Neuropeptides in Alzheimer type dementia

Cortical somatostatin, neuropeptide Y, and NADPH diaphorase neurons: normal anatomy and alterations in Alzheimer's disease

Somatostatin and neuropeptide Y are two neuropeptides that are of particular interest in Alzheimer's disease because they are reported to be depleted in cerebral cortex. In the present study we examined somatostatin, neuropeptide Y, and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase neurons in nine cortical regions in both normal and Alzheimer's disease brains. These three neurochemical markers show a high degree of co-localization (greater than 90%) in nonpyramidal neurons that are primarily distributed in cortical layers II-III, V-VI, and, most prominently, in infracortical white matter. The highest cell density was in temporal and parietal association cortex. The major morphological abnormality in Alzheimer's disease brains was a marked pruning and distortion of fiber plexuses with an apparent reduction in fiber density. In contrast, perikaryal density was preserved except for a reduction in parietal association cortex. Approximately 10 to 15% of senile plaques in the inferior temporal gyrus contained abnormal neurites. Additional abnormal collections of neurites without plaque cores were frequently found in layers II-III and V-VI. Neuropeptide Y and somatostatin were co-localized in abnormal neurites, suggesting an origin from local intrinsic neurons in which the two peptides are co-localized. Double immunofluorescence staining for both tau protein, a major antigenic component of paired helical filaments, and either somatostatin or neuropeptide Y showed that these neurons do not contain tau-immunoreactive neurofibrillary tangles. The morphological correlate of reduced somatostatin and neuropeptide Y content in Alzheimer's disease brain therefore appears to be a distortion and reduction in fiber plexuses. In addition, it is apparent that these neurons can develop widespread morphological abnormalities in the absence of neurofibrillary tangle formation.

Somatostatin in neuropsychiatric disorders

1. Somatostatin is a peptide that is widely and discretely distributed throughout the central nervous system. 2. Its relevance to neuropsychiatric disorders is suggested both by the existence of disease-related alterations in somatostatin content in brain and cerebrospinal fluid as well as by the manifold neuroregulatory capabilities of somatostatin and related peptides. 3. This article will summarize the central nervous system effects of somatostatin, identify those neuropsychiatric disorders that are characterized by changes in somatostatin, and review the evidence for and potential significance of decreases in cerebrospinal fluid somatostatin in depression.

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.

Comparison of DSIP- (delta sleep-inducing peptide) and P-DSIP-like (phosphorylated) immunoreactivity in cerebrospinal fluid of patients with senile dementia of Alzheimer type, multi-infarct syndrome, communicating hydrocephalus and Parkinson's disease

The concentrations of delta sleep-inducing peptide (DSIP)-like (DSIP-LI) and P-DSIP-like (phosphorylated, Ser7) immunoreactivity (P-DSIP-LI) were measured by specific radioimmunoassay in the cerebrospinal fluid (CSF) of patients with senile dementia of the Alzheimer type [SDAT, subdivided into early (S1), middle (S2) and late dementia (S3)], multi-infarct dementia (MD), Parkinson's disease (PD), vascular disease (VD) and communicating hydrocephalus (H), as well as in control patients (C1, C2). Mean DSIP-LI and P-DSIP-LI concentrations were found to be significantly higher in the elderly control group (C1, mean age 83 +/- 5 years) than in the middle-aged control group (C2, mean age 40 +/- 16 years). DSIP-LI and P-DSIP-LI were positively correlated with age in both control groups. Significant decreases of DSIP-LI compared with age-matched controls (C1) were observed for S2, S3, MD, PD, VD and H. In contrast, no significant differences corresponding to pathology were found for P-DSIP-LI.

Reduced somatostatin-like immunoreactivity in the brain of dogs with an Eck fistula

Somatostatin-like immunoreactivity (SLI) in the brains of Eck fistula dogs, prepared as an experimental model of hepatic encephalopathy, was measured to investigate the pathogenesis of hepatic encephalopathy. The values were studied in comparison with the concentrations of amino acids where the imbalance was suggested to cause hepatic encephalopathy. SLI levels in the parietal and temporal cortex of Eck fistula dogs were 76.0 +/- 12.0 (mean +/- S.E.M., fmol/mg wet wt.) and 113.4 +/- 23.7, and those of controls were 144.0 +/- 11.8 and 186.9 +/- 19.2, respectively, the differences being statistically significant (P less than 0.005, P less than 0.05). No significant difference in gel filtration profiles of SLI in extracts from parietal and temporal cortex was observed between Eck fistula dogs and controls. Tyrosine and phenylalanine, which are suggested to be precursors of false neurotransmitters, were significantly increased in the parietal cortex of the Eck fistula dogs, and phenylalanine was significantly increased in the temporal cortex of these dogs. There was a significant negative correlation between SLI and phenylalanine concentrations in the parietal and temporal cortex (r = -0.7171, P less than 0.01). These results suggest that the reduced SLI may be one of the factors which cause the neuropsychiatric disturbances in hepatic encephalopathy.

