Reticular inhibition of internuncial cells in the rat lateral geniculate body

Abstract

Summary Reticular influence upon unitary and mass activities of the lateral geniculate body (LGB) was studied in urethane-anesthetized rats. Two types of cells were identified: one, principal (P) cells and the other, internuncial (I) cells which are presumably inhibitory interneurons acting upon P cells. With activation of the mesencephalic reticular formation (MRF) by high-frequency electrical shocks, most spontaneous and evoked activities of the I cells were inhibited. Suppression was observed in P-waves recorded from P cells in response to optic tract stimulation as an extracellular representation of IPSPs produced by repetitive discharges of I cells. The postexcitatory recovery og LGB mass potential was accelerated by activation of the MRF and prolonged after deepening anesthesia by Nembutal injection. In contrast to I cells, a majority of P cells received a facilitatory influence from the MRF. This was proved with single unit activities, both spontaneous and evoked, and with the mass potential evoked by optic tract stimulation. The possibility that the reticular facilitation of the P cell activity may be due to inhibition of I cells (dis-inhibition) was discussed.