A comparative study of ventrolateral and recurrent excitatory postsynaptic potentials in large pyramidal tract cells in the cat.

In acute cats deeply anesthetized with Nembutal, monosynaptic excitatory postsynaptic potentials (EPSPs) triggered by stimulation of the ventrolateral (VL) thalamic nucleus and the pes pedunculus were recorded in large pyramidal tract cells (PT cells). Deep anesthesia, low intensities of stimulation and an averaging technique were used in order to get VL and recurrent EPSPs free of polysynaptic potentials. Comparison of the time course of both EPSPs revealed a much faster rise time and shorter half-width for VL EPSPs than for recurrent EPSPs. This would suggest a more proximal location for VL synaptic contacts than for recurrent ones with respect to the soma of PT cells. The separation of the sites of origin of both EPSPs is further suggested by their almost perfect linear summation. It is suggested that VL EPSPs are produced on the apical dendritic tree, while recurrent EPSPs could originate on the basilar dendritic branches.