Dopamine receptors participate in acquisition and consolidation of latent learning of spatial information in zebrafish (Danio rerio)

There is growing appreciation that various aspects of learning and memory are strongly influenced by dopamine neurotransmission, and that zebrafish hold particular promise in the study of neurotransmitter systems. In this study, we sought to investigate the effect of dopamine receptors on acquisition and consolidation of memory in zebrafish using a latent learning paradigm. To this end, fish were subjected to a 30 min training trial each day for 16 days during which fish were allowed to freely explore a complex maze with the left or right path blocked and without the presence of a reward. During 16 days fish were treated with dopaminergic agonists (apomorphine, SKF-38393, and quinpirole) and antagonists (SCH-23390 and eticlopride) before or after training trials. To assess cognitive performance of fish, a subsequent probe trial was performed on day 17 while all paths leading to a reward chamber were open and the maze now contained stimulus fish as a reward. Pre- and post-training exposure to apomorphine, SKF-38393, and quinpirole significantly impaired learning and memory in fish. In contrast, fish exposed to eticlopride before and after training exhibited improved performance in a latent learning task. Administration of SCH-23390 before training did not affect zebrafish learning ability, but produced significant memory enhancement when given after training trials. Taken together, these findings are the first indications that D1 and D2 receptors are critically involved in acquisition and consolidation of latent learning in zebrafish, with a more prominent role for D2 receptors. The current study opens the door to future studies to investigate the involvement of dopamine receptors in various aspects of cognitive processes.