Connections of the Posterior Pallium in the Crested Newt, <i>Triturus carnifex</i>

Abstract

The connections of the posterior pallial regions were studied in the crested newt, Triturus carnifex, by means of the horseradish peroxidase technique. The tracer was injected into the lateral and medial pallia, caudal to the interventricular foramen. In addition, the connections between the posterior pallium and the infundibular hypothalamus were investigated with both horseradish peroxidase and the fluorescent dye DiI. The results show important differences between the connection patterns of the medial and lateral pallia. The lateral pallium receives inputs from the main olfactory bulb and send fibers to the contralateral hemisphere through the anterior commissure. It also shows modes extra-telencephalic connections. Conversely, the medial pallium receives direct afferent inputs from the amygdala (pars medialis) and the anterior dorsal thalamus. It is reciprocally connected to the contralateral homologue region through the hippocampal commissure, and its main efferent system is the medial forebrain bundle, which reaches the infundibular hypothalamus. The infundibulum also receives a prominent projection from the amygdala (pars lateralis). The connectivity of the posterior pallium is comparable to that reported previously for the anterior pallium, although a few differences are noted. These differences in the connectivity of the lateral pallium and the medial pallium may reflect different functional properties of these telencephalic regions.