's disease.

Decreased levels of protein kinase C in Alzheimer brain

Protein kinase C (PK-C) levels were determined using [3H]phorbol-12,13-dibutyrate (PDB) binding and the in vitro phosphorylation of histone H I (III-S), in autopsied human frontal cortex of age- and postmortem time-matched normal and Alzheimer patients. PK-C levels in Alzheimer particulate fractions determined by both methods were about 50% of those in controls. PK-C levels in Alzheimer cytosol fractions were not significantly different from those in controls. In a parallel study, we measured the phosphorylation of a Mr 86,000 protein (P86), the major protein kinase C substrate in the cytosol fraction prepared from Alzheimer frontal cortex, and found it to be reduced to 43% of that in control brains. This reduction in P86 protein phosphorylation compared to controls was not detected in brain samples prepared from demented patients without Alzheimer's disease. We considered 3 extraneous factors (postmortem delay, age and sex) which may have affected the extent of P86 phosphorylation and concluded that the reduced P86 phosphorylation in the Alzheimer samples is not due to any of them. Reduced PK-C levels and Mr 86,000 protein phosphorylation may reflect a biochemical deficit related specifically to the pathogenesis of Alzheimer's disease.

Differential modification of muscarinic cholinergic receptors in the hippocampus of patients with Alzheimer's disease: an autoradiographic study

We have used quantitative light microscopic autoradiographic techniques to analyze changes in muscarinic cholinergic receptors in the hippocampus in Alzheimer type dementia (ATD). The density and distribution of muscarinic cholinergic receptors has been correlated with the density of neurons, neuritic plaques and neurofibrillary tangles in the CA1 subfield of the hippocampus of control and ATD patients. The number of pyramidal cells per mm2 in the CA1 sector was significantly decreased in ATD cases as compared to controls, although there were large variations among cases. The most marked reductions in cell counts were observed in patients with a history of profound dementia. The densities of muscarinic receptors, as well as the proportions of M1 and M2 subtypes, in the CA1 sector and dentate gyrus were not significantly different between ATD and old non-demented patients. Neuritic plaques, even in high numbers, did not affect the density of muscarinic receptors; moreover, the densities of receptors over the neuritic plaques did not differ from the surrounding neuropil. However, in some ATD cases there was a marked decrease in the concentration of these receptors in the CA1 sector and subiculum, with no change in the proportions of muscarinic receptor sybtypes. These patients exhibited frequent extracellular remnants of neurofibrillary tangles (ghost tangles), but scarce neuritic plaques, and were those showing severe losses of pyramidal cells. There was a significant positive correlation between the total concentration of muscarinic receptors in the CA1 and the density of pyramidal cells, suggesting that decreases in receptor concentration result from a severe neuronal loss. We observed that the ratio of muscarinic receptors per pyramidal cell was significantly increased in ATD patients. This might indicate a possible up-regulatory mechanism for muscarinic receptors in the population of remaining neurons in ATD However, decreases of receptor numbers following severe neuronal fall out suggest that compensatory mechanisms are no longer possible in such cases. The question is raised whether these differences between cases reflect different diseases or different stages of the same disease.

VIP-sensitive adenylate cyclase, guanylate cyclase, muscarinic receptors, choline acetyltransferase and acetylcholinesterase, in brain tissue afflicted by Alzheimer's disease/senile dementia of the Alzheimer type

Biochemical parameters were determined in autopsy material from several brain regions of thirteen patients with Alzheimer's disease/senile dementia of Alzheimer type (AD/SDAT) (mean age 75 years) and from brains of ten age-matched controls (mean age 76 years). Choline acetyltransferase specific activity was significantly lower in the nucleus caudatus, putamen, left thalamus, hippocampus and the cortex from gyrus hippocampus and the temporal lobe in AD/SDAT, acetylcholinesterase specific activity was significantly lower in the hippocampus, parietal and left frontal lobe in AD/SDAT samples than in corresponding samples from aged-matched controls. A compensatory increase of muscarinic receptors was found in the nucleus caudatus and left frontal lobe samples in AD/SDAT. Guanylate cyclase activity was not significantly altered in AD/SDAT in the brain regions examined. The basal, non-stimulated activity of adenylate cyclase was significantly (p less than 0.05) elevated in hippocampus samples from AD/SDAT patients and the enzyme activity stimulated by the vasoactive intestinal polypeptide VIP (2 microM) or forskolin (10 microM) was also elevated in AD/SDAT although not significantly.