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Biomedical subjects

G Sperk

Publications and source records attributed to G Sperk.

At least 73 records · Page 4Linked to original sources
PubMed1991

Enhanced rate of expression and biosynthesis of neuropeptide Y after kainic acid-induced seizures.

Recent studies have shown marked increases in brain content of neuropeptide Y (NPY) after seizures induced by intraperitoneal injection of kainic acid and after pentylenetetrazole kindling in the rat. We have now investigated possible changes in the rate of biosynthesis of NPY after kainic acid treatment, by using pulse-labeling of the peptide and by determining prepro-NPY mRNA concentrations. For pulse labeling experiments, [3H]tyrosine was injected into the frontal cortex, and the incorporation of the amino acid into NPY was determined after purifying the peptide by gel filtration chromatography, antibody affinity chromatography, and reversed-phase HPLC. At 2 and 30 days after kainic acid treatment, the rate of tyrosine incorporation was enhanced by approximately 380% in the cortex. In addition, concentrations of pre-pro-NPY mRNA were determined in four different brain areas by hybridization of Northern blots with a complementary 32P-labeled RNA probe 2, 10, 30, and 60 days after kainic acid treatment. Marked increases were observed in the frontal cortex (by up to 350% of controls), in the dorsal hippocampus (by 750%), and in the amygdala/pyriform cortex (by 280%) at all intervals investigated. In the striatum only a small, transient increase was observed. The data demonstrate increased expression of prepro-NPY mRNA and an enhanced rate of in vivo synthesis of NPY as a result of seizures induced by the neurotoxin kainic acid.

Amygdala↗
PubMed1990

Chromogranins in rat brain: characterization, topographical distribution and regulation of synthesis.

The properties and distribution of chromogranins A, B and secretogranin II in rat brain were analyzed by quantitative immunoblotting. In contrast to endocrine tissues brain contains a significant amount of the proteoglycan form of chromogranin A. For secretogranin II a significant degree of endogenous proteolytic processing is apparent. Chromogranin A and secretogranin II had a similar topographical distribution with the highest concentrations found in the hypothalamus, amygdala/piriform cortex and hippocampus, whereas for chromogranin B by far the highest concentration was found in the cerebellum. Compared with adrenal medulla the concentration of all three proteins is low, however, secretogranin II appears relatively enriched. The synthesis of chromogranin A in brain does not depend on glucocorticoids since neither adrenalectomy nor dexamethasone treatment changed its levels. This is in contrast to adrenal medulla and to the anterior pituitary. Three days after kainic acid-induced seizures the levels of chromogranin A in frontal cortex and hippocampus were significantly elevated. For frontal cortex there was also an increase of the respective mRNA. This result establishes that the synthesis of chromogranin A can be regulated like that of neuropeptides.

Animals↗
PubMed1990

Effect of anticonvulsant treatment on kainic acid-induced increases in peptide levels.

The influence of anticonvulsant treatment upon (1) chronically increased seizure susceptibility, (2) on late increases in peptide levels and (3) on seizure-induced brain damage was investigated during various stages of acute kainic acid (10 mg/kg i.p.)-induced seizures. The seizures were interrupted at various stages of the syndrome (50 min to 24 h after injection of the toxin) by injecting thiopental (50 mg/kg i.p.) or the excitatory amino acid antagonist, MK-801 (10 mg/kg i.p.). The increase in neuropeptide Y and somatostatin levels in the frontal cortex could be prevented by early injection of either anticonvulsant (up to 180 min after kainic acid). No protection against the increase in peptide levels was observed when the anticonvulsants were applied later. Kainic acid-induced neuronal damage in the amygdala, with glutamate decarboxylase as a neurochemical marker, was entirely prevented by interrupting seizures up to 2 h after kainic acid. Partial protection (about 40-50%) was even found when the anticonvulsant treatment was applied after the acute syndrome, as late as 8 h after kainic acid injection. Chronically increased seizure susceptibility induced by kainic acid was not prevented, even by early injection (90 min after kainic acid) of the anticonvulsant drugs. The data indicate that (1) the late increase in seizure susceptibility may be initiated early after injection of kainic acid. (2) the late increase in peptide levels may be related to the frequency of acute seizures rather than to a change in seizure threshold or brain damage and (3) even late anticonvulsant therapy may antagonize seizure-induced brain damage in the amygdala.

