Medullary neurons with projections to lamina X of the rat as demonstrated by retrograde labeling after HRP microelectrophoresis

Brainstem neurons were retrogradely labeled with microelectrophoresis of HRP or WGA-HRP into lamina X of the cervical or lumbar cord of rats. The results reveal that lamina X of the lumbar cord receives bulbar projections originating mainly within the nucleus raphe magnus and the nucleus reticularis paragigantocellularis (including the medial or alpha-ventral part and lateral part) and that lamina X of the cervical cord receives projections from similar but more extensive regions in the lower brainstem. These findings provide a neuroanatomical substrate for medullary descending modulation of nociceptive transmission in lamina X.