The terminal distribution pattern of spinocerebellar fibers. An anterograde labelling study in the posthatching chick

Abstract

The terminal fields of spinocerebellar fibers from different levels (cervical, thoracic and lumbar) of the spinal cord in the chick were determined by using wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP), an anterograde labelling technique. More terminals were found in the anterior lobe than in the posterior lobe. Following injections in the lumbar spinal cord, mossy fiber terminals were found mostly in the anterior lobe (lobules I-V). The highest density of labelled terminals was found in lobule I, and labelled terminals were found in all parts of the lobule. However in lobules II-IV, labelled fibers were mediolaterally arranged in three longitudinal strips on both sides of the midline, and formed a distinct zonal distribution pattern. Labelled terminals were distributed evenly from the apical to basal regions of lobules I-V. A large number of mossy fiber terminals originating from the thoracic spinal cord were located in the anterior lobe and lobule VI; some labelled terminals were found in lobule IX. Three less distinct longitudinal strips, compared to those following WGA-HRP injections in the lumbar spinal cord, were recognized on each side of the midline. Labelled mossy terminals were observed in lobules II-IX following WGA-HRP injections in the cervical spinal cord. In transverse sections two longitudinal strips were found at the apical parts of lobules II and III, whereas four thin longitudinal strips were located in lobules IV and V. The present study showed that the terminal fields of spinocerebellar fibers from each level of the spinal cord have different distribution patterns.