Spatial learning and goldfish telencephalon NMDA receptors.

Recent results have demonstrated that the mammalian hippocampus and the dorso-lateral telencephalon of ray-finned fishes share functional similarities in relation to spatial memory systems. In the present study, we investigated whether the physiological mechanisms of this hippocampus-dependent spatial memory system were also similar in mammals and ray-finned fishes, and therefore possibly conserved through evolution in vertebrates. In Experiment 1, we studied the effects of the intracranial administration of the noncompetitive NMDA receptor antagonist MK-801 during the acquisition of a spatial task. The results indicated dose-dependent drug-induced impairment of spatial memory. Experiment 2 evaluated if the MK-801 produced disruption of retrieval of a learned spatial response. Data showed that the administration of MK-801 did not impair the retrieval of the information previously stored. The last experiment analyzed the involvement of the telencephalic NMDA receptors in a spatial and in a cue task. Results showed a clear impairment in spatial learning but not in cue learning when NMDA receptors were blocked. As a whole, these results indicate that physiological mechanisms of this hippocampus-dependent system could be a general feature in vertebrate, and therefore phylogenetically conserved.