QUANTITATIVE-ANALYSIS OF CONVERGING SPINAL AND CUNEATE MOSSY FIBER AFFERENT-PROJECTIONS TO THE RAT CEREBELLAR ANTERIOR LOBE

The convergence/divergence of messy fibre afferent projections to the cerebellar anterior lobe from a single lumbar segment, from adjacent o r widely separated lower thoracic and lumbar segments, and finally fro m the lower thoracic-upper lumbar spinal cord and the brainstem cuneat e nuclei was quantitatively analysed in adult rats. Spinal and cuneate messy fibre terminals were differentially labelled with biotinylated dextran amine and cholera toxin subunit B, immunohistochemically ident ified in the same histological sections, and their spatial distributio ns quantitatively plotted in computer reconstructions of the unfolded anterior lobe cortex. Afferent convergence was quantified by calculati ng the number of biotinylated dextran amine-labelled terminals that ra dially overlapped with cholera toxin-labelled terminals at points on t he unfolded cortical map that represented theoretical Purkinje cells. Spino- and cuneocerebellar messy fibre terminals are organized in patc hes that are oriented in parasagittally-oriented stripes or transverse ly oriented bands. Afferent convergence was greatest following biotiny lated dextran amine and cholera toxin injections in the same or adjace nt spinal lumbar segments (60 and 52%, respectively). When biotinylate d dextran amine and cholera toxin were injected in a sin le segment di fferentially labelled terminals appeared randomly intermingled in comm on patches. There was a trend for terminals labelled from adjacent lum bar segments to be more segregated in the patches. Segmentally separat ed biotinylated dextran amine and cholera toxin spinal cord injections (four lumbar segments) resulted in clearly segregated (80%) biotinyla ted dextran amine from cholera toxin-labelled terminal patches or patc hes with distinct divergence of the differentially labelled terminals in the patch. Cuneocerebellar terminals labelled with biotinylated dex tran amine were located in patches, stripes, and bands spatially segre gated from terminal patches, stripes, and bands of cholera toxin-label led spinal afferents except at their immediate borders where some radi al overlap occurred (9-22%). These anatomical findings for a fractured somatotopy of spinal and cuneate inputs to the cerebellar anterior lo be complement neurophysiological findings for a very similar pattern o f organization of cutaneous inputs to the posterior lobe, and are disc ussed in light of potential mechanisms for anterior lobe processing of somatosensory information. (C) 1997 IBRO. published by Elsevier Scien ce Ltd.