Conditioned place-preference analysis in the goldfish with the H1 histamine antagonist chlorpheniramine

The aim of this study was to investigate whether the histamine H1-receptor blocker, chlorpheniramine (CPA), has a reinforcing effect in goldfish. We used a place-preference procedure in an aquarium with two chambers colored black and white. On day 1, the animals were placed in the test chamber for 10 min for habituation. On day 2, they were placed in the start compartment for 30 s, the sliding doors were opened, and the time spent in each compartment was recorded over the 10 min to determine the natural compartment preference for each animal. On day 3, they were injected either with 0.1, 0.4, 1.0, or 4.0 mg/kg of CPA or only with vehicle and placed in the less preferred compartment for 25 min. On day 4, the animals were placed in the start compartment and the time spent in each compartment during the 10-min test period was recorded again. The groups treated with 1.0 and 4.0 mg/kg of CPA, spent significantly more time in the compartment in which they experienced the drug effect than the group treated with vehicle. On the other hand, the group treated with 0.4 mg/kg spent significantly less time in the drug-paired compartment. The results indicate a biphasic effect of CPA. Considering that there is evidence that low doses of CPA can also block H3-receptors, we suggest that in goldfish the histaminergic neural system has an inhibitory role in the reinforcing process.