GABA(A) RECEPTOR-MEDIATED CL- CURRENTS IN RAT THALAMIC RETICULAR AND RELAY NEURONS

Spontaneous and evoked inhibitory postsynaptic currents (sIPSCs and eI PSCs) and responses to exogenously applied gamma-aminobutyric acid (GA BA), mediated by GABA type A (GABA(A)) receptors, were recorded in inh ibitory neurons of nucleus reticularis thalami (nRt) and their target relay cells in ventrobasal (VB) nuclei by using patch clamp techniques in rat thalamic slices. The decay of sIPSCs in both nRt and VB neuron s was best fitted with two exponential components. The decay time cons tants of sIPSCs in nRt neurons were much slower (tau(1) = 38 ms; tau(2 ) = 186 ms) than those previously reported in a variety of preparation s and two to three times slower than those in VB neurons (tau(1) = 17 ms; tau(2) = 39 ms). GABA(A) receptor-mediated Cl- currents directly e voked by local GABA application also had a much slower decay time cons tant in nRt (225 ms) than in VB neurons (115 ms). Slow decay of GABA r esponses enhances the efficacy of recurrent intranuclear inhibition in nRt. The results suggest a functional diversity of GABA(A) receptors that may relate to the known heterogeneity of GABA(A) receptor subunit s in these two thalamic nuclei.