Animals↗
PubMed1990

Neuropeptide Y biosynthesis is markedly induced in mossy fibers during temporal lobe epilepsy of the rat.

Neuropeptide Y (NPY) immunoreactivity and gene expression was investigated in the hippocampus after kainic acid-induced seizures and pentylenetetrazol kindling in the rat. Pronounced increases of NPY immunoreactivity were found in the terminal field of mossy fibers in both animal models. In kainic acid-treated rats the peptide progressively accumulated in the hilus and the stratum lucidum of CA3, 5-60 days after injection of the toxin and, at the later intervals, extended to the supragranular molecular layer of the dentate gyrus indicating sprouting of these neurons. Unilateral injection of colchicine into the hilus abolished NPY staining of the mossy fibers. Using in situ hybridization, in both animal models markedly enhanced expression of prepro-NPY mRNA was observed in the granular layer, containing the perikarya of the mossy fibers. It is suggested that sustained expression of the neuromodulatory neuropeptide NPY, in addition to the observed plastic changes, may contribute to altered excitability of hippocampal mossy fibers in epilepsy. Neither somatostatin immunoreactivity nor gene expression were enhanced in granule cells/mossy fibers.

Animals↗
PubMed1990

Differential changes in tachykinins after kainic acid-induced seizures in the rat.

Changes in concentrations of the tachykinins substance P, neurokinin A and neurokinin B were investigated in rat brains after kainic acid-induced seizures. Two different antisera, one detecting substance P specifically and one recognizing neurokinins A and B but not substance P, were used. Subsequently to the acute seizures (3 h after kainic acid) significant decreases (by 25-40%) in total neurokinin (A + B) and substance P immunoreactivities were observed in the frontal cortex, dorsal hippocampus and striatum. Depending on the brain area neurokinin immunoreactivity recovered 1-3 days after injection of the toxin and was significantly increased in the frontal cortex (by 40-60%) and the hippocampus (by 100-300%) after 10-60 days. Further analysis by high pressure liquid chromatography revealed that increases in both neurokinin A and neurokinin B concentrations contributed to the increases in total neurokinin immunoreactivity 30 days after kainic acid. At the same time significantly increased levels were also observed for substance P in the frontal cortex (by 30%). Furthermore, increases were also observed in the concentrations of neuropeptide K and gamma-preprotachykinin-A(72-92) in the frontal cortex and the hippocampus 30 days after the kainic acid treatment.

Animals↗
PubMed1990

Cholinergic deficit induced by ethylcholine aziridinium (AF64A) transiently affects somatostatin and neuropeptide Y levels in rat brain.

The question whether during the process of cholinergic degeneration somatostatin- and/or neuropeptide Y-containing neurons in rat hippocampus and cortex react to the withdrawal of cholinergic function was addressed. After bilateral intracerebroventricular injection of the cholinotoxin ethylcholine aziridinium (AF64A; 1 or 2 nmol/ventricle) in rats, the activity of choline acetyltransferase (ChAT) started to decline in the hippocampus within 24 h. The reduction of ChAT activity reached its maximum within 4 days (34 and 55% after 1 and 2 nmol of AF64A/ventricle, respectively) and persisted during the observation period of 14 days. In the parietal cortex, ChAT activity decreased by 23% 4 days after 2 nmol of AF64A/ventricle. The loss in ChAT activity was accompanied by a transient decline in the levels of somatostatin and a transient increase in the levels of neuropeptide Y in both brain areas. In the hippocampus, the reduction in somatostatin content was most pronounced after 2 days (by 22 and 33% after 1 and 2 nmol of AF64A/ventricle, respectively). Within 14 days, somatostatin levels returned to control values. Neuropeptide Y levels increased slightly by approximately 25% of control values in the hippocampus. The changes described were present in both the dorsal and ventral subfields of the hippocampus. Similar but less pronounced changes in levels of both neuropeptides were observed in the parietal cortex. The present data provide further evidence for a close neuronal interrelationship between cholinergic and somatostatin- and/or neuropeptide Y-containing neurons in rat hippocampus and parietal cortex.

