PubMed Health⌕ Search

Biomedical subjects

R Ravid

Publications and source records attributed to R Ravid.

At least 91 records · Page 5Linked to original sources
PubMed1992

Preservation of Gi-protein inhibited adenylyl cyclase activity in the brains of patients with Alzheimer's disease.

The coupling of inhibitory guanine nucleotide binding (Gi) proteins to the adenylyl cyclase signal transduction complex was compared in 4 brain regions from a series of Alzheimer's disease and matched control subjects by measuring the inhibition of membrane enzyme activities in response to guanosine 5'-[beta gamma-imido]diphosphate (Gpp[NH]p) and aluminium fluoride (AlF4-). Basal adenylyl cyclase activities were significantly lower in preparations of angular gyrus and frontal and temporal cortices, but not cerebellum, from the Alzheimer's disease cases compared to controls. Gpp[NH]p and AlF4- gave significant inhibitions of adenylyl cyclase activity in all brain regions. The magnitude of these inhibitions, when corrected for altered basal activities, were similar for the Alzheimer's disease and control cases. These results indicate that there is no impairment of Gi-protein mediated inhibition of adenylyl cyclase activity in Alzheimer's disease brain.

Adenylyl Cyclases↗
PubMed1992

Brain banking and the human hypothalamus--factors to match for, pitfalls and potentials.

The study of an increasing number of processes occurring in the human brain can be carried out on autopsy material. The availability of this material, whether fresh, frozen or fixed, makes it possible to develop methodologies for studying the neuroanatomical and neurochemical aspects of the human brain. It has also become possible in recent years to correlate functional changes with neurochemical changes and with neuroanatomical abnormalities in disease states. Some compounds and structures are damaged irreversibly within minutes after death and some brain components are known to disintegrate within seconds. This led to the widespread idea that autopsy material would not be suitable for basic research purposes and would not supply the necessary answers on the various fundamental questions regarding processes occurring in normal or diseased brain. However, from data published in recent years in which autopsy material has been routinely used, it becomes more and more evident that this is a misconception. There is an increasing number of reports based on the use of normal and pathological human brain tissue obtained by autopsies in spite of the fact that there is a worrying continuous decline in autopsy rate which causes serious concern among scientists world-wide (Anderson and Hill, 1989). It also became evident that when using the proper fixation procedures, sufficient structural integrity is retained in the tissue to allow morphological and morphometrical studies (Swaab and Uylings, 1988). Electron microscopic examination of synaptosomal preparations from post-mortem human brain showed them to be only slightly less pure than preparations from fresh tissue although there was some degree of damage (Hardy et al., 1982). Agonal state effects the stability of brain compounds and causes brain hypoxia. This again forms a tremendous difficulty for the study of human neurological and psychiatric diseases as one of the frequent causes of death is bronchopneumonia which leads to brain hypoxia and results in pronounced lactic acidosis. The Netherlands Brain Bank has succeeded to partly circumvent some of the serious problems encountered in providing human tissue for research by performing rapid autopsies with an average post-mortem delay of 2-4 h. This has become possible by a close collaboration of numerous nursing homes in Amsterdam and its vicinity and with the neuropathologists of the Free University in Amsterdam. We also measure the pH of the tissue as indicator of agonal state in order to reveal unsuitable specimens. The human hypothalamus contains various nuclei manifesting a wide variety of changes in different conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1992

Phosphatidylinositol kinase is reduced in Alzheimer's disease.

Phosphatidylinositol (PI) kinase and PI phosphate (PIP) kinase activities were measured in postmortem samples of brain tissue from patients with Alzheimer's disease and nondemented control subjects. A membrane-free cytosolic fraction from four neocortical locations, with exogenous inositol lipids as the substrate, was used. Tissue from patients with Alzheimer's disease was characterized by reduced PIP formation; the reduction was 50% in prefrontal cortex, temporal cortex, and parietal cortex and 40% in precentral gyrus. In contrast, no alterations were found in PI bisphosphate formation in these four neocortical locations. The specific changes in PI kinase but not PIP kinase activity suggest that the findings may have functional relevance to the involvement of brain membrane processes in Alzheimer's disease.

1-Phosphatidylinositol 4-Kinase↗
PubMed1992

Adenylyl cyclase activity in postmortem human brain: evidence of altered G protein mediation in Alzheimer's disease.

