Postnatal development of micturition reflex in rats.

The postnatal development of the micturition reflex and factors related to its initiation have been investigated by means of cystometric techniques under urethan anesthesia. In rats less than 10 days of age, micturition is not elicited in response to bladder distension. In these animals voiding is triggered by application of a somatic stimulus in the perineal area. In rats greater than or equal to 15 days of age the response to bladder filling is similar to that observed in adults. In rats 10-15 days of age an intermediate pattern is frequently observed; i.e., bladder filling elicited micturition at high values of pressure threshold. The myogenic (tetrodotoxin insensitive) contractile activity of the bladder is absent at birth and developed postnatally, similar to that described in the isolated organ [C. A. Maggi, P. Santicioli, and A. Meli. Am. J. Physiol. 247 (Regulatory Integrative Comp. Physiol. 16): R972-R978, 1985]. The ability of topical capsaicin to induce tetrodotoxin-sensitive contractions of rat bladder (micturition reflex) appeared at day 10 and increases thereafter in parallel with ability of the bladder to respond to distension. These findings demonstrate that peripheral factors, such as myogenic contractile activity and sensory innervation, which are involved in the initiation of bladder voiding undergo a postnatal development in rats.