Journal of neurochemistry
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Journal of neurochemistry · Jun 1992
Purification and characterization of naturally occurring benzodiazepine receptor ligands in rat and human brain.
Chemicals that are active at the benzodiazepine receptor (endozepines) are naturally present in the CNS. These substances are present in tissue from humans and animals and in plants and fungi. Using selective extraction protocols, HPLC purification, receptor binding displacement studies, and selective anti-benzodiazepine antibodies, we have identified six or seven peaks of endozepines in rat and human brain. ⋯ Although endozepine peaks 1 and 2 had HPLC retention profiles similar to those of nordiazepam and diazepam, respectively, gas chromatography-mass spectrometry as well as high-performance TLC revealed biologically insignificant amounts of diazepam (less than 0.02 pg/g) and nordiazepam (less than 0.02 pg/g) in the purified material. Electrophysiologically, some purified endozepines positively modulated gamma-aminobutyric acid (GABA) action on Cl- conductance, monitored in patch-clamped cultured cortical neurons or in mammalian cells transfected with cDNA encoding various GABAA receptor subunits. These studies demonstrate that mammalian brains contain endozepines that could serve as potent endogenous positive allosteric modulators of GABAA receptors.
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Journal of neurochemistry · May 1992
Development of prolonged focal cerebral edema and regional cation changes following experimental brain injury in the rat.
The present study examined the formation of regional cerebral edema in adult rats subjected to lateral (parasagittal) experimental fluid-percussion brain injury. Animals receiving fluid-percussion brain injury of moderate severity over the left parietal cortex were assayed for brain water content at 6 h, 24 h, and 2, 3, 5, and 7 days post injury. Regional sodium and potassium concentrations were measured in a separate group of animals at 10 min, 1 h, 6 h, and 24 h following fluid-percussion injury. ⋯ Potassium concentrations fell significantly 1 h post injury within the injured cortex (p less than 0.05), whereas significant decreases were not observed until 24 h post injury within the injured hippocampus. Cation alterations persisted throughout the 24-h post injury period. These results demonstrate that regional brain edema and cation deregulation occur in rats subjected to lateral fluid-percussion brain injury and that these changes may persist for a prolonged period after brain injury.
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Journal of neurochemistry · Sep 1991
Comparative StudyGlucocorticoids regulate the synthesis of glial fibrillary acidic protein in intact and adrenalectomized rats but do not affect its expression following brain injury.
Short (5 days)- to long-term (4 months) corticosterone (CORT) administration by injection, pellet implantation, or in the drinking water decreased glial fibrillary acidic protein (GFAP) by 20-40% in hippocampus and cortex of intact rats. In contrast to CORT, adrenalectomy (ADX) caused elevations (50-125%) in hippocampus and cortex GFAP within 12 days of surgery that persisted for at least 4 months. CORT replacement of ADX rats decreased GFAP amount in hippocampus and cortex. ⋯ Thus, glucocorticoids and injury appear to regulate the expression of GFAP through different mechanisms. In contrast to the lack of effects of CORT on brain damage-induced increases in GFAP, CORT treatment begun in 2-week ADX rats, after an increase in GFAP had time to occur, did reverse the ADX-induced increase in GFAP. These results suggest that the increase in GFAP resulting from ADX is not mediated through an injury-linked mechanism.
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Journal of neurochemistry · Dec 1990
The general anesthetic propofol enhances the function of gamma-aminobutyric acid-coupled chloride channel in the rat cerebral cortex.
The effect of the general anesthetic propofol on t-[35S]butylbicyclophosphorothionate ([35S]TBPS) binding to unwashed membrane preparations from rat cerebral cortex was studied and compared to that of other general anesthetics (pentobarbital, alphaxalone) which are known to enhance GABAergic transmission. Propofol produced a concentration-dependent complete inhibition of [35S]TBPS binding, an effect similar to that induced by pentobarbital and alphaxalone, although these agents differ markedly in potency (alphaxalone greater than propofol greater than pentobarbital). The concomitant addition of propofol either with alphaxalone or pentobarbital produced an additive inhibition of [35S]TBPS binding, suggesting separate sites of action or different mechanisms of these drugs. ⋯ In fact, propofol, like alphaxalone and pentobarbital, markedly enhanced [3H]GABA binding in the rat cerebral cortex. Finally, propofol was able to enhance [3H]GABA binding in membranes previously incubated with the specific chloride channel blocker picrotoxin. Taken together these data strongly suggest that propofol, like other anesthetics and positive modulators of GABAergic transmission, might exert its pharmacological effects by enhancing the function of the GABA-activated chloride channel.
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Journal of neurochemistry · Jun 1989
Introduction of macromolecules into bovine adrenal medullary chromaffin cells and rat pheochromocytoma cells (PC12) by permeabilization with streptolysin O: inhibitory effect of tetanus toxin on catecholamine secretion.
Conditions are described for controlled plasma membrane permeabilization of rat pheochromocytoma cells (PC12) and cultured bovine adrenal chromaffin cells by streptolysin O (SLO). The transmembrane pores created by SLO invoke rapid efflux of intracellular 86Rb+ and ATP, and also permit passive diffusion of proteins, including immunoglobulins, into the cells. SLO-permeabilized PC12 cells release [3H]dopamine in response to micromolar concentrations of free Ca2+. ⋯ Reduced tetanus toxin, although ineffective when applied to intact chromaffin cells, inhibits Ca2+-induced exocytosis by both types of permeabilized cells studied. Omission of dithiothreitol, toxin inactivation by boiling, or preincubation with neutralizing antibodies abolishes the inhibitory effect. The data indicate that plasma membrane permeabilization by streptolysin O is a useful tool to probe and define cellular components that are involved in the final steps of exocytosis.