Cytoarchitecture and fibre connections of the Edinger-Westphal nucleus in the filefish

Abstract

Many teleosts have an intraocular lens muscle which causes lens movement for visual accommodation. Central pathways for visual accommodation were traced in the filefish ( Novodon modestus ) using horseradish peroxidase (HRP) tracing method. After HRP injection into the lens muscle, large cells were labelled in the ciliary ganglion. After HRP injections into the ciliary ganglion, a compact cell group was retrogradely labelled in an area rostrodorsal to the somatic oculomotor nuclei in the midbrain. The nucleus consisted of about 90 cells which were slightly smaller than the somatic oculomotor neurons. This nucleus was considered to be homologous with the mammalian Edinger-Westphal nucleus. After injections of HRP into the Edinger-Westphal nucleus, cells in the nucleus of the posterior commissure were retrogradely labelled. Because the nucleus of the posterior commissure receives retinal projections (Ito et al. 1984), it is considered that the cells in the nucleus of the posterior commissure are the first central neurons in the pathway for visual accommodation in teleosts.