engleski

Benzodiazepine site agonists: diazepam vs. zolpidem (in vitro study)

Prolonged exposure of GABA-A receptors to benzodiazepine site agonists, drugs which have potency to produce tolerance and dependence and to be abused, leads to adaptive changes of these receptors. The aim of this study was to better understand and to compare the phenomena induced by long-term exposure to diazepam and zolpidem. In order to evaluate the effects of long-term diazepam and zolpidem treatment on GABAA receptors HEK 293 cells stably expressing recombinant alpha1beta2gamma2s subtype of GABA-A receptors were exposed to diazepam (50 μM) or zolpidem (10 μM) for 48h. Radioligand binding studies were used to determine the parameters of [3H]flunitrazepam, [3H]muscimol and [3H]TBOB binding sites. Semi-quantitative RT-PCR and Western blot analysis were used to asses mRNA and protein levels. Long-term exposure of these cells to diazepam, as well as to zolpidem, increased the number of binding sites for GABA, benzodiazepines and convulsants, suggesting the enhancement the total GABAA receptor number. Moreover, the results suggested increased de novo synthesis of receptor subunits at transcriptional and translational level. Our results give evidence that long-term diazepam and zolpidem administration produce a decrease in the allosteric coupling between benzodiazepine and GABA binding sites at GABA-A receptor. Following 24 h discontinuation of long-term diazepam and zolpidem treatment enhanced number of binding sites, mRNA for alpha1 subunit and gamma2 subunit proteins returned to control values. Moreover, withdrawal from zolpidem normalized functional interactions between GABA and benzodiazepine binding sites, while allosteric uncoupling was still present 24 h following the termination of diazepam treatment. The results suggest that in our model, characterized by the presence of a single well defined receptor subtype, long-term exposure of GABA-A receptors to diazepam and zolpidem induce similar adaptive changes. On the other hand, the functional recovery of GABA-A receptors was achieved sooner after zolpidem than after diazepam withdrawal. If decreased ability of GABA to stimulate [3H]flunitrazepam binding, as suggested, is related to the development of tolerance and dependence to the effects of benzodiazepines, one could expect that treatment with diazepam stimulate enduring consequences.

benzodiazepines; diazepam; zolpidem; recombinant receptors; radioligand binding studies; mRNA; proteins

nije evidentirano