THE CONNECTIONS OF THE RETINAL ON AND OFF PATHWAYS TO THE LATERAL GENICULATE-NUCLEUS OF THE MONKEY

The manner in which in on and off systems originating in the retina make their connections with the lateral geniculate nucleus (LGN) of the rhesus monkey was examined. 2-Amino-4-phosphonobutyric acid (APB) was either infused or injected into the vitreous chamber of the eye to block the on channel while the response properties of LGN cells were assessed. APB in concentrations of 50-600 .mu.m effectively blocked on-center cell responses in the LGN. The responses of off-center cells were not affected significantly, although some cells showed a brief period of response increment following APB infusion while other cells showed a small response decrement. The sustained component of the response of on-center cells was blocked more effectively, more quickly and at lower concentrations than was the transient component of the response. Parvocellular cells were blocked at lower concentrations and for longer time periods than were magnocellular cells. Both the center and the surround responses of on-center cells were blocked by APB. The center and the surround responses of off-center cells were not affected differentially by APB administration. Blue on-center responses were also blocked by APB. In the monkey the on and off channels originating in the retina may remain functionally separated at the level of the LGN.