Edinger-Westphal nucleus: Projections to the brain stem and spinal cord in the cat

Abstract

The efferent connections of the Edinger-Westphal (EW) nucleus of the cat have been examined using the autoradiographic anterograde axonal transport technique. Following injections of [ 3H]amino acids into the EW nucleus, fibers could be traced from this region to a number of sites in the caudal brain stem and spinal cord heretofore not known to receive an afferent input from this nucleus. Two descending pathways have been identified. One pathway travels in the medialmost aspect to the medial longitudinal bundle and terminates in the dorsal accessory olive. The other pathway leaves the nucleus laterally, coursing through the medial tegmentum, and then shifts to a ventrolateral position in the rostral rhombencephalon. Some fibers of this lateral pathway curve dorsally and terminate in the medial parabrachial nucleus. The remainder of this fiber system lies ventral to the spinal trigeminal complex, with some axons terminating in the subtrigeminal nucleus, while other fibers continue ventral to the caudal part of the spinal trigeminal nucleus and appear to terminate in the marginal layer and ventromedial part of this nucleus. Another component of this system terminates between the gracile and medial cuneate nuclei. The main pathways from the EW nucleus to the spinal cord include (1) some fibers which course through the dorsal column nuclei into the ventromedial part of the dorsal columns, and (2) other fibers which continue caudally immediately along the ventrolateral aspect of the spinal trigeminal nucleus and then proceed to the spinal cord in the region between the dorsal horn and the lateral cervical nucleus. These EW fibers appear to terminate mainly in Rexed's lamina I (marginal layer); other fibers, from both tracts appear to terminate in lamina V. There was no evidence for any ascending projections from the EW nucleus. Confirmatory data were obtained from a series of horseradish peroxidase (HRP) experiments, in which EW neurons were retrogradely labeled following injections into the dorsal column nuclei, spinal trigeminal nucleus, inferior olivary nucleus, or spinal cord. These results clearly indicate that the traditional view of the EW nucleus as merely a parasympathetic preganglionic nucleus should be seriously questioned.