In neonatal kittens, micturition is induced by a spinal somatovesical reflex pathway that is activated by the mother cat licking the perigenital region of the kitten. The somatovesical reflex pathway disappears about the time of weaning and is replaced by a vesicovesical reflex pathway that produces micturition via a supraspinal reflex pathway that is activated by distension of the urinary bladder. Furthermore, stimulation of the perigenital region in adult cats actually inhibits the supraspinal vesicovesical micturition reflex. Spinalization prompts the return of the somatovesical reflex, immediately in weaned kittens but over a course of days to weeks in adult cats. The purpose of the present experiments was to determine if the somatovesical reflex could be demonstrated acutely, and reversibly, in adult cats with an intact spinal cord via pharmacological suppression of the serotonergic system. The serotonergic system was suppressed by the intravenous administration of 5-methoxy- N, N-dimethyltryptamine (5-MeODMT), a serotonin agonist that inhibits the firing of serotonergic neurons via activation of inhibitory somatodendritic autoreceptors. 5-MeODMT in low doses (20–50 μ/kg) abolished inhibition of the bladder produced by either light tactile stimulation of the perigenital region or by electrical stimulation of the pudendal nerve, which carries the afferent fibers from the perigenital region, in 9 of 10 adult cats. Furthermore, in 8 of the 10 cats, the bladder inhibition was reversed to an excitation of variable amplitudes in each cat. Higher doses of 5-MeODMT (100–1000 μ/kg) abolished spontaneous bladder activity but did not inhibit perigenital-induced bladder contractions in those 8 animals in which the drug unmasked the excitatory somatovesical reflex. Electrophysiological recordings of sympathetic and somatic efferent neural activity from the hypogastric nerve and EMG electrodes in the striated muscle of the external urethral sphincter, respectively, showed a decrease in both activities at low doses of 5-MeODMT and an increase in activity at high doses. In chronic spinal cats and neonatal kittens, 5-MeODMT did not affect perigenital-induced bladder contractions, even at high doses, and only produced excitation of sympathetic and somatic efferent activities. These results suggest that the switch of the effects of perigenital stimulation from bladder excitation to inhibition, which occurs during postnatal development, may reflect maturation of bulbospinal serotonergic mechanisms. Conversely, the switch of the effects of perigenital stimulation from bladder inhibition to excitation, which occurs following spinal transection, may reflect a loss of bulbospinal serotonergic mechanisms.