Inhibition of pudendal reflexes in spinal rats - Reassessing the role of serotonin

The effects of serotonin (5-HT) and thyrotropin-releasing hormone (TRH) on penile reflexes were investigated in intact and spinally transected male ra ts. Doses of intrathecal 5-HT (0.0, 1.13, 2.26, 11.3, 22.6, and 113.0 nmol) , in a range previously shown to inhibit pudendal reflexes in anesthetized spinal preparations, prolonged the latency to the first penile erection in awake intact rats. However, these doses also provoked hyperreactivity and v ocalization. Doses of intrathecal TRH (100 and 500 pmol) that effectively i nhibited penile erection in intact animals were less effective in spinalize d animals, Finally, a combination of subthreshold doses of TRH (100 pmol) a nd 5-HT (4.0 nmol) at a ratio known to affect other TRH/5-HT-mediated circu its significantly extended erection latency in animals with spinal transect ions. These data suggest that 5-HT and TRH are both involved in the inhibit ory circuits regulating penile erection, either through corelease onto the same population of cells or through independent release onto different popu lations of neurons. (C) 2001 Elsevier Science Inc. All rights reserved.