Location and morphology of dorsal spinocerebellar tract neurons that receive monosynaptic afferent input from ankle extensor muscles in cat hindlimb.

1. The present experiments were carried out to investigate the morphology and somatotopic location of dorsal spinocerebellar tract (DSCT) neurons that receive monosynaptic group 1 afferent input from hindlimb ankle extensor muscles in the cat. 2. Intracellular recordings were obtained from DSCT neurons throughout the rostrocaudal extent of the L3 dorsal root entry zone of the spinal cord. DSCT neurons, physiologically identified as receiving monosynaptic group I input from the ankle extensor muscles, were injected with horseradish peroxidase (HRP) and subsequently reconstructed under the light microscope. 3. In contrast to previous HRP studies of DSCT neurons, these cells were found to have extremely extensive and complex dendritic trees, that often extend beyond the region of Clarke's column. Dendrites were found to extend into the white matter of the dorsal columns, and/or into the spinal gray matter in a ventrolateral direction. The large dendritic spread of DSCT neurons was found to occupy up to 60% or more of the cross-sectional area of Clarke's column. 4. DSCT neurons receiving monosynaptic group I input from the single functional group of ankle extensor muscles were not found to be confined within a specific transverse region of Clarke's column, in contrast to a previous proposal. Instead, these cells could be found throughout Clarke's column. 5. The present results demonstrate that DSCT neurons, physiologically identified as receiving group I muscle afferent input, exhibit dendritic trees that are considerably more extensive and morphologically complex than indicated by previous studies. In addition, the present results do not support a previous proposal of a strict somatotopic arrangement for DSCT neurons and their dendritic envelopes within Clarke's column in the transverse plane.