Defining the pupillary component of the perioculomotor preganglionic population within a unitary primate...

The primate Edinger-Westphal nucleus (EW) contains perioculomotor preganglionic (pIII(PG)) motoneurons that control the lens and pupil. Separate subdivisions have been described in EW and termed visceral columns, with the lateral visceral column (lvc) reportedly receiving pretectal inputs for the pupillary light reflex. However, choline acetyl transferase staining reveals a single paired column of cells dorsal to the oculomotor nucleus, suggesting the EW is not subdivided. We investigated this issue by transneuronal retrograde labelling of pIII(PG) neurons in three monkey species. In all three, pIII(PG) neurons were contained in a single column. We have also examined which part of the macaque pIII(PG) population receives pretectal input. Injections of biocytin into the pretectum anterogradely labelled terminals that lay in close association with pIII(PG) motoneurons retrogradely labelled by ciliary ganglion injections of WGA-HRP. These close associations were concentrated in the ventromedial portion of the middle third of EW, suggesting this pIII(PG) region mediates pupillary control. In other cases, pretectal WGA-HRP injections, in addition to labelling terminals in the EW, produced a circular field of labelled neurons, and terminals in the periaqueductal grey, dorsolateral to EW. This region may represent the previously designated lvc, but it does not contain pIII(PG) motoneurons.