Ontogeny of influence of clonidine on high potassium-induced release of noradrenaline and specific [3H]clonidine binding in the rat brain cortex.

A high (20 mM) K+-induced, Ca2+-dependent release of L-[3H]-noradrenaline (NA) from cerebral cortex slices was detected in rats on day 18 of gestation. Depolarization-evoked release (% of total radioactivity) increased with age between day 18 of gestation and day 70 of postnatal life. Clonidine (0.1 microM) significantly (p less than 0.05) reduced a high K+-induced L-[3H]NA release on days 7 and 70 but not on day 1. Both KD and Bmax of specific [3H]clonidine binding to cerebral cortex membranes rapidly increased between days 1 and 7, followed by a gradual increase to the adult level. Presynaptic alpha 2-adrenoceptors which regulate NA release seems to become sensitive to alpha 2-agonists and to reach functional maturity between days 1 and 7 after birth in the cerebral cortex of rats.