Correlation in Development of Structures Associated with Transplanted Eyes.

Abstract

Eyes were transplanted in normal position between embryos (tailbud stage) of Amblystoma punctatum and A. tigrinum, forms of contrasting size, and the animals reared until the approach of metamorphosis. The grafted organs retain their specific size on the foreign species, and are hence out of scale with the associated structures of the host. In response, the latter exhibits certain morphological adjustments, particularly in the brain, eye-muscles, and chondrocranium.

When the nerve of the large transplanted tigrinum eye makes normal connection with the brain of punctatum, the smaller species, there follows a hyperplasia of 10-20% in the gray matter of the opposite half of the midbrain, while in the reciprocal combination, or with one eye totally extirpated, there is a corresponding hypoplasia of 5-10%. In the diencephalic optic centers changes in cell-proliferation are relatively unimportant, and often lacking. In the region of the chiasma (preoptic nucleus), however, there are almost invariably strong hyper- or hypoplastic changes on the same side as the grafted eye. This suggests the possibility that there is normally a homolateral innervation of this region by fibers from the retina, contrary to general belief. In animals with grafted tigrinum eyes the gray matter in the dorsal part of the diencephalon opposite the transplant shows a tendency, often quite pronounced, to shift ventrally as if to meet the ascending optic tracts from the large eye. It seems probable that the visual fibers exert an attractive influence on the cells of this optic center.

The eye-muscles, developing from the host, adjust their size in the direction indicated by the size of the grafted eye, although they never attain the size characteristic for the normal muscles of the eye in question. The hypertrophy or atrophy, as the case may be, is accomplished by changes in the number, rather than the size, of the individual fibers. The hyperplasia of fibers in the punctatum muscles developing upon a grafted tigrinum eye was found to average about 50%.