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

Objectives. To investigate whether there is an oxytocinergic neurotransmission at the hippocampus involved in the central regulation of penile erection in the rat. Methods. Male adult Sprague-Dawley (n = 27) rats anesthetized with pentobarbital were used. A 26-gauge needle was inserted into the corpus cavernosum to measure the intracavernous pressure (ICP) and the systemic and mean arterial pressure and heart rate simultaneously. The following studies were performed: stereotaxic delivery of oxytocin acetate (3 pmol/100 nL) into the hippocampus; microinjection of a mixture of [d(CH2)(5)-Tyr(Me)(2)-Orn(8)]-vasotocin (3 pmol/100 nL) and oxytocin (3 pmo1/100 nL) into the hippocampus; injection of saline into the hippocampus; and intracavernous injection of oxytocin (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 significant increase in the ICP occurred from resting (8.8 +/-1.7 mm Hg) to a peak at 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 oxytocin into the hippocampus. In addition, no elevation of ICP occurred after administration of saline to the hippocampus or after intracavernous injection of oxytocin. Conclusions. The results demonstrate that administration of oxytocin into the hippocampus induces penile erection in the rat. However, concomitant administration of oxytocin and its antagonist was ineffective in eliciting penile erection. These observations suggest that oxytocinergic neurotransmission at the hippocampus may be involved in the central neural regulation of the penile erection in the rat. UROLOGY 58: 107-112, 2001. (C) 2001, Elsevier Science Inc.