Time course of inhibition induced by a putative saccadic suppression circuit in the dorsal lateral geniculate nucleus of the rabbit.

Psychological studies have revealed that a visual suppression occurs during the saccadic eye movements to maintain the stable visual image. This visual suppression is named saccadic suppression. A typical saccadic suppression precedes the saccadic eye movements by 30-60 ms, lasts 120-180 ms, and is followed by a 100-150 ms facilitation. Recently, we have revealed an inhibitory circuit connecting the deep layers of the superior colliculus (SC) to the dorsal lateral geniculate nucleus (LGN), via the central lateral nucleus in the thalamus (CL) and thalamic reticular nucleus (TRN). We speculated that this inhibitory circuit might mediate saccadic suppression in the rabbit. In the present study, we used intracellular recording technique to further examine the synaptic and intrinsic responses of CL cells, TRN cells, and LGN cells to the activation of this inhibitory circuit. We found that the stimulation of the deeper layers of the SC induced a fast excitation post-synaptic potential (EPSP) in CL cells, followed by a robust EPSP in TRN cells and a prolonged inhibitory postsynaptic potential (IPSP) in LGN cells. The EPSP in TRN cells was always followed by a small inhibitory postsynaptic potential (IPSP). The IPSP in LGN cells lasted about 133 +/- 27 ms. Sometimes, a rebound bursting occurred after the IPSP in LGN cells. We also examined whether activation of this inhibitory circuit could suppress the retino-geniculo-cortical pathway. We found that the SC stimulation always suppressed the evoked potential in the visual cortex induced by the stimulation of the optic chiasm. Our results of the inhibitory circuit can induce an inhibition in the LGN and a suppression on the retino-geniculo-cortical pathway. The time courses of the inhibition and suppression were compatible with that of saccadic suppression revealed by psychological and physiological studies. These results support the idea that the inhibitory circuit of SC (deeper layers)-CL-TRN-LGN may mediate the saccadic suppression in the rabbit LGN.