Interstitial nucleus of Cajal (INC) projections to the region of Probst's tract.

These studies were designed to investigate projections of the interstitial nucleus of Cajal (INC) to the region of the contralateral Probst's tract (PrTr). In electrophysiological experiments, INC neurons were antidromically activated from the contralateral PrTr, the medial longitudinal fasciculus (MLF) at medullary levels and the MLF at spinal cord levels. Some INC cells could be antidromically activated only from PrTr and others from both PrTr and the MLF. Anatomical experiments confirmed the existence of an INC projection into the region of the contralateral PrTr. Following injections of fluorescent dyes into the PrTr area, retrogradely labeled neurons were observed in the contralateral INC, with only occasional labeling ipsilaterally. Injections which included the medial vestibular nucleus labeled a greater number of INC cells ipsilaterally. After injections of dyes into the medullary MLF, retrogradely labeled cells were observed bilaterally in INC, although in greater numbers ipsilaterally. In experiments in which different dyes were injected into PrTr and the MLF, double labeled cells were found in the contralateral INC.