Abstract
Loop connections between thalamic and cortical cells are anatomical basis for interactive bottom-up and top-down streams of sensory information processing. The thalamic reticular nucleus (TRN), receiving thalamic and cortical inputs, plays a pivotal role in modulating loop connectivity by providing inhibition to thalamic cells. Previously, we have revealed the tonotopy-related topographies of TRN projection to the medial geniculate nucleus (MG) and cortical projections to the TRN and MG in the rat. In the present study, we further determined features of MG projection to the TRN, based on axonal projections of single auditory cells that were labeled with biocytin using juxta-cellular recording and labeling techniques. We isolated two types of auditory cells (S and L cells) that exhibited unit discharges (single and/or burst) to noise burst stimuli (duration, 100 ms) with short (<50 ms) and long (>100 ms) response latencies. Of particular interest is that the projections of S cells were topographic along the dorsoventral neural axis while those of L cells were topographic along the rostrocaudal axis. Since tonotopy is primarily organized along the dorsoventral axis in the MG and TRN, it is suggested that S cells, directly receiving ascending auditory inputs, activate the TRN with regard to tonotopic organization and L cells, most likely receiving corticofugal inputs, activate the TRN for other information processing less relevant to tonotopic organization. [J Physiol Sci. 2008;58 Suppl:S170]
