Corticospinal tract collaterals to the dorsal column nuclei of cats. An anatomical single and double retrograde tracer study.

A double-labelling anatomical strategy employing horseradish peroxidase and tritiated, enzymatically inactive horseradish peroxidase allowed simultaneous visualization of corticospinal neurones and cortical neurones projecting to the dorsal column nuclei in cats. By this approach it is shown that although most cortical fibres to these nuclei are not branches of corticospinal axons, neurones projecting to both targets are present in all areas of the sensorimotor cortex and especially in area 3a. Thus, cortical control upon the dorsal column nuclei is mediated via descending fibres that differ as to their origin and to their branching pattern.