Neuropeptides in Alzheimer type dementia

Neuropeptides in Alzheimer's disease: a review and morphological results

The anatomic distribution of classical neurotransmitters, i.e. NA, DA, 5HT, ACH and GABA in the post-mortem autopsied brain of Alzheimer's disease (AD) has been reviewed. In addition, the results and reviews reported in this paper give evidence for the change of a large number of neuropeptides in AD on the basis of immunohistochemical criteria. Among numerous peptidergic systems, abnormalities in SP, SS, NT and VIP have been observed. Therefore, no changes in the concentrations of CCK and TRH were reported. In this study, using immunohistochemical methods for SS changes in post-mortem brain material of three cases of AD and two controls, the following changes were observed: An important reduction of the SS-positive cell bodies and fibres in the cortex, the hippocampus, parahippocampic cortex, and neocortex, particularly in the parietal and frontal areas, as well as a reduction of SS cell bodies and fibres in the sub-cortical white matter. An amorphous SS-positive material in or close to the corona of a number of senile plaques. An important decrease of SS fibres and cell bodies in the lateral septi nuclei. An increase of the number and immunoreactive intensity of SS-positive fibres in the substantia innominata. In animal studies, an interaction between SS- and ACH turnover in the substantia innominata is reported. The GABA decrease as well as the SS deficit in the cortex area and sub-cortical white matter may lead to the interaction between SS and other neurotransmitters in AD.

CSF neurotransmitter markers in Alzheimer's disease

CSF neurotransmitter markers may reflect neurochemical alterations in Alzheimer's disease (AD). The best studied neurochemical deficit in AD is that of acetylcholine. Both acetylcholinesterase and butyrylcholinesterase activity have been reported to be reduced in some but not all studies of AD CSF. Studies of monoamine metabolites have also been controversial but most authors have found reduced concentrations of CSF HVA, lesser reductions in HIAA and no change in MHPG. CSF GABA concentrations have been found to be reduced in AD. Studies of CSF neuropeptides in AD have shown reduced concentrations of somatostatin and vasopressin, normal concentrations of vasoactive intestinal polypeptide and either normal or decreased concentrations of beta-endorphin and corticotropin releasing factor. Although no individual CSF neurochemical markers are specific for AD it may be possible to develop a profile of several neurochemical markers which will have enhanced specificity.

Loss of endoplasmic reticulum-associated enzymes in affected brain regions in Huntington's disease and Alzheimer-type dementia

Post-mortem brain samples from patients with either Huntington's disease, Alzheimer-type dementia or appropriate controls were assayed for endoplasmic reticulum enzymes, NADPH-cytochrome c reductase, neutral alpha-glucosidase, inosine diphosphatase, alpha-mannosidase and glucose-6-phosphatase and for Golgi enzymes, fucosyl- and galactosyl-transferases. In Alzheimer-type dementia there was a selective decrease in alpha-glucosidase activity in the temporal cortex. In Huntington's disease there was a selective decrease of putamen alpha-glucosidase and fucosyl-transferase activities. It is suggested that these changes reflect highly specific alterations in glycoprotein synthesis and processing and may contribute to the underlying pathology of these disorders.

Somatostatin immunoreactivity in cortical and some subcortical regions in Alzheimer's disease

Reverse phase HPLC analysis of somatostatin immunoreactivity in the cerebral cortex in elderly normal individuals revealed that the majority of the immunoreactivity co-eluted with synthetic somatostatin-14. While an immunoreactive peak corresponding to somatostatin-28 was not detected there was a peak of immunoreactivity which eluted after somatostatin-14. In cases of senile dementia of Alzheimer type (SDAT), where abundant neurofibrillary tangles and senile plaques (density greater than 30 per 1.3-mm2 field) were present in the cerebral cortex, somatostatin immunoreactivity was found to be significantly decreased in either the frontal or temporal cortex. Chromatographic analysis, however, revealed that both the major immunoreactive peaks detected in the normal group were reduced in SDAT in the temporal and frontal cortex. Using a punch microdissection technique somatostatin immunoreactivity has been assessed in the nucleus of Meynert and amygdala of SDAT and elderly normal cases. While there was no change in somatostatin immunoreactivity in the nucleus of Meynert in the SDAT group, tissue punches taken from the amygdala revealed a selective decrease in somatostatin immunoreactivity in the basal nucleus, in the SDAT cases.

