p-Chloroamphetamine (PCA)-induced penile erection and ejaculatory responses have previously been characterised in the urethane-anaesthetised rat (Yonezawa et al. 2000). The present study investigates activity in the vas deferens nerve (VDN) and intraluminal vas deferens pressure, and also tests the effects of the intravenous administration of PCA, an indirect 5-HT agonist.

Male Sprague-Dawley rats (300-325g) (n = 4) were anaesthetised (urethane 0.15-0.25 mg kg^-1 I.V.). The VDN (a hypogastric branch) was identified in the abdominal cavity and isolated, and nerve activity recorded. A second group of rats (n = 4) were spinalised (T8/9, under urethane) and prepared as above. In two animals the ipsilateral vas deferens was isolated, and a 19G needle was inserted and connected to a pressure transducer and recorded. PCA was dissolved in saline (1.0 mg ml^-1) and given I.V. (1ml kg^-1). The effect of PCA on VDN activity and intraluminal vas deferens pressure was recorded. Animals were killed by an overdose of anaesthesic. Results are displayed as means ± S.E.M.

PCA evoked a sequence of responses, each consisting of synchronous bursts of activity (n = 4), beginning with a gradual increase (from 7.0 ± 1.1 Hz baseline) followed by several short bursts (3.8 ± 0.03 repeating at 0.36 ± 0.01 Hz) of escalating frequency (82.1 ± 16.0 Hz max). A single dose of PCA elicited 4.5 ± 0.3 responses lasting 19.7 ± 5.6 min. Intraluminal vas deferens pressure increased (18.6 ± 3.8 mmHg min to 24.1 ± 5.1 mmHg max) in bursts, as well as bulbocavernous muscles contractions, corresponding to bursts of nerve activity. Ejection of the seminal plug also occurred. One hour after the first dose, a subsequent PCA administration evoked further similar responses. Responses to PCA were observed unchanged in acutely spinalised animals. Removal of the efferent pathway by crushing the VDN central to the recording site abolished the PCA effects. Single shock stimulation of the VDN caused contraction of the vas deferens and an increase in intraluminal pressure.

This study shows that PCA-induced VDN activity closely correlates with ejaculatory reflexes and indicates that recording of VDN activity may be a valuable tool in the study of ejaculation. Furthermore we conclude that the rhythmic pattern of activity in the VDN associated with ejaculation represents the output of a spinal pattern generator like that suggested by Carro-Juárez et al. (2003). Importantly excitability of this pattern generator is enhanced by 5-HT-like receptor activation.

This study was funded by BBSRC and Pfizer Ltd.