The effect of the gene for microphthalmia (mi) on the dorsal lateral geniculate nucleus of the cinnamon mouse.

The dystrophic retina of the cinnamon mouse homozygous for the gene for microphthalmia (mi/mi) has a population of large ganglion cells. Unilateral enucleation and examination of the dorsal lateral geniculate nucleus using the Fink-Heimer technique showed that, while there was continuing degeneration argyrophilia in the dorsal lateral geniculate nucleus secondary to the retinopathy, there was additional degeneration attributable to enucleation. In addition, the pattern of degeneration indicated that the axon terminals were less mature than those of the cinnamon and heterozygous (mi/+) mice. Quantitative study of the dorsal lateral geniculate nucleus in the homozygous (mi/mi) mouse showed that the nucleus is small with fewer neurons and that the markers for protein metabolism, namely volume of nucleoli and cytoplasmic RNA, are reduced when compared to the cinnamon and heterozygous (mi/+) mice. It is concluded that the portion of the retino-geniculate pathway represented by the large ganglion cells in the retina, develops in the absence of patterned visual stimuli, but is less mature and has a more limited functional activity than controls.