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Differential effects of short- and long-term zolpidem treatment on recombinant alpha 1 beta 2 gamma 2s subtype of GABA(A) receptors in vitro

Zolpidem is a non-benzodiazepine agonist at benzodiazepine binding site in GABAA receptors, which is increasingly prescribed. Recent studies suggest that prolonged zolpidem treatment induces tolerance. The aim of this study was to explore the adaptive changes in GABAA receptors following short and long-term exposure to zolpidem in vitro. Human embryonic kidney (HEK) 293 cells stably expressing recombinant α1β2γ2s GABAA receptors were exposed to zolpidem (1 and 10 μmol/L) for short-term (2 h daily for 1, 2 or 3 consecutive days) or long-term (continuously for 48 h). [3H] flunitrazepam binding assay was conducted using the membrane prepared from the cells. A single (2 h) or repeated (2 h daily for 2 or 3 d) short-term exposure to zolpidem affected neither the maximum number of [3H]flunitrazepam binding sites nor the affinity. In both control and short-term zolpidem treated groups, addition of GABA (1 nmol/L–1 mmol/L) enhanced [3H] flunitrazepam binding in a concentration-dependent manner. The maximum enhancement of [3H]flunitrazepam binding in short- term zolpidem treated group was not significantly different from that in the control group. In contrast, long-term exposure to zolpidem resulted in significantly increase in the maximum number of [3H]flunitrazepam binding sites without changing the affinity. Furthermore, long-term exposure to zolpidem significantly decreased the ability of GABA to stimulate [3H] flunitrazepam binding. The results suggest that continuous, but not intermittent and short-term, zolpidem- exposure is able to induce adaptive changes in GABAA receptors that could be related to the development of tolerance and dependence.

zolpidem; GABAA receptor; benzodiazepine; drug tolerance; drug dependence; HEK 293 cells; [3H] flunitrazepam binding

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