Thalamocortical projections from the mediodorsal nucleus in the virginia opossum

Abstract

The projections from the mediodorsal nucleus to cortex were studied in the opossum by the Fink-Heimer stain for anterograde axonal degeneration. The results show that lesions of the mediodorsal nucleus produce fiber degeneration in the head of the caudate nucleus and in layers IV and I of preorbital cortex; this cortical area lies on the dorsolateral convexity of the hemisphere just rostral to the orbital sulcus. Preorbital cortex shows distinct lamination, with a well developed stratum of large pyramidal cells in layer V. In contrast to somatic sensory cortex, layer VI neurons in preorbital cortex are mostly stellate cells and do not possess prominent apical dendrites that traverse the overlying cortical layers.