Prolonged negative surface potentials of the cat sensomotor cortex and responses of neurons and glial cells.

Evoked potentials to stimulation of the ventrolateral and intralaminar thalamic nuclei, the surface of the sensomotor cortex, and the pyramidal pathways, derived from the same point, and also corresponding postsynaptic responses of pyramidal neurons were studied in acute experiments on cats anesthetized with ether or superficially with pentobarbital (25-30 mg/kg, intraperitoneally), and immobilized with muscle relaxants. Surface application of strychnine inhibits the slow negative potential arising in response to direct and primary responses, and the corresponding slow potentials of the IPSP. The action of iontophoretic application of strychnine on IPSP of pyramidal neurons and responses of cortical glial cells also were studied. Both methods of application of strychnine block mainly the early component of the IPSP, during which the input resistance is significantly lower than that during the late component, evidence of their different genesis. The results of the investigation show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons, and that the separate components of the responses have a common genesis.