Retinofugal pathways in the longnose gar Lepisosteus osseus (linnaeus)

Abstract

Retinal projections were studied with autoradiographic and silver methods in the gar, Lepisosteus osseus , one of the two surviving members of the holostean actinopterygians. Contralaterally, the retina projects to the preoptic nucleus of the hypothalamus, and, via the medial optic tract, to the dorsal thalamus, medial ventral thalamic nucleus, nucleus pretectalis profundus pars ventralis and pars dorsalis, and the medial portion of the deep layer of the central zone in the optic tectum. The dorsal optic tract projects to the lateral ventral thalamic nucleus, nucleus pretectalis centralis, and the superficial white and gray zone of the optic tectum. The ventral optic tract terminates in the nucleus of the ventral optic tract, the lateral and medial ventral thalamic nuclei, nucleus pretectalis superficialis, nucleus pretectalis centralis, nucleus pretectalis profundus pars ventralis, the basal optic nucleus, and the superficial white and gray zone of the optic tectum. Ipsilateral projections are to similar sites, except for an absence of inputs to the lateral ventral thalamic nucleus from the dorsal tract and to the nucleus pretectalis superficialis, nucleus pretectalis profundus pars ventralis, and the basal optic nucleus from the ventral tract. The presence of ipsilateral retinal projections in gars is compared to their presumed absence in teleosts, and comparisons of retino-recipient targets in gars are made with teleosts and with non-actinopterygian vertebrates.