Frontal cortex stimulation evoked neostriatal potentials in rats: intracellular and extracellular analysis.

Evoked potentials, action potentials and intracellular events were recorded in the neostriatum of urethane anesthetized rats to electrical stimulation of frontal cortex white matter, motor cortex and pre-limbic cortex. Five major waves of the evoked potential were identified. Wave N1 (3.9 msec latency) was small, preceded cellular events and probably represents activation of corticostriate terminals. Wave P1 (10.8 msec latency to peak following white matter stimulation) coincided with an EPSP and neuronal firing. Both wave N2 (38.0 msec latency to peak) and P2 (approximately 110 msec duration) overlapped the intracellularly recorded hyperpolarization and inhibition of cell firing. Based upon this correspondence and upon the behavior of waves N2 and P2 with changing current and during conditioning-test paired pulse stimulation, it was concluded that the waves represent different processes contributing to the cellular hyperpolarization. A late wave, N3 (175 msec onset latency) corresponded to a late rebound firing and cellular depolarization. This late wave was eliminated from the neostriatum, but not from the overlying sensorimotor cortex, by kainic acid lesions that destroyed medial thalamus but left thalamic lateral nuclei and reticular nucleus intact.