title: Hypergravity modulates behavioral nociceptive responses in rats.
abstract: Hypergravity (2G) exposure elevated the nociceptive threshold (pain suppression) concomitantly with evoked neuronal activity in the hypothalamus. Young Wistar male rats were exposed to 2G by centrifugal rotation for 10 min. Before and after 2G exposure, the nociceptive threshold was measured as the withdrawal reflex by using the von Frey type needle at a total of 8 sites of each rat (nose, four quarters, upper and lower back, tail), and then rats were sacrificed. Fos expression was examined immunohistochemically in the hypothalamic slices of the 2G-treated rats. When rats were exposed to 2G hypergravity, the nociceptive threshold was significantly elevated to approximately 150 to 250% of the 1G baseline control levels in all the examination sites. The 2G hypergravity remarkably induced Fos expression in the paraventricular and arcuate nuclei of the hypothalamus. The analgesic effects of 2G hypergravity were attenuated by naloxone pretreatment. Data indicate that hypergravity induces analgesic effects in rats, mediated through hypothalamic neuronal activity in the endogenous opioid system and hypothalamo-pituitary-adrenal axis.
authors.affiliation: Biochemistry, Department of Hard Tissue Engineering, Graduate School, Tokyo Medical and Dental University, Tokyo, JAPAN.
authors.forename: Y
authors.initials: Y
authors.lastname: Kumei
authors.forename: R
authors.initials: R
authors.lastname: Shimokawa
authors.forename: K
authors.initials: K
authors.lastname: Toda
authors.forename: Y
authors.initials: Y
authors.lastname: Kawauchi
authors.forename: K
authors.initials: K
authors.lastname: Makita
authors.forename: M
authors.initials: M
authors.lastname: Terasawa
authors.forename: K
authors.initials: K
authors.lastname: Ohya
authors.forename: H
authors.initials: H
authors.lastname: Shimokawa
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism; D001522:Behavior, Animal; D002498:Centrifugation; D018471:Hypergravity; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology*; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
chemical_list: D009292:Narcotic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D009270:Naloxone