Distance-dependent interactions between the rod and the cone systems in goldfish retina.

We recorded from ganglion cell axons in the optic tracts of self-respiring goldfish, and examined the interaction of rod-effective and cone-effective stimuli within their receptive fields. The summation of influences due to the rod system and the long wavelength sensitive cone system was analyzed by the methods of response-summation and sensitivity-summation. Different spatial relationships between the rod- and cone-effective stimuli allowed examination of distance-dependent effects. Both the response-summation and sensitivity-summation analyses showed a difference in non-linearity between a configuration in which the rod- and cone-effective stimuli were spatially overlapped and a configuration in which they were not. This difference in both analyses demonstrates a distance dependent interaction between the rod and cone systems. Both analyses also showed a difference in non-linearity between a configuration in which the rod-and cone-effective stimuli were nearby (but not overlapped) and one in which they were more distant. This demonstrates that the interaction is not limited to receptors that are immediate neighbors. An estimate of the strength of interaction in each case showed that the differences among the three configurations were relatively slight, indicating a broad spread of the effect. The interaction was found to be relatively powerful; assuming a specific simple model for the interaction mechanism, we found that each system exerts an effect upon the other which accounts for about 1/3 of its signal.