title: Photoperiod alters the time course of brain cyclooxygenase-2 expression in Siberian hamsters.
abstract: Fever is initiated by activation of the arachidonic acid cascade and the biosynthesis of prostaglandins within the brain. Inducible cyclooxygenase (COX-2) is a rate-limiting enzyme in prostaglandin synthesis, and the number of blood vessels expressing COX-2 correlates with elevated body temperature following peripheral lipopolysaccharide (LPS). Despite its importance in host defense, fever is energetically expensive and we hypothesized that fever may be limited by available metabolic resources. During winter, when competing metabolic demands are constrained by low temperatures and food availability, it was predicted that fever duration would be reduced in seasonally breeding Siberian hamsters (Phodopus sungorus). We measured LPS-induced COX-2 expression in blood vessels of hamsters to test whether photoperiodic alterations in fever duration are centrally mediated, or whether they reflect changes in peripheral modulation of body temperature. Hamsters housed in long, 'summer-like' or short, 'winter-like' day lengths for 10 weeks were injected with LPS, and brains were collected 2, 4, or 8 h later. COX-2 expression was comparably increased in long- and short-day hamsters by 2 h and 4 h post-LPS; however, short-day hamsters exhibited significantly fewer COX-2-positive cells and blood vessels by 8 h post-LPS compared to long-day hamsters, corresponding with reduced fever duration in short-day hamsters. Cortisol concentrations increased more than two-fold in short-day compared to long-day hamsters by 4 h; this increase may have contributed to the decrease in COX-2 expression observed by 8 h in short days. We conclude that short photoperiods significantly altered the time course of central COX-2 protein expression in hamsters in a manner consistent with reduced fever duration.
authors.affiliation: Department of Psychology, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Bilbo
authors.forename: N
authors.initials: N
authors.lastname: Quan
authors.forename: B J
authors.initials: BJ
authors.lastname: Prendergast
authors.forename: S L
authors.initials: SL
authors.lastname: Bowers
authors.forename: R J
authors.initials: RJ
authors.lastname: Nelson
mesh_terms: D000276:Adjuvants, Immunologic / Q000502:physiology; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D001835:Body Weight / Q000187:drug effects; D001921:Brain / Q000166:cytology / Q000201:enzymology*; D006224:Cricetinae; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000096:biosynthesis; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D005334:Fever / Q000139:chemically induced / Q000378:metabolism; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000096:biosynthesis*; D008070:Lipopolysaccharides; D008297:Male; D009419:Nerve Tissue Proteins / Q000096:biosynthesis; D009929:Organ Size / Q000187:drug effects; D017111:Phodopus; D017440:Photoperiod; D011301:Preoptic Area / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000096:biosynthesis; D011863:Radioimmunoassay; D013737:Testis / Q000187:drug effects; D013997:Time Factors
chemical_list: D000276:Adjuvants, Immunologic; D007527:Isoenzymes; D008070:Lipopolysaccharides; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone