Oxytocin injected into the hippocampal ventral subiculum induces penile erection in male rats by increasing glutamatergic neurotransmission in the ventral tegmental area.

Oxytocin (100 ng) injected unilaterally into the ventral subiculum of the hippocampus induces penile erection episodes, which started 30 min after treatment and were abolished by the prior injection of d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin (2 μg), an oxytocin receptor antagonist, into the ventral subiculum. Oxytocin-induced penile erection occurred 15 min after the increase of the concentration of extracellular dopamine in the dialysate obtained from either the nucleus accumbens or the prelimbic medial prefrontal cortex, which was also abolished by d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin. An increase in extracellular glutamic acid concentration was also observed in the same dialysate obtained from the ventral tegmental area, but not from the prelimbic medial prefrontal cortex or the nucleus accumbens in which dopamine concentration was measured, 15 min after the injection of oxytocin into the ventral subiculum. This effect was also abolished by the prior injection of d(CH(2))(5)Tyr(Me)(2)-Orn(8)-vasotocin into the ventral subiculum. These results confirm previous findings showing that ventral subiculum oxytocin-induced penile erection is mediated by an increase of glutamic acid neurotransmission in the ventral tegmental area. This in turn increases mesolimbic and mesocortical dopaminergic activity, releasing dopamine in the nucleus accumbens and in the prelimbic medial prefrontal cortex. These results are in line with previous studies supporting the hypothesis that the ventral subiculum participates in a complex neural circuit controlling not only penile erection and copulation, but also sexual motivation, arousal and rewarding.