In the present study,we investigated the relationship between c-fos expression in the auditory thalamus and corticofugal activation.The contribution of neurotransmitters and related receptors,the involvement of thalamic reticular nucleus (TRN) and the role of neuronal firing pattems in this process were also examined.The principal nuclei of the medial geniculate body (MGB) showed c-fos expression when the auditory cortex (AC) was activated by direct injection of bicuculline methobromide (BIM).However,no expression was detectable with acoustic stimuli alone.This indicated that c-fos expression in the principal nuclei of the MGB was triggered by the corticofugal projection.c-fos expression could be elicited in the MGB by direct injection of glutamate.Direct administration of acetylcholine,altematively,had no effect.