THE POSTNATAL-DEVELOPMENT OF THE GABA(A) BENZODIAZEPINE RECEPTOR IN THE RAT RED NUCLEUS

The development of the GABA(A)/Benzodiazepine receptor (GABA(A)R) in the red nucleus was studied using H-3-flunitrazepam (FNZ) as the probe. Saturation binding assay showed that the B-max of the ligand to the membranes of the nucleus increased from 0.50 +/- 0.04 nmol/mg protein at postnatal day 4, to 0.71 +/- 0.1 and 0.78 +/- 0.08 at day 7 and day 10. At day 20 the B-max decreased to a level near day 4 and persisted until day 40. However, the affinity of H-3-FNZ to the receptor remained quite constant. At least 4 proteins of 51kD, 53kD, 59kD and 62kD in the nucleus were labeled by H-3-FNZ, as revealed from photoaffinity binding and SDS-PAGE. The labeling of 53kD, 59kD and 62kD was high at earlier ages than day 10, whereas the 51kD was predominent from day 10 to day 40. Receptor binding autoradiography of the nucleus also showed that the most dense labeling was seen around day 10. The early transient increase in the GABA(A)R of the red nucleus may indicate the plasticity of the nucleus in response to environmental changes after birth.