title: Effects of a TRPV1 agonist capsaicin on respiratory rhythm generation in brainstem-spinal cord preparation from newborn rats.
abstract: The heat-sensitive transient receptor potential vanilloid 1 (TRPV1) channels are expressed in the peripheral and central nervous systems. However, there is no report on how the activation of TRPV1 causes the modulation of neuronal activity in the medullary respiratory center. We examined effects of capsaicin, a specific agonist of TRPV1 channels, on respiratory rhythm generation in brainstem-spinal cord preparation from newborn rats. Capsaicin induced a biphasic response in the respiratory rhythm (a transient decrease followed by an increase in the C4 rate). The second-phase excitatory effect (but not the initial inhibitory effect) in the biphasic response was partly blocked by capsazepine or AMG9810 (TRPV1 antagonists). Capsaicin caused strong desensitization. After its washout, the strength of C4 burst inspiratory activity was augmented once per four to five respiratory cycles. The preinspiratory and inspiratory neurons showed tonic firings due to membrane depolarization during the initial inhibitory phase. In the presence of TTX, capsaicin increased the fluctuation of the membrane potential of the CO2-sensitive preinspiratory neurons in the parafacial respiratory group (pFRG), accompanied by slight depolarization. The C4 inspiratory activity did not stop, even 60-90 min after the application of 50/100 μM capsaicin. Voltage-sensitive dye imaging demonstrated that the spatiotemporal pattern of the respiratory rhythm generating networks after application of capsaicin (50 μM, 70-90 min) was highly similar to the control. A histochemical analysis using TRPV1 channel protein antibodies and mRNA demonstrated that the TRPV1 channel-positive cells were widely distributed in the reticular formation of the medulla, including the pFRG. Our results showed that the application of capsaicin in the medulla has various influences on the respiratory center: transient inhibitory and subsequent excitatory effects on the respiratory rhythm and periodical augmentation of the inspiratory burst pattern. The effects of capsaicin were partially blocked by TRPV1 antagonists but could be also induced at least partially via the non-specific action. Our results also suggested a minor contribution of the TRPV1 channels to central chemoreception.
authors.affiliation: Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan.
authors.forename: Mariho
authors.initials: M
authors.lastname: Tani
authors.affiliation: Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan.
authors.forename: Sayumi
authors.initials: S
authors.lastname: Kotani
authors.affiliation: Department of Orthopedic Surgery, Showa University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
authors.forename: Chikara
authors.initials: C
authors.lastname: Hayakawa
authors.affiliation: Department of Pharmacotherapeutics, Division of Clinical Pharmacy, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo, 142-8555, Japan.
authors.forename: Shih-Tien
authors.initials: ST
authors.lastname: Lin
authors.affiliation: Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan.
authors.forename: Saki
authors.initials: S
authors.lastname: Irie
authors.affiliation: Division of Biology, Hyogo College of Medicine, 1-1 Mukogawa-cho, Nishinomiya, Hyogo, 663-8501, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Ikeda
authors.affiliation: Division of Biology, Center for Molecular Medicine, Jichi Medical University, Shimotsuke, Tochigi, 329-0498, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kawakami
authors.affiliation: Department of Physiology, Showa University School of Medicine, Tokyo, 142-8555, Japan. oni@med.showa-u.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Onimaru
mesh_terms: D000178:Acrylamides / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001933:Brain Stem / Q000187:drug effects*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002211:Capsaicin / Q000031:analogs & derivatives / Q000494:pharmacology*; D008526:Medulla Oblongata / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects*; D050916:TRPV Cation Channels / Q000819:agonists* / Q000037:antagonists & inhibitors; D056969:Voltage-Sensitive Dye Imaging / Q000379:methods
chemical_list: C500530:3-(4-t-butylphenyl)-N-(2,3-dihydrobenzo(b)(1,4)dioxin-6-yl)acrylamide; D000178:Acrylamides; D019086:Bridged Bicyclo Compounds, Heterocyclic; D050916:TRPV Cation Channels; C493922:Trpv1 protein, rat; C071423:capsazepine; D002211:Capsaicin
keywords: Capsaicin; Medulla; Respiratory rhythm; TRPV1