['To distinguish whether the improvement of hepatic encephalopathy by benzodiazepine receptor antagonists is mediated by their antagonistic or their inverse agonistic properties, the neurobehavioral effects of a variety of benzodiazepine receptor ligands in rats with thioacetamide-induced acute liver failure were tested.', 'The neural inhibitory effect of the benzodiazepine agonist flunitrazepam and its reversibility by the "pure" antagonist Ro 14-7437 were examined in thioacetamide-treated rats and controls. The effects of Ro 14-7437, of the partial inverse agonist Ro 15-4513, and the inverse agonist DMCM in rats with hepatic encephalopathy grade II/III were tested. Encephalopathic rats were pretreated with Ro 14-7437 or vehicle and then injected with Ro 15-4513.', 'Thioacetamide-treated rats were more sensitive to flunitrazepam than controls. In both groups, its effect was completely antagonized with Ro 14-7437. Encephalopathy was significantly improved by Ro 15-4513, although Ro 14-7437 and vehicle had no effect. DMCM worsened the condition of encephalopathic rats but had no effect in controls. Pretreatment with Ro 14-7437 abolished the beneficial effects of Ro 15-4513.'] Is hepatic encephalopathy in rats with thioacetamide-induced acute liver failure mediated by endogenous benzodiazepines?