Origin of brain stem and temporal cortical afferent fibers to the septal region in the squirrel monkey

The origins of the brain stem and temporal cortical projections to the septal region in the squirrel monkey were investigated with the horseradish peroxidase (HRP) retrograde axonal transport technique. After HRP injections placed into the septal region, labeled cells were observed in brain stem sites which generally correspond to regions which are associated with known monoamine cell groups previously identified in the primate. These structures include the nucleus locus ceruleus, dorsal tegmental nucleus of Gudden, nucleus reticularis tegmenti pontis, nucleus annularis, ventral tegmental region, and the medial aspect of the lateral hypothalamus. Temporal cortical efferent fibers to the septal region arise principally from layers II and III of the perirhinal region, suggesting the presence of a second-order olfactory innervation of this structure.