The projection from nucleus raphe magnus and other brainstem nuclei to the spinal cord in the rat: a study using the HRP blue-reaction

Abstract

Horseradish peroxidase injections, or solid HRP placements, were made into the dorsolateral quadrant of the spinal cord in ten adult rats, processed according to the blue-reaction (benzidine dihydrochloride) protocol [6]. When the interventions involved the dorsal lateral funiculus (DLF) HRP-labelled somata were observed primarily in the ipsilateral nucleus raphe magnus (NRM), with an occasional cell in nucleus raphe obscurus (NRO) and pallidus (NRP). Other brainstem raphe nuclei consistently lacked labelled neurons. The red nucleus and paralemniscal reticular formation of the rostal pons also contained appreciable numbers of HRP back-filled perikarya. The direct NRM-spinal projection in the rat, involved in the modulation of pain transmission in the spinal cord dorsal horn, originates primarily from the expanded region of the nucleus in the rostralmost medulla.