title: Muscle pain activates a direct projection from ventrolateral periaqueductal gray to rostral ventrolateral medulla in rats.
abstract: Activation of the ventrolateral periaqueductal gray (vlPAG) evokes a reaction of quiescence, immobility, hypotension and bradycardia. Pain of deep somatic or visceral origin also often triggers a reaction of quiescence, immobility, hypotension and bradycardia and further, evokes a selective increase in immediate-early-gene (c-Fos) expression within the vlPAG. Vasodepression evoked from the vlPAG is thought to be mediated by an inhibition of presympathetic neurons within the rostral ventrolateral medulla (RVLM). In this study the prior injection of retrograde tracer into the RVLM was combined with the use of Fos expression as a marker of neuronal activation, to determine if deep (muscle) pain-evoked vasodepression could be mediated by a direct vlPAG-RVLM pathway. It was revealed that intramuscular injection of formalin, in the anaesthetised rat, evoked a significant increase in Fos expression within the caudal vlPAG, and that approximately 25% of the Fos-immunoreactive neurons projected to the RVLM.
authors.affiliation: Department of Anatomy & Histology, The University of Sydney, NSW 2006, Sydney, Australia. keay@anatomy.usyd.edu.au
authors.forename: K A
authors.initials: KA
authors.lastname: Keay
authors.forename: Q F
authors.initials: QF
authors.lastname: Li
authors.forename: R
authors.initials: R
authors.lastname: Bandler
mesh_terms: D000818:Animals; D008297:Male; D008526:Medulla Oblongata / Q000473:pathology / Q000503:physiopathology*; D009132:Muscles / Q000294:innervation* / Q000473:pathology / Q000503:physiopathology*; D009434:Neural Pathways / Q000473:pathology / Q000503:physiopathology*; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D009619:Nociceptors / Q000473:pathology / Q000503:physiopathology; D010146:Pain / Q000473:pathology / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000473:pathology / Q000503:physiopathology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013564:Sympathetic Nervous System / Q000473:pathology / Q000503:physiopathology*
chemical_list: D016760:Proto-Oncogene Proteins c-fos