Penile erections of rats

Rats in which only chronic guide cannulas were implanted were placed individually in Plexiglas cages. After a 30-min habituation period, oxytocin or vehicle alone was injected into the ventral subiculum or the PMCo in a volume of 0.3 lL over a period of 2 min through the microinjection cannula connected by polyethylene tubing to a 10-lL Hamilton syringe driven by a Stoelting microsyringe pump. When d(CH2)5Tyr(Me)2-Orn8-vasotocin was used, the compound was injected into the ventral subiculum or the PMCo 15 min before oxytocin.

When cis-flupentixol and (+)MK-801 were used, the compounds were injected into the nucleus accumbens or the VTA 15 min before oxytocin. When microdialysis was
performed, the microdialysis probe was connected via polyethylene tubing to a 2500-lL Hamilton syringe driven by a Stoelting microsyringe pump at one end and to the polyethylene collecting loop at the other end.

After a 2-h period of equilibration of the dialysis probe with Ringer’s solution, three dialysate aliquots of 37.5 lL were collected for the determination of basal levels of dopamine and DOPAC, oxytocin or vehicle was injected into the ventral subiculum or the PMCo, and five additional dialysate aliquots were collected.

When d(CH2)5Tyr(Me)2-Orn8-vasotocin was used, this was injected into the ventral subiculum or the PMCo 15 min before oxytocin. In all of the above experimental conditions, after treatments rats were observed for the entire duration of the experiment in order to count penile erection episodes and, in those experiments during which microdialysis was performed, to replace filled loops with empty ones every 15 min. Penile erections were scored when the penis emerged from the penile sheath, which was usually accompanied by penile grooming and hip flexions.


In those experiments in which only microinjections through chronic guide cannulas were performed, one-way anova followed by Tukey’s multiple comparison test was performed in order to show significant differences between groups for penile erection. When microdialysis was performed, the areas under the curves obtained by plotting penile erection, dopamine and DOPAC values vs. time in each animal were first calculated with the classic trapezoidal rule. The AUCs were then statistically compared between groups with one-way anova followed by Tukey’s multiple comparison test, in order to show significant differences between groups. P < 0.025 was considered to be significant.

Effect of oxytocin injected into the dorsal and ventral subiculum or into the PMCo on penile erection: dose–response curves Oxytocin (20, 40, 80 and 100 ng) microinjected into the ventral subiculum or the PMCo, but not into the dorsal subiculum, induced penile erection episodes in a dose-dependent manner. In both cases,
penile erection started about 30 min after the injection and disappeared in about 60 min. In the ventral subiculum, the minimal effective dose was 40 ng, which increased penile erection episodes from 0.35 ± 0.09 to 1.30 ± 0.33 (P < 0.01), and the maximal effective dose was 100 ng, which increased penile erection episodes up to
3.0 ± 0.35 (P < 0.01).

Similar results were found when oxytocin was injected into the PMCo: the minimal effective dose was 40 ng, which increased penile erection episodes from 0.38 ± 0.09 to 1.20 ± 0.21 (P < 0.01), and the maximal effective dose was 100 ng, which increased penile erection episodes up to 2.50 ± 0.31 (P < 0.01). In contrast, oxytocin injected into the dorsal subiculum was ineffective (P > 0.1).