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 MΩ 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 afterhyperpolarizations. 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.