Are hypothalamo-cerebellar fibers collaterals from the hypothalamo-spinal projection?

Retrograde transport of fluorescent tracer molecules (Fast Blue and Nuclear Yellow) was used to restudy the feline hypothalamo-cerebellar and hypothalamo-spinal projections in order to decide whether hypothalamo-cerebellar and hypothalamo-spinal fibers are branches of the same axons. The finding of a significant hypothalamo-cerebellar projection from lateral, dorsal and posterior hypothalamic areas is confirmed. Scattered hypothalamo-cerebellar fibers were found to come from the supraoptic, dorsomedial, periventricular, infundibular and paraventricular nuclei, tuber cinereum and the anterior hypothalamic area. A topographical organization is proposed for the hypothalamo-cerebellar projection; the cerebellar anterior lobe receives fibers mainly from the rostral (anterior) hypothalamus while the posterior lobe receives fibers mainly from its caudal (posterior) part. The hypothalamo-spinal pathway originates principally within the dorsal, posterior and lateral hypothalamic areas, but receives small contributions also from the periventricular and paraventricular nuclei, tuber cinereum and the anterior hypothalamic area. Hypothalamic neurons retrogradely labeled from the spinal cord and from cerebellum were often located adjacent to each other, but only few double labeled neurons were found. This indicates that spinal and cerebellar projecting cells are mainly two different populations.