A double-labelling study of reticular collaterals to the spinal cord and cerebellum of the North American opossum.

Injections of horseradish peroxidase into either the spinal cord or cerebellum label neurons in the gigantocellular and lateral reticular nuclei of the North American opossum. In order to determine if neurons which project to the spinal cord and cerebellum are intermingled in these two nuclei and if single neurons provide collaterals to both areas, we have employed fluorescent markers in double-labelling experiments. Our results show that reticular neurons innervating either the spinal cord or cerebellum are often close together and that a few provide collaterals to both areas. Neurons providing such collaterals are rare, however, comprising 2% or less of those innervating either target alone.