The topography of aberrant ipsilateral retinogeniculate projections following neonatal ablation of the superior colliculus in rats.

The topography of aberrant ipsilateral retinogeniculate projections following ablation of the superior colliculus in infancy has been examined. Rat pups received a unilateral ablation of the superior colliculus in infancy, which is known to produce an aberrant ipsilateral retinogeniculate projection in the caudal quarter of this nucleus, ipsilateral to the ablation. When adult, each rat received a retinal lesion in the eye ipsilateral to the ablation at varying locations along the temporal crescent and the brains were subsequently processed for anterograde degeneration. The topographic relationship between the retina's temporal crescent and the ipsilateral dorsal lateral geniculate nucleus appeared normal in the rostral three quarters of the nucleus, but an aberrant projection from the far temporal retina (the upper temporal crescent) was demonstrated in the caudal quarter of the nucleus, residing dorsolaterally beneath the optic tract. This location within the dorsal lateral geniculate nucleus normally receives its retinal input from the contralateral temporal retina at reduced eccentricity. As these two retinal regions are likely to be binocularly conjugate, it is proposed that these rearrangements in retinal terminal fields following early collicular ablation produce an ocularly aberrant yet visuotopically appropriate retinogeniculate projection.