Benzodiazepine-induced spatial learning deficits in rats are regulated by the degree of modulation of α1 GABAA receptors

Abstract

Despite significant advances in understanding the role of benzodiazepine (BZ)-sensitive populations of GABAA receptors, containing the α1, α2, α3 or α5 subunit, factual substrates of BZ-induced learning and memory deficits are not yet fully elucidated. It was shown that α1-subunit affinity-selective antagonist β-CCt almost completely abolished spatial learning deficits induced by diazepam (DZP) in the Morris water maze. We examined a novel, highly (105 fold) α1-subunit selective ligand - WYS8 (0.2, 1 and 10 mg/kg), on its own and in combination with the non-selective agonist DZP (2 mg/kg) or β-CCt (5 mg/kg) in the water maze in rats. The in vitro efficacy study revealed that WYS8 acts as α1-subtype selective weak partial positive modulator (40% potentiation at 100 nM). Measurement of concentrations of WYS8 and DZP in rat serum and brain tissues suggested that they did not substantially cross-influence the respective disposition. In the water maze, DZP impaired spatial learning (acquisition trials) and memory (probe trial). WYS8 caused no effect per se, did not affect the overall influence of DZP on the water-maze performance and was devoid of any activity in this task when combined with β-CCt. Nonetheless, an additional analysis of the latency to reach the platform and the total distance swam suggested that WYS8 addition attenuated the run-down of the spatial impairment induced by DZP at the end of acquisition trials. These results demonstrate a clear difference in the influence of an α1 subtype-selective antagonist and a partial agonist on the effects of DZP on the water-maze acquisition.

Insights into functional pharmacology of α1 GABAA receptors: how much does partial activation at the benzodiazepine site matter?

“…In addition, Figure 2 shows in vitro activity at α 1 β 3 γ 2 GABA A receptors of 10 nM and 1 μM WYS8, on their own and in combination with 1 μM diazepam. While diazepam exerted significant potentiation of GABA EC 3 at all GABA A receptor subtypes, WYS8 behaved as a weak partially effective positive modulator at α 1 β 3 γ 2 and produced a borderline significant effect at α 3 β 3 γ 2 GABA A receptors; this pattern of activity was essentially similar to that already reported (Joksimović et al 2013). The addition of WYS8 at concentration of 100 nM resulted in a significant reduction of diazepam’s potentiation of only α 1 -containing GABA A receptors.…”

“…Besides modulatory influences on α 1 -, α 2 -, α 3 - and α 5 β 3 γ 2 GABA A receptors, which have been published previously (Joksimović et al 2013), here we additionally report on the effects of WYS8 at BZ-insensitive α 4 - and α 6 -containing GABA A receptor subtypes. In a manner analogous to the actions of WYS8 at other non-α 1 GABA A receptors, no considerable modulation was reached at concentrations lower than 100 nM (α 4 GABA A receptors) or 10 μM (α 6 GABA A receptors) (Fig.…”

“…In order to further elucidate this issue, it seems necessary to use pharmacologically selective modulation of effects of standard BZs at these receptors in wild-type animals. We have recently shown that WYS8, one of the most selective ligands for α 1 GABA A receptors reported to date (Yin et al 2010), acts as a weak partial positive modulator at these receptors, devoid of behavioral activity in the water maze paradigm (Joksimović et al 2013). Here, we report on the influence of WYS8 on diazepam-induced potentiation of recombinant GABA A receptors, and also on the further behavioral characterization in rats of WYS8 on its own and in combination with diazepam.…”

“…In addition to experiments performed previously (Joksimović et al, 2013) the presently performed experiments aimed to obtain: 1) concentration effect curves for WYS8 at recombinant α 4 β 3 γ 2 and α 6 β 3 γ 2 , as well as at α 1 β 1 γ 2 , α 1 β 2 γ 2 and α 1 β 3 γ 2 GABA A receptors; 2) electrophysiological recordings for 1 μM diazepam and 10 nM, 100 nM and 1 μM WYS8, on their own and in respective combinations at α 1 β 3 γ 2 GABA A receptors, and for 1 μM diazepam and 100 nM WYS8, on their own and in combination at α 2 β 3 γ 2 , α 3 β 3 γ 2 and α 5 β 3 γ 2 GABA A receptors.…”

“…The effects of BZs mediated by α 1 GABA A receptors have been studied using pharmacological manipulation with the approximately 20 times α 1 -subunit selective neutral modulator (antagonist) β -CCt (t-butyl-β-carboline-3-carboxylate) (Rowlett et al 2005). In addition, recently we have demonstrated that WYS8 (8-ethynyl-β-carboline-3-carboxylate-t-butyl ester), a close congener of β -CCt with even higher selectivity in affinity for α 1 GABA A receptors (Yin et al 2010) behaves as a weak partial positive modulator (Joksimović et al 2013). When combined with diazepam, the in vivo actions of these two close congeners were clearly differentiable: β -CCt proved to be an antagonist of diazepam’s effects (Savić et al 2009), while WYS8 not only did not antagonize, but even potentiated some of diazepam’s effects in the water maze (Joksimović et al 2013).…”