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

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

Cortical neurons immunoreactive with antisera against neuropeptide Y are altered in Alzheimer's-type dementia

Neurons identified by their immunoreactivity with antisera against neuropeptide Y (NPY) were studied in three selected areas of the cerebral cortex in brains from controls and in senile dementia of the Alzheimer type (ATD). Changes were more profound in temporal cortex than in parietal cortex, and more severe in parietal cortex than in frontal cortex, paralleling the severity of neuritic plaque formation and incidence of neurofibrillary tangles in these regions. NPY-i neurons became distorted, with enlarged misshapen cell somata and reduced, thickened, and gnarled dendrites. There was a sharp reduction in the extensiveness and delicacy of the axonal plexus; the reorganized axons were haphazard compared to the normal symmetry of these fibers. Besides the alteration in form and sizes, there were also appreciably fewer cells. Nevertheless, the NPY population is not eliminated. Double-label studies of NPY-i and thioflavin indicate that NPY-i fibers can participate in neuritic plaque formation although not all neuritic plaques contained NPY-i axons and not all NPY-i axons were associated with plaques. The surviving NPY cells were evident in all cortices examined, thus giving rise to the speculation that these peptide neurons may have unusual survival and reorganization potential even in terminal neurological disease.

Reduced numbers of somatostatin receptors in the cerebral cortex in Alzheimer's disease

Somatostatin receptor concentrations were measured in patients with Alzheimer's disease and controls. In the frontal cortex (Brodmann areas 6, 9, and 10) and temporal cortex (Brodmann area 21), the concentrations of somatostatin in receptors in the patients were reduced to approximately 50 percent of control values. A 40 percent reduction was seen in the hippocampus, while no significant changes were found in the cingulate cortex, postcentral gyrus, temporal pole, and superior temporal gyrus. Scatchard analysis showed a reduction in receptor number rather than a change in affinity. Somatostatin-like immunoreactivity was significantly reduced in both the frontal and temporal cortex. Somatostatin-like immunoreactivity was linearly related to somatostatin-receptor binding in the cortices of Alzheimer's patients. These findings may reflect degeneration of postsynaptic neurons or cortical afferents in the patients' cerebral cortices. Alternatively, decreased somatostatin-like immunoreactivity in Alzheimer's disease might indicate increased release of somatostatin and down regulation of postsynaptic receptors.

Dissociation of neuropeptide Y and somatostatin in Parkinson's disease

The concentration of neuropeptide Y has been determined in the cortex and hippocampus of subjects with Parkinson's disease and compared to changes of activity of dopamine beta-hydroxylase and concentration of somatostatin. Despite a marked reduction in the concentration of somatostatin in the severely demented subject, in both cortex and hippocampus, no significant change in concentration of NPY was found in either region. This finding therefore suggests that the majority of NPY within the cortex is independent of somatostatin. This study provides some further evidence of neurochemical similarities between the dementia of Parkinson's disease and Alzheimer's disease.

Two types of somatostatin receptors differentiated by cyclic somatostatin analogs

Somatostatin receptors in rat brain, pituitary, and pancreas were labeled with two radioiodinated analogs of somatostatins 14 and 28. Two cyclic analogs of somatostatin, SMS201-995 and cyclo(Ala-Cys-Phe-D-Trp-Lys-Thr-Cys), showed biphasic displacement of binding to somatostatin receptors by these radioligands. In contrast, all other somatostatin analogs, including somatostatin-14, competed for the receptor sites with monophasic displacement of radioligand receptor binding. Thus two types of somatostatin receptors were identified. It was found that the pituitary and pancreas have predominantly one type of somatostatin receptor whereas the brain has both, and that different regions of the brain have various proportions of the two types. These findings suggest methods to characterize other types of somatostatin receptors subserving somatostatin's diverse physiological functions, including a potential role in cognitive function and extrapyramidal motor system control.

Location of neuronal tangles in somatostatin neurones in Alzheimer's disease

Senile dementia of the Alzheimer type is a chronic, progressive neuropsychiatric condition characterized clinically by global intellectual impairment and neuropathologically by the presence of numerous argyrophilic plaques and tangles. Neurochemical investigations have established loss of the cholinergic and aminergic projections to the cerebral cortex and a loss of the content of somatostatin, with preservation of cholecystokinin and vasoactive intestinal polypeptide, neuropeptides also located in cells intrinsic to the cortex. We describe here the relationship between cortical somatostatin immunoreactivity and the plaques and tangles of diseased tissue by immunocytochemical and silver impregnation techniques on paraffin-embedded tissue. In sections of Alzheimer's tissue, cortical somatostatin-immunoreactive perikarya exhibited morphological changes consistent with neuronal degeneration. Silver-stained material immunostained subsequently showed that many neurones containing tangles were also somatostatin positive. No such colocalization was observed using antisera to other neuropeptides. Our findings indicate that a subclass of somatostatin-positive neurones are affected selectively in Alzheimer's disease and that these neurones also contain neuronal tangles. Thus, destruction of somatostatin-containing neurones is an early and perhaps critical event in the disease process.

