DEVELOPMENT AND ISOPROTERENOL-INDUCED REGULATION OF ADRENOCEPTOR BINDING IN CULTURED RAT NEOCORTICAL EXPLANTS IS SEEN ONLY WITH THE BETA-1,NOT WITH THE BETA-2 SUBTYPE

The presence and time-course of beta-adrenoceptor density in cultured explants of neocortex obtained from 6-day-old rat pups were investigat ed using a [I-125]ICYP binding assay. A delayed, but more pronounced, increase in the receptor expression was observed as compared to the si tuation previously described in vivo. These changes only occurred for the beta(1)-subtype of the receptor, whereas the beta(2)-subtype bindi ng remained constant up to 3 weeks in vitro. The delay of beta(1)-adre noceptor expression may be due to the incomplete presence of the prope r maturational input, and the late enhancement of receptor expression to upregulation related to the absence in vitro of noradrenergic input . Decreased beta-adrenoceptor levels could be induced by chronic treat ment of the beta-agonist isoproterenol (1 mu M) introduced either for 3 or 13 days. Again, changes in density were found only for the beta(1 )-adrenoceptor binding sites. There is no reduction of receptor densit y following return to control conditions for 10 days after a 3-day tre atment with isoproterenol, demonstrating the ability of this model to attain its final receptor density notwithstanding the developmental in sult.