Substrate for rapid feedforward inhibition of the auditory forebrain.

A sizeable, feedforward, GABAergic projection exists from the inferior colliculus to the medial geniculate body in cats. We compared the dimensions of GABA-immunoreactive and non-immunoreactive axons in the brachium of the cat inferior colliculus, and demonstrate that GABA-immunoreactive axons are among the largest of brachial axons. We propose that, based on their large size, GABAergic tectothalamic axons provide a substrate for rapid feedforward inhibition of geniculate neurons.