Auditory neurons in the rat thalamic reticular nucleus.

In the thalamic reticular nucleus (TR) of the rat a cluster of neurons has been located which receives auditory inputs and acts as a source of inhibition for relay neurons of the medial geniculate nucleus (MG). These TR neurons (auditory thalamic reticular neurons; A-TR neurons) showed a repetitive burst of grouped discharge upon electrical stimulation of the inferior colliculus (IC) or of the auditory cortex. Many of them responded to tonal stimuli such as clicks or pips. Adjacent to the cluster of A-TR neurons there were the cluster of TR neurons receiving visual inputs (V-TR neurons) and that receiving somatosensory inputs (S-TR neurons). The cluster of A-TR neurons was situated ventrally to the cluster of V-TR neurons, both extending caudally from the level of the rostral tip of the dorsal lateral geniculate nucleus. The S-TR neurons distributed rostrally to the clusters of A- and V-TR neurons. Some of the sensory TR neurons, usually found around the boundaries between the clusters of different sensory modalities, were activated from stimulation of different central sensory pathways. Single electric shocks directly applied to the cluster of A-TR neurons suppressed discharges of relay neurons of the MG, either spontaneous or evoked by click stimuli or by electric shocks to the IC. The postexcitatory suppression of MG relay neurons was similar in time course to the suppression following electrical stimulation of A-TR neurons. Response latencies of the A-TR neurons to IC shocks were found to be 1.0-1.5 ms longer than those of the MG relay cells with respect to the modal and shortest values. It is suggested that A-TR neurons are intercalated in the axon collateral circuit of the thalamocortical projection arising from relay neurons of the MG.