An immunohistochemical study of pro-somatostatin-derived peptides in the human brain

The distribution of pro-somatostatin-derived-peptide-positive profiles was examined by indirect immunohistofluorescence in nine post-mortem human brains (age 58-73 years). Three specific antisera were used for this study which recognize, respectively, somatostatin-28, somatostatin-28 (1-12) and somatostatin (1-14). Pro-somatostatin-derived-peptide-positive immunoreactive profiles were observed throughout the neuraxis. Cell bodies were found within archeo-, paleo- and neocortical areas, the subcortical white matter, in the nucleus accumbens, caudate nucleus and putamen, as well as in the hypothalamus, the reticular thalamic nucleus and the reticular formation of the brainstem. Fibers and terminals were seen in the same areas as well as in various thalamic nuclei, in the brainstem and spinal cord. Pro-somatostatin-derived-peptide-positive fibre tracts include the bed nucleus of the stria terminalis, the diagonal band of Broca, the stria medullaris, the inter-thalamic adhesion, the posterior commissure and the spinothalamic tract. Furthermore, differences between human and animal brains were noted and some somatostatin systems reported which may be implicated in certain human neuropathological states.

The regional distribution of somatostatin and neuropeptide Y in control and Alzheimer's disease striatum

Somatostatin-like immunoreactivity (SLI) and neuropeptide Y-like immunoreactivity (NPYLI) were measured in subdissections of both normal and Alzheimer's disease (AD) striatum at 5 coronal levels. Concentrations of both neuropeptides were relatively homogeneously distributed in the coronal and anterior-posterior planes except for a trend towards increased concentrations in the tail of the caudate and the posterior putamen. The nucleus accumbens showed 2-3-fold higher concentrations of both SLI and NPYLI than the rest of the striatum. There were no significant differences between control and AD brains. The high concentrations of SLI and NPYLI in the nucleus accumbens suggest that this region may receive somatostatin-neuropeptide Y afferents and that somatostatin and neuropeptide Y may play a role in the modulation of motor activity.

Neurotensin in the human brain

The localization of neurotensin-immunoreactive sites in the adult human brain was investigated by the indirect immunoperoxidase method of Sternberger [Sternberger (1979) Immunocytochemistry. Wiley, New York]. Our results demonstrate a widespread, albeit uneven occurrence of neurotensin-immunoreactive cells and processes throughout the central nervous system. Immunoreactive cells are prominent in the medial hypothalamus and in various regions of the limbic system, including the amygdaloid body, septal area, bed nucleus of the stria terminalis and piriform cortex. A few cells were also found in the dorsal synencephalon, superior colliculus, periaqueductal grey and spinal trigeminal nucleus. The distribution of immunoreactive fibres corresponds well with that reported for rodents. Areas with the highest concentration of neurotensin-immunoreactive processes included all the areas where immunoreactive neurons were found and, in addition, periventricular thalamic nuclei, the sublenticular region, lateral parts of the brainstem reticular formation and the vagus-solitarius complex. Comparison mapping studies of melanin-containing neurons on sections treated with neurotensin antiserum revealed an anatomical relation between almost all the catecholaminergic cell clusters with peptide-containing fibres.

Aminergic systems in Alzheimer's disease and Parkinson's disease

Biochemical markers for serotoninergic and catecholaminergic neurons in frontal and temporal poles were examined post mortem in brains of patients with Alzheimer's disease, Parkinson's disease, and the two combined. Binding of [3H] citalopram to serotoninergic uptake sites and levels of serotonin were decreased by 40 to 50% in brains of persons in each disease category. In contrast, significant reductions of catecholaminergic markers were not detected. In all three disease groups, the choline acetyltransferase activity was reduced by 50 to 60%. Binding sites for adenosine (A1), muscarinic cholinergic, phencyclidine, beta-adrenergic, and calcium antagonist receptors were unchanged. We conclude that substantial damage to serotoninergic neurons occurs in persons with Parkinson's and Alzheimer's diseases.

Somatostatin 28 and neuropeptide Y innervation in the septal area and related cortical and subcortical structures of the human brain. Distribution, relationships and evidence for differential coexistence

Somatostatin 28- and neuropeptide Y-containing innervations were mapped in the human medial forebrain (eight control brains) with immunohistochemistry, using the sensitive avidin-biotin-peroxidase method. Peptidergic perikarya and fibers had an extensive distribution: they were densest in the ventral striatum (nucleus accumbens, olfactory tubercle and bed nucleus of the stria terminalis) and infralimbic cortex, of intermediate density in the medial septal area and of lowest density in the dorsal and caudal lateral septal nucleus. Somatostatin-like immunoreactive perikarya and fibers were generally more numerous than the neuropeptide Y-like immunoreactive ones, but more faintly labeled. Their pattern of distribution was strikingly similar in some of the limbic structures studied but clearly distinct in others. Excellent overlap of neuropeptide Y and somatostatin-like immunoreactivity was detected in: (1) the medial septal area, where innervation occasionally formed perivascular clusters; (2) the nucleus accumbens and olfactory tubercle, characterized by dense patchy innervation; and (3) the laterodorsal septal nucleus, scarcely innervated. In the latter structures, most peptidergic neurons were double-labeled. On the other hand, both peptidergic innervations clearly differed in the lateroventral septal nucleus and the bed nucleus of the stria terminalis which contained distinct clusters of somatostatin-like immunoreactive neurons devoid of neuropeptide Y-like immunoreactivity. Also, the perineuronal and peridendritic axonal plexuses ('woolly fibers') present in these structures were only labeled with somatostatin. In the infralimbic cortex, the relation between the peptides varied according to the cortical laminae. Coexistence of somatostatin and neuropeptide Y frequently occurred in layer VI and in the subcortical white matter, whereas layer V and particularly layers II and III contained a contingent of neurons labeled only with somatostatin. Dense horizontal terminal networks in layers I and VI however were similar for both peptides. These findings support the existence of two different types of somatostatin-like immunoreactive perikarya as regards colocalization with neuropeptide Y. Their particular topographical segregation within the cortical and subcortical structures analysed suggest that they could have different connections and functional properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin immunoreactive neurons in the human hippocampus and cortex shown by immunogold/silver intensification on vibratome sections: coexistence with neuropeptide Y neurons, and effects in Alzheimer-type dementia

