title: Rostral ventromedial medulla connections in Cavia porcellus and their relation with tonic immobility defensive behavior: a biotinylated dextran amine neurotracing study.
abstract: The rostroventromedial medulla (RVM), together with the periaqueductal gray matter (PAG), constitutes the descendent antinociceptive system. Additionally, these structures mutually regulate defensive behaviors, including tonic immobility (TI) in guinea pigs. The current study was undertaken to evaluate the connections of the RVM with the PAG and the spinal cord in guinea pigs in order to provide an anatomical basis for the role played by RVM in the modulation of TI. To address this goal, five guinea pigs were treated with non-fluorescent biotinylated dextran amine (BDA) neurotracer by injection into the RVM. After four days of survival, the encephalon and spinal cord were removed from each rodent, and BDA labeling was visualized with a standard avidin-biotinylated horseradish peroxidase method through reaction with nickel-intensified peroxidase 3,3'-diaminobenzidine dihydrochloride. The microinjection of BDA into the RVM stained fibers in the ventral horn, dorsal horn and intermediate gray matter of the spinal cord. BDA-labeled fibers, terminal buttons suggesting synaptic contacts, and perikarya were found in the dorsomedial, dorsolateral, lateral and ventrolateral PAG, and neuronal somata were identified in the cuneiform nucleus. Together, the current data demonstrate neuroanatomical evidence that supports the role of the RVM in the modulation of TI defensive behavior.
authors.affiliation: Veterinary Science Department, Centre for Agrarian Sciences, University of Paraíba, 58397-000 Areia, Paraíba, Brazil.
authors.forename: Luis Felipe Souza
authors.initials: LF
authors.lastname: da Silva
authors.forename: Norberto Cysne
authors.initials: NC
authors.lastname: Coimbra
authors.forename: Leda
authors.initials: L
authors.lastname: Menescal-de-Oliveira
mesh_terms: D000818:Animals; D001710:Biotin / Q000031:analogs & derivatives*; D003911:Dextrans; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D046353:Immobility Response, Tonic; D008297:Male; D008526:Medulla Oblongata / Q000502:physiology*; D010487:Periaqueductal Gray / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology
chemical_list: D003911:Dextrans; D005456:Fluorescent Dyes; C076397:biotinylated dextran amine; D001710:Biotin