RAPID PLASTIC RESPONSE FOLLOWING EARLY RETINAL LESIONS IN RATS

Following an early retinal lesion, aberrant uncrossed projections from the opposite, undamaged, retina form in the target visual nuclei. The present study has examined the development of such aberrant projectio ns by making retinal lesions in newborn rat pups, and then examining t he nature of the uncrossed retinocollicular projection at different ag es following the lesion. Intravitreal injections of horseradish peroxi dase were made into the intact eye, and the uncrossed projection was s ubsequently revealed histochemically. A mature aberrant projection for ms as early as postnatal day 9. On postnatal days 5 and 2, aberrant pr ojections are discernable amongst the exuberant uncrossed terminals of normal developing rats, although the former have not matured to form the dense terminal fields characteristic of older projections. Aberran t projections were also detectable as early as 12 h following the lesi on, revealed as a relative increase in the density of uncrossed label. These results indicate that lesion-induced plastic responses by intac t retinal arbors are initiated shortly after the insult, and they caut ion the use of retinal lesions in studies of normal retinotopic connec tivity during development.