The distribution of somatostatinlike immunoreactivity was studied in the hippocampal formation, retrohippocampal region, and temporal cortex in the human brain. Tissues from surgical biopsy and postmortem cases were used, and the immunogold/silver method on vibratome sections was introduced for routine applications in conjunction with primary antisera that recognise somatostatin-14 or somatostatin-28. Somatostatin-28 antisera readily stained numerous neurons, dendrites, and extensive axonal networks throughout the hippocampus and neighbouring cortex. Liquid phase absorption provided controls for specificity. The most prominent accumulations of somatostatin immunoreactive neurons and axons occurred in the hilus of the area dentata, in CA1, and in the entorhinal and perirhinal cortices. Axonal plexuses occurred throughout the hippocampal subfields but were particularly dense in those regions rich in somatostatin neurons. The distribution of somatostatin immunoreactive neurons and fibers parallels the distribution of neuropeptide Y (NPY) neurons and fibers in the hippocampus and cerebral cortex to a remarkable extent. Double labelling experiments with antisera against neuropeptide Y and somatostatin indicate a considerable frequency of coexistence of the two peptides in single neurons, particularly in large multipolar cortical neurons and also in the small bipolar white matter neurons. Regional variations exist in the amounts of coexistence found in the hippocampal subfields; somatostatin-NPY coexistence is particularly high in the hilus of the area dentata, the subicular complex, and the deep layers of the entorhinal and perirhinal cortices. In the hippocampi and temporal cortices in cases of Alzheimer-type dementia compared to those of age-matched control brains, there is a significant to severe loss of somatostatin immunoreactive neurons and axons. This loss is most severe in those regions with the highest indices of neurofibrillary tangles and neuritic plaques-the hilus of the area dentata, CA1, and the entorhinal and perirhinal cortices. Surviving somatostatin neurons are distorted with short dendrites and truncated axons. Neuritic plaques identified on double label experiments with thioflavin include somatostatin axons but not neurons.

Subset of neurons characterized by the presence of NADPH-diaphorase in human substantia innominata

The substantia innominata encompasses an area of the basal forebrain that is ventral to the lenticular nucleus and anterior commissure, medial to the claustrum and external capsule, and lateral to the hypothalamus. The nucleus basalis of Meynert consists primarily of large acetylcholinesterase (AchE)-positive neurons embedded within the substantia innominata. Damage to these neurons may be important in the pathogenesis of cortical dysfunction in Alzheimer's disease. In order to characterize other neuronal elements in the substantia innominata and their relationship to the nucleus basalis, we chose to study a biochemically distinct neuronal subset containing the enzyme nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d). The substantia innominata was blocked from six normal brains obtained postmortem and fixed in neutral-buffered formalin at 4 degrees C for 48 hours. Free-floating 50-micron sections from several levels were stained for NADPH-d or AchE activities. Selected sections were double stained for NADPH-d and AchE. NADPH-d activity was present in a network of pleomorphic neurons that extended through all levels of the substantia innominata and into the striatum and amygdala. NADPH-d neurons were particularly numerous at the level of the anterior commisure and were closely associated with the cholinergic neurons of the nucleus basalis. They were not seen in the ventral pallidum, or the vertical limb of the diagonal band of Broca or in the islands of Calleja. The cell bodies of NADPH-d neurons were quite varied in shape, ranging from ovoid to fusiform, and about half the cells were bipolar. Where neuronal density was high, their dendrites formed an interlacing pattern. NADPH-d-positive fibres were seen coursing through the external capsule, hypothalamus, and amygdala. This novel set of neurons in the substantia innominata may be part of a more extensive network that interacts with the magnocellular basal forebrain system at the level of the nucleus basalis. Whether other neurotransmitters are present within these neurons and whether NADPH-d neurons are involved in Alzheimer's disease remain to be elucidated.

A quantitative morphometric analysis of the neuronal and synaptic content of the frontal and temporal cortex in patients with Alzheimer's disease

A quantitative morphometric analysis was used to estimate neurone and synapse densities in cerebral cortical biopsy tissues from patients with dementia under 65 years of age and pathologically verified as suffering from Alzheimer's disease. Estimates of the numerical density of neurones and synapses were made in layers II-III and V of both frontal and temporal cortex. A greater loss of synapses than that of neurones was found in Alzheimer's disease, amounting to a minimum (uncorrected for atrophy) of 25% in layers II-III and 36% in layer V of the temporal cortex, and 27% in layer V of the frontal cortex. Values of synapse to neurone ratio also demonstrated this greater loss of synapses, there being on average 38% fewer synapses associated with each surviving neurone in layers II-III of the temporal cortex, 30% fewer in layer V, and a deficit of 14% in layer V of the frontal cortex. It is concluded that a major loss of synapses occurred in this group of patients with Alzheimer's disease, probably at an early stage of the disease, and that the loss is likely to form a fundamental part of the pathological process that underlies the cortical damage of this condition.

