Retinal projections in the Australian lungfish.

Autoradiographic analysis of the primary retinofugal projections in the Australian lungfish reveals contralateral retinal projections to a ventral portion of the periventricular preoptic nucleus, throughout its rostrocaudal extent, and to 4 distinct terminal fields in the thalamus. Only one of these thalamic fields (t4) likely receives dendrites solely from dorsal thalamic neurons. Thalamic terminal field 1 probably receives dendrites from both dorsal and ventral thalamic neurons, and fields 2 and 3 from only ventral thalamic neurons. Contralateral retinofugal fibers terminate in the pretectum and in the superficial and central tectal zones. The central tectal terminal field is restricted to the medial one-third of the tectum. At pretectal levels a contralateral basal optic tract arises from the marginal optic tract and terminates along the lateral edge of the tegmentum, as a series of glomerular puffs, and in the rostral pole of a superficial isthmal nucleus. The Australian lungfish, unlike the African and South American lungfish, possesses ipsilateral retinal projections to all of the nuclei that receive contralateral retinal input.