Presynaptic involvement of nitric oxide in dopamine D1/D5 receptor-inducedsustained enhancement of synaptic currents mediated by ionotropic glutamate receptors in the rat hippocampus

Using whole-cell patch-clamp recordings, the study tested the possibility w hether nitric oxide (NO) was involved in dopamine D1/D5 receptor (D1/D5r)-i nduced sustained enhancement of excitatory postsynaptic currents (EPSCs) me diated by ionotropic glutamate receptors in rat hippocampal slices. Activat ion of D1/D5r by a selective agonist, 50 mu M (+/-)-6chloro-PB hydrobromide , elicited not only a sustained enhancement but also an increased frequency of spontaneous EPSC. The D1/D5r-induced effect was associated with decreas es in paired-pulse facilitation (PPF). A selective inhibitor of neuronal NO synthase (nNOS), 100 mu M 7-nitroindazole monosodium salt, substantially a ttenuated both the magnitudes of D1/D5r-induced enhancement and PPF decreas e. These results suggest that presynaptic effects mediated by NO, possibly synthesized by nNOS, are involved in D1/D5-induced sustained enhancement of synaptic currents mediated by ionotropic glutamate receptors in the hippoc ampus. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.