Somatostatin content and release measured in cerebral biopsies from demented patients

Somatostatin-like immunoreactivity (SLIR) has been assayed in frontal and temporal cortex obtained at diagnostic craniotomy and post-mortem from patients with histologically verified Alzheimer's disease. SLIR content was not significantly different from controls in the frontal and temporal lobes, except in the temporal cortex post-mortem. The K+-stimulated release of endogenous SLIR from tissue prisms ('mini-slices') prepared from neocortex obtained at diagnostic craniotomy from Alzheimer patients was not below the control values. Indices of cholinergic varicosities in similar samples from the frontal and temporal lobes are reduced; accordingly, somatostatin does not seem to be as prominently involved in these regions. Patients with Alzheimer's disease underwent neuropsychological assessment shortly before sampling the temporal lobe. Scores for WAIS full scale and the verbal subscale and the Token Test (measure of language comprehension) significantly correlated with the SLIR content; mean values (fmole/mg protein) were 817, 1468 and 1363 for aphasic and non-aphasic Alzheimer patients and controls, respectively. Ventricular fluid obtained from Alzheimer patients during surgery, did not have a significantly different SLIR content compared to controls. SLIR contents of ventricular fluid and neocortex from demented patients, without any specific histological changes in the sample obtained at diagnostic craniotomy, were also not significantly different from controls. Previously, we have shown that these demented patients, as well as those with histologically verified Alzheimer's disease, have a reduced SLIR content of lumbar fluid so it seems that somatostatin neurones located outside the frontal and temporal lobes are affected relatively early in the disease process.

Pharmacological studies of somatostatin and somatostatin-analogues: therapeutic advances and perspectives

This article is aimed at reviewing and analyzing studies that are related to the possible therapeutic use of a potent and ubiquitously-distributed hormone--somato-statin (SS-14), and its analogues. Administration of these substances has provided beneficial effects in treating acromegaly, gastro-intestinal hemorrhagic and hypersecretory disorders, acute pancreatitis, diabetes mellitus, and certain types of cancer. Further studies with SS-14-analogues might provide new therapies for treating certain life-threatening disorders of man.

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

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

Regional distribution of high-affinity [3H]somatostatin binding sites in the human brain

The distribution of high-affinity binding sites for [3H]somatostatin has been studied in membrane preparations from a number of regions of normal human brain. The highest densities of binding sites (greater than 48 fmol/mg protein) were found in the cerebral and cerebellar cortices and the hippocampus, with intermediate binding densities (30-46 fmol/mg protein) being present in the basal ganglia, amygdala, septum and claustrum. The lowest densities of binding sites (less than 14 fmol/mg protein) were observed in the hypothalamus, thalamus and substantia nigra. The binding of [3H]somatostatin in both the frontal cortex and cerebellar cortex demonstrated pharmacological specificity, since somatostatin-28, but not somatostatin-28(1-12) or Des AA1,2,4,5,12,13, D-Trp8-somatostatin, competed for the binding sites. Scatchard analysis of the binding in both frontal cortex and cerebellar cortex revealed the presence of two classes of high-affinity binding sites.

Choline acetyltransferase immunoreactivity in neuritic plaques of Alzheimer brain

We have observed dystrophic choline acetyltransferase (ChAT)-positive processes surrounding the amyloid core of neuritic plaques in human neocortex, amygdala and hippocampus, using a polyclonal anti-human ChAT antiserum. These data, and those from studies of the aged monkey by other investigators, provide a morphologic counterpart for the biochemical abnormality of the cholinergic system in Alzheimer's disease and senile dementia of the Alzheimer type.

Neuropeptides in neurological disease

Neuropeptides are widely distributed in the central nervous system, where they serve as neuroregulators. Recent interest has focused on their role in degenerative neurological diseases. We describe the normal anatomy of neuropeptides in both the cerebral cortex and basal ganglia as a framework for interpreting neuropeptide alterations in Alzheimer's disease (AD), Huntington's disease, and Parkinson's disease. Concentrations of cortical somatostatin are reduced in AD and in dementia associated with Parkinson's disease. Concentrations of neuropeptide Y and corticotropin-releasing factor are also reduced in AD cerebral cortex. The reduced cortical concentrations of somatostatin and neuropeptide Y in AD cerebral cortex may reflect a loss of neurons or terminals in which these two peptides are co-localized. In Huntington's disease, basal ganglia neurons in which somatostatin and neuropeptide Y are co-localized are selectively preserved. Cerebrospinal fluid concentrations of neuropeptides in AD reflect alterations in cortical concentrations. Improved understanding of neuropeptides in degenerative neurological illnesses will help define which neuronal populations are specifically vulnerable to the pathological processes, and this could lead to improved therapy.

