A further study on fast and slow principal cells of rat lateral geniculate body: an analysis of flash-evoked responses.

In the lateral geniculate body (LGB) of urethane-anesthetized and Flaxedil-immobilized rats, unit responses of principal cells (P-cells) were recorded by using flash stimulation of the eyes. By measuring response latencies to electrical stimulation of the optic tract, all P-cells were classified into the fastor slow group according to the criterion established by Fukuda. Flash-evoked unit responses consisted of the two kinds of discharges, i.e. the early discharge (ED) with latencies less than 100 msec and the late discharges of spike burst (LDs) often recurring twice or more (LD1, LD2 and so on). Cells' firings were suppressed during the interval between ED and LD1 and those between successive LDs. The ED- and LD1-latencies, measured in dark with strong flashes, were shorter in the fast cells than in the slow one. The interval between ED and LD1 was shorter in the fast cells than in the slow ones. It was common to the both types of P-cells that as flash intensity was reduced, the ED-latency increased and the LD1-latency decreased. However, the ED-LD1 interval remained shorter in the fast cells than in the slow ones. Upon shifting from dark to light, the LD1-latency markedly increased or decreased in the slow cells, whereas such was not seen in the fast cells. These findings seem to provide a further support for the classification of P-cells into the fast and slow types.