Articles: gaba-modulators-pharmacology.
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E-6375 (4-butoxy-2-[4-(2-cyanobenzoyl)-1-piperazinyl] pyrimidine hydrochloride) is a new intravenous general anaesthetic with an anaesthetic potency, in mice, comparable to propofol, or etomidate. Here, we examined the effect of E-6375 upon the GABAA receptor, a putative target of intravenous anaesthetic action. E-6375 reversibly enhanced GABA-evoked currents mediated by recombinant GABAA (alpha1beta2gamma2L) receptors expressed in Xenopus laevis oocytes, with little effect on NMDA- and kainate-evoked currents mediated by NR1a/NR2A and GluR1o/GluR2o glutamate receptors, respectively. ⋯ The selectivity of E-6375 was largely governed by the identity (serine or asparagine) of a single amino acid residue within the second transmembrane domain of the beta-subunit. The various in vivo actions of general anaesthetics may be mediated by GABAA receptor isoforms that have a differential distribution within the CNS. The identification of agents, such as E-6375, that discriminate between GABAA receptor subtypes may augur the development of general anaesthetics with an improved therapeutic profile.
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The Journal of physiology · Dec 2001
Modulation of GABA(A) receptor channel gating by pentobarbital.
1. We have studied the kinetic properties of channel gating of recombinant alpha 1 beta 2 gamma 2L GABA(A) receptors transiently expressed in human embryonic kidney 293 cells, using the cell-attached, single-channel patch-clamp technique. The receptors were activated by GABA, beta-alanine or piperidine-4-sulfonic acid (P4S), and the effects of pentobarbital (PB) on single-channel activity were examined. 2. ⋯ The actions on receptors activated by P4S or beta-alanine are also broadly consistent with this idea. However, the changes in open-time distributions caused by PB appear to be more complex. Possible explanations of the effects of PB on gating by different agonists are considered.
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J. Pharmacol. Exp. Ther. · Sep 2001
Potency of positive gamma-aminobutyric acid(A) modulators to substitute for a midazolam discriminative stimulus in untreated monkeys does not predict potency to attenuate a flumazenil discriminative stimulus in diazepam-treated monkeys.
In monkeys discriminating midazolam (0.56 mg/kg s.c.) from saline, substitution for midazolam was elicited by various positive gamma-aminobutyric acid(A) (GABA(A)) modulators, including the benzodiazepines (BZs) triazolam, midazolam, and diazepam; the BZ(1)-selective ligands zaleplon and zolpidem; the barbiturates amobarbital and pentobarbital; and the neuroactive steroid pregnanolone. In another group of diazepam (5.6 mg/kg/day p.o.)-treated monkeys discriminating flumazenil (0.32 mg/kg s.c.) from vehicle, these positive GABA(A) modulators shifted the flumazenil dose-effect function to the right, i.e., attenuated diazepam withdrawal. The potency of positive GABA(A) modulators to substitute for midazolam in untreated monkeys did not predict their potency to attenuate the flumazenil stimulus in diazepam-treated monkeys. ⋯ The greater potency of non-BZ site ligands to attenuate diazepam withdrawal might be due to actions at a subtype of GABA(A) receptor not modulated by BZ site ligands, to the development of BZ tolerance without cross-tolerance to non-BZ site ligands, or to noncompetitive interactions at the GABA(A) receptor complex. Thus, interactions among GABA(A) modulators in BZ-dependent subjects are not predicted by their acute actions in nondependent subjects. It is not clear whether attenuation of BZ withdrawal is determined by subunit specificity or site of action on the GABA(A) receptor complex.
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Acta Anaesthesiol Scand · Aug 2001
High-dose flumazenil potentiates the hypnotic activity of propofol, but not that of thiopental, in ddY mice.
Flumazenil is a specific benzodiazepine agonist, which is reported to have a partial benzodiazepine agonist-like effect at a high dose. This study investigated the effects of flumazenil and midazolam on the hypnotic dose of propofol and thiopental in ddY mice, using a behavioral model. ⋯ These results suggest that the hypnotic activity of propofol is potentiated by the partial agonist activity of flumazenil in ddY mice.
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The intravenous anesthetic, propofol, has been shown to increase sleep when microinjected into the medial preoptic area (MPA) of the rat. Similar increases in sleep have also been observed with triazolam, pentobarbital and ethanol microinjection. Together, these findings implicate the MPA as an important anatomic site mediating the effects of sedatives on naturally occurring sleep. ⋯ To assess this possibility, we microinjected propofol alone, and in combination with the benzodiazepine receptor antagonist flumazenil, into the MPA. At a dose of 0.76 microg, flumazenil had no effect on sleep when given alone, and completely blocked the increase in sleep caused by a 40-ng dose of propofol although it did not affect the increase in sleep caused by an 80-ng dose of propofol. These data suggest that the sleep inducing property of propofol is in part mediated by direct or indirect actions on the GABA(A)-benzodiazepine receptor complex.