Thalamotelencephalic projections in the turtle (<i>Pseudemys scripta</i>)

TLDR

The study mapped turtle thalamic telencephalic projections using the Fink‑Heimer axonal degeneration staining technique. Lesion studies showed that thalamic projections terminate in basal telencephalic nuclei, dorsal ventricular ridge core, and outer layer I of cortex, with spatial organization such that the dorsal lateral geniculate projects to general cortex, and comparative analysis with hedgehog and opossum suggests homologous forebrain structures.

Abstract

Abstract The telencephalic projections of the turtle thalamus were studied using the Fink‐Heimer ('67) technique for staining degenerated axons and their terminals. Large thalamic lesions produced terminal degeneration in the basal telencephalic nuclei, the core of the dorsal ventricular ridge and the outer half of layer I in general cortex. A variety of control lesions confirmed that these projections arise in the thalamus. Circumscribed thalamic lesions revealed first, that there is some degree of spatial organization in the turtle's thalamocortical projection system and second, that at least one sensory relay nucleus, the dorsal lateral geniculate, projects to general cortex. Detailed comparisons of the turtle's thalamotelencephalic projections with those present in two primitive mammalian species, the hedgehog and the opossum, provided a basis for identifying probable homologies in the forebrains of reptiles and mammals.