Somatostatin and Alzheimer's disease: a hypothesis

Recent data suggest a disturbance of some brain somatostatin neurons in Alzheimer's disease. Moreover, some endocrine activities known to be regulated by somatostatin, such as growth hormone, thyroid-stimulating-hormone, somatomedins, as well as insulin and glucose metabolism, also seem to be affected in some patients. It is speculated that these changes are due to a global CNS and endocrine somatostatin defect in Alzheimer's disease and that the described endocrine imbalance may indirectly be responsible for at least part of the CNS pathology.

Widespread reduction of somatostatin-like immunoreactivity in the cerebral cortex in Alzheimer's disease

Although several studies have documented reduced concentrations of somatostatin-like immunoreactivity (SLI) in the cerebral cortex in Alzheimer's disease, there is controversy concerning the extent and importance of these changes. We measured SLI in brains obtained post mortem from 12 patients with pathologically confirmed Alzheimer's disease and from 13 neurologically normal controls. All major cortical and subcortical regions were examined. Widespread reductions of SLI in Alzheimer's disease cerebral cortex were found, with the most profound changes seen in temporal lobe; but there also were major reductions in both the frontal and occipital cortex. There were no significant reductions in subcortical regions. Characterization of SLI by high-pressure liquid chromatography showed no significant difference in profiles between Alzheimer's disease and control frontal cortex. These results suggest that the reduction in somatostatin immunoreactivity in Alzheimer's disease may be caused by degeneration of intrinsic somatostatin cortical neurons.

Perforant pathway changes and the memory impairment of Alzheimer's disease

The perforant pathway is a large neuronal projection that arises from layers II and III of the entorhinal cortex of the parahippocampal gyrus. It is the principal source of cortical input to the hippocampal formation. In 11 cases of Alzheimer's disease, we have found that neurofibrillary tangles develop in the cells of origin of the perforant pathway. In addition, the termination zone of the perforant pathway, in the outer two thirds of the molecular layer of the dentate gyrus, contains a distinct layer of neuritic plaques. None of the 8 control subjects had such changes. These profound alterations effectively disconnect the hippocampal formation from the association and limbic cortices. Because of the central role of the hippocampus and parahippocampal gyrus in learning, it is likely that pathological changes in the perforant pathway, by precluding normal hippocampal operation, account for some aspects of the memory impairment in Alzheimer's disease.

Neurofibrillary degeneration of cholinergic and noncholinergic neurons of the basal forebrain in Alzheimer's disease

Two principal features of Alzheimer's disease (AD) are (1) the occurrence of neurofibrillary tangles (NFTs) and senile plaques, and (2) the loss of cortical cholinergic activity because of dysfunction of neurons in the basal forebrain cholinergic system. The relationship of these two abnormalities is an unresolved issue in the pathology of AD. We used polyclonal antibodies specific for paired helical filaments (PHFs), combined with acetylcholinesterase (AChE) histochemistry, to assess the cytoskeletal changes of cholinergic and noncholinergic neurons in the basal forebrain in AD. In both sporadic and familial AD, the nucleus basalis of Meynert (nbM) showed a marked decrease in AChE-positive (AChE+) perikarya and abundant immunoreactive NFTs. In double-labeling studies of the nbM, PHF reactivity was found both in surviving AChE+ neurons and in many AChE- NFTs that were not associated with microscopically recognizable cell structures. Some surviving AChE+ perikarya did not contain NFTs. Numerous NFTs and senile plaques were identified by PHF immunoreactivity in other basal forebrain areas, including subnuclei of the amygdala that showed low or absent AChE activity. We conclude that the dysfunction and death of cholinergic neurons in the nbM is associated with extensive NFT formation, including apparently residual NFTs in loci where nbM neurons once existed; and many noncholinergic neurons and neurites in the basal forebrain show NFT and senile plaque formation. The cytopathology of AD involves neurons of varying transmitter specificities, including cholinergic neurons in the basal forebrain.

Decreased somatostatin immunoreactivity but not neuropeptide Y immunoreactivity in cerebral cortex in senile dementia of Alzheimer type

The content of two neuropeptides, somatostatin (SRIF) and neuropeptide Y (NPY) has been determined in two cerebral cortical areas of Alzheimer's disease brain and in age-matched control brains. The content of SRIF-like immunoreactivity (SRIF-LI) was found to be decreased in Alzheimer temporal cortex (Brodmann area 21) compared to control temporal cortex. The decreased content of SRIF was significantly correlated with the observed number of neuritic plaques and neurofibrillary tangles. No difference was observed in NPY-LI between Alzheimer cerebral cortex and control cortex. Furthermore, no correlations were observed between NPY content and plaque count, neurofibrillary tangle estimate or SRIF content despite widespread reports of NPY/SRIF coexistence.

