TP003 is a non-selective benzodiazepine site agonist that induces anxiolysis via α2GABAA receptors

The regional distribution of binding sites on the GABAA receptor and their kinetic parameters were measured by quantitative autoradiography in brains from normal rats and rats with a portacaval shunt, a model of portal systemic encephalopathy in which GABA neurotransmission may be altered. The ligands used were [3H]flunitrazepam (a benzodiazepine-site agonist), [3H]-Ro 15-1788 (a benzodiazepine-site antagonist), [3H]muscimol (a GABA-site agonist), and [35S] t-butylbicyclo-phosphorothionate (35S-TBPS, a convulsant that binds to a site near the chloride channel). Some brains were analyzed by computerized image analysis and three-dimensional reconstruction. The regional distribution of binding of the benzodiazepines was very similar, but the patterns obtained with [3H]muscimol and [35S]TBPS were different in many areas, suggesting a heterogeneous distribution of several subtypes of the GABAA receptor. The kinetic parameters were determined in brain regions for [3H]flunitrazepam, [3H]Ro15-1788, and [3H]muscimol. For each ligand, the Kd showed a significant heterogeneity among brain regions (at least threefold), contrary to conclusions drawn from earlier studies. In portacaval shunted rats, binding of all four ligands was essentially unchanged from that in control rats, indicating that, if there was an abnormality in GABA neurotransmission during portal systemic shunting, it was not reflected by altered binding to the main sites on the GABAA receptor.

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Benzodiazepine site inverse agonists and locomotor activity in rats: Bimodal and biphasic influence

Pharmacology Biochemistry and Behavior ◽

10.1016/j.pbb.2006.04.001 ◽

2006 ◽

Vol 84 (1) ◽

pp. 35-42 ◽

Cited By ~ 6

Author(s):

Miroslav M. Savić ◽

Dragan I. Obradović ◽

Nenad D. Ugrešić ◽

James M. Cook ◽

Wenyuan Yin ◽

...

Keyword(s):

Locomotor Activity ◽

Inverse Agonists ◽

Benzodiazepine Site

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Classic Benzodiazepines Modulate the Open–Close Equilibrium in α1β2γ2Lγ-Aminobutyric Acid Type A Receptors

Anesthesiology ◽

10.1097/00000542-200504000-00014 ◽

2005 ◽

Vol 102 (4) ◽

pp. 783-792 ◽

Cited By ~ 45

Author(s):

Dirk Rüsch ◽

Stuart A. Forman

Keyword(s):

Gabaa Receptors ◽

Sulfonic Acid ◽

Site Occupancy ◽

Type A ◽

Aminobutyric Acid ◽

Clinical Effects ◽

Gamma Aminobutyric Acid ◽

Wild Type ◽

Acid Type ◽

Benzodiazepine Site

Background Classic benzodiazepine agonists induce their clinical effects by binding to a site on gamma-aminobutyric acid type A (GABAA) receptors and enhancing receptor activity. There are conflicting data regarding whether the benzodiazepine site is allosterically coupled to gamma-aminobutyric acid binding versus the channel open-close (gating) equilibrium. The authors tested the hypothesis that benzodiazepine site ligands modulate alpha1beta2gamma2L GABAA receptor gating both in the absence of orthosteric agonists and when the orthosteric sites are occupied. Methods GABAA receptors were recombinantly expressed in Xenopus oocytes and studied using two-microelectrode voltage clamp electrophysiology. To test gating effects in the absence of orthosteric agonist, the authors used spontaneously active GABAA receptors containing a leucine-to-threonine mutation at residue 264 on the alpha1 subunit. To examine effects on gating when orthosteric sites were fully occupied, they activated wild-type receptors with high concentrations of a partial agonist, piperidine-4-sulfonic acid. Results In the absence of orthosteric agonists, the channel activity of alpha1L264Tbeta2gamma2L receptors was increased by diazepam and midazolam and reduced by the inverse benzodiazepine agonist FG7142. Flumazenil displayed very weak agonism and blocked midazolam from further activating mutant channels. In wild-type receptors activated with saturating concentrations of piperidine-4-sulfonic acid, midazolam increased maximal efficacy. Conclusions Independent of orthosteric site occupancy, classic benzodiazepines modulate the gating equilibrium in alpha1beta2gamma2L GABAA receptors and are therefore allosteric coagonists. A Monod-Wyman-Changeux coagonist gating model quantitatively predicts these effects, suggesting that benzodiazepines minimally alter orthosteric ligand binding.

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