Parameters of retinal graft-mediated responses are related to underlying target innervation

Retinae taken from embryonic mice were transplanted to the brain of newborn rats. One eye was removed from the recipients at this time to promote innervation of host visual centers. After 4-6 weeks the optic nerve of the remaining eye was transected to eliminate all visual afferents of host origin and 4-6 days later the grafts were exposed surgically for testing. Nineteen animals with grafts located on the dorsal surface of the cerebellum form the basis of this study. Animals differing markedly in behavioral performance were selected for simultaneous immunohistochemical processing. Measurements of peak density and area of mouse-specific immunoreactivity associated with the olivary pretectal nuclei (OPN) were compared to pupillary response parameters using the Pearson correlation coefficient. This analysis was performed on the combined data from all groups and revealed a number of highly significant correlations between both area and density of labelling and pupillary response parameters. In all 7 co-processed groups, the best responders within each group showed the heaviest innervation of the olivary pretectal nucleus. These findings indicate therefore that the degree to which a transplanted retina innervates the appropriate host brain target is an important determinant of graft efficacy. The xenograft-mediated pupillary reflex provides a model which permits detailed analysis of the relationship between connectivity and behavior in a simple relay system.