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Biomedical subjects

A Guidotti

Publications and source records attributed to A Guidotti.

At least 217 records · Page 12Linked to original sources
PubMed1983

Methodological aspects of classifying low--and medium intensity of hyperostosis spongiosa orbitae.

Low- and medium expressions of hyperostosis spongiosa orbitae are occurring rather frequently compared to strong or very strong ones, yet their notation and differentiation is sometimes rather difficult. By means of original photographs of low and medium intensity degrees of this pathological trait methodological facilitation of notation is intended. This could serve as a stimulus for a more frequent incorporation of this bone condition in skeletal studies let alone minimal interobserver differences.

Exostoses↗
PubMed1983

Modulation of nicotinic receptor function by opiate recognition sites highly selective for Met5-enkephalin[Arg6Phe7].

Adrenal medullary cells contain opiate recognition sites that cannot be classified with any of the accepted conventional criteria. In primary cultures of bovine adrenal chromaffin cells, stimulation of nicotinic receptors by acetylcholine causes an increase in the release of catecholamines. When the action of acetylcholine is studied in the presence of opiate receptor agonists, the acetylcholine secretory action is curtailed. The action of the opiates is stereoselective and is blocked by naloxone and diprenorphine. The blocking activity of each opiate correlates with its Ki for the displacing of [3H]etorphine bound to specific recognition sites of adrenal medulla. Enkephalin-like opiate peptides are stored in the splanchnic nerves; they appear to act as a cotransmitter because they decrease the gain at which nicotinic receptors operate. This regulation appears to involve a down-regulation of the nicotinic receptor recognition sites because these opiate peptides elicit a decrease in the Bmax of the specific binding to adrenal medullary membranes of a radioactive fraction of alpha-bungarotoxin, a compound that inhibits the action of acetylcholine in releasing catecholamines from chromaffin cells.

Acetylcholine↗
PubMed1982

Isolation, characterization, and purification to homogeneity of a rat brain protein (GABA-modulin).

gamma-Aminobutyric acid (GABA)-modulin is a brain neuropeptide that appears to modulate specific high-affinity (20 nM) GABA recognition sites in brain. When added to crude synaptic membranes this peptide inhibits binding of [3H]GABA to the high-affinity site and prevents facilitation of [3H]diazepam binding elicited by GABA. GABA-modulin has been purified to homogeneity by ammonium sulfate precipitation, gel chromatography, and reverse-phase HPLC. Homogeneity was confirmed by a variety of means, including chromatography under four different HPLC conditions, two different polyacrylamide gel electrophoreses, and end group analysis. Purified GABA-modulin contains approximately 126 amino acids and has a molecular weight of 16,500. The GABA-modulin molecule contains an abundance of hydrophilic basic residues, and neither cysteine nor GABA is present. End group analyses of GABA-modulin showed that histidine is the free COOH terminus and the NH2 terminus is blocked. GABA-modulin specifically blocked both [3H]GABA binding to synaptic membranes (IC50, 0.5 microM) and GABA-stimulated [3H]diazepam binding; the binding of [3H]GABA to low-affinity sites was not affected.

Amino Acids↗
PubMed1982

gamma-Aminobutyric acid- and benzodiazepine-binding sites in human anterior pituitary tissue.

The existence of a gamma-aminobutyric acid (GABA) system in human anterior pituitary tissue was examined. Crude membrane fractions prepared from human anterior pituitary tissue bound tritiated GABA. The binding was saturable, and Scatchard analysis indicated a single binding site of high affinity (Kd = 40 nM) and a maximum binding of 1.2 pmol/mg protein. Binding was displaced in a dose-related manner by the GABA agonists muscimol (KI = 1 X 10(-8) M), isoguvacine (KI = 6 X 10(-7) M), THIP (4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol); KI = 5 X 10(-6) M), and the antagonist (+)bicuculline (KI = 5 X 10(-5) M) but not its inactive stereoisomer (-)bicuculline (KI greater than 10(-3) M). In anterior pituitary tissue, a significant concentration of GABA was found (mean, 2.5 +/- 0.5 nmol/mg protein) but no glutamic acid decarboxylase activity, the enzyme synthesizing GABA, was detected using a highly sensitive assay. In addition, benzodiazepine binding was present. An affinity of approximately 15 nM and a Bmax of approximately 0.75 pmol/mg protein were observed when using [3H]diazepam as the ligand. No saturable clonazepam binding occurred, and only slight GABA stimulation of diazepam binding was observed (mean, 18%; range, 6-38%). The ability of GABA and benzodiazepine to alter PRL secretion in rats suggests that the human pituitary GABA-binding sites described here might also mediate effects on PRL release.

Adult↗
PubMed1981

Endogenous inhibitors of Na+-independent [3H]GABA binding to crude synaptic membranes.

