A GABAergic component in the commissure of the inferior colliculus in rat

The commissure of the inferior colliculus is significant as the final point of interconnection between homologous structures on the two sides of the auditory pathway at the subcortical level. The presence of excitatory fibres is well established in this tract, but the existence of an inhibitory component is controversial. Using rats, we injected biotinylated dextran amine into the inferior colliculus on one side to retrogradely label cells projecting through the commissure from the contralateral inferior colliculus. Immunocytochemistry for gamma-amino-n-butyric acid in neighbouring semithin sections revealed that 20% of biotinylated dextran amine cell profiles were also labelled for gamma-amino-n-butyric acid. We conclude that monosynaptic inhibitory connections contribute to the inhibition observed in the contralateral inferior colliculus in functional studies of the commissural projection.