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Biomedical subjects

R J Prince

Publications and source records attributed to R J Prince.

7 recordsLinked to original sources
PubMed1992

Propofol potentiates the binding of [3H]flunitrazepam to the GABAA receptor complex.

Propofol (2,6-diisopropylphenol) robustly stimulated the binding of 1 nM [3H]flunitrazepam (FNZ) to rat brain membranes with an EC50 of 146 microM in chloride-free buffer and 23 microM in buffer containing 200 mM NaCl. NaCl showed an EC50 of 40 mM for its ability to increase the potency of propofol. The ability of a range of anions to potentiate propofol's interactions with the GABAA-benzodiazepine receptor was closely correlated with their permeabilities at this ion channel. Propofol, at a concentration of 300 microM, decreased the EC50 for the potentiation of FNZ binding by NaCl from 39 mM to 13 mM, with no change in the maximal potentiation. At a concentration of 30 microM, propofol significantly decreased the EC50 for potentiation of FNZ binding by the neurosteroid alphaxalone whilst increasing that for potentiation by pentobarbitone. We conclude that propofol is a potent barbiturate-like modulator of [3H]flunitrazepam binding.

Animals↗
PubMed1992

Temperature and anion dependence of allosteric interactions at the gamma-aminobutyric acid-benzodiazepine receptor.

The temperature dependence of [3H]flunitrazepam ([3H]FNZ) binding to rat brain membranes was examined in the presence of the anaesthetics, pentobarbitone, alphaxalone and propofol. Van't Hoff plots showed the binding of FNZ to be largely enthalpy driven. Alphaxalone and propofol increased the entropy of the binding reaction but not the enthalpy and therefore did not show temperature dependence in their efficacy. In contrast, pentobarbitone increased the enthalpy of FNZ binding and, therefore, is more efficacious at low temperatures. The EC50 values of all three modulators increased with temperature indicating that their interactions with the receptor may be enthalpy driven. The EC50 values of all three modulators were also anion dependent, showing a decrease in the presence of gamma-aminobutyric acid (GABAA)-channel permeant anions. The efficacies of alphaxalone and pentobarbitone, but not that of propofol, also increased with increasing chloride ion concentration. The results indicate that all three modulators interact with the GABAA receptor at distinct recognition sites.

Animals↗
PubMed1992

5 beta-pregnan-3 beta-ol-20-one, a specific antagonist at the neurosteroid site of the GABAA receptor-complex.

Studies were made on the potentiation of [3H]flunitrazepam binding to rat brain membranes by gamma-aminobutyric acid (GABA), pentobarbitone and pregnanolone (5 beta-pregnan-3 alpha-ol-20-one). Epipregnanolone, the 3 beta isomer of pregnanolone, inhibited competitively the potentiation by pregnanolone with a Ki of 10.5 microM without affecting that of GABA. The potentiation by pentobarbitone was slightly enhanced. Epipregnanolone alone showed only slight potentiation of benzodiazepine binding. These findings demonstrate that epipregnanolone is a specific antagonist of the neurosteroid site of the GABAA receptor and raise the possibility of a physiological role for 3 beta-hydroxysteroids in modulating this receptor.

Animals↗
PubMed1992

Steroid modulation of the strychnine-sensitive glycine receptor.

Electrophysiological responses to glycine (0.25-5 mM) were obtained on preparations of rat optic nerve. The log dose-response curve for glycine was shifted to the left by a factor of 2 by 1 microM 20 alpha-dihydrocortisol and by a factor of about 1.5 by 1 microM alpha-cortol and 10 microM hydrocortisone. A similar effect was obtained with 100 microM chlormethiazole but the GABA-potentiating steroid alphaxalone (1 microM) was ineffective on responses to glycine. 20 alpha-Dihydrocortisol and chlormethiazole also appeared to increase the antagonistic potency of strychnine against glycine. These observations suggest that the active steroids and chlormethiazole increase the functional interaction of both glycine and strychnine with the glycine-gated chloride channel.

Animals↗
PubMed1990

Effect of exogenous insulin on meal patterns and stomach emptying in the spiny mouse.

Male adult spiny mice (Acomys cahirinus) were acutely challenged with a single dose of regular insulin or saline vehicle SC; either food intake, meal frequency and meal duration, or stomach emptying were then measured. Meal frequency, as well as amount eaten, was significantly higher over a 6-hr period following both 10 and 30 U/kg of insulin than following vehicle injection. Meal duration remained essentially the same across all conditions. When 30 U/kg of insulin was administered either 15 min prior to, or immediately after, a solid food meal, stomach emptying (as measured by dry weight of recovered stomach contents) was accelerated relative to vehicle controls. These data are generally consistent with and extend the comparative literature suggesting a possible link between rate of stomach emptying and insulin-induced hyperphagia in some species.

Animals↗
PubMed1990

The Barnum effect in a computerized Rorschach interpretation system.

Twelve psychiatric outpatients were administered the Rorschach test, and results were interpreted using the Exner (1983, 1986) Report for the Comprehensive System computer-based test interpretation (CBTI) program. Four psychiatrists made accuracy ratings for both real and bogus reports for each of their patients. Data were analyzed using two-way analyses of covariance (ANCOVAs), where report type was a repeated main effect, psychiatrist was a random main effect, and the number of statements in the report was the covariate. Results indicated that this CBTI provided only 5% discriminating power for any one patient, with 60% of the interpretive statements merely describing typical characteristics of the outpatient population. No significant psychiatrist, interaction, or covariate effects were encountered.

Adolescent↗