Projections of the medial and lateral prefrontal cortices to the amygdala: a Phaseolus vulgaris leucoagglutinin study in the rat.

The projections of different subfields of the medial and lateral prefrontal cortices to the amygdala were studied in the rat using the sensitive Phaseolus vulgaris leucoagglutinin anterograde tract tracing technique. Injections into the infralimbic cortex produced anterograde labeling in the lateral capsular subdivision of the central nucleus, superficial (corticomedial) amygdaloid nuclei, lateral and accessory basal nuclei, and the anterior amygdaloid area. Injections into the caudal portion of the infralimbic cortex produced additional labeling in the intermediate subdivision of the central nucleus. The prelimbic cortex had projections to the medial portion of the magnocellular basal nucleus and adjacent portions of the lateral nucleus and lateral capsular subdivision of the central nucleus. The medial precentral cortex had projections to the rostromedial part of the magnocellular basal nucleus and adjacent portions of the lateral capsular subdivision of the central nucleus. Injections into the lateral orbital and ventral agranular insular cortices produced labeled fibers in the rostral part of the superficial amygdala, lateral capsular subdivision of the central nucleus, and the lateral and accessory basal nuclei. The dorsal agranular insular area had projections to several different subdivisions of the central nucleus as well as to the rostrolateral magnocellular basal nucleus; the latter projections were complementary to those originating in the prelimbic area. The present study indicates that each portion of the prefrontal cortex has a distinctive projection to the amygdala. The ventral areas of the lateral and medial prefrontal cortices, which receive olfactory projections, are the only prefrontal cortical areas with projections to the olfactory-related superficial amygdaloid nuclei. The more dorsally situated prefrontal areas, the dorsal agranular insular area and prelimbic cortex, have complementary projections to the basal nucleus, suggesting that they modulate separate prefrontal cortico-striatal-pallid circuits. The specificity of prefrontal cortico-amygdaloid projections is indicative of their involvement in discrete functions.