Oxytocinergic neurotransmission at the hippocampus in the central neural regulation of penile erection in the rat

Objectives. To investigate whether there is an oxytocinergic neurotransmiss ion at the hippocampus involved in the central regulation of penile erectio n in the rat. Methods. Male adult Sprague-Dawley (n = 27) rats anesthetized with pentobar bital were used. A 26-gauge needle was inserted into the corpus cavernosum to measure the intracavernous pressure (ICP) and the systemic and mean arte rial pressure and heart rate simultaneously. The following studies were per formed: stereotaxic delivery of oxytocin acetate (3 pmol/100 nL) into the h ippocampus; microinjection of a mixture of [d(CH2)(5)-Tyr(Me)(2)-Orn(8)]-va sotocin (3 pmol/100 nL) and oxytocin (3 pmo1/100 nL) into the hippocampus; injection of saline into the hippocampus; and intracavernous injection of o xytocin (3 pmol/100 muL). The ICP and hemodynamic parameters were monitored after each administration of the experimental agents. Results. After administration of oxytocin into the hippocampus, a significa nt increase in the ICP occurred from resting (8.8 +/-1.7 mm Hg) to a peak a t 49.6 +/- 12.5 mm Hg and persisted for 18.6 +/-9.4 minutes after an onset latency of 500.0 +/- 389.7 seconds. However, no change in the ICP occurred after administration of [d(CH2)(5)-Tyr(Me)(2)-Orn(8)]-vasotocin plus oxytoc in into the hippocampus. In addition, no elevation of ICP occurred after ad ministration of saline to the hippocampus or after intracavernous injection of oxytocin. Conclusions. The results demonstrate that administration of oxytocin into t he hippocampus induces penile erection in the rat. However, concomitant adm inistration of oxytocin and its antagonist was ineffective in eliciting pen ile erection. These observations suggest that oxytocinergic neurotransmissi on at the hippocampus may be involved in the central neural regulation of t he penile erection in the rat. UROLOGY 58: 107-112, 2001. (C) 2001, Elsevie r Science Inc.