PRESENCE OF ENDOGENOUS INHIBITORS OF BENZODIAZEPINE BINDING IN DEVELOPING CHICK OPTIC LOBE

AN endogenous inhibitor of benzodiazepine receptor binding was removed from synaptic membranes of developing chick optic lobe by an exhausti ve buffer washing procedure. This treatment increased [H-3]flunitrazep am binding at all stages of development, although this effect was grea ter at early stages (embryonic day 14-16). Scatchard analysis performe d on exhaustively washed membranes at embryonic day 16 and postnatal d ay 15 revealed the presence of a single population of flunitrazepam bi nding sites with apparent dissociation constants (K-d) of 1.99 +/- 0.1 1 and 3.28 +/- 0.10 nM and a maximal number of binding sites (B-max) o f 1.07 +/- 0.08 and 1.22 +/- 0.11 pmol mg(-1) protein, respectively. A t both stages of development, the addition of inhibitory material, pre sent in the supernatants obtained after the washing procedure, reduced the affinity of recognition sites for [H-3]flunitrazepam with K-d of 4.92 +/- 0.13 and 5.62 +/- 0.12 nM, respectively while their B-max val ues remained unchanged. These studies demonstrate the presence of an e ndogenous material in developing chick optic lobe which competitively inhibits [H-3]flunitrazepam binding to its receptor site.