Journal of Biochemistry Advance Access originally published online on December 13, 2007
Journal of Biochemistry 2008 143(3):385-393; doi:10.1093/jb/mvm233
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© 2007 The Japanese Biochemical Society.
Impaired Basal Thermal Homeostasis in Rats Lacking Capsaicin-sensitive Peripheral Small Sensory Neurons
1Department of Biomedical Sciences, College of Life and Health Sciences, Chubu University, Kasugai 487-8501, Japan; 2Department of Physiology, University of Alberta, 7-29 Medical Sciences Building, Edmonton, Alberta, T6G 2H7, Canada; 3Department of Surgery, UT Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX75390, USA; 4Department of Foods and Nutrition, Sonoda Women's University, 7-29-1 Minami-Tsukaguchi, Hyogo; 5Department of Food Science for Health, Faculty of Health and Nutrition, Minami-Kyushu University, 5-1-2 Kirishima, Miyazaki 880-0032; 6Department of Health Science, Faculty of Psychological and Physical Sciences, Aichi Gakuin University, Nisshin 470-0195; and 7Department of Anatomy and Neurobiology, Nagasaki University School of Medicine, Nagasaki 852-8523, Japan
To whom correspondence should be addressed: Tel: +81 568 51 6017, Fax: +81 568 51 017, E-mail: hyamashi{at}isc.chubu.ac.jp.
Received October 3, 2007; Accepted November 19, 2007
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Abstract |
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We studied the effects of selective loss of capsaicin-sensitive primary sensory neurons on thermosensation and thermoregulation in rats. Neonatal capsaicin treatment in rats caused a remarkable decrease in the number of small-diameter neurons in the dorsal root ganglion (DRG) compared with their number in the control rats. Gene expression analysis for various thermo-sensitive transient receptor potential (TRP) channels indicated marked reductions in the mRNA levels of TRPV1 (70%), TRPM8 (46%) and TRPA1 (64%), but not of TRPV2, in the DRG of capsaicin-treated rats compared with those in the control rats. In addition to the heat and cold insensitivity, capsaicin-treated rats showed lower rectal core temperature, higher skin temperature and decreased sensitivity to ambient temperature alteration under normal housing at room temperature, suggesting impaired thermosensation and change in thermoregulation in the rats. Uncoupling protein 1 (UCP1) expression and the thermogenic ability in brown adipose tissues were attenuated in the capsaicin-treated rats. These results indicate a critical role of capsaicin-sensitive sensory neurons in both heat and cool sensation and hence in basal thermal homeostasis, which is balanced by heat release and production including UCP1 thermogenesis, following sensation of the ambient temperature.
Key Words: dorsal root ganglion, sensory neuron, thermoregulation, transient receptor potential channel, uncoupling protein 1
Abbreviations: BAT, brown adipose tissue; DRG, dorsal root ganglia; LE, living environment; TE, test environment; Trectal, rectal temperature; TRP, transient receptor potential; Tskin, tail skin temperature; UCP, uncoupling protein
*These two authors contributed equally to this work.