Direct connections between hypothalamus and lumbar spinal cord in rabbits

Horseradish peroxidase (HRP) was injected into the L6 spinal cord in seven rabbits and the labeling in the hypothalamus traced. The distribution of the retrogradely labeled cells was studied and the anterogradely labeled fibers and terminal branches were unequivocally identified. Hypothalamo-spinal projection cells were found predominantly on the ipsilateral side, mainly distributed in the posterior, dorsal, and lateral hypothalamic areas, and the paraventricular nucleus. Some were found in the perifornical nucleus and a few could be seen in the tuber area, supramammillary nucleus and the region dorsal to the supraoptic nucleus. Spino-hypothalamic projections were found to terminate mainly on the contralateral side via two routes: (i) The dorsal longitudinal fasciculus, distributed to the posterior hypothalamic area. Some might end in the supramammillary nucleus; (ii) Fibers running latero-medially ventral to the mammillothalamic tract to terminate in the dorsal parts of the medial and lateral hypothalamus. Some are dispersed into the ventral areas.