Involvement of histamine receptors in the acquisition of inhibitory avoidance in Carassius auratus.

This study investigated the involvement of H(1) and H(2) histaminegic receptors on the acquisition of a new task in Carassius auratus by using an inhibitory avoidance paradigm in which the animals had to learn to avoid an aversive stimulus. Before training, the fish received injections of H(2) antagonist zolantidine at a dose of 20 mg/kg, or H(1) antagonist chlorpheniramine at a dose of 4 or 16 mg/kg. Control animals were injected with distilled water. A facilitatory effect of chlorpheniramine was observed at the dose of 16 mg/kg. On the other hand, the administration of 20 mg/kg of zolantidine inhibited acquisition. Place preference conditioning was used to observe the aversive or reinforcing effects of the drugs, which could interfere with the inhibitory avoidance procedure; however, no effects were observed. Thus, it can be suggested that both receptors, H(1) and H(2), are involved in the acquisition of a new task in this species.