Animals↗
PubMed1989

Concentrations of mRNAs encoding for preprosomatostatin and preprocholecystokinin are increased after kainic acid-induced seizures.

Concentrations of preprosomatostatin-mRNA and preprocholecystokinin-mRNA were determined by Northern blot analysis in rats 2, 10, and 30 days after strong seizures induced by a single intraperitoneal injection of kainic acid. At all time intervals examined, levels of preprosomatostatin-mRNA were increased in the frontal cortex; so were levels of preprocholecystokinin-mRNA in the striatum. Transient increases, i.e., 2 days after kainic acid, of preprocholecystokinin-mRNA were observed in the frontal cortex and the substantia nigra. Preprocholecystokinin-mRNA was reduced in the hippocampus 2 and 10 days after kainic acid. Both preprosomatostatin- and preprocholecystokinin-mRNA levels showed a tendency to be reduced in the amygdala/pyriform cortex at all three time intervals. The increases in mRNA levels suggest enhanced rates of synthesis of the respective neuropeptides subsequent to kainic acid-induced seizures. They may also reflect a prolonged increase in the activity of the respective peptide-containing neurons. This is of special interest in the frontal cortex, since in this area both neuropeptides are found in interneurons and are widely colocalized with gamma-aminobutyric acid.

Animals↗
PubMed1989

Co-localization of chromogranin A and B, secretogranin II and neuropeptide Y in chromaffin granules of rat adrenal medulla studied by electron microscopic immunocytochemistry.

The co-localization of various antigens in rat chromaffin granules was investigated by the immunogold staining procedure. In ultrathin serial sections staining of chromaffin granules was obtained with antisera against chromogranin A, chromogranin B, secretogranin II and neuropeptide Y. These results indicated that these antigens are costored within chromaffin granules. To further corroborate this point a double immunogold staining procedure was used. This method unequivocally established that chromogranin A, chromogranin B, secretogranin II and neuropeptide Y are co-localized in the same chromaffin granules. These results are relevant for studies demonstrating changes in the level of these peptides in adrenal medulla. The co-localization makes it likely that such changes lead to a different relative composition of the secretory quanta of chromaffin granules.

Adrenal Medulla↗
PubMed1989

Biochemical events in spontaneous seizures in the Mongolian gerbil.

The Mongolian gerbil, with its spontaneous epileptiform seizures, was chosen as an experimental model of human epilepsy. Neurochemical parameters possibly related to the seizure process were studied. In the immediate seizure process amino acid profiles of cortex, hippocampus, and striatum were not different in seizuring animals when compared to seizure-resistance controls. Of two peptides analyzed, only somatostatin appeared elevated in the cortex 2 hr postictal (143 fmol/mg protein; controls, 123 fmol/mg protein); neuropeptide Y was not affected. A follow up of the time course of cyclic AMP and cyclic GMP showed significant elevations of both substances as a consequence of seizures. Most prominent was a 5.5-fold increase in cyclic GMP in the cerebellum 30 sec after seizure onset.

Amino Acids↗
PubMed1989

Insulin hypoglycemia increases the levels of neuropeptide Y and calcitonin gene-related peptide, but not of chromogranins A and B, in rat chromaffin granules.

