INVOLVEMENT OF MECHANISMS DEPENDENT ON NMDA RECEPTORS, NITRIC-OXIDE AND PROTEIN-KINASE-A IN THE HIPPOCAMPUS BUT NOT IN THE CAUDATE-NUCLEUS IN MEMORY

The effects of the NMDA receptor antagonist AP5, the nitric oxide synt hase (NO) inhibitor NO-arg or the protein kinase A (PKA) inhibitor KT5 720 on memory were evaluated. Rats bilaterally implanted in the CA1 re gion of the dorsal hippocampus were trained and tested in a step-down inhibitory avoidance task, and rats unilaterally implanted in the left posteroventral region of the caudate nucleus were trained and tested in a cued water maze task. Previous findings from this and other labor atories had found that lesions or pharmacological treatments of these sites significantly altered memory of these two tasks. Immediately aft er training, animals received intrahippocampal or intracaudate 0.5 mu l microinfusions of saline, AP5, NO-arg or KT5720. All three drugs imp aired retention of inhibitory avoidance, but did not affect retention of the cued water maze. The findings suggest that NMDA receptor-, NO- and PKA-mediated processes in the dorsal hippocampus, but not in the c audate nucleus, are involved in memory.