Demonstration of a somatotopically organized projection onto the paramedian lobule and the anterior lobe from the lateral reticular nucleus: an experimental study with the horseradish peroxidase method.

Using the retrograde axonal transport of horseradish peroxidase, the projection from the lateral reticular nucleus (NRL) to the cerebellar anterior lobe and paramedian lobule has been studied in 13 cats. Both the anterior lobe and the paramedian lobule receive a somatotopically organized projection from the NRL. The projection to the paramedian lobule is nearly exclusively ipsilateral and originates mainly in the dorsal part of NRL, while the projection to the anterior lobe is bilateral (with ipsilateral predominance) and takes origin from all parts of the NRL. The lateral part of the NRL (closely coinciding with the parvocellular nucleus) projects to the rostral part of the anterior lobe and caudal parts of the paramedian lobule (both representing the hindlimb), while the medial part of the NRL (magnocellular nucleus) projects to the caudal parts of the anterior lobe and rostral parts of the paramedian lobule (representing the forelimb). The small subtrigeminal nucleus projects onto the anterior lobe as well as the paramedian lobule, but apparently mainly to their forelimb areas.