title: Distinct effect of 5-HT1A and 5-HT2A receptors in the medial nucleus of the amygdala on tonic immobility behavior.
abstract: The tonic immobility (TI) response is an innate fear behavior associated with intensely dangerous situations, exhibited by many species of invertebrate and vertebrate animals. In humans, it is possible that TI predicts the severity of posttraumatic stress disorder symptoms. This behavioral response is initiated and sustained by the stimulation of various groups of neurons distributed in the telencephalon, diencephalon and brainstem. Previous research has found the highest Fos-IR in the posteroventral part of the medial nucleus of the amygdala (MEA) during TI behavior; however, the neurotransmission of this amygdaloid region involved in the modulation of this innate fear behavior still needs to be clarified. Considering that a major drug class used for the treatment of psychopathology is based on serotonin (5-HT) neurotransmission, we investigated the effects of serotonergic receptor activation in the MEA on the duration of TI. The results indicate that the activation of the 5HT1A receptors or the blocking of the 5HT2 receptors of the MEA can promote a reduction in fear and/or anxiety, consequently decreasing TI duration in guinea pigs. In contrast, blocking the 5HT1A receptors or activating the 5HT2 receptors in this amygdalar region increased the TI duration, suggesting an increase in fear and/or anxiety. These alterations do not appear to be due to a modification of spontaneous motor activity, which might non-specifically affect TI duration. Thus, these results suggest a distinct role of the 5HT receptors in the MEA in innate fear modulation.
authors.affiliation: Psychobiology Graduate Program, University of São Paulo - Ribeirão Preto Dentistry School - Dept. Morphology, Physiology and Basic Pathology 14040-901, SP, Brazil.
authors.forename: Bruna Balbino
authors.initials: BB
authors.lastname: de Paula
authors.affiliation: Psychobiology Graduate Program, University of São Paulo - Ribeirão Preto Dentistry School - Dept. Morphology, Physiology and Basic Pathology 14040-901, SP, Brazil; Departament of Morphology, Physiology and Basic Pathology of Dentistry School of Ribeirão Preto, University of São Paulo, 14040-904 SP, Brazil. Electronic address: christie@forp.usp.br.
authors.forename: Christie Ramos Andrade
authors.initials: CR
authors.lastname: Leite-Panissi
mesh_terms: D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000008:administration & dosage; D000818:Animals; D001007:Anxiety / Q000503:physiopathology; D066276:Corticomedial Nuclear Complex / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D006168:Guinea Pigs; D046353:Immobility Response, Tonic / Q000187:drug effects; D007650:Ketanserin / Q000008:administration & dosage; D008297:Male; D044282:Receptor, Serotonin, 5-HT1A / Q000502:physiology*; D044402:Receptor, Serotonin, 5-HT2A / Q000502:physiology*; D058825:Serotonin 5-HT1 Receptor Agonists / Q000008:administration & dosage; D058830:Serotonin 5-HT2 Receptor Antagonists / Q000008:administration & dosage
chemical_list: D044402:Receptor, Serotonin, 5-HT2A; D058825:Serotonin 5-HT1 Receptor Agonists; D058830:Serotonin 5-HT2 Receptor Antagonists; D044282:Receptor, Serotonin, 5-HT1A; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; D007650:Ketanserin
keywords: 5-HT receptors; Amygdala; Defensive behavior; Innate fear