LOWER THORACIC UPPER LUMBAR SPINOCEREBELLAR PROJECTIONS IN RATS - A COMPLEX TOPOGRAPHY REVEALED IN COMPUTER RECONSTRUCTIONS OF THE UNFOLDEDANTERIOR LOBE

The topography of wheatgerm agglutinin-horseradish peroxidase/horserad ish peroxidase-labeled mossy fiber terminals of lower thoracic-upper l umbar (T12-L3) spinal projections to the cerebellar anterior lobe was quantitatively analysed in adult rats. Computer-based image analysis m apped the orthogonal (parallel to the surface) distribution of labeled terminals in two-dimensional reconstructions of the unfolded anterior lobe cortex. The radial (perpendicular to the surface) distribution o f terminals within the granule cell layer was mapped by computing whet her the terminals were in either the outer- or inner-halves of this la yer. The number of labeled terminals in each lobule was calculated. In the anterior lobe, lower thoracic-upper lumbar spinocerebellar projec tions terminate primarily in lobules II (mean 27.14%), III (mean 38.68 %), and IV (mean 19.31%). Different-sized bilateral injections restric ted to L1 were used to study the organization of intrasegmental spinoc erebellar projections. Small injections into L1 labeled a limited numb er of terminals which were located either in clusters or were spatiall y isolated. Intermediate-sized intrasegmental injections resulted in a dditional clusters of labeled terminals. Many of the terminal clusters were spatially related and formed larger irregularly shaped patches. Large intrasegmental injections labeled terminal clusters and patches that were discontinuous but aligned parallel to the longitudinal (tran sverse) axis of lobules II-IV. Injections including segments rostral a nd caudal to L1 were used to study the topography of intersegmental lo wer thoracic-upper lumbar spinocerebellar projections. Multisegmental injections increased the number of labeled terminal clusters and patch es which obscured the pattern of segmental input, but there was still a transversely oriented pattern of termination. Distinct transversely aligned terminal free areas remained apparent. Lower thoracic-upper lu mbar spinocerebellar projections terminated in both the outer- and inn er-halves of the granule cell layer, but overall were more numerous in the outer-half of this layer. In serially spaced sagittal sections, h owever, the majority of terminals alternated between the outer- and in ner-halves of the granule cell layer. Outer- and inner-terminals were not spatially segregated in their orthogonal distribution. These resul ts indicate lower thoracic-upper lumbar spinocerebellar projections ha ve a complex three-dimensional topography in the anterior lobe. These findings are discussed in relation to previous findings for a sagittal ly oriented topography for lower thoracic-upper lumbar spinocerebellar projections and in the context of how cerebellar somatosensory affere nt input may be organized.