Anatomical demonstration of the location and collateralization of rubral neurons which project to the spinal cord, lateral brainstem and inferior olive in the North American opossum.

Rubral neurons innervating the spinal cord, the lateral brainstem and the inferior olivary nucleus have been identified in the North American opossum by the retrograde transport of horseradish peroxidase and fluorescent markers. Neurons which project to the spinal cord are found mainly in caudal and rostroventral parts of the red nucleus. In contrast, rubral neurons which innervate the facial nucleus and lateral areas of the medulla are most numerous rostrodorsally. There is overlap in the location of rubral neurons which project to the spinal cord and lateral brainstem, however and; double-labelling techniques show that some rubral neurons provide collaterals to both areas. Neurons which innervate the inferior olive are located primarily in rostromedial portions of the red nucleus with some overlap with those innervating the spinal cord. Few rubral neurons provide collaterals to both the spinal cord and inferior olive.