Retinal projections in the ringtailed possum Pseudocheirus peregrinus

Abstract

The retinal projections in the ringtailed possum, Pseudocheirus peregrinus were determined using Fink‐Heimer material and autoradiography. At least seven regions in the brain receive retinal projections. These are (1) the suprachiasmatic nucleus of the hypothalamus (2) the dorsal lateral geniculate nucleus (3) the ventral lateral geniculate nucleus (4) the lateral posterior nucleus (5) the pretectum (6) the superior colliculus, and (7) the accessory optic system. The accessory optic system and lateral posterior nucleus receive a contralateral retinal projection only and the other five regions receive a bilateral retinal projection.The dorsal lateral geniculate nucleus consists of two parts: an outer α division of closely packed cells and an inner β division containing loosely scattered cells. There are no cell layers apparent within the α division in Nissl sections. The autoradiographs and Fink‐Heimer material reveal four concealed laminae within the α division. Lamina 1, which is adjacent to the optic tract and lamina 3 receive a predominantly contralateral input. Laminae 2 and 4 receive a predominantly ipsilateral input. The β segment contains a fifth lamina which receives contralateral retinal input.