Retinogeniculate projections in the rabbits of the albino allelomorphic series

Retinogeniculate pathways have been studied by fiber degeneration and autoradiographic methods in rabbits that are homozygous for alleles of the albino series of genes. It has been found that albino and Himalayan rabbits, which both lack all melanin pigment in the eye, have a similar abnormality of the retinogeniculate pathway. The number of ipsilateral optic fibers going to the lateral geniculate nucleus is reduced in these rabbits, the ipsilateral projection forms a discontinuous terminal zone instead of the normal continuous zone, and some of the ipsilateral axons terminate in an inappropriate part of the nucleus, so that regions receiving a crossed input in normal rabbits receive an uncrossed input in the abnormal rabbits. Chinchilla rabbits show a slightly reduced fur pigmentation but have a normal distribution of pigment in the retinal pigment epithelium and these rabbits have normal retinogeniculate pathways. In addition, the normal retinogeniculate pathway was studied. Autoradiographic methods show that the β segment of the lateral geniculate nucleus receives a contralateral input. Hence, earlier views that this segment projects to the visual cortex but receives no retinal input, are untenable. Further, in the autoradiographic material it was not possible to identify separate ipsilateral laminae and it was concluded that in the normally pigmented rabbit the ipsilateral retinogeniculate projection forms one relatively continuous group.