Individual auditory thalamic reticular neurons have large and cross-modal sources of cortical and thalamic inputs.

In the present study, the sources of thalamic and cortical inputs of thalamic reticular nucleus (TRN) neurons were examined by investigating the responses of the TRN neurons to electrical stimulation of different sites in the thalamus and the cortex of the rat. The recurrent excitation of the corticothalamic system that is triggered by electrical stimulation was eliminated by ablating the auditory cortex and by temporarily inactivating the medial geniculate body (MGB), when studying the sources of thalamic and cortical inputs, respectively. Single TRN neurons responded to electrical stimulation of 50-100 μA of the thalamus over a large area (dorsoventrally 1.2-2.4 mm and mediolaterally 1.0-2.3 mm, n=9). Four of 16 auditory TRN neurons responded to electrical stimulation of the lateral geniculate nucleus. The TRN neurons responded to cortical stimulation over a rostrocaudal distance of 2.6±0.5 mm (range: 1.5-3.5 mm, n=24) of the auditory cortex. Visual or auditory TRN neurons also responded to electrical stimulation in the auditory or visual cortices, respectively. The present study revealed that each TRN neuron received a wide range of inputs from both ascending thalamic and descending cortical projections. The projection could be cross-modal. Having a strong and lasting inhibition on the thalamus, the TRN neurons are likely to be involved in adjusting global states relating to awareness and attention in the thalamocortical system.