Ontogeny of the benzodiazepine receptor in human brain: fluorographic, immunochemical, and reversible binding studies

The prenatal and postnatal human ontogeny of the central benzodiazepine receptor was investigated in six different brain regions between week 24 postconception and age 14 years. Binding studies, which were performed with [3H]flunitrazepam [( 3H]FNZ), revealed a steep increase in receptor density postnatally in frontal cortex and cerebellum. Bmax values were higher in medulla oblongata, pons, and thalamus than in cortex and cerebellum up to week 26. After that, receptor densities declined significantly in medulla and olive. The same tendency was apparent in pons, whereas receptor density remained unchanged in thalamus. The early ontogeny of the benzodiazepine receptor was also evaluated in fluorographs [( 3H]FNZ) and immunoblots using the alpha 1-subunit-specific monoclonal antibody (mAb) bd-24. Specific radiolabeled proteins with molecular weights of 53K and 59K were visible in cortical membranes from gestational week 8, the earliest time investigated. During further development, the intensity of the 53K band increased without changes in the 59K band. As in other species, postmortem proteolysis in human brain led to a specifically labeled peptide of 47K. The mAb bd-24 immunolabeled only the 53K protein and the 47K peptide.