Anatomical analysis of pupillary reflex pathways in the rhesus monkey

Abstract

Abstract The pupillary light reflex was analyzed by producing lesions in afferent and efferent pathways in a series of monkeys. Unilateral enucleation and autoradiographic technics utilizing axoplasmic flow were used to determine afferent pathways. Lesions also were made in the pregeniculate nucleus (PGN) and individual components of the oculomotor visceral nuclei. Degeneration was studied in Wiitanen and Nissl stained sections. Infrared pupillographic records were made before and after surgery. Enucleation and autoradiographic studies revealed: (1) bilateral retinal projections to the pretectal olivary nuclei (PON) and PGN, and (2) predominautly contralateral projections to parts of the optic tract and sublentiform nuclei. PGN appeared to project to the ipsilateral PON. Unilateral lesions in the anterior median nucleus (AM) with direct, or indirect, involvement of the medial visceral cell column (MVCC) produced: (1) “static” and “dynamic contraction” anisocoria and (2) ipsilateral reductions in direct and consensual pupillary responses. Lesions in the rostral MVCC with no involvement of AM produced only static anisocoria. Degeneration from these lesions was found rostrally in the ipsilateral oculomotor roots, but no retrograde cell changes were detected in the pretectal region. Lesions in the caudal MVCC, the lateral visceral cell column (LVCC) and PGN produced no anisocoria or reductions in the pupillary light reflex. Both anterograde and retrograde degeneration in the contralateral PON were observed with lesions in LVCC, but no degeneration was seen in the oculomotor root fibers.