The levels and subcellular distribution of chromogranin A and B, of calcitonin gene-related peptide (CGRP) and of neuropeptide Y (NPY) were investigated in rat adrenals before and after insulin treatment. Six days after insulin-induced hypoglycemia the levels of chromogranin A and B were similar to controls, however those of NPY and CGRP were increased by a factor of 2.5 and 35, respectively. This treatment also elevated mRNA levels of NPY and CGRP, establishing an increased biosynthesis of these two neuropeptides. As shown by subcellular fractionation, all peptides were present in chromaffin granules after insulin treatment. Furthermore, immunostaining at the ultrastructural level demonstrated the co-localization of chromogranin A, NPY and CGRP within the same chromaffin granules. These results establish that insulin-induced hypoglycemia changes the levels of the secretory peptides in chromaffin granules leading to an altered composition of the secretory cocktail. Apparently, the biosynthesis of the secretory peptides and their storage organelles can be regulated in distinct patterns.

Animals↗
PubMed1989

Pronounced increases in brain levels of calcitonin gene-related peptide after kainic acid induced seizures.

Changes in immunoreactivity of calcitonin gene-related peptide (CGRP) were investigated in the brains of rats subsequently to seizures induced by intraperitoneal injection of kainic acid (10 mg/kg, i.p.). Increased levels of the neuropeptide were observed in the frontal cortex (increase of 1300% of control value), striatum (900%), dorsal hippocampus (400%) and amygdala/pyriform cortex (135%) three days after injection of the neurotoxin. Intravenous infusion of mannitol (1.5 g/kg, under thiopental anesthesia) which prevents seizures and post-seizure brain damage suppressed the changes in CGRP-like immunoreactivity. Injection of pentylenetetrazol causing generalized motor seizures resulted in no change of CGRP-immunoreactivity after three days. The pronounced but reversible increases of brain CGRP levels suggest a strong but short-lasting activation of the peptide system. The failure of pentylenetetrazol to produce a similar effect and the protective action of mannitol suggest that sustained seizures and/or post-seizure brain damage may be required to produce the rise in peptide levels.

Animals↗
PubMed1989

Purification and characterization of prosomatostatin from rat brain.

A high molecular weight somatostatin-immunoreactive polypeptide, presumably prosomatostatin, was purified from rat brain and characterized. Purification steps included extraction with 2 M acetic acid, precipitation of contaminating proteins at pH 6.5, Sephadex G-50 chromatography, immunoaffinity chromatography, and HPLC steps (size exclusion and reversed-phase HPLC). The protein was purified more than 30,000-fold. It is heat stable. Sodium dodecyl sulfate-gel electrophoresis and immunoblotting revealed one major immunoreactive band of approximately 13,000 molecular weight which roughly corresponds to the size of prosomatostatin as derived from its DNA sequence. Isoelectric focusing and two-dimensional sodium dodecyl sulfate-gel electrophoresis gave a single immunoreactive spot at a pI of 5.4. The polypeptide did not bind to concanavalin A or to wheat germ lectin columns, suggesting lack of N-glycosylation in the molecule. Regional distribution of prosomatostatin varied between 6%, 10%, and 18% of total immunoreactivity in the brainstem, cortical areas, and striatum, respectively.

Animals↗
PubMed1989

An increased pool of secretory hormones and peptides in adrenal medulla of stroke-prone spontaneously hypertensive rats.

Secretory components of the adrenal medulla were compared in normotensive Wistar-Kyoto (WKY) rats and in stroke-prone spontaneously hypertensive rats (SHRSP) at both 4 and 12 months of age. Noradrenaline, adrenaline, dopamine, neuropeptide Y, and chromogranins A and B were significantly higher in adrenal glands of SHRSP than those of WKY rats at 4 months. At 12 months, the levels of these components in SHRSP had increased even more (about 200% in WKY rats). There was no change in the relative composition of the adrenal "secretory cocktail." Neither the chromogranin A/chromogranin B ratio nor their apparent proteolytic processing in chromaffin granules differed between SHRSP or WKY rats. The lack of a significant change in membrane-bound cytochrome b561 and the small increase in dopamine beta-hydroxylase suggest that the higher levels of secretory components in SHRSP are not simply caused by an increase in the number of chromaffin granules, but possibly by a selective increase in the secretory content of these organelles providing a larger package for quantal release by exocytosis. This may be relevant for the elevation of blood pressure in this strain. The immunological methods described in this paper allow for the first time a determination of the secretory quantal levels in catecholamine storage. This should be useful for further studies in hypertensive models.

