Different temporal effects of serotonergic antagonists on passive avoidance retention.

The experiments examined the effects of acute administration of three different serotonergic receptor antagonists (ketanserin, pirenperone and mianserin) on one-trial passive avoidance retention in mice. Administration of each antagonist 30 min before training produced a dose-dependent impairment in retention. In contrast, administration of each of the antagonists immediately after training produced a dose-dependent improvement in retention. The time-dependent effects of pre- and post-train antagonist administration were assessed using pirenperone. In both cases, the effects on test performance were determined to be time-dependent. The results provide additional evidence suggestive of a differential role of the serotonergic nervous system in the processes underlying learning and memory.