HETEROGENEITY AND DIFFERENTIAL EXPRESSION OF THE GAMMA-AMINOBUTYRIC ACID(A) (GABA(A)) BENZODIAZEPINE RECEPTOR IN THE AVIAN BRAIN DURING DEVELOPMENT/

1. The changes in the GABA,/benzodiazepine receptor in chicken brain d uring development has been studied by using H-3-flunitrazepam as the p robe for the benzodiazepine modulator site and the antibodies recogniz ing the receptor protein, In the telencephalon and optic tectum, the p roteins of 48, 50, and 51 kD were markedly labeled by H-3-flunitrazepa m from embryonic day 18 to postnatal days, as revealed by photoaffinit y labeling and SDS-PAGE of the brain membranes; the 51-kD protein appe ared to be the predominant one in labeling intensity except at embryon ic day 18 and postnatal days 14 and 28, whereas the 47- and 50-kD prot eins were dominant in the cerebellum, However, the 47- and 48-kD prote ins were faintly seen after postnatal day 28 in the three regions exam ined. 2. Immunoblotting using a monoclonal antibody against the 50- an d 51-kD proteins showed that the straining pattern ill the developing telecephalon or optic tectum was similar to the 50 kD/51 kD pattern ob tained from fluorography. The antibody also stained the 50- and 51-kD proteins in the cerebellum despite the fact that the 51-kD protein was barely seen in the fluorogram. Moreover, the 50-kD protein was recogn ized by an antiserum raised against a partial sequence of the alpha 1 subunit of the receptor expressed in bacteria. The staining levels for the 50-kd protein by the antiserum on immunoblots of the brain region s were low in embryonic animals but higher during postnatal stages, co nsistent with that seen in fluorograms. 3. Receptor binding autoradiog raphy using H-3-flunitrazepam exhibited that varying degrees of labeli ng intensity occurred among various brain areas at different ages. Hig h densities of binding were present in the olfactory bulb, paleostriat um, optic tectum, and midbrain. These results support the diversity of the GABA(A)/benzodiazepine receptor in the vertebrate CNS.