The origins of supraspinal projections to lumbosacral and cervical levels of the spinal cord in the gray short-tailed Brazilian opossum, Monodelphis domestica.

Retrograde tracing techniques were used to identify supraspinal neurons that project to sacral, lumbar and cervical levels of the spinal cord in the gray short-tailed Brazilian opossum, Monodelphis domestica. Injections of Fast Blue, True Blue or wheat germ agglutinin conjugated to horseradish peroxidase into the sacral or lumbar cord labeled neurons in hypothalamic and brainstem nuclei reported to innervate the same levels in other mammals. Injections at cervical levels produced extensive labeling in the same areas as well as labeling within the isocortex, the medial preoptic area, the central and basomedial amygdaloid nuclei, the medial and interposed nuclei of the cerebellum, and several additional areas of the brainstem. In some of the cases, lumbar injections of wheat germ agglutinin conjugated to horseradish peroxidase were combined with a contralateral hemisection of the thoracic cord in order to determine laterality. The origins of monoaminergic projections were assessed using the retrograde transport of True Blue from the cervical cord and immunofluorescence for serotonin and tyrosine hydroxylase. Our results suggest that the origins of supraspinal projections to the spinal cord of Monodelphis are similar to those described for the North American opossum, Didelphis virginiana. Differences appear to exist, however, particularly in the amount of isocortex containing corticospinal neurons, the existence of spinal projections from the amygdala and preoptic area, the degree of rubrospinal somatotopy, and the origins of certain monoaminergic projections.