Binding of flunitrazepam to differentiating neurons cultured in a chemically defined, hormone-supplemented medium

[3H]Flunitrazepam (FNZ) binding to cortical neurons from fetal rat brain was investigated in vitro. The use of a synthetic medium specific for neurons made it possible to plot a developmental curve of 3H-FNZ binding in an almost pure neuronal culture. Detectable specific binding was present in vitro at time 0 (that is, the 16th gestational day). A progressive increase of binding, due to an increment in the number of recognition sites, was observed on the subsequent days. The affinity of the specific binding sites to 3H-FNZ was enhanced by the addition of exogenous GABA, whereas the density was not affected.