Different inner retinal pathways mediate rod-cone input in irradiance detection for the pupillary light reflex and regulation of behavioral state in mice.

PURPOSE: Detection of light in the eye contributes both to spatial awareness (form vision) and to responses that acclimate an animal to gross changes in light (irradiance detection). This dual role means that eye disease that disrupts form vision can also adversely affect physiology and behavioral state. The purpose of this study was to investigate how inner retinal circuitry mediating rod-cone photoreceptor input contributes to functionally distinct irradiance responses and whether that might account for phenotypic diversity in retinal disease.
METHODS: The sensitivity of the pupillary light reflex and negative masking (activity suppression by light) was measured in wild-type mice with intact inner retinal circuitry, Nob4 mice that lack ON-bipolar cell function, and rd1 mice that lack rods and cones and, therefore, have no input to ON or OFF bipolar cells.
RESULTS: An expected increase in sensitivity to negative masking with loss of photoreceptor input in rd1 was duplicated in Nob4 mice. In contrast, sensitivity of the pupillary light reflex was more severely reduced in rd1 than in Nob4 mice.
CONCLUSIONS: Absence of ON-bipolar cell-mediated rod-cone input can fully explain the phenotype of outer retina degeneration for negative masking but not for the pupillary light reflex. Therefore, inner retinal pathways mediating rod-cone input are different for negative masking and the pupillary light reflex.