The characteristics of the Na+-independent high-affinity binding of [3H]GABA to various types of crude synaptic membranes (CSM) prepared from rat brain cortex were studied. In freshly prepared CSM the content of GABA was so high that the high-affinity [3H]GABA binding could not be determined. In contrast when the frozen-thawed CSM were incubated at 37 degrees for 30 min with or without Triton X-100 or phospholipase C and then washed repeatedly, there was a virtual disappearance of GABA from the supernatant extracts and the binding constants of [3H]GABA to CSM could be determined. Two apparent populations of [3H]GABA binding sites, one with a low- and the other with a high-affinity constant, were detected. The ratio of the number of high- to low-affinity binding sites varies with the method used to prepare the membranes. The lowest value of this ratio was observed with membranes incubated at 37 degrees for 30 min. However, when frozen-thawed CSM were treated with 0.05% Triton X-100 repeatedly, the ratio of the number of high- to low-affinity binding sites increased progressively. This increase in ratio is due to a selective increase in the number of the high-affinity sites without significant changes in the number of the low-affinity sites. The extent of the increase in the number of sites that bind [3H]GABA with high affinity after repeated Triton X-100 treatments was paralleled by a decrease of an endogenous protein which inhibits GABA binding. The reapplication of this endogenous material to membranes repeatedly treated with Triton X-100 reduces the number of high-affinity binding sites for [3H]GABA to values similar to those measured in membranes that were not treated with Triton X-100. The inhibitory preparation extracted from CSM incubated with Triton X-100 was shown to be free of GABA or phospholipids. The gel filtration chromatography reveals the presence of two molecular forms of the inhibitor; of these, the high-molecular-weight material fails to bind GABA, whereas the low-molecular-weight material appears to bind GABA. The high-molecular-weight endogenous inhibitor has been termed GABA modulin.

Amino Acids↗
PubMed1981

Regulation of acetylcholine receptors by endogenous cotransmitters: studies of adrenal medulla.

The coexistence of neuropeptides and amine transmitters in the same neuron and the presence of postsynaptic receptors for these compounds invite speculation that the compounds may interact postsynaptically. To study this interaction, we selected the synapse between the splanchnic nerve and the chromaffin cells of adrenal medulla because the splanchnic nerve contains acetylcholine and neuropeptides (multiple molecular forms of enkephalin-like peptides), while the membranes of chromaffin cells contain receptors for acetylcholine and opiate peptides. When the opiate receptors are occupied by specific agonists, these agonists inhibit the expression of acetylcholine receptors. Both the acetylcholine binding and catecholamine release by acetylcholine were inhibited. It is suggested that peptides and acetylcholine coexisting in the splanchnic nerve might act as cotransmitters, there by modulating the sensitivity of acetylcholine receptors. Multiple molecular forms of enkephalin-like peptides are stored in chromaffin cells and are released by acetylcholine. A role for the opiate receptors in the modulation of the secretion of opiate peptides stored in chromaffin cells is not evident.

Adrenal Medulla↗
PubMed1981

Characterization of benzodiazepine and gamma-aminobutyric recognition sites and their endogenous modulators.

The solubilization and partial purification from rat brain cortex homogenates of [3H]gamma-aminobutyric acid (GABA) and [3H]diazepam recognition sites and of their endogenous modulators (GABA-modulin and an endogenous compound which specifically bound [3H]diazepam) are reported. A high percentage of GABA binding sites (virtually free of benzodiazepine binding sites) was solubilized from homogenates of rat brain cortex incubated at 0 degree C with 1% Triton X-100 and a mixture of protease inhibitors. A large proportion of benzodiazepine binding sites was solubilized in the absence of apparent GABA binding capacity by incubating crude synaptic membrane preparations at 37 degree C with 0.05% Triton X-100. The characteristics of these two solubilized binding sites resemble those of the membrane-bound binding sites. However, unlike the membrane-bound sites, solubilized GABA and benzodiazepine binding sites are insensitive to GABA stimulation, while solubilized GABA binding sites are no longer protected by the benzodiazepines against heat inactivation. These results indicate that GABA and benzodiazepine recognition sites reside in two different molecules which, when bound to membranes, can interact reciprocally and modulate their binding affinity for specific ligands.

Animals↗
PubMed1980

Potentiation by intraventricular muscimol of the anticonflict effect of benzodiazepines.

The anticonflict action of muscimol (a potent GABA receptor agonist) and its ability to potentiate the anticonflict action of the benzodiazepines was studied in rats using VOgel's procedure. Rats were injected intraventricularly with a dose of muscimol from 50 to 200 ng to study whether the anticonflict action was dose-related. The potency of a 200 ng dose of muscimol is comparable to the potency of an anticonflict dose of 0.5 mg i.v. of diazepam. THIP (a muscimol analogue with weaker intrinsic GABA-mimetic activity) is active in doses 10 times higher than muscimol. The threshold dose of diazepam (0.2 mg/kg i.v.) to elicit anticonflict action was markedly potentiated when it was injected 5 min after intraventricular muscimol (150 ng). These data support the concept that GABA receptors may be involved in the anticonflict effects of the benzodiazepines.

Animals↗