title: Hypovolemic shock: critical involvement of a projection from the ventrolateral periaqueductal gray to the caudal midline medulla.
abstract: Previous research has suggested that the ventrolateral column of the periaqueductal gray (vlPAG) plays a crucial role in triggering a decompensatory response (sympathoinhibition, hypotension, bradycardia) to severe blood loss. vlPAG excitation triggers also quiescence, decreased vigilance and decreased reactivity, the behavioral response which usually accompanies hypovolemic shock. The aim of this study was to identify, in unanesthetized rats, the main descending pathway(s) via which vlPAG neurons trigger sympathoinhibition and bradycardia in response to severe blood loss. Firstly, immediate early gene (c-Fos) expression was used to identify vlPAG neurons selectively activated by severe blood loss. Subsequently, the specific medullary projections of these vlPAG neurons were defined by combined c-Fos, retrograde tracing (double-label) experiments. It was found that vlPAG neurons selectively activated by severe hemorrhage project overwhelmingly to the vasodepressor portion of the caudal midline medulla (CMM). Previous studies indicate that this CMM region mediates behaviorally-coupled cardiovascular adjustments and the findings described here fit with the idea that CMM neurons are uniquely recruited by salient challenges, the adaptive responses to which require more than reflexive homeostatic cardiovascular adjustments.
authors.affiliation: School of Medical Sciences (Anatomy and Histology), Anderson Stuart Building, The University of Sydney, NSW, Australia.
authors.forename: D J
authors.initials: DJ
authors.lastname: Vagg
authors.forename: R
authors.initials: R
authors.lastname: Bandler
authors.forename: K A
authors.initials: KA
authors.lastname: Keay
mesh_terms: D000344:Afferent Pathways / Q000502:physiology; D000578:Amidines / Q000378:metabolism; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001931:Brain Mapping; D005786:Gene Expression Regulation / Q000502:physiology; D006470:Hemorrhage / Q000473:pathology; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D009599:Nitroprusside / Q000494:pharmacology; D016761:Oncogene Proteins v-fos / Q000378:metabolism; D010487:Periaqueductal Gray / Q000473:pathology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012769:Shock / Q000473:pathology*; D013266:Stilbamidines / Q000378:metabolism; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D000578:Amidines; D016761:Oncogene Proteins v-fos; D013266:Stilbamidines; D014665:Vasodilator Agents; C031455:diamidino compound 253-50; D009599:Nitroprusside