Projections of the amygdala in rats during development.

Unilateral electrolytic lesions of the amygdaloid nucleus were made in rats during development to study the timing of sequential connectivity. The patterns of neural degeneration were detected by the Fink-Heimer technique and light microscopy. The main projections were to the accumbens, caudate, septal area, habenula, hypothalamus, cingulum, thalamus, and mesencephalon. In all cases degenerated fibers were progressively more apparent with increasing age. A clear and consistent pattern of degeneration was first observed at 30 days postnatally. Because the amygdala is widely connected with numerous limbostriatal and other CNS structures, the data presented favor the possibility that the amygdaloid complex can be a crucial region for the triggering of patterns of endocrine and autonomic, as well as somatic responses.