Effects of eye-enucleation on substance P-immunoreactive fibers of some retinorecipient nuclei of the rat in relation to their origin from the superior colliculus.

We have previously shown that retinal deafferentation causes a decrease in immunoreactive dendrites of substance P-positive neurons of the superficial superior colliculus of the rat. Since some retinorecipient thalamic and pretectal nuclei are putative targets for substance P-containing cells of the superior colliculus, the present study attempted to ascertain whether substance P-immunoreactive fibers in these nuclei are also affected by retinal denervation. We found that unilateral eye removal produced a progressive increase in fibrous substance P immunoreactivity in the nucleus of the optic tract, lateral posterior nucleus, and lateral geniculate nucleus of the side contralateral to the enucleation. On the other hand, unilateral lesions to the superficial layers of the superior colliculus produced a dramatic reduction in substance P immunoreactivity in the ipsilateral nucleus of the optic tract, lateral posterior nucleus, and dorsal and ventral lateral geniculate nuclei. In bilaterally enucleated animals, unilateral lesion to the superior colliculus produced, as expected, loss of immunoreactive fibers only in the lateral posterior nucleus and the retinorecipient nuclei ipsilateral to the lesion. These results suggest that transneuronal changes in the distribution of substance P in collicular neurons observed after enucleation could be reflected in their projections to the other primary visual centers and to the lateral posterior nucleus.