title: Possible mechanisms of hypothermia after inhibition of the median or dorsal raphe nucleus of freely moving rats.
abstract: We previously reported that tetrodotoxin (TTX) perfusion into the median raphe nucleus (MRN), which contains the cell bodies of serotonin (5-HT) neurons, induced a considerable body temperature reduction under normal and low ambient temperatures (23 and 5°C, respectively) in freely moving rats but showed no such effect under high ambient temperature (35°C). In the present study, we aimed to determine the mechanism(s) of body temperature reduction after TTX perfusion into the MRN by measuring tail skin temperature (an index of heat loss), heart rate (an index of heat production), and locomotor activity (Act) under normal ambient temperature (23°C). We performed similar experiments in the dorsal raphe nucleus (DRN), another area containing cell bodies of 5-HT neurons, to compare any functional differences with the MRN. TTX perfusion into the MRN or DRN induced significant hypothermia (from 37.4±0.2 to 33.7±0.4°C or from 37.4±0.1 to 34.5±0.4°C, respectively; P<0.001) with increased tail skin temperature (from 26.1±0.8 to 31.1±1.3°C or from 26.3±0.9 to 31.7±0.4°C, respectively; P<0.001), but no change in heart rate. However, TTX perfusion into the MRN or DRN differentially affected Act. TTX perfusion into the MRN induced hyperactivity (from 10.7±4.6 to 67.6±25.1 counts/min; P<0.01), whereas perfusion into the DRN induced immobility. Thus, the 5-HT projections from the MRN and DRN may play similar roles in thermoregulation, both in the heat production system and in the heat loss system, but their roles in the regulation of Act might be distinct and opposite.
authors.affiliation: aGraduate School of Community & Human Services, Rikkyo University, Niiza bDepartment of International Business Management, Faculty of International Business Management, Kyoei University, Kasukabe, Saitama cDepartment of Human System Science, Tokyo Institute of Technology dDepartment of Central Nervous System, Tokyo Metropolitan Institute of Gerontology eDepartment of Biology, Graduate School of Science, Tokyo Metropolitan University, Tokyo fGraduate School of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Hiroshima, Japan gDepartment of Psychology, College of Liberal Arts & Sciences, University of Colorado Denver, Denver hDepartment of Cell and Developmental Biology, Neuroscience Program, and Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Aurora, Colorado, USA.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Ishiwata
authors.forename: Arisa
authors.initials: A
authors.lastname: Oshimoto
authors.forename: Takehito
authors.initials: T
authors.lastname: Saito
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Kotani
authors.forename: Shigeki
authors.initials: S
authors.lastname: Nomoto
authors.forename: Yasutsugu
authors.initials: Y
authors.lastname: Aihara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hasegawa
authors.forename: Benjamin N
authors.initials: BN
authors.lastname: Greenwood
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D007035:Hypothermia / Q000139:chemically induced / Q000473:pathology*; D008297:Male; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012881:Skin Temperature / Q000187:drug effects / Q000502:physiology; D026941:Sodium Channel Blockers / Q000633:toxicity; D013779:Tetrodotoxin / Q000633:toxicity; D013997:Time Factors; D014851:Wakefulness / Q000502:physiology*
chemical_list: D026941:Sodium Channel Blockers; D013779:Tetrodotoxin