Agonistic action of a benzodiazepine antagonist: effects of Ro 15-1788 and midazolam on hypertonic NaCl intake.

Rats adapted to a 23-hr water deprivation regimen were allowed a daily 1-hr water rehydration session. On test days the session drinking fluid was 1.5% NaCl solution rather than water. One group was injected (SC) with the benzodiazepine antagonist Ro 15-1788 (2.5-10 mg/kg) and another group with the agonist agent midazolam (0.13-2.0 mg/kg) every 5-6 days at 10 and 15 min before a test session, respectively. Both Ro 15-1788 and midazolam increased 1.5% NaCl solution intake in a dose-related manner. In this study and in previous research, benzodiazepines and barbiturates were shown to increase the intake of hypertonic NaCl solutions. The present results reveal a similar effect for Ro 15-1788, indicating an agonistic dimension to the spectrum of action of this specific receptor antagonist.