Projections from the cerebral cortex to the accessory oculomotor nuclei of the rat: a neuroanatomical and immunohistochemical study

The projections from the cerebral cortex to the accessory oculomotor nuclei, i.e. the nucleus of posterior commissure (NPC), the nucleus of Darkschewitsch (NDK) and the interstitial nucleus of Cajal (INC) and the putative neurotransmitters subserving this pathway have been studied in adult rats. Retrograde labeling with Fluoro-Gold showed that only the more medial part of the agranular cortex, which is considered the rat's analogous to the frontal eye fields of the monkey, sends axon to the ipsilateral accessory oculomotor nuclei. The retrogradely-labeled cells were located primarily in the fifth layer of this cortical region. Following an injection of horseradish peroxidase conjugated with wheat germ agglutinin in this cortical area, we observed corticofugal labeled fibers reaching the accessory oculomotor nuclei and terminating as a fine dust-like terminal labeling in the NDK, in the dorso-lateral division of the INC and in the NPC, as well as in the medial oculomotor accessory nucleus, the red nucleus, the superior colliculus and, even though to a lesser extent, in the mesencephalic reticular formation and the central gray. With regard to the immunohistochemical approach, we observed that all the cells retrogradely labeled from the accessory oculomotor area were also stained by using glutamate or aspartate antisera.