Gaba-antagonists alter spatial summation in receptive field centres of rod- but not cone-drive cat retinal ganglion Y-cells.

1. When Y-type cat retinal ganglion cells were driven by cones, the i.v. administration of the GABA-antagonist picrotoxin failed to alter receptive field centre size. 2. This result is in marked contrast to our previous finding that when Y-cells were driven by rods, GABA-antagonists led to specific and reversible changes in centre size. 3. These results taken together suggest that for centre signals of Y-cells, the rod and cone pathways are pharmacologically distinct.