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• Spatial learning in fish are dependent of telencephalic NO. • NO synthesis has scarcely any effect on retrieval process of information in fish. • Inhibition of NO production produced a selective deficit in place learning. Nitric oxide plays a role in the long term potentiation mechanisms produced in the mammalian hippocampus during spatial learning. A great deal of data has demonstrated that the dorsolateral telencephalon of fish could be homologous to the mammalian hippocampus sharing functional similarities. In the present study, we analyzed the role of nitric oxide in spatial learning in teleost fish. In Experiment 1, we studied the effects of the inhibition of telencephalic nitric oxide in goldfish during the acquisition of a spatial task. The results showed that nitric oxide is involved in the learning of a spatial task. Experiment 2 evaluated the effects of the inhibition of telencephalic nitric oxide in goldfish for the retrieval of a learned spatial response. The results indicated that the retrieval of the information previously stored is not dependent of the nitric oxide. The last experiment analyzed the role of the telencephalic nitric oxide in place and cue learning. Results showed a clear impairment in place but not in cue learning. As a whole, these results indicate that fish and mammals, could have a relational memory system mediated by similar biochemical mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: There is some experimental evidence that the pallial areas of a fish''s brain are involved in distincted learning functions. Recently published data suggest that the medial pallium is essential for avoidance learning and the lateral pallium is crucial for spatial learning and is also involved in temporal aspects of the learning processes. This data joined to the proposal of homologies between medial and lateral fish pallia and pallial amygdala and hippocampus respectively, suggest that the pallial areas could have preserved their functions throughout vertebrates’ evolution. However, the functional implication of dorsal pallium that has been proposed as homologous to mammalian isocortex and transition cortex is largely unknown. In this study we analyze the role of dorsal pallium in trace and non-trace avoidance learning. Our results show the implication of this area in trace conditioning, but not in non-trace conditioning. This result allows discussion of homology proposals among lateral, dorsal, and medial pallia and hippocampus, isocortex, and pallial amygdala respectively. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]