5-Hydroxytryptamine2A/2Creceptors of nucleus raphe magnus and gigantocellularis/paragigantocellularis pars α reticular nuclei modulate the unconditioned fear-induced antinociception evoked by electrical stimulation of deep layers of the superior colliculus and dorsal periaqueductal grey matter.
The electrical stimulation of the dorsolateral columns of the periaquedutal grey matter (dlPAG) or deep layers of the superior colliculus (dlSC) evokes defensive behaviours followed by an antinociceptive response. Monoaminergic brainstem reticular nuclei are suggested to comprise the endogenous pain modulatory system. The aim of the present work was to investigate the role played by 5-HT2subfamily of serotonergic receptors of the nucleus raphe magnus (NRM) and the gigantocellularis/paragigantocellularis pars α reticular nuclei (Gi/PGiα) in the elaboration of instinctive fear-induced antinociception elicited by electrical stimulation of dlPAG or of dlSC. The nociceptive thresholds were measured by the tail-flick test in Wistar rats. The 5-HT2A/2C-serotonergic receptors antagonist ritanserin was microinjected at different concentrations (0.05, 0.5 and 5.0μg/0.2μL) either in Gi/PGiα or in NRM. The blockade of 5-HT2receptors in both Gi/PGiα and NRM decreased the innate fear-induced antinociception elicited by electrical stimulation of the dlSC or the dlPAG. These findings indicate that serotonin is involved in the hypo-algesia induced by unconditioned fear-induced behavioural responses and the 5-HT2A/2C-serotonergic receptor subfamily in neurons situated in the Gi/PGiα complex and NRM are critically recruited in pain modulation during the panic-like emotional behaviour.
Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil; Behavioural Neurosciences Institute (INeC), Avenida do Café, 2450, Ribeirão Preto, 14220-030, São Paulo, Brazil; Mato Grosso Federal University Medical School (UFMT), Av. Alexandre Ferronato, 1200, Reserva 35, Setor industrial, 78550-000, Sinop, Mato Grosso, Brazil.
Ricardo
R
de Oliveira
Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil.
Rithiele Cristina
RC
de Oliveira
Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil.
Luiz Luciano
LL
Falconi-Sobrinho
Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil.
Raimundo
R
da Silva Soares
Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil; Multiuser Centre of Neuroelectrophysiology, Department of Anatomy and Surgery, Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil; NAP-USP-Neurobiology of Emotions Research Centre (NuPNE), Ribeirão Preto Medical School of the University of São Paulo (FMRP-USP), Av. Bandeirantes, 3900, Ribeirão Preto, 14049-900, São Paulo, Brazil; Behavioural Neurosciences Institute (INeC), Avenida do Café, 2450, Ribeirão Preto, 14220-030, São Paulo, Brazil. Electronic address: nccoimbr@fmrp.usp.br.
Norberto Cysne
NC
Coimbra
D000818:Animals; D003214:Conditioning, Classical; D004558:Electric Stimulation; D005239:Fear / Q000502:physiology*; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D065846:Nucleus Raphe Magnus / Q000378:metabolism*; D010146:Pain / Q000473:pathology / Q000503:physiopathology; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology; D010487:Periaqueductal Gray / Q000502:physiology*; D011903:Raphe Nuclei / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism*; D044405:Receptor, Serotonin, 5-HT2C / Q000378:metabolism*; D016713:Ritanserin / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D013477:Superior Colliculi / Q000502:physiology*
D044402:Receptor, Serotonin, 5-HT2A; D044405:Receptor, Serotonin, 5-HT2C; D012702:Serotonin Antagonists; D016713:Ritanserin
5-HT(2)-serotonergic receptor; Gigantocellularis/paragigantocellularis pars α reticular nuclei; Nucleus raphe magnus; Periaqueductal grey matter; Superior colliculus; Unconditioned fear-induced antinociception