ONTOGENY OF 2 DIFFERENT BENZODIAZEPINE BINDING-SITES IN THE CHICK OPTIC LOBE

THE developmental time-course of type I and type II benzodiazepine rec eptors in the chick optic lobe was determined using a triazolopyridazi ne, CL 218872. At embryonic day 13 most of the binding sites correspon ded to type II (98.23%), while type I represented only a minor proport ion (1.77%). During development there was an increase in type I bindin g sites which reached 62.88% in adulthood, while type II binding sites decreased to 37.12%. These results demonstrate a differential ontogen y of two benzodiazepine receptor subtypes. Changes in the benzodiazepi ne binding population may account for the variability in the GABA-benz odiazepine receptor interaction during chick optic lobe development.