Electrophysiology of rat thalamo-cortical relay neurons: an in vivo intracellular recording and labeling study.

Membrane properties and responses to frontal cortical stimulation were studied on electrophysiologically and morphologically identified thalamo-cortical neurons in anesthetized rats. Those neurons generated membrane responses resembling the low-threshold Ca-spike, gK(Ca) and IA that have been previously demonstrated in in vitro studies of thalamic neurons. Stimulation of the frontal cortex evoked a sequence of responses; antidromic spike, initial depolarization, long duration hyperpolarization and a short period of depolarization. The initial depolarization was considered to be a monosynaptic excitatory postsynaptic potential (EPSP) which overlapped with an inhibitory postsynaptic potential (IPSP). Major constituents of the long duration hyperpolarization were considered to be short duration IPSPs and long duration disfacilitations of cortical inputs.