The center for controlling the near reflex in the midbrain of the monkey: a double labelling study.

The center for controlling the near reflex was studied in the midbrain of the monkey using Diamidino yellow dihydrochloride (DY) and Fast blue (FB) as retrograde neuronal tracers. After injection of DY into the ciliary ganglion, many labelled neurons were found ipsilaterally in the anteromedian nucleus, the Edinger-Westphal nucleus, and the nucleus of Perlia. In contrast, after injection of FB into the medial rectus muscle, labelled cells were found ipsilaterally only in the Edinger-Westphal nucleus of the visceral nuclei as well as in the somatic ipsilateral nuclei. No double labelling of cells was noted in the Edinger-Westphal nucleus, establishing the premise that FB-labelled cells were subserving medial rectus muscle and pupillary/accommodative functions and DY cells were subserving pupillary/accommodative functions independently.