title: Effect of melatonin injection into the periaqueductal gray on antinociception and tonic immobility in male rats.
abstract: Melatonin (MLT) is a neurohormone with significant involvement in several biological functions, of which antinociception and tonic immobility (TI) may be the key neurobehavioral components to survive in adverse conditions such as a predator attack. TI-induced antinociception can be elicited, facilitated, or increased through opioid and γ-aminobutyric acid (GABA) among other chemical mediators at several levels of the central nervous system, mainly in the periaqueductal gray (PAG). The aim of this study was to assess the effect of the microinjection of MLT into the main PAG regions that are related to different integrated defensive responses, namely dorsal (D) and ventrolateral (VL), on both antinociception through the tail-flick (TF) test and TI duration as single behavioral response and on combined behavioral responses (TF/TI). We found that the microinjection of MLT into the main PAG areas produced antinociception but did not affect the TI duration. The microinjection of MLT into the D-PAG decreased TF latency during TI in the combined trial (TF/TI), which implies that TI-induced antinociception was blocked. The microinjection of MLT into the VL-PAG maintained the antinociceptive capability of the TI without addition or increase in the antinociceptive effects, implying a permissive effect by MLT on the TI-induced antinociception. MLT administration into the D-PAG decreased the TI duration on the TF/TI, whereas MLT administration into the VL-PAG had the opposite effect of significantly increasing TI duration with the TF/TI trial.
authors.affiliation: Departamento de Fisiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Wilfrido Massieu esq. Manuel Stampa s/n Col. Nueva Industrial Vallejo, CP 07738, Del. Gustavo A. Madero, México City, Mexico. Electronic address: abmipa@hotmail.com.
authors.forename: Abraham
authors.initials: A
authors.lastname: Miranda-Páez
authors.affiliation: Departamento de Fisiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Wilfrido Massieu esq. Manuel Stampa s/n Col. Nueva Industrial Vallejo, CP 07738, Del. Gustavo A. Madero, México City, Mexico.
authors.forename: Sergio R
authors.initials: SR
authors.lastname: Zamudio
authors.affiliation: Departamento de Fisiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Wilfrido Massieu esq. Manuel Stampa s/n Col. Nueva Industrial Vallejo, CP 07738, Del. Gustavo A. Madero, México City, Mexico.
authors.forename: Priscila
authors.initials: P
authors.lastname: Vázquez-León
authors.affiliation: Departamento de Fisiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Wilfrido Massieu esq. Manuel Stampa s/n Col. Nueva Industrial Vallejo, CP 07738, Del. Gustavo A. Madero, México City, Mexico.
authors.forename: Vicente
authors.initials: V
authors.lastname: Sandoval-Herrera
authors.affiliation: Departamento de Fisiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Wilfrido Massieu esq. Manuel Stampa s/n Col. Nueva Industrial Vallejo, CP 07738, Del. Gustavo A. Madero, México City, Mexico.
authors.forename: Ivan
authors.initials: I
authors.lastname: Villanueva-Becerril
authors.affiliation: Department of Medicine, Surgery and Neuroscience, University of Siena, Via A. Moro, 2, Room 10/127, 53100 Siena, Italy.
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Carli
mesh_terms: D000818:Animals; D002492:Central Nervous System Depressants / Q000008:administration & dosage / Q000494:pharmacology*; D046353:Immobility Response, Tonic / Q000187:drug effects*; D008297:Male; D008550:Melatonin / Q000008:administration & dosage / Q000494:pharmacology*; D059225:Nociception / Q000187:drug effects*; D010487:Periaqueductal Gray / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002492:Central Nervous System Depressants; D008550:Melatonin
keywords: Antinociception; Melatonin; Periaqueductal gray; Tonic immobility