title: Projections of neurons in the ventromedial medulla to pontine catecholamine cell groups involved in the modulation of nociception.
abstract: Stimulation of neurons in the nucleus raphe magnus (RMg) or the adjacent gigantocellular nucleus pars alpha (Gi alpha) and paragigantocellular nucleus (PGi) produces antinociception which is partially mediated by bulbospinal noradrenergic neurons. Since no norepinephrine-containing neurons are located in either the RMg or the Gi alpha/PGi, it is likely that neurons located in these nuclei have axonal connections with the spinally-projecting catecholamine neurons located in the A5, A6 (locus coeruleus), or A7 catecholamine cell groups. To provide evidence for such connections, the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), was injected into the RMg or Gi alpha/PGi and labeled axons were identified near catecholamine-containing neurons labeled with dopamine-beta-hydroxylase-immunoreactivity (D beta H-ir). A dense field of PHA-L-positive terminals was seen within the A7 cell group which was mainly ipsilateral to PHA-L injections made into either the RMg or the Gi alpha/PGi. Many PHA-L-positive terminals were closely apposed to D beta H-ir A7 perikarya or proximal dendrites. A modest number of terminals was seen within the A5 and LC cell groups. In the second experiment, a unilateral injection of the retrograde tracer, Fluoro-Gold, was made into the A7 cell group and brainstem sections were processed for serotonin (5-HT) immunocytochemistry. Many neurons retrogradely labeled with Fluoro-Gold were seen in the RMg, but a much larger number were found in the Gi alpha/PGi. Less than 5% of these Fluoro-Gold-labeled cells contained 5-HT-immunoreactivity. The results of these experiments indicate that the RMg and Gi alpha/PGi have a substantial population of non-serotonergic neurons which project to the A7 noradrenergic cell group.
authors.affiliation: University of Illinois, Department of Pharmacology, Chicago 60612.
authors.forename: F M
authors.initials: FM
authors.lastname: Clark
authors.forename: H K
authors.initials: HK
authors.lastname: Proudfit
mesh_terms: D000818:Animals; D001370:Axonal Transport; D001369:Axons / Q000648:ultrastructure; D001933:Brain Stem / Q000033:anatomy & histology / Q000502:physiology; D002395:Catecholamines / Q000502:physiology*; D004299:Dopamine beta-Hydroxylase / Q000032:analysis*; D004558:Electric Stimulation; D005260:Female; D007150:Immunohistochemistry; D008526:Medulla Oblongata / Q000033:anatomy & histology / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology*; D010835:Phytohemagglutinins; D011149:Pons / Q000033:anatomy & histology / Q000502:physiology*; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000032:analysis
chemical_list: D002395:Catecholamines; D010835:Phytohemagglutinins; C100156:leukoagglutinins, plants; D012701:Serotonin; D004299:Dopamine beta-Hydroxylase