Opposite effects of cholinergic agents and benzodiazepine receptor ligands in a passive avoidance task in rats.

Benzodiazepine (Bzd) agonist, diazepam (Dzp) and inverse agonist methyl beta-carboline-3-carboxylate (beta-CCM); acetylcholinesterase inhibitor, physostigmine (Physo) and muscarinic antagonist, scopolamine (Scopo), were investigated for their mnesic effect in a passive avoidance (PA) task in rats. Impairments were observed after Dzp- and/or Scopo-pretraining treatments. Physo was without effect but antagonized the Dzp-induced impairments. beta-CCM enhanced acquisition and antagonized the Scopo-induced impairing effect. All these drugs had no effect in posttraining administration.