Afferents to the optic tectum of the leopard frog: an HRP study.

Following unilateral HRP injections in the optic tectum of Rana pipiens, HRP-positive cells were seen in three pretectal nuclei: bilaterally in the dorsal posterior nucleus; in the dorsal half of the ipsilateral posterior nucleus; and ipsilaterally in the large-called pretectal nucleus. HRP-positive cells were also seen ipsilaterally in the anterodorsal, posterodorsal and posteroventral tegmental fields, the nucleus isthmi, and the dorsal gray columns of the cervical spinal cord; bilaterally in the suprapeduncular nucleus, a paramedian cell group dorsal to the interpeduncular nucleus; and in the deep layers of the contralateral tectum. In addition, evidence for a bilateral ventral preopto-tectal projection was seen in half the experimental animals. No tectal afferents from telencephalic or rostal thalamic areas were seen. Both the ascending and descencing tectal efferent fibers were also filled with reaction product. The pale reaction indicative of terminating tectal efferents was seen in the dorsal pretectum, partially overlapping the lateral nucleus and uncinate neuropil; in the core of nucleus isthmi; and in the superior olive.