An experimental study on the efferent connections of the amygdaloid complex in the cat

The amygdalofugal fibers were studied III the cat with the silver method of NAUTA-GYGAX. 1. The amygdalofugal fibers are distributed by way of the stria terminalis, the longitudinal association bundle, the inferior thalamic peduncle, and the medial forebrain bundle. 2. The amygdalofugal fibers running through the longitudinal association bundle arise in the lateral principal, intermediate principal nuclei and the lateral and possibly intermediate parts of the periamygdaloid cortex, and terminate in the lateral preoptic nucleus, the bed nucleus of the anterior commissure, the olfactory tubercle, the nucleus of the diagonal band of Broca, the nucleus accumbens, the medial and posterior septal nuclei and the basal part of the head of the caudate nucleus. In addition, there are scattered fibers coursing along the longitudinal association bundle proper. These fibers may have a widespread origin from the amygdaloid complex. The longitudinal association bundle contributes no fibers to the medial forebrain bundle. 3. The fibers, originating from the lateral principal, intermediate principal and medial principal nuclei, join the medial forebrain bundle to distribute widely in the lateral hypothalamic nucleus. A few fibers are seen to reach the ventromedial hypothalamic nucleus, and are considered to arise in the medial principal nucleus. 4. By way of the inferior thalamic peduncle some fibers from the amygdaloid complex course dorsally into the medial part of the dorsomedial thalamic nucleus at its caudal levels. They may arise widely from the amygdaloid complex. A few of them extend farther dorsally to reach the lateral habenular nucleus and the parataenial nucleus. They probably originate from the lateral principal nucleus. 5. The fibers forming the stria terminalis originate from the medial principal nucleus, the medial nucleus, the periamygdaloid cortex and the cortical nucleus, and are distributed in the bed nucleus of the stria terminalis and the lateral preoptic nucleus (preoptic component), as well as the medial preoptic nucleus, the anterior hypothalamic nucleus and the ventromedial hypothalamic nucleus (supracommissural component). The cortical nucleus, particularly its caudal part, and possibly the medial part of the periamygdaloid cortex are regarded as the main sources of the stria terminalis fibers ending in the hypothalamic region. The intermediate principal and lateral principal nuclei do not appear to contribute fibers to the stria terminalis. 6. The ventromedial hypothalamic nucleus receives amygdalofugal fibers both from the medial principal nucleus by way of the medial forebrain bundle, and from the cortical nucleus via the stria terminalis. 7. In addition to intrinsic internuclear fibers within the amygdaloid complex, some of the fibers from the complex are distributed to the ventralmost part of the putamen, the medial part of the claustrum, the periamygdaloid cortex, the prepiriform area and the anterior amygdaloid area, but do not reach the hippocampus.