The effects of agonal status, postmortem delay, and age on human brain adenylyl cyclase activity were determined in membrane preparations of frontal cortex from a series of 18 nondemented subjects who had died with no history of neurological or psychiatric disease. Basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were not significantly reduced over an interval from death to postmortem of between 3 and 37 h and were also not significantly different between individuals dying with a long terminal phase of an illness and those dying suddenly. Basal and aluminum fluoride-stimulated enzyme activities showed a negative correlation with increasing age of the individual. In subsequent experiments, basal and guanosine 5'-O-(3-thiotriphosphate)-, aluminum fluoride-, and forskolin-stimulated enzyme activities were compared in five brain regions from a series of eight Alzheimer's disease and seven matched nondemented control subjects. No significant differences were observed between the groups for either basal activity or activities in response to forskolin stimulation of the catalytic subunit of the enzyme. In contrast, enzyme activities in response to stimulation with guanosine 5'-O-(3-thiotriphosphate) and aluminum fluoride were significantly reduced in preparations of neocortex and cerebellum from the Alzheimer's disease cases compared with the nondemented controls. Lower guanosine 5'-O-(3-thiotriphosphate)-, but not aluminum fluoride-, stimulated activity was also observed in preparations of frontal cortex from a group of four disease controls compared with nondemented control values. The disease control group, which contained Parkinson's disease and progressive supranuclear palsy patients, showed increased forskolin-stimulated activity compared with both the nondemented control and the Alzheimer's disease groups. These findings indicate a widespread impairment of G protein-stimulated adenylyl cyclase activity in Alzheimer's disease brain, which occurs in the absence of altered enzyme catalytic activity and which is unlikely to be the result of non-disease-related factors associated with the nature of terminal illness of individuals.

Adenylyl Cyclases↗
PubMed1991

Increased vasopressin immunoreactivity in the rat brain after a postmortem interval of 6 hours.

Enhanced immunocytochemical staining of vasopressin-containing neurons was observed after incubation of rat brain slices in Ringer medium for 6 h at room temperature, as compared to brain tissue fixed immediately after death. Hypothalamic vasopressin neurons in the supraoptic nucleus, the paraventricular nucleus and the suprachiasmatic nucleus stained more intensely after a postmortem interval of 6 h. Extrahypothalamic vasopressin neurons (VP) in the bed nucleus of the stria terminalis, the medial amygdala and the locus coeruleus proved to be stained as well. Extrahypothalamic VP neurons in the locus coeruleus could, until now, only be visualized after in vivo pretreatment with colchicine. In addition, staining was observed at two new sites, the dorsal raphe nucleus and the lateral septum. Staining of VP was corroborated by application of different antibodies directed against the intact vasopressin molecule as well as by antibodies directed against the other parts of the vasopressin precursor molecule, i.e. neurophysin and glycopeptide. The specificity of the VP-staining was validated by using pre-immune serum and using Brattleboro rat brain tissue, resulting in a negative staining in both cases. Furthermore, homogenated punches of the suprachiasmatic nucleus were submitted to iso-electric focussing on polyacrylamide gel, followed by press blotting and subsequent immunocytochemical staining for vasopressin. Iso-electric foccussing enabled us to characterize and quantify peptides in the suprachiasmatic nucleus. The vasopressin content increased 6 h postmortem, while c-terminal glycopeptide and neurophysin levels remained stable. Similar results were observed in the suprachiasmatic nucleus from decapitated rats whose brains were left intact in the skull for 6 h at room temperature.

Animals↗
PubMed1991

The hypothalamic lateral tuberal nucleus in Alzheimer's disease.

The hypothalamic lateral tuberal nucleus was investigated in 5 young patients, aged 45 to 64 years, with Alzheimer's disease (AD) and in 5 age-matched control subjects. Combining conventional histopathological and immunocytochemical staining with neuronal counts, a peculiar form of neuronal pathology was characterized. Although neurons and neurites in the lateral tuberal nucleus of AD specimens were heavily stained by Alz-50, silver and thioflavine-S stains disclosed few neurofibrillary tangles or neurites. The numbers of neurons in the lateral tuberal nucleus of patients with AD (67,450; SEM = 5,050) were no different from those of control subjects (58,900; SEM = 2,450). In the AD patients, few plaques were present and were almost exclusively of the amorphous variety. We conclude that neurons in the lateral tuberal nucleus show an early stage of AD-related cytoskeletal pathology (Alz-50 positivity), but without plaques or neuronal death.

Alzheimer Disease↗
PubMed1990

Biochemical assay of Alzheimer's disease--associated protein(s) in human brain tissue. A clinical study.

