The effects of 5-HT receptor blockade on memory formation in the chick: possible interactions between...

An antagonist, 21-009, with high affinity for 5-HT1B receptors and some for beta-adrenergic receptors, induces amnesia in the domestic chick when given centrally before training, using a one-trial passive avoidance task. Nonspecific behavioral effects, or effects upon performance at test, almost certainly do not cause the observed amnesia. The 5-HT2 antagonist ketanserin and the 5-HT3 antagonist ICS 205-930, did not have any effects when given before training at the same dose as that at which 21-009 was effective. The unusual pattern of action of 21-009 (sensitivity only at, or around the time of learning, combined with very delayed memory loss) resembles that of certain beta-antagonists, but not others. The results are discussed in terms of both direct action on 5-HT systems involved in memory formation and possible interactions between 5-HT and beta-adrenergic systems.