The direct spinal projections from the cerebellar nuclei in the rabbit were retro gradely traced by unilateral injection of WGA-HRP into different levels of the spinal cord, including the cervical, thoracic and lumbar segments. The labeled neurons in the cerebellar nuclei were constantly seen in those animals, in which the upper cervical segments (C_(2-4)) were injected. No labeled neurons could be found in the cerebellar nuclei following injection into the lower cervical cord (C_(6-8)) or more caudal segments. All labeled neurons were located in the caudal parts of the fastigial and the interposed nuclei on the side contralateral to the injection. The results show that there are crossed projections from the cerebellar nuclei directly to the upper cervical cord. This study provide certain morphological evidences for further investigation of some aspects of cerebellar functions on motor coordination.

Following injection of HRP into the cerebellum of the rat, the retrogradely labeled′spinal border cells′ in L_1-L_3 of the spinal cord were examined electron microscopically for understanding the synaptology. Six types of terminal boutons (S, F, Cf, T, G and P types) which terminated on the surface of cell bodies or dendrites of the spinal border cells were recognized. The S- and F-boutons contain spherical and elliptical vesicles respectively. These two types of boutons had relatively broad area contacting with the surface of either cell bodies or dendrites. They could be derided into two sub-types respectively. One was the elonagted giant bouton and the other was the round. Cf-type contain flattened vesicles and it make membraneous′contact′ lacking in specialized pre-and postsynaptic membrane thickenings. T-type contain spherical and large granular vesicles, and dense body was seen beneath the post synaptic membrane. G-type boutons contain large granular vesicles in area of presynaptic. P-type boutons form synapses upon the large S-type boutons and contain pleomorphic vesicles. The postsynaptic membrane of S-, T- and G-types is apparently thicker than the presynaptic membrane and showed to be asymmetrical. Further study is necessary with regard to the sources of different terminal boutons contacting with different portions of the spinal border cells.