The concentration of Alzheimer's disease-associated protein (ADAP) was measured in postmortem brain tissue samples of temporal or frontal cortex from 111 human brains using a sandwich immunoassay. Alzheimer's disease-associated protein has three major ALZ-50-reactive subunits, including A-68. This assay utilizes ALZ-50 and a rabbit antibody raised against a highly ADAP-enriched brain protein fraction. The frequently observed cross-reactivity of ALZ-50 with normal brain components in direct immunoassays is minimized by this configuration. There were 27 normal controls, 28 neurologic disease controls, and 56 Alzheimer's disease cases. The normal control and neurologic disease control cases had essentially no detectable level of ADAP, while ADAP was clearly detected in 85.7% of the Alzheimer's disease cases. Clinical dementia, neuritic plaques, and old age per se are not correlated with increased ADAP levels. This biochemical assay of ADAP may prove to be helpful as an adjunct in the clinicopathologic diagnosis of Alzheimer's disease.

Aged↗
PubMed1988

Immunocytochemically stained vasopressin binding sites on blood vessels in the rat brain.

Following two weeks of cerebroventricular administration of arginine-vasopressin (AVP) by Accurel implants, two types of binding sites for this peptide were immunocytochemically visualized in blood vessels in the brain of Brattleboro (di/di) rats: (1) endothelial cells of capillaries were stained with the highest density in hippocampus, striatum, and locus coeruleus (LC), whereas only few such stained cells were present in the septum and cerebral cortex. (2) Bound AVP was also present on endothelial cells and pericyte-like cells in larger blood vessels in striatum and the LC. Both types of vasopressin binding site staining on blood vessels were dose-dependent and could be further enhanced by additional in vitro preincubation of the fixed sections with AVP. This staining was not present in rats implanted with either oxytocin or alpha-melanocyte-stimulating hormone.

Animals↗
PubMed1987

Changes in vasopressin and testosterone in the senescent brown-Norway (BN/BiRij) rat.

Although earlier reports in the literature suggested degenerative changes in the senescent hypothalamo-neurohypophyseal system (HNS), recent investigation showed hyperactivity of this system in the old Wistar (WAG/Rij) rat. In the brain, changes were found in those sites of extrahypothalamic vasopressin (VP) fiber termination that are testosterone-dependent. In the present study, further evaluation of these changes was performed in male Brown-Norway (BN/BiRij) rats. Immunocytochemical staining of VP binding sites in renal tubuli of the senescent, 33-month-old rats was occasional, and could only slightly be enhanced up to weak staining by in vitro preincubation with the peptide, in contrast to the intense staining observed in young, 3-month-old rats. Although VP plasma levels of young and old rats did not differ significantly and no change in either urine or plasma osmolality was observed, urinary VP concentration and 24-hour urinary VP excretion were significantly increased in senescent rats. The activation of the hypothalamo-neurohypophyseal system (HNS) in the senescent rat seems thus to compensate for a decreased responsiveness to VP in the aged kidney. Testicular weight in the senescent animals declined by 40% and a highly significant decrease of 80-90% was observed in total and free testosterone plasma levels. Consequently, changes in peripheral organs in senescent rats may well underly the changes observed in the brain of these animals.

Aging↗
PubMed1986

Immunocytochemically stained binding sites for oxytocin and alpha-melanocyte-stimulating hormone in rat brain following ventricular administration.

Binding sites for oxytocin (OXT) and alpha-melanocyte-stimulating hormone (alpha-MSH) in brain of homozygous Brattleboro rats were immunocytochemically visualized after ventricular administration of the peptides by Accurel implants. Two patterns were found: 'ring type' staining in perineuronal structures was observed in CA1 and CA3 areas of ventral hippocampus and in subiculum for OXT implanted brains and a very weak staining in striatum for alpha-MSH-implanted brains; cytoplasmic staining of intracellular binding sites was observed in the bed nucleus of the stria terminalis (BST) in brains with OXT implants and in the anterodorsal thalamic nucleus (AD) and postcingulate cortex in brains with alpha-MSH implants. These localizations are different from those described for vasopressin binding sites in the same rat strain.

Animals↗
PubMed1986

Localisation of oxytocin, vasopressin and parts of precursors in the human neonatal adrenal.

Being a possible alternative source for the production of vasopressin (AVP) and oxytocin (OXT), a study was undertaken of the fetal adrenal. The concentrations of these peptides within the fetal adrenal turned out to be low, viz., approx. 1 pg/mg in the rat and within the pg/g range in the human. Immunocytochemistry was performed either on conventional autopsy material kept till 12 years in paraffin blocks, or on more recently obtained formalin or glutaraldehyde-paraformaldehyde fixed material. In both types of material staining was good. In order to localize AVP cells, anti-AVP, an antibody against its associated neurophysin (anti-NSN) or an antibody raised against the c-terminal glycopeptide part of the AVP precursor (anti-GP) was used. OXT cells were localized by means of anti-OXT or an auto-antibody of a multiple sclerosis patient (auto-MS) probably recognizing OXT-neurophysin. The antibodies were characterized on human and rat brain material. In the external zone of the definitive cortex, apart from parenchyma cells, anti-AVP, anti-NSN and anti-GP stained fibre-like structures running in the connective tissue septa and around parenchyma cells and the cytoplasma of these cells. Anti-OXT and auto-MS stained droplets in the cytoplasm of the fetal zone cells. Similar distinct staining patterns for AVP and OXT cells were obtained in human anencephalics. These observations show that the peptides are not derived from the fetal brain, but are rather produced in the fetal adrenal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Glands↗
PubMed1986

Immunocytochemically-stained vasopressin binding sites in rat brain. Ventricular application of vasopressin/Accurel in the Brattleboro rat.

