Disinhibition of perigeniculate reticular neurons following chronic ablation of the visual cortex in rats.

Effects of chronic ablation of the visual cortex (VC) were studied in the perigeniculate reticular neurons (PGR neurones) which were located in the thalamic reticular nucleus immediately adjacent to the dorsal nucleus of the lateral geniculate body and identified as the I-cells of Burke and Sefton. In rats with the intact VC the PGR neurons responded to single shock stimulation of the optic tract (OT) with bursts of spike spaced regularly. During the inter-burst period the neurons were inhibited, indicating that except for the primary spike burst, others were postinhibitory rebound excitation. In the VC-ablated PGR neurons there were no changes in the primary spike burst, but the remaining ones were very weak or sometimes missing, suggesting that the inhibition was poorly developed. With double shock stimulation of OT it was established that after showing the primary spike burst, the VC-ablated PGR neurons suffered a less intense inhibition than control. To a diffuse, sustained illumination, the normal PGR neurons showed on- and off- responses, whereas the VC-ablated ones were tonically activated during the presence of illumination. These findings were taken as indicating that the inhibitory mechanism for the PGR neurons were made less active after the VC had been ablated chronically.