NADPH diaphorase histochemistry in the macaque striate cortex

The distribution of the enzyme dihydronicotinamide adenine dinucleotide phosphate (NADPH) diaphorase was examined in the striate cortex of the rhesus monkey. The pattern of activity in the neuropil matched that of cytochrome oxidase in adjacent sections and the enzymes were similarly modulated by monocular deprivation. Scattered individual cells were also intensely positive for NADPH diaphorase. Labelled cells were most common in the white matter and layers 2 and 3; they were least common in layers 4 and 5. Diaphorase cells were morphologically diverse, but no pyramidal or spiny cells were labelled. Labelled cells often had multiple varicose processes, which extended laterally for over 1 mm. Although the function of this enzyme is unknown, the morphology and distribution of the diaphorase-positive cells resembles published reports of cortical cells containing somatostatin, avian pancreatic polypeptide, and neuropeptide Y-like immunoreactivity, and NADPH diaphorase is colocalized with these substances in the rodent striatum (S.R. Vincent, O. Johansson, T. Hökfelt, L. Skirboll, R.P. Elde, L. Terenius, J. Kimmel, and M. Goldstein, J. Comp. Neurol. 217:252-263, '83).

Subcellular pathology of human neurodegenerative disorders: Alzheimer-type dementia and Huntington's disease

Activities of enzyme markers of subcellular organelles have been measured in brain tissue from subjects with Alzheimer-type dementia (ATD) and Huntington's disease (HD). Significant increases in the activity of the lysosomal enzyme beta-glucuronidase were observed in both ATD temporal cortex and HD putamen. It is suggested that beta-glucuronidase activity may be a useful biochemical indicator of cellular damage in the CNS. A significant reduction in neutral alpha-glucosidase activity was observed in ATD temporal cortex and HD putamen. This change may reflect an alteration in glycoconjugate processing and may relate to the susceptibility of neurones to the degenerative processes of ATD and HD.

Neuropeptide Y immunoreactivity is reduced in cerebral cortex in Alzheimer's disease

Neuropeptide Y is a 36-amino acid peptide that is found in high concentrations in cerebral cortex and is contained in cortical neurons. We measured concentrations of this peptide in postmortem tissue from patients with Alzheimer's disease and controls using a sensitive and specific radioimmunoassay. High-performance liquid chromatography showed that more than 95% of immunoreactivity co-migrated with synthetic standards in both Alzheimer's disease and control frontal cortex. Significant reductions in neuropeptide Y-like immunoreactivity were found in eleven cortical regions, the hippocampus, and the locus ceruleus. The regions particularly affected included the temporal lobe, frontal lobe, and occipital cortex. As neuropeptide Y is co-localized with somatostatin in a considerable proportion of cortical neurons, the loss of immunoreactivity may in part reflect degeneration of these neurons. Further study of the selective vulnerability of these neurons in Alzheimer's disease cortex may provide clues to the nature of the underlying disease process.

Patients with Alzheimer's disease show an increased content of 15 Kdalton somatostatin precursor and a lowered level of tetradecapeptide in their cerebrospinal fluid

The relative proportions of both somatostatin-14 and its precursors somatostatin-28 and the 15 Kdalton prosomatostatin were evaluated by radioimmunoassay in the cerebrospinal fluid of patients with Alzheimer's disease. It was observed that the patients have a lowered content in the tetradecapeptide somatostatin while they exhibit a significant increase in unprocessed 15 Kda precursor. These results indicate that these patients possess impaired processing mechanisms which may be responsible for the lowered content in mature somatostatin-14. These observations may provide a valuable test for the ante-mortem diagnosis of the disease. They are discussed in connection with others suggesting that Alzheimer's patients may be selectively altered in their somatostatinergic neurones of their cerebral cortex (Morrison et al. (1985) Nature 314, 90-92. Roberts et al. (1985) Nature 314, 92-94).

Extrahypophyseal distribution of alpha-melanocyte stimulating hormone (alpha-MSH)-like immunoreactivity in postmortem brains from normal subjects and Alzheimer-type dementia patients

Using a sensitive double-antibody solid-phase enzyme immunoassay method alpha-melanocyte stimulating hormone-like immunoreactivity (alpha-MSH-LI) was measured in 21 regions of postmortem brains from 8 normal subjects and 5 patients with Alzheimer-type dementia (ATD). In the brains from the normal subjects, the highest concentration of alpha-MSH-LI was found in the hypothalamus. Relatively high concentration were also measured in the locus coeruleus, substantia innominata, substantia nigra, amygdala and medial nucleus of thalamus. alpha-MSH-LI in other regions was approximately 1/100 of the hypothalamic content. This data is consistent with the existence of alpha-MSH in extrahypophyseal regions and indicates its regional distribution in the human brain. In the Alzheimer brains, although the temporal cortex and hippocampus had normal concentrations of alpha-MSH-LI, the cingulate cortex, caudate and substantia nigra showed significantly lower concentrations of alpha-MSH-LI than those of the control brains. This data suggests that further studies of alpha-MSH content in a larger number of ATD brains would be useful.

A comparison of regional somatostatin and neuropeptide Y distribution in rat striatum and brain

Somatostatin-like immunoreactivity (SLI) and neuropeptide Y-like immunoreactivity (NPYLI) were detected using specific radioimmunoassays in extracts from rat brain. Since we have previously found a topographic distribution of SLI in rat striatum the distribution of NPYLI was examined in the same regions. NPYLI showed an identical distribution to SLI in rat striatum and levels were significantly correlated (r = 0.93, P less than 0.01). Concentrations of both neuropeptides were consistently highest in ventromedial striatum and nucleus accumbens while they were lowest in dorsolateral striatum. These findings provide further evidence of neurochemical heterogeneity in the striatum. Concentrations of NPYLI and SLI were also significantly correlated in cerebral cortex (r = 0.99, P less than 0.01). Concentrations of NPYLI were generally higher than SLI and showed a similar predilection for limbic system nuclei. The present findings support the concept that somatostatin and neuropeptide Y may be co-localized in both striatal and cortical neurons.

