Fetal, neonatal and adult expression of benzodiazepine receptor subtypes in human visual cortex.

We have investigated the relative distributions of type I and type II benzodiazepine receptors in fetal, neonatal and adult human visual cortex using [3H]flunitrazepam and the triazolopyridazine, CL218872. Microdensitometry of autoradiograms show that while both benzodiazepine subtypes are found in visual area 17 early in life, the type II benzodiazepine receptors predominate. In adult human visual cortex comparable mounts of type I and type II subtypes occur in a laminar specific distribution concentrated in layers 4c and 2/3. The results may suggest a role for age-dependent expression of benzodiazepine receptor subtypes in visual cortex development and neuroplasticity.