Central pupillary light reflex circuits in the cat: I. The olivary pretectal nucleus

Abstract

The central pathways subserving the feline pupillary light reflex were examined by defining retinal input to the olivary pretectal nucleus (OPt), the midbrain projections of this nucleus, and the premotor neurons within it. Unilateral intravitreal wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) injections revealed differences in the pattern of retinal OPt termination on the two sides. Injections of WGA-HRP into OPt labeled terminals bilaterally in the anteromedian nucleus, and to a lesser extent in the supraoculomotor area, centrally projecting Edinger-Westphal nucleus and nucleus of the posterior commissure. Labeled terminals, as well as retrogradely labeled multipolar cells, were present in the contralateral OPt, indicating a commissural pathway. Injections of WGA-HRP into the anteromedian nucleus labeled fusiform premotor neurons within the OPt, as well as multipolar cells in the nucleus of the posterior commissure. Connections between retinal terminals and the pretectal premotor neurons were characterized by combining vitreous chamber and anteromedian nucleus injections of WGA-HRP in the same animal. Fusiform shaped, retrogradely labeled cells fell within the anterogradely labeled retinal terminal field in OPt. Ultrastructural analysis revealed labeled retinal terminals containing clear spherical vesicles. They contacted labeled pretectal premotor neurons via asymmetric synaptic densities. These results provide an anatomical substrate for the pupillary light reflex in the cat. Pretectal premotor neurons receive direct retinal input via synapses suggestive of an excitatory drive, and project directly to nuclei containing preganglionic motoneurons. These projections are concentrated in the anteromedian nucleus, indicating its involvement in the pupillary light reflex.

A central mesencephalic reticular formation projection to the Edinger–Westphal nuclei

“…Due to the fact that saccades and attention have been closely correlated, one might posit that this projection was related to attentional changes in pupil diameter. However, in this study, we saw cMRF terminals spread throughout the rostrocaudal extent of the EWpg with close associations present on nearly all the motoneurons, not just the pupillary component of the EWpg, which is small, and topographically restricted (Warwick 1954; Erichsen and May 2002; May et al 2008b; Sun and May 2014a, b). This argues against a role for this cMRF projection in independent control of pupillary function, such as would be expected for attention, emotion or the pupillary light reflex.…”

From Whole-Brain Data to Functional Circuit Models: The Zebrafish Optomotor Response

“…The mammalian anatomy of retinal projections and the Pt suggests that binocular integration may occur via the PC (Sun and May, 2014). The zebrafish OMR is established by separate visual channels controlling multiple behavioral parameters.…”

A central mesencephalic reticular formation projection to the supraoculomotor area in macaque monkeys

“…Based on the presence of tectal terminals in this area, they suggested that the ventral portion of the periaqueductal gray that rests just dorsal to III, represents a separate region whose function is tied to the underlying oculomotor nucleus. In fact, terminal fields have been observed in SOA that originate from a number of oculomotor-related structures, including the superior colliculus [primates: (Harting 1977)], the caudal fastigial nuclei [primate: (May et al 1992)], lateral accessory optic nucleus [marmoset: (Blanks et al 1995)], pretectum [primate: (Büttner-Ennever et al 1996; Sun and May 2014; Wasicky et al 2004)] and the frontal and supplemental eye fields [primate: (Shook et al 1990; Stanton et al 1988)]. The present findings add another oculomotor-related structure to the list of SOA inputs, strengthening the supposition about its function made by Edwards and Henkel (1978).…”