Changes in the orthodromic and antidromic response of optic tract during the eye movements of sleep.

Abstract

To test the excitability of optic tract (OT) terminals during rapid eye movements (REMs) of sleep, electrodes were chronically implanted in the lateral geniculate (LG) and OT of the cat. The eye movements triggered pulses to OT, giving rise to presynaptic and postsynaptic responses in LG. For control, identical stimuli were delivered during the intervals between REMs. The presynaptic spikes showed a maximum decrease of 10% 20-30 msec, after the beginning of the eye movement. The excitability of OT terminations in LG was tested by recording the antidromic response to LG stimulation during REMs. This antidromic response in the chiasma revealed a facilitation lasting 60 msec. When eye movements were used to trigger a flash, the evoked response was reduced in LG and visual cortex but unchanged in OT. The reduction of OT orthodromic and increase of OT antidromic responses, together with the changes in the flash-evoked responses, are consistent with the occurrence of presynaptic inhibition at OT terminals during the REM.