Developmentally different onset of alpha 1- and alpha 2-adrenergic responses in the neonatal rat dorsal motor nucleus of the vagus in vitro.

Development of noradrenergic responses in the rat dorsal motor nucleus of the vagus (DMV) from postnatal days 0 to 22 was studied by a conventional microelectrode technique using brain slice preparations. Between postnatal days 0 and 6, noradrenaline (NA) caused only alpha 1-adrenoceptor-mediated depolarizations. By postnatal day 14, alpha 2-adrenoceptor-mediated hyperpolarization appeared. During the next postnatal week, the response pattern to NA became similar to that in adults, including both alpha 1- and alpha 2-adrenergic responses. These results suggest that alpha 2-adrenergic responses in DMV neurons are absent at birth but develop rapidly in the 3 weeks after birth. Furthermore, alpha 1-adrenoceptors have already been functioning in the fetal period.