Posterior commissural connections of area pretectalis and neighboring structures in cat, with special reference to pupilloconstrictory pathway via posterior commissure.

The overall distribution of posterior commissural connections of the area pretectalis and the neighboring structures was studied in the cat, by the methods of anterograde fiber degeneration and retrograde axonal transport of horseradish peroxidase (HRP). After a localized lesion was made within the posterior commissure, dense degenerated terminals were distributed in the most rostral part of the nucleus pretectalis posterior, the nucleus of posterior commissure, the interstitial nucleus of Cajal, and the central tegmental field. A medium amount of degenerated terminals were observed in the nucleus pretectalis anterior (pars reticularis), the dorsal part of the periaqueductal grey at its most rostral levels, the caudolateral parts of the nucleus pretectalis posterior and the nucleus of optic tract, the H field of Forel, parts of the somatic cell columns of the oculomotor nucleus and the trochlear nucleus. A small amount of degenerated terminals were seen in the ventromedial part of the caudal periaqueductal grey, the ventral lateral geniculate nucleus and the zona incerta. However, the amount of degenerated terminals was very small in the nucleus pretectalis medialis and the nucleus pretectalis olivaris. Following an HRP (dissolved in 5% alkyl-phenol ethylene oxide) injection into the unilateral area pretectalis where fibers of the posterior commissure fan out, retrogradely labeled cells were observed in all of the above described (posterior commissural fiber recipient) regions of the pretectal and neighboring structures, with the exception of the somatic cell columns of the oculomotor nucleus and the trochlear nucleus. The number of labeled cells appeared roughly proportional to the amount of degenerated terminals of the posterior commissural fibers described above with the apparent exception of the nucleus pretectalis anterior, pars reticularis, where only a few labeled cells were identified. The findings were discussed with special reference to the pupilloconstrictory pathway via the posterior commissure.