The projection of GABA-ergic neurons of the medial terminal accessory optic nucleus to the pretectum in the rat.

Large numbers of neurons were retrogradely labeled in both the dorsal and ventral medial terminal nucleus (MTN) after fluoro-gold injections into the rat pretectal nucleus of the optic tract/dorsal terminal nucleus (NOT/DTN). Fluorescence immunocytochemistry for GABA in the same brains revealed GABA-positive neurons distributed mainly in the dorsal MTN. Approximately half of all the GABAergic neurons in the MTN were double-labeled. Therefore, GABAergic neurons comprise a significant component of the MTN-NOT/DTN projection which most likely inhibits the pretectal pathway mediating horizontal optokinetic nystagmus.