Zolpidem withdrawal induced uncoupling of GABAA receptors in vitro associated with altered GABAA receptor subunit mRNA expression

Hypnotic zolpidem produces its effects via the benzodiazepine binding site in α1-containing GABAA receptors. The aim of the study was to assess the influence of duration of zolpidem treatment and its withdrawal, as well as the role of alpha1-containing GABAA receptors in the development of physical dependence and tolerance. Namely, recombinant receptors can be used to characterize mechanisms involved in different processes in the brain and to delineate the contribution of specific receptor subtypes. To address the influence of chronic zolpidem treatment we exposed HEK293 cells stably expressing alpha1beta2gamma2S recombinant GABAA receptors for seven consecutive days, while withdrawal periods lasted for 24, 48, 72 and 96 hours. Using radioligand binding studies we determined that chronic zolpidem treatment did not induce changes in either GABAA receptor number or in the expression of subunit mRNAs. We observed the enhancement of binding sites and upregulated expression of subunit mRNAs only following 96-hour withdrawal. Moreover, zolpidem treatment and its withdrawal (All time points) induced functional uncoupling between GABA and benzodiazepine binding sites in the GABAA receptor complex. Accordingly, it might be assumed that zolpidem withdrawal-induced uncoupling of GABAA receptors is associated with altered GABAA receptor subunit mRNA expression. The results presented here provide an insight into molecular and cellular mechanisms probably underlying adaptive changes of GABAA receptor function in response to chronic usage and withdrawal of zolpidem and perhaps the observed molecular changes could be linked to the tolerance and dependence produced upon prolonged treatment with other GABAergic drugs.