Erectile dysfunction is a serious and common complication of diabetes mellitus. The proposed mechanisms for erectile dysfunction in diabetes include central and autonomic neuropathy, endothelial dysfunction and smooth muscle dysfunction. The paraventricular nucleus (PVN) of the hypothalamus is known to be involved in centrally mediated penile erection. This study was designed to examine the role of nitric oxide (NO) within the central nervous system component of the behavioral responses including erection in diabetic rats. N-methyl-D-aspartic acid (NMDA)-induced erection, yawning and stretch through the PVN can be blocked by prior administration of NO synthase (NOS) blocker, L-NMMA, in freely moving, conscious male normal rats. Four weeks after streptozotocin (STZ) and vehicle injections, NMDA-induced erection, yawning and stretch responses through the PVN are significantly blunted in diabetic rats compared to control rats. Examination of neuronal NOS (nNOS) protein by western blot analysis indicated a reduced amount of nNOS protein in the PVN of rats with diabetes compared to control rats. Furthermore, restoring nNOS within the PVN by gene transfer using adenoviral transfection significantly restored the erectile and yawning responses to NMDA in diabetic rats. These data demonstrate that a blunted NO mechanism within the PVN may contribute to erectile dysfunction observed in diabetes mellitus.