Telencephalic connections in lizards. I. Projections to cortex.

The afferent connections to five cortical regions in two distantly related species of lizards (Gekko gecko and Iguana iguana) were studied by means of retrograde transport of horseradish peroxidase conjugated to wheat germ agglutinin. Each of the five cortical regions is characterized by a specific pattern of projections from telencephalic, thalamic, hypothalamic, and brainstem regions. Subdivisions within the five cortical regions also receive different patterns of projections. The thalamo-cortical projections are as follows: The small-celled mediodorsal cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The large-celled mediodorsal cortex receives projections from nucleus dorsolateralis anterior pars parvicellularis and pars magnocellularis. The dorsal cortex receives a projection from nucleus dorsolateralis anterior pars parvicellularis. The lateral cortex receives a projection from nucleus dorsolateralis anterior pars magnocellularis. The pallial thickening receives projections from nucleus dorsomedialis and nucleus intercalatus. The latter nucleus receives a direct retinal projection. Thus, the pallial thickening is the recipient of a retino-thalamocortical projection. To date, comparisons of data from experimental studies have suggested that the cortical regions in lizards and turtles may be organized differently. However, the results of the present study suggest that the organization of cortical regions among reptiles is more similar than previously realized.