Differential response dynamics of corticothalamic glutamatergic synapses in the lateral geniculate nucleus and thalamic reticular nucleus.

The corticothalamic feedback pathway provides excitatory synaptic input to both the thalamic reticular nucleus and the lateral geniculate nucleus. We studied excitatory postsynaptic currents elicited from corticothalamic stimulation in the visual sector of the thalamic reticular nucleus and the lateral geniculate nucleus to compare the response of these neurons to stimulation of their common input pathway. Using whole cell patch clamp recordings in ferret thalamic slices, we compared single excitatory postsynaptic current decay kinetics, presynaptic glutamate release dynamics through paired pulse facilitation and responses to corticothalamic train stimulation. We found that single thalamic reticular nucleus excitatory postsynaptic currents were significantly sharper than lateral geniculate nucleus responses. The mean thalamic reticular nucleus excitatory postsynaptic current decay constant (tau) was 4.9+/-0.5 ms, while the mean lateral geniculate nucleus excitatory postsynaptic current tau value was 11.8+/-0.8 ms. Presynaptic release dynamics as measured by responses to paired stimuli were conserved between the thalamic reticular nucleus and lateral geniculate nucleus. However, facilitating responses to train stimulation were markedly different between nuclei. Lateral geniculate nucleus responses showed proportionately larger facilitation (reaching 842.9 +/- 76.4% of excitatory postsynaptic current 1 amplitude) than thalamic reticular nucleus responses (reaching 223.1 +/- 44.0% of excitatory postsynaptic current 1 amplitude). These data indicate that while the corticothalamic pathway produces excitatory postsynaptic currents in both the thalamic reticular nucleus and lateral geniculate nucleus, other factors uniquely affect the functional integration of the inputs in each nucleus.