SACCADE-INDUCED ACTIVITY OF DORSAL LATERAL GENICULATE-NUCLEUS X-CELLSAND Y-CELLS DURING PHARMACOLOGICAL INACTIVATION OF THE CAT PRETECTUM

The influence of neurons projecting from the prerectal nuclear complex to the ipsilateral dorsal lateral geniculate nucleus (LGNd) was inves tigated in awake cats. Responses from relay cells in the A-laminae of the LGNd were extracellularly recorded and analyzed during saccadic ey e movements and visual stimulation in association with reversible inac tivation of the ipsilateral pretectum with the GABA agonist, muscimol. Prerectal inactivation (PTI) resulted in spontaneous nystagmic eye mo vements in the dark with slow phases directed away from the injected s ide. In the control situation, all Y-cells and about two thirds of X-c ells were excited during saccades or saccade-like visual stimulation b ut one third of X-cel:ls were inhibited. During PTI all recorded X-cel ls were inhibited, either during saccades or saccade-like visual stimu lation. The PTI-associated inhibition was stronger than in inhibited X -cells in control experiments only during saccades but not during stim ulation with a moving pattern while the eyes were stationary. In Y-cel ls a reduction in the response peak width at half-height was seen duri ng PTI, again only during saccades but not during stimulation with a m oving pattern. These results indicate that during saccades the pretect o-geniculate pathway has a stronger influence on X LGNd relay cells th an on Y-cells. The findings are discussed in terms of saccadic suppres sion and postsaccadic facilitation.