Neurotensin immunoreactivity in post-mortem brain is increased in Down's syndrome but not in Alzheimer-type dementia

Neurotensin immunoreactivity and choline acetyltransferase (ChAT) activity were measured in post-mortem brain from 10 cases of Down's syndrome (7 aged 53-63 years, one aged 27 years, one aged 16 months and one aged 10 months), 6 cases of Alzheimer-type dementia (ATD) and 19 control subjects (13 aged 40-88 years and 6 aged 9-18 months). Neurotensin concentrations in anterior and basal hypothalamus, amygdala, septal area, caudate nucleus and temporal cortex were unaltered in ATD. The concentrations of neurotensin were significantly increased in the caudate nucleus, temporal cortex and frontal cortex in the cases of Down's syndrome aged 53-63 years with the neuropathological features of ATD, and were also increased in the cerebral cortex of the 27-year-old, which did not have the neuropathological features of ATD, and in two infant Down's cases. ChAT activity was reduced in the ATD and the 53-63-year-old cases of Down's syndrome, but not in the 27-year or 10-month-old Down's cases. The increased neurotensin concentrations appear to be a feature of Down's syndrome not related to the presence of plaques and neurofibrillary tangles or to a deficit in ChAT activity.

Serotonin receptor changes in dementia of the Alzheimer type

Serotonin receptors were assessed in post-mortem brains of control and Alzheimer-type dementia (ATD) patients using ligand binding techniques. Differential losses of serotonin S1 and S2 receptors were present in neocortex, hippocampus, and amygdala of ATD patients, whereas no significant changes were observed in basal forebrain and basal ganglia. Losses of S1 receptors were significantly age-related in the ATD group, suggesting they occurred at a later stage of the disease process. Losses of S2 receptors were considerably greater (with a reduction to 35% of control in temporal cortex) and were not age-related in ATD. Significant correlations were observed within the ATD group between S2 receptor binding and somatostatin immunoreactivity in temporal and frontal cortices. Thus the loss of S2 receptors in ATD may be a relatively early change in the disease process, and may precede the changes in ascending serotonergic neurones.

Somatostatin and vasoactive intestinal polypeptide in postmortem brains from patients with Alzheimer-type dementia

Somatostatin- and vasoactive intestinal polypeptide (VIP)-like immunoreactivities (SLI and VLI, respectively) were measured, by radioimmunoassay, in 21 regions of postmortem brains from 7 histologically verified cases of patients with Alzheimer-type dementia (ATD) and 10 histologically normal controls. SLI was significantly reduced in the orbital cortex, hippocampus and putamen of ATD brains. Significant reduction of VLI in the ATD brains was also found in the insular and angulate cortex, which have not previously been examined biochemically for peptides. These results suggest that involvement of not only somotostatin- but also VIP-containing neurons may not be ruled out in ATD brains.

Elevation of neuropeptide Y (NPY) in substantia innominata in Alzheimer's type dementia

Concentrations of neuropeptide Y (NPY) have been determined in 12 areas of control brains and compared to those found in brains from patients with Alzheimer's type dementia (ATD). The distribution of NPY in the control brains was compared with those reported previously. Highest concentrations were identified in the subcortical structures, in particular, nucleus accumbens (203 +/- 21.7 pmol/g), amygdala (136.7 +/- 15.8 pmol/g), and substantia innominata (109.0 +/- 12.6 pmol/g). A significant elevation in NPY concentrations was identified in the region of the substantia innominata of Alzheimer brains (controls: 109.0 +/- 12.6 pmol/g, ATD: 206 +/- 28.2 pmol/g, P less than 0.001). This change in NPY concentration was similar to the increase in somatostatin concentration in this region of ATD brain. In contrast, although cortical concentrations of somatostatin were reduced in ATD, no change was found in the concentrations of NPY in the 4 regions of cerebral cortex and the remaining subcortical areas examined.