Retrograde changes in the nucleus basalis of the rat, caused by cortical damage, are prevented by exogenous ganglioside GM1

In rats with extensive unilateral cortical damage, retrograde effects upon the cholinergic cells of the basal nucleus were observed. Cells of the basal nucleus stained immunocytochemically for choline acetyltransferase were shrunken and choline acetyltransferase enzymatic activity in that region was reduced. Both these effects could be prevented by the administration of the ganglioside GM1.

Learning impairment following lesion of the basal nucleus of Meynert in the marmoset: modification by cholinergic drugs

Five common marmosets (Callithrix jacchus) received unilateral ibotenic acid lesions of the basal nucleus of Meynert (nBM). Seven days later, choline acetyltransferase activity was significantly reduced by 50% in the frontal and temporal neocortex, 40% in the amygdala, and approximately 30% in the motor, parietal and occipital cortex in the ipsilateral hemisphere. Four marmosets receiving equivalent bilateral ibotenic acid lesions were severely impaired on new visual object discrimination learning and on relearning an object discrimination learnt prior to surgery when compared with operated controls. New learning in lesioned animals was substantially improved by i.m. administration of the cholinergic agonist arecoline. Lesioned animals' learning ability improved with time but these animals were then differentially sensitive to the disruptive effect of scopolamine on discrimination learning. These results show that lesions of the nBM which destroy the rising cholinergic pathways impair learning ability but that this ability can be substantially restored by administration of a cholinergic agonist.

Distribution of altered hippocampal neurons and axons immunoreactive with antisera against neuropeptide Y in Alzheimer's-type dementia

This paper provides detailed information on the distribution of neuropeptide tyrosine (neuropeptide Y; NPY) immunoreactive neurons and fibers in the hippocampal region of eight neuropathologically confirmed cases of Alzheimer's-type dementia (ATD) at postmortem. These neuronal networks are detected by a polyclonal antibody raised against the unconjugated peptide and controls were obtained by using liquid phase absorption immunocytochemistry. The description covers the subfields area dentata, CA3 and CA1, the subicular complex, and the entorhinal area. The hippocampal regions in which the NPY-i neuron networks are most severely affected are the hilus, CA1, the parasubiculum, and the entorhinal cortex. Less obvious reductions occurred in CA3, subiculum, and the presubiculum. Parallel semiquantitative estimates were made of the numbers of neuritic plaques and neurofibrillary tangles in the other hippocampus of the brains in every ATD case. The areas of heaviest pathological changes by these indices are CA1 and the entorhinal cortex. The subicular complex CA3 and the area dentata are less affected. These findings show that the areas with the most severe loss of NPY-i neurons and axons, CA1 and the entorhinal cortex, are the same as those areas most severely affected by the other indices of ATD. Thus NPY-i networks are involved in the ATD disease process. However, other NPY-i networks survive, in some subfields better than in others. The cumulative evidence suggests a population of hippocampal peptide neurons that are remarkably resistant in terminal neurological disease. These neurons have the capability to participate in the maintenance of minimal functioning circuits in target areas of the disease and as such hold significant links for our understanding of synaptic plasticity in disease.

Cerebrospinal fluid somatostatin and psychiatric illness

Somatostatin is a tetradecapeptide that is assuming increasing importance as a regulator of central nervous system activity. Originally identified as the hypothalamic growth hormone release-inhibiting factor, somatostatin has subsequently been shown to be extensively and selectively distributed throughout the central nervous system, to alter neuron excitability, to regulate and be regulated by the activity of classical neurotransmitters and neuropeptides, to exert a number of direct behavioral actions, and to display neuropsychiatric disorder-related alterations. In this article, a three-part study of cerebral spinal fluid (CSF) somatostatin in affective illness and schizophrenia is presented. In part 1, significant reductions in CSF somatostatin were observed in 49 bipolar and unipolar depressed patients relative to 47 controls. Values during depression were also significantly lower than those observed in affective disorder during the improved state or in schizophrenia. Diurnal studies involving paired AM and PM lumbar punctures revealed that depressed patients and normal volunteers had similar somatostatin values in the evening, despite having significantly different values in the morning. In part 2, the effects of several psychopharmacological agents on CSF somatostatin were examined, particularly the tricyclic anticonvulsant carbamazepine. A significant reduction of CSF somatostatin during treatment with carbamazepine was observed. The effect of carbamazepine on somatostatin could be related to its anticonvulsant, analgesic, or psychotropic effects. Part 3 deals with somatostatin as a major regulator of hypothalamic-pituitary-adrenal (HPA) axis activity. Somatostatin affects HPA activity by inhibiting, at a number of cellular levels, the stimulated release of adrenocorticotrophic hormone (ACTH) from the pituitary. A significant negative relationship between CSF somatostatin and the postdexamethasone plasma cortisol level in 22 depressed and 16 schizophrenic patients was observed. This relationship between low CSF somatostatin and escape from dexamethasone suppression was observed irrespective of diagnosis (i.e., depression or schizophrenia). Thus, there is indirect supporting evidence for a role for somatostatin dysregulation in the most consistently observed biological abnormality in depression, escape from dexamethasone suppression. Further study of somatostatin in neuropsychiatric disorders, and particularly depressive illness, offers great promise for better understanding their underlying affective, vegetative, cognitive, and physiological dysregulations.

