Introduction: The urethrogenital (UG) reflex is an autonomic and somatic response that mimics some of the physiological changes seen during ejaculation. The UG reflex is tonically inhibited by neurons in the ventral medulla, an area containing serotonin neurons. AIM; To examine the effect of lesions of brain neurons containing the serotonin reuptake transporter (SERT) on ejaculatory-like reflexes.
Methods: Anti-SERT saporin (80 nL, 1 mM) or saline was injected bilaterally into the ventrolateral medulla of male Sprague-Dawley rats. Ten to 18 days later, animals were deeply anesthetized and the presence of the UG reflex was examined before and after acute spinal cord transection (T9-10). Following the experiment the presence and number of serotonin and norepinephrine containing neurons (using tryptophan hydroxylase and dopamine beta-hydroxylase, respectively) was performed.
Main outcome measures: The UG reflex and cell counts.
Results: In saline-injected controls the UG reflex was not evoked in the anesthetized, intact preparation, indicating the presence of the supraspinal inhibition, as previously reported. Injection of anti-SERT saporin into the ventrolateral medulla allowed the UG reflex to be activated in the intact preparation, thus removed the inhibition. This was associated with a decrease in the number of serotonin neurons in the ventrolateral medulla and raphe. No change in the number of noradrenergic neurons was observed.
Conclusion: These studies suggest that ventral medullary neurons containing SERT are involved in the tonic inhibition of the UG reflex.