Adrenal Medulla↗
PubMed1988

Concomitant increase of somatostatin, neuropeptide Y and glutamate decarboxylase in the frontal cortex of rats with decreased seizure threshold.

The neuropeptides somatostatin and neuropeptide Y and the activity of glutamate decarboxylase were determined in the frontal cortex of rats subjected to experimental epilepsy. Two different animal models, (1) rats kindled for 4 weeks by daily injection of pentylenetetrazole, and (2) rats which had undergone strong limbic seizures induced by kainic acid, were used. Decreased seizure threshold, as shown by injection of a subconvulsive dose of pentylenetetrazole, was observed 10 days after the last kindling session and 1 month after injection of kainic acid, respectively. Significantly increased levels of somatostatin (by 60%), neuropeptide Y (135%) and increased activity of glutamate decarboxylase (22%) were found in the frontal cortex of rats previously treated with kainic acid. Separation of somatostatin-like immunoreactivity by size exclusion high-performance liquid chromatography showed a marked increase of immunoreactivity in fractions containing the somatostatin precursor (by 200%) and less prominently of somatostatin-14 and somatostatin-28 (by 60 and 80%, respectively). Michaelis-Menten kinetics of glutamate decarboxylase revealed an increased maximal velocity (Vmax) in the frontal cortex of kainic acid-treated rats, but no change in the Km value was found. Similar results were also obtained in pentylenetetrazole-kindled rats. Injection of cysteamine (100 mg/kg, i.p.) resulting in a 30% decrease of cortical somatostatin in kainic acid-pretreated rats markedly suppressed seizures induced by an otherwise subconvulsive dose of pentylenetetrazole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Effect of local injection of cysteamine and cystamine on somatostatin and neuropeptide Y levels in the rat striatum.

Cysteamine and its dimeric form cystamine have been applied to the rat striatum by local injection. Both compounds resulted in a dose-dependent decrease of somatostatin levels. Maximal reduction of somatostatin (by about 50%) was obtained at a dose of 50 micrograms of cysteamine or cystamine after about 6 h. All three molecular weight forms of somatostatin--somatostatin-14, somatostatin-28, and the 13,000 molecular weight form of somatostatin--were reduced, as shown by size exclusion HPLC. Injection of radiolabeled cystamine revealed a fast conversion of the compound to cysteamine, suggesting it is active in the monomeric form. The levels of neuropeptide Y, which is colocalized with somatostatin in striatal neurons, failed to be changed by local or intraperitoneal injection of cysteamine, suggesting that this treatment does not affect vesicles of somatostatin/neuropeptide Y neurons.

Animals↗
PubMed1987

Local injection of cysteamine into the rat striatum decreases number and intensity of staining of neurons by indirect NADPH diaphorase reaction.

Cysteamine (100 micrograms) markedly reduces the number (by about 60%) and intensity of staining of NADPH diaphorase-reactive neurons 6 h after local injection into the striatum. This effect was reversible (after 24 h) and was only observed when the indirect staining procedure was applied in which NADPH formed by endogenous malate dehydrogenase is used. However, no direct effect of cysteamine on the malate dehydrogenase reaction was found. The decrease in NADPH diaphorase activity parallels the previously reported cysteamine induced decrease in somatostatin contained in the same neurons and may point to a biochemical interrelation of somatostatin and NADPH diaphorase in these neurons.

Animals↗