Membrane potential oscillations and corticothalamic connectivity in rat associational thalamic neurons in vitro

Thalamic relay neurons were recorded from the dorsolateral and lateroposterior nuclei of the rat thalamus in a superfused explant preparation. The mean membrane potential of these cells was -67 +/- 7 mV, input resistance 114 +/- 31 M omega and spike amplitude 75 +/- 6 mV. Low-threshold slow membrane potential oscillations (1-4 Hz) were present in about 46% of the neurons. They occurred either spontaneously or following a membrane potential perturbation. In a subpopulation of cells, we also observed a high-threshold membrane oscillation when cells were depolarized above -45 mV. This oscillation consisted of bursts of low-amplitude spikes interrupted by rhythmic after-hyperpolarizations. Stimulation of the corticothalamic pathway elicited prolonged inhibitory postsynaptic potentials in associational thalamic neurons. In the presence of picrotoxin, corticothalamic input evoked prominent excitatory postsynaptic responses that showed marked short-term synaptic plasticity. Our results suggest that associational thalamic neurons maintained in vitro have a strong tendency to exhibit membrane oscillations. In addition, they receive a direct excitatory cortical input that remained functional in explant preparation.