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

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

Reciprocal changes in corticotropin-releasing factor (CRF)-like immunoreactivity and CRF receptors in cerebral cortex of Alzheimer's disease

Alzheimer's disease is a progressive degenerative disease of the nervous system characterized neuropathologically by the presence of senile plaques and neurofibrillary tangles in amygdala, hippocampus and neocortex. Dysfunction and death of basal forebrain cholinergic neurones projecting to forebrain targets are associated with marked decreases in cholinergic markers, including the activity of choline acetyltransferase (ChAT). Although cortical levels of somatostatin and somatostatin receptors are reduced in Alzheimer's, no consistent changes have been reported in other neuropeptide systems. We have now examined in control and Alzheimer's brain tissues pre- and postsynaptic markers of corticotropin-releasing factor (CRF), a hypothalamic peptide regulating pituitary-adrenocortical secretion which also seems to act as a neurotransmitter in the central nervous system (CNS). We have found that in Alzheimer's, the concentrations of CRF-like immunoreactivity (CRF-IR) are reduced and that there are reciprocal increases in CRF receptor binding in affected cortical areas. These changes are significantly correlated with decrements in ChAT activity. Our results strongly support a neurotransmitter role for CRF in brain and demonstrate, for the first time, a modulation of CNS CRF receptors associated with altered CRF content. These observations further suggest a possible role for CRF in the pathophysiology of the dementia. Future therapies directed at increasing CRF levels in brain may prove useful for treatment.

Somatostatin binding sites in human and monkey brain: localization and characterization

A radioiodinated analogue of somatostatin 28, 125I [Leu8,D-Trp22,Tyr25] SS-28, was used to localize and characterize somatostatin binding sites in both human and monkey brain. High-affinity binding sites (approximately 1 nM) were found in cerebral cortex. The highest binding was in cerebral cortex with intermediate binding found in hippocampus, striatum, and amygdala and low binding in hypothalamus and brainstem. There was a rough correlation between somatostatin receptor binding and concentrations of somatostatin-like immunoreactivity (SLI) in human brain. Somatostatin receptors were stable for up to 24 h in an animal model simulating human autopsy conditions and there was no correlation between postmortem interval and receptor binding in human brain. Pharmacologic characterization in human cortex showed that there was a correlation between the inhibition of receptor binding by somatostatin analogues and their known abilities to inhibit growth hormone secretion. These findings demonstrate that a highly specific membrane-associated receptor for somatostatin is present in both monkey and human brain. Examination of somatostatin receptor binding in Alzheimer's disease and Huntington's disease may improve understanding of the role of somatostatin in both these illnesses.

High-molecular-weight forms of somatostatin are reduced in Alzheimer's disease and Down's syndrome

Four molecular forms of somatostatin-like immunoreactivity (SOM-LI) are present in the human temporal cortex: SOM-14, SOM-28 and high-molecular-weight forms (HMW-SOM) of 7500 and 12,000 daltons. SOM-14 and HMW-SOM are depleted in cortical tissue from cases of pre-senile Alzheimer-type dementia (ATD), but there is a disproportionate reduction in HMW-SOM. In cases of Down's syndrome (DS) with the neuropathological and neurochemical changes of ATD, the total concentration of SOM-LI was similar to that in control cases and the proportions of molecular forms present were comparable. However, there was a significant reduction in the concentration of HMW-SOM. These results show that ATD and DS may share a common abnormality in the biosynthesis and/or post-translational processing of cortical SOM.

The selectivity of the reduction of serotonin S2 receptors in Alzheimer-type dementia

The high-affinity binding of thirteen ligands to putative neurotransmitter receptors was studied in temporal cortex of control and Alzheimer-type dementia (ATD) patients. A selective reduction of serotonin S2 receptors was observed in the ATD patients, to 57% of controls with no change in S1 receptors. Of the other ligand binding sites studied, only 3H-flunitrazepam binding was significantly reduced, to 84% of controls. Ligand binding sites which were unchanged in ATD temporal cortex included those labelled by adrenergic, adenosine, histamine, opiate, GABA, benzodiazepine and cholinergic ligands.

Changes in nicotinic and muscarinic cholinergic receptors in Alzheimer-type dementia

Nicotinic and muscarinic cholinergic receptors were studied in autopsied brains from four histologically normal controls and five histopathologically verified cases of Alzheimer-type dementia (ATD), using ligand binding techniques. Nicotinic and muscarinic cholinergic receptors were assessed by (-)-[3H]nicotine and [3H]quinuclidinyl benzilate [( 3H]QNB), respectively. Compared with the controls, (-)-[3H]nicotine binding sites in the ATD brain regions examined were significantly reduced in the putamen and the nucleus basalis of Meynert (NbM). [3H]QNB binding was significantly reduced in the hippocampus and NbM. These findings suggest that there are significant changes of nicotinic and muscarinic cholinergic receptors in selected regions of ATD brains.