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Changes in relative potency among positive GABA(A) receptor modulators upon discontinuation of chronic benzodiazepine treatment in rhesus monkeys.

McMahon LR, Javors MA, France CP

Department of Pharmacology, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.

RATIONALE: Benzodiazepine treatment can result in dependence as evidenced by signs of withdrawal upon discontinuation of use. OBJECTIVE: Positive GABA(A) receptor modulators were examined for their capacity to attenuate flumazenil-like discriminative stimulus effects (i.e., withdrawal) that emerge upon discontinuation of chronic benzodiazepine treatment. METHODS: Rhesus monkeys receiving chronic diazepam (5.6 mg(-1) kg(-1) 24 h(-1) p.o.) discriminated flumazenil (0.1 mg/kg s.c.) from vehicle. RESULTS: Upon discontinuation of diazepam treatment, responding switched from the vehicle to the flumazenil lever, although at different times among monkeys. The shorter-acting benzodiazepine lorazepam (3.2 mg(-1) kg(-1) 8 h(-1)) was substituted for diazepam and, 11 h after lorazepam, monkeys consistently responded on the flumazenil lever. Flumazenil-lever responding after acute lorazepam deprivation was attenuated not only by benzodiazepines (lorazepam and midazolam) but also by positive GABA(A) receptor modulators acting at neuroactive steroid (pregnanolone and alfaxalone) and barbiturate sites (pentobarbital). Deprivation-induced responding on the flumazenil lever was not attenuated by low efficacy positive GABA(A) modulators (bretazenil and L-838,417) or non-GABA(A) receptor ligands (ketamine and cocaine). Neuroactive steroids were relatively more potent than other positive GABA(A) receptor modulators in attenuating deprivation-induced flumazenil-lever responding, as compared to their relative potency in monkeys discriminating midazolam and otherwise not receiving benzodiazepine treatment. CONCLUSIONS: These results suggest that positive GABA(A) receptor modulators acting at different sites attenuate withdrawal induced by discontinuation of benzodiazepine treatment, consistent with previous studies suggesting that the same compounds attenuate flumazenil-precipitated withdrawal. Differences in the relative potency of positive modulators as a function of acute versus chronic benzodiazepine treatment suggest that neuroactive steroids, in particular, are especially potent in benzodiazepine-dependent animals.

Published 26 April 2007 in Psychopharmacology (Berl), 192(1): 135-45.
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