GABAERGIC FEEDFORWARD PROJECTIONS FROM THE INFERIOR COLLICULUS TO THEMEDIAL GENICULATE-BODY

A novel and robust projection from gamma-aminobutyric acid-containing (GABAergic) inferior colliculus neurons to the medial geniculate body (MGB) was discovered in the cat using axoplasmic transport methods com bined with immunocytochemistry. This input travels with the classical inferior colliculus projection to the MGB, and it is a direct ascendin g GABAergic pathway to the sensory thalamus that may be inhibitory. Th is bilateral projection constitutes 10-30% of the neurons in the audit ory tectothalamic system. Studies by others have shown that comparable input to the corresponding thalamic visual or somesthetic nuclei is a bsent. This suggests that monosynaptic inhibition or disinhibition is a prominent feature in the MGB and that differences in neural circuitr y distinguish it from its thalamic visual and somesthetic counterparts .