The relationship of the locus coeruleus to the amygdala in the cat

In eight cats a unilateral lesion was produced in the locus coeruleus using either a 20 degree or a 30 degree rostrocaudal parasagittal electrode approach. The animals were killed after a survival period of 10 days. Ascending locus coeruleus projections found in the five animals with the best area destruction went through the dorsal pontine tegmentum into the mesencephalic central tegmental tract, entered the thalamic centromedian--parafascicularis nuclear complex, and divided into dorsal and ventral fascicles. The dorsal fascicle spread into much of the rostral thalamus, while the ventral one passed to the lateral hypothalamus and zona incerta. The lateral hypothalamic fibres extended rostrally into the preoptic area. No degeneration was seen passing in or through the amygdaloid body or stria terminalis. Critical analysis of our own findings and those of other investigators forces the conclusion that apparent projections to the amygdaloid area are really fibres of passage to the pyriform cortex and septum.