A proposal for a common nomenclature for some optic nuclei in vertebrates and the evidence for a common origin of two such cell groups.

Abstract

Comparative studies on the connections of the optic nuclei in a great variety of vertebrates have revealed striking common features. The findings prompted the proposal for a simpler nomenclature which is useful in ordering our present concepts concerning cell groups related to the optic system. The suggested equivalents are summarized below.The dorsomedial optic nucleus (DMO) has previously been called the pretectal area in elasmobranchs, the 'dorsolateral thalamic nucleus' or the 'nucleus pretectalis dorsomedialis' in teleosts, the 'pretectal area' in amphibians, the 'nucleus posterodorsalis' in reptiles, and 'pretectal area' or 'olivary pretectal nucleus' in mammals.The label dorsolateral optic nucleus (DLO) is suggested instead of the 'lateral geniculate nucleus' in elasmobranchs, the visual part of 'dorsal thalamus' in amphibians, 'dorsal lateral geniculate nucleus' in reptiles, ‘nucleus dorsolateralis anterior' in birds, and the 'dorsal nucleus of the lateral geniculate body' in mammals.The ventrolateral optic nucleus (VLO) was formerly not identified in elasmobranchs and was called the 'ventral nucleus of the lateral geniculate body' in reptiles, birds, and mammals.The ventromedial optic nucleus (VMO) is the most ventromedial recipient of retinal fibers (which are usually large) and has earlier been called a variety of names including the 'accessory optic nucleus' in teleosts, the 'ectomammilIary nucleus' in amphibians, reptiles, and birds, and the 'medial terminal nucleus in mammals.The central optic nucleus (CO) characteristically receives no direct retinal fibers but a strong tectal contribution, and it projects to the telencephalon. The nucleus is thought to be incorporated in the DLO in amphibians and elasmobranchs, hence, the label DLOC (dorsolateral optic complex) in these classes. The CO has previously been called the 'nucleus prethalamicus' or 'nucleus rotundus' in teleosts, 'nucleus rotundus' in birds and reptiles, and the 'lateral posterior nucleus' or 'pulvinar' in mammals.Evidence is presented that the DLO and the CO may have evolved from the same aggregate and that the telencephalic regions that are recipients of fibers from DLO-CO may also have evolved from one aggregate. The variation in the parcellation of this system encountered in various vertebrates would then reflect adaptations to selective pressures. Some of the combinations of arrangements that have evolved are described. The significance of variations should become clear with behavioral and electrophysiological analysis.