The migration and neurochemical differentiation of gamma-aminobutyric acid (GABA)-immunoreactive neurons in rat visual cortex as demonstrated by a combined immunocytochemical-autoradiographic technique.

The development of some cortical local circuit neurons was traced using a technique which combined immunocytochemistry to label gamma-aminobutyric acid-immunoreactive (GABA+) neurons and [3H]thymidine autoradiography to identify cells with similar times of origin. Double-labeled neurons (GABA+ neurons with autoradiographic silver grains over their nuclei) are evident only after migration is complete. GABA+ neurons born on gestational day 16 are first identified in layer VIa on postnatal day 0 and those born on day 19 are in layer III on postnatal day 6. The frequency of double-labeled neurons increases during the week following their appearance. Therefore, the migration and the neurochemical differentiation of GABA+ neurons follow inside-to-outside sequences.