Postnatal development of myogenic contractile activity and excitatory innervation of rat urinary bladder.

Bladder strips from newborn compared with adult rats exhibited marked differences in both myogenic properties and postganglionic excitatory innervation. In the first 2-wk of life myogenic contractile activity progressively changed from a quiescent state (at birth) to the asynchronous contractile activity typical of bladder strips from adult animals. After birth activation of muscarinic cholinoceptors changed the myogenic contractile activity in a manner similar to that observed at later stages of development. Neurogenic contractions of bladders from newborn animals were atropine sensitive in the whole range of frequencies studied. During the first 2 wk the atropine-resistant component of these contractions increased progressively to reach an adult-like condition, i.e., atropine-resistant contractions account for over 90% and approximately 60% of contractions elicited at 0.1 and 1-20 Hz, respectively.