An immunocytochemical procedure was developed to localize binding sites for vasopressin (VP) in the brain of Brattleboro (di/di) rats after 2 weeks of continuous ventricular administration of the peptide. Accurel-polypropylene tubing loaded with 0.15, 1.5 or 15 micrograms vasopressin was implanted into the lateral ventricle. Subsequently, bound VP was detected immunocytochemically in 2 distinct patterns: in perineuronal structures and dots between cells, in the lateral septum (dorsorostral part), striatum, cingulate cortex, granular cells of the dentate gyrus of the hippocampus, pyramidal cells of CA1 and CA3 hippocampal areas and around cerebellar Purkinje cells. The high dose (15 micrograms) loaded implants revealed the most intense staining; in the cytoplasm of neuronal cell bodies in the lateral and medial septum, striatum, cingulate cortex, bed nucleus of the stria terminalis, organum vasculosum of the laminae terminalis and locus coeruleus. The most intense staining in cell bodies was observed in brains which had low-loaded implants (0.15-1.5 microgram). A variety of controls, proved that no aspecific uptake was involved in the present procedure. The distribution of VP binding sites was only partly coincident with known sites of VP fiber innervation, and largely agrees with data obtained by autoradiographic techniques for [3H]VP binding. The present immunocytochemical technique gave a higher resolution than the currently used autoradiographic techniques. The differences in pattern and intensity of staining due to increasing the dosage rate of the in vivo vasopressin treatment, might mean that the current procedure retains preferentially either low or high affinity populations of binding sites depending on the implanted dose.

Animals↗
PubMed1986

[Increased vasopressin production in senescence and dementia].

Vasopressin (VP) is involved as a neurotransmitter in a number of central functions that are frequently disturbed during aging and dementia. Therefore, this peptide has been used in clinical trials as a 'substitution therapy' for the degenerating peptidergic neurons, aimed at improving cognitive functions in aged and demented individuals with unequivocal results. In order to investigate whether the VP systems indeed show the claimed degenerative changes during aging and dementia, we focused in the first place on the Supra Optic Nucleus (SON) and Para Ventricular Nucleus (PVN). VP cells were identified by means of immunocytochemistry in a series of 32 formalin-fixed human hypothalami, including 4 patients with senile dementia of the Alzheimer type (SDAT). In the SON and PVN, VP cell and nucleolar size was determined by means of a digitizer device, as parameter for peptide synthesizing activity. VP cell size and nucleolar size increased beyond 80 years of age, both in the PVN and in the SON. In SDAT patients these measures fell within the range for their age group. Instead of degenerative changes, these results show an activation of the vasopressinergic system in senescence and in SDAT patients, similar to earlier observations in the aged rat and in accordance with a rise in human neurophysin and VP levels reported recently. The cause for these changes might be in the kidney. Immunocytochemical staining of VP binding sites in the renal tubuli was strongly diminished in kidneys of old (25 and 34 months) as compared to young (3 and 5 months) Wistar and Brown-Norway rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Immunocytochemical localization of vasopressin-binding sites in the rat kidney.

The rat kidney and brain are major target organs for vasopressin (VP). A procedure was developed for immunocytochemical staining of VP and its binding sites in the kidney. This procedure involved preincubation of kidney sections with the ligand, followed by immunocytochemical detection of VP. The staining in renal tubules from Wistar rats was enhanced by preincubation of tissue sections with increasing concentrations of VP (6-6000 nmol/l). Staining was present in the epithelium of distal convolutions and collecting ducts (medullary and cortical portions) and more pronounced in the apical zone of the tubular epithelium. With high concentrations of VP in the preincubation, staining was also obtained in the thick ascending limb of the loop of Henle. There was no staining under any circumstances in proximal tubules. In the kidney of the Brattleboro rat homozygous for hypothalamic diabetes insipidus (DI) which congenitally lacks VP but responds to the peptide, exactly the same staining pattern was observed after preincubation with VP, but the maximal staining was less intense. The VP binding to the DI rat kidney, after 2 weeks treatment with VP (using Accurel implants), reached levels seen in the Wistar kidney after in-vitro preincubation with high doses of VP.

Animals↗