Requirement of α₅-GABA_AReceptors for the Development of Tolerance to the Sedative Action of Diazepam in Mice

Abstract

Despite its pharmacological relevance, the mechanism of the development of tolerance to the action of benzodiazepines is essentially unknown. The acute sedative action of diazepam is mediated via ␣ 1 -GABA A receptors. Therefore, we tested whether chronic activation of these receptors by diazepam is sufficient to induce tolerance to its sedative action. Knock-in mice, in which the ␣ 1 -, ␣ 2 -, ␣ 3 -, or ␣ 5 -GABA A receptors had been rendered insensitive to diazepam by histidine-arginine point mutation, were chronically treated with diazepam (8 d;) and tested for motor activity. Wild-type, ␣ 2 (H101R), and ␣ 3 (H126R) mice showed a robust diminution of the motor-depressant drug action. In contrast, ␣ 5 (H105R) mice failed to display any sedative tolerance. ␣ 1 (H101R) mice showed no alteration of motor activity with chronic diazepam treatment. Autoradiography with [ 3 H]flumazenil revealed no change in benzodiazepine binding sites. However, a decrease in ␣ 5 -subunit radioligand binding was detected selectively in the dentate gyrus with specific ligands. This alteration was observed only in diazepam-tolerant animals, indicating that the manifestation of tolerance to the sedative action of diazepam is associated with a downregulation of ␣ 5 -GABA A receptors in the dentate gyrus. Thus, the chronic activation of ␣ 5 -GABA A receptors is crucial for the normal development of sedative tolerance to diazepam, which manifests itself in conjunction with ␣ 1 -GABA A receptors.

Are GABAA Receptors Containing α5 Subunits Contributing to the Sedative Properties of Benzodiazepine Site Agonists?

“…There exist data that support the possibility of substantial motor manifestations of a5-containing GABA A receptor modulation, besides the indirect consequences brought on by the effects on learning and memory processes, where pertinent (Collinson et al, 2002;Crestani et al, 2002). Somatic and preganglionic motoneurons in the spinal cord exhibit a moderate-to-strong staining for the a5 subunit (Bohlhalter et al, 1996), whereas the knock-in mice harboring the a5 subunit insensitive to diazepam are refractory to development of tolerance to the sedative effect of diazepam dosed subchronically, presumably due to a downregulation of a5 subunits in the dentate gyrus (van Rijnsoever et al, 2004). Hence, we hypothesize that any locomotor activity changes induced by ligands possessing a substantial a5-efficacy may be, at least partly, contributed by modulation at GABA A receptors containing this subunit.…”

“…In the spinal cord, somatic and preganglionic motoneurons (lamina IX and lateral cell column) exhibited a moderate to strong staining for the a5 subunit (Bohlhalter et al, 1996). Knock-in mice with the GABA A receptor a5 subunit rendered insensitive to diazepam were refractory to development of tolerance to the sedative effect of diazepam dosed subchronically (van Rijnsoever et al, 2004). These two sets of evidence indicate that the motor influence of a5-GABA A receptor modulation, if present, is not necessarily an indirect consequence of the established effects on learning and memory processes (Collinson et al, 2002;Crestani et al, 2002).…”

Effects of the 5-HT_1A Receptor Agonist Tandospirone on ACTH-Induced Sleep Disturbance in Rats

“…Conversely, alpha5-GABA A receptors were insensitive and developed tolerance to the sedative actions of benzodiazepines. [21][22][23] Verkuyl et al 24) reported that expression of alpha5, not alpha1-GABA A receptors was increased in patients with hyperfunctional HPA axes. Therefore the absence of a flunitrazepam-induced hypnotic effect may be the result of tolerance developed by upregulation of alpha5-GABA A receptors in ACTH-treated rats.…”

Maintenance time of sedative effects after an intravenous infusion of diazepam: A guide for endoscopy using diazepam

“…The sedative effects of diazepam are mediated via a1-GABA A receptors in the brain [22,23] , and the minimum plasma concentration of diazepam to yield sedative effects is more than 300 ng/mL to 400 ng/mL [18,19] . The pharmacokinetics of diazepam are affected by age [24,25] , gender [26] , obesity [26] , liver disease [27] and CYP2C19 genotype status [5][6][7][8][9] .…”