Projections of the superior cerebellar peduncle in rats and the development of new connections in response to neonatal hemicerebellectomy

Topographical organization of ascending cerebellar projections from the dentate and interposed nuclei in Macaca mulatta: an anterograde degeneration study

Discrete electrolytic lesions were placed in the dentate and interpositus cerebellar nuclei in th monkey Macaca mulatta and anterograde degeneration was traced in the ascending limb of the brachium conjunctivum using the Wiitanen technique. The dentate and interpositus anterior (IA) nuclei project topographically onto the two somatotopically organized divisions of the red nucleus and the ventrolateral-ventral intermediate nuclei of the thalamus (VL-Vim). Caudal parts of the dentate project to face areas in medial parts of the parvocellular red nucleus (RNpc) and VL-Vim, rostrolateral parts to central arm areas in these nuclei. There is a small projection from the rostroventral dentate to lateral hindlimb areas in RNpc and VL. Dorsal parts of the dentate project to ventral parts of RNpc and VLc-Vim (distal limb musculature area) exclusively, whereas ventral parts of the dentate project to dorsal parts of RNpc with some overlap ventrally dorsomedial VLc (proximal limb musculature and premotor areas). Caudal parts of IA project to medial forelimb and rostral parts to lateral hindlimb areas in the magnocellular red nucleus (RNmc) and VL-Vim. Projections from IA are greatest to distal musculature areas in VL-Vim. No projections from the interpositus posterior nucleus (IP) to the red nucleus could be identified positively, but projections to VL-Vim are to proximal hindlimb musculature and premotor areas.

Retrograde changes in Clarke's column following neonatal hemicerebellectomy in the rat

Long-Evans black-hooded rat pups underwent hemicerebellectomies at various postnatal ages. The animals were killed at 28 days of age and thoracolumbar segments of the spinal cord were removed and processed according to Golgi and Nissl techniques. Hemicerebellectomy at two and three days postnatally produced, in addition to cellular hypotrophy in Clarke's column, dendritic alterations which included a decrease in the number of primary dendrites and a reduction of the remaining dendrites to truncated stubs. Hemicerebellectomy at 21 days postnatally had little effect on either cell size or dendritic arborization. The role of the target nucleus in maintaining cell growth and dendritic arborization during critical developmental periods is discussed.

Plasticity of spinovestibular projections in response to hemicerebellectomy in newborn rats

Spinal cord projections to the lateral vestibular nucleus (LVN) are relatively sparse in normal adult black-hooded rats. However, in response to hemicerebellectomy in 2--3-day-old rats an increase in spinovestibular fibers to the ipsilateral lateral vestibular nucleus was observed. This increased input appears to be due to fibers which would normally be destined for the cerebellum but which alternatively project to the functionally related lateral vestibular nucleus. Considering the neuroanatomical relationships between the cerebellum and the vestibular nuclei and in view of the functional compensation frequently reported after cerebellar lesions, the observed remodelling may represent a partial anatomical basis for recovery of function.