Post-Trial Administration of H1 Histamine Receptor Blocker Improves Appetitive Reversal Learning and Memory in Goldfish, Carassius auratus

Based on the hypothesis that neuronal histamine exerts an inhibitory influence on learning and reinforcement, goldfish were tested for post-trial effects of the H ₁ receptor blocker chlorpheniramine (CPA) on learning the location of a food source in one of two compartments, one black the other white, with a feeder located in each compartment. Testing was carried out over 6 days. On the training day a food pellet was placed into the feeder of one of the compartments. After consumption of the food the fish were injected i.p. with either vehicle or CPA either immediately after training or 3 h later. Twenty-four-hours later, food was placed in the same compartment and the time to begin feeding was recorded. On the next day the location of the food pellet was reversed, and testing was continued for 4 days. On the first test day the time to begin feeding was significantly longer for the vehicle injected fish as compared with those injected with CPA. The vehicle group also took longer to begin feeding than the CPA group on the first reversal test day. The results of the 3-h delay groups indicated no significant differences between vehicle and drug for any experimental session. These results suggest that post-trial blockade of the H ₁ histamine receptor can affect appetitive learning in goldfish either by improving long-term memory consolidation and/or by the additive reinforcing effects of CPA (known from previous studies) on behavior.