Retinal projections to the medial terminal nucleus of the rat with induced unilateral congenital eye defects.

Retinal projections, particularly the ipsilateral projections, to the medial terminal nucleus (MTN) of the accessory optic system were investigated by autoradiography in adult rats after being reared in one of three different conditions: (1) normal visual experiences, (2) an application of trypan blue for intrauterine induction of congenital unilateral anophthalmia; and (3) the procedures for intrauterine production of congenital microphthalmia in which both eyes are reduced in size. In congenital monocular rats, there was an increase of uncrossed retinal projections to the MTN which does not normally exist. The expansion of the ipsilateral projection was markedly greater in the monocular rats than those inflicted with microphthalmia. The expansion may be due to the failure of the retraction of the ipsilateral retinal projections to the MTN and the collateral sprouting of optic fibers from the remaining eye.