The ascending and descending connections of the hypothalamus in the cat

The ascending and descending projections of the lateral preopticohypothalamus were studied with radioautographic methods. Injections of [ −3H]leucine were placed throughout the rostral to caudal extent of the lateral preopticohypothalamic zone in adult cats. Ascending fibers of the rostral two-thirds of the lateral preopticohypothalamus terminate primarily in a nonspecific manner within the lateral and intermediolateral parts of septum and to a limited extent in the medial septum. Fibers from the rostral two-thirds of the lateral preopticohypothalamus also project to the lateral habenular nucleus via the stria medullaris. The caudal third of lateral hypothalamus appears to provide little or no contribution to the septum and habenular complex. Neurons from all parts of the lateral hypothalamus contribute to the total projection to both the ventral tegmental region and lateral preoptic region and adjacent structures. Projections from the lateral hypothalamus to midline thalamus could not be identified in the present study.