Efferent projections of the superior colliculus in the opossum.

Abstract

AbstractThe Fink and Heimer technique was used to study the ascending and descending fiber degenerations resulting from unilateral electrolytic lesions in the superior colliculus of sixteen adult opossums. The ascending fiber degeneration left the colliculus by way of a small parabrachial bundle or with the brachium of the superior colliculus. The former bundle contributed degenerating terminals to the suprageniculate, parabrachial, and magnocellular medial geniculate nuclei and appeared to terminate in the lateral terminal nucleus of Hayhow (Hayhow, '66). The latter bundle contributed fibers to the pretectal and posterolateral nuclei as well as discrete projections to the ventral lateral geniculate nucleus and ventral thalamus.Descending degenerating fibers in the brainstem were destributed along three tracts: (1) a medial predorsal bundle, (2) an intermediate tectoreticular, and (3) a lateral tectopontine. These tracts were seen to terminate mainly in tegmental and reticular centers as well as in the lateral basilar nucleus of the pons. Degenerating fibers of the predorsal bundle were followed to lower medullary levels but could not be traced to spinal levels.The present findings are descussed in relation to data reported for more developed mammalian species.