Unmasking of a neonatal somatovesical reflex in adult cats by the serotonin autoreceptor agonist 5-methoxy-N,N-dimethyltryptamine.

In newborn kittens, urination is triggered by the mother licking the genital area, activating a spinal reflex. This reflex disappears around weaning and is replaced by a brain-controlled reflex that responds to bladder fullness. In adult cats, genital stimulation actually inhibits urination. The experiments tested whether temporarily suppressing the serotonergic system could restore the infant reflex in adult cats with intact spinal cords. Low doses of a serotonin agonist (5-MeODMT, 20-50 micrograms/kg) blocked the inhibition of bladder activity caused by genital touch or nerve stimulation in 9 of 10 adult cats. In 8 of those cats, the inhibition reversed to bladder contractions of varying strength, revealing the infant reflex. Higher doses (100-1000 micrograms/kg) stopped spontaneous bladder activity but did not prevent genital-triggered contractions.

Study at a glance

Abstract

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 micrograms/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 micrograms/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.(ABSTRACT TRUNCATED AT 250 WORDS)