Visual connections of the atypical diencephalic nucleus rostrolateralis in Pantodon buchholzi (Teleostei,...

Among the many thousands of teleost fish species, a diencephalic nucleus rostrolateralis (RL) has been identified in only six widely divergent species. In one of these, Pantodon buchholzi, its retina projects to both RL and the optic tectum, the latter in a visuotopic manner. The ventral part of the retina beneath a horizontal black-pigmented septum connects to the dorsomedial optic tectum and nucleus RL. The dorsal part of the retina connects to the lateroventral optic tectum and little, if at all, to RL. Using DiI tracing, the position of RL in the optic pathway of this fish has been directly demonstrated. Cells in the stratum periventriculare of the dorsomedial optic tectum contribute to the afferent input of RL (bilaterally); cells in the ventrolateral tectum do not. RL is also reciprocally connected with the torus longitudinalis and may project to three nuclei of the preglomerular complex. Ganglion cells in the retina that project to RL are sparsely distributed throughout the ventral hemiretina compared with ganglion cells that project to the optic tectum. Since this fish is an obligatory surface feeder, the neuroanatomical connectivity of nucleus RL in P. buchholzi suggests a role in the fish's visual identification of targets for feeding behavior.