Differential central distribution of optic nerve components in the rat.

The distribution of Fink-Heimer positive degeneration and neurofibrillar proliferation has been examined in the dorsal lateral geniculate nucleus (dLGN) and superior colliculus of albino and pigmented rats following enucleation between post-natal days 12 and 30 and as adults. With survival times of 6 h to 5 days following enucleation, the location of maximum degenerative reaction stained by the Fink-Heimer method changes with increasing survival time in both regions. In the dLGN contralateral to the eye removal the earliest degeneration appears in a lamina occupying the medioventral extent of the nucleus and is rapidly removed; later degeneration fills a central lamina of the nucleus with a patch of degeneration extending to the outer surface of the nucleus at the mediodorsal margin. The latest occurring degeneration fills the outermost lamina and is still obvious when degeneration is largely dispersed from the inner and central laminae; this outer lamina shows an early filamentous degenerative reaction in the adult. The uncrossed optic pathway occupies a portion of the central lamina of the nucleus, and in albino animals it shows a rapid degeneration and dispersion similar to the innermost lamina on the crossed side; in the pigmented animals degeneration of the uncrossed projection starts as early as that of the albino but persists as long as the degeneration of the central lamina on the crossed side. The degeneration time of the sprouted, uncrossed pathway resulting from unilateral enucleation at birth is similar in albino and pigmented rats and resembles in timing the normal uncrossed pathway of pigmented rats. These results suggest that there are at least 3 different fiber populations in the rat optic nerve with different distribution in the dLGN. The uncrossed optic pathway of albino and pigmented rats appears to differ in fiber composition; this may relate to aberrations in mapping of uncrossed projections in the albino.