title: Attenuated pain response of obese mice (B6.Cg-lep(ob)) is affected by aging and leptin but not sex.
abstract: Genetically obese mice (B6.Cg-lep(ob)) manifest decreased responses to noxious thermal stimuli (hotplate test) suggesting endogenous analgesia (Roy et al., 1981). To examine further the analgesic response of these mice, we conducted 4 experiments. Experiment 1 assessed the response of ob/ob mice to tail flick, another noxious thermal test. Tail-flick testing was performed on B6.Cg-lep(ob) mice (n=14) and B6.Cg-lep(OB/?) (n=12) across a range of temperatures. Ob/ob mice exhibited longer latencies than control mice at all temperatures tested. In Experiment 2, potential sex differences were examined. Tail-flick latencies in male and female ob/ob mice (n=6/group) did not differ. The final 2 experiments examined factors that could modulate endogenous analgesia. Experiment 3 assessed the effects of aging in ob/ob mice (n=10/group). Older mice displayed longer tail-flick latencies than did younger mice. Experiment 4 examined the effect of leptin administration in the leptin-deficient ob/ob mice. Two groups (n=10/group) of ob/ob mice received osmotic pump implants filled with either leptin or vehicle, and were tail-flick tested at days 7 and 14 post-implantation. Ob/ob mice receiving leptin showed shorter latencies than did vehicle-receiving ob/ob mice. Taken together, these results support earlier reports of heightened analgesia in ob/ob mice and suggest that aging further reduces the already impaired pain response. Furthermore, leptin deficiency partially contributes to decreased pain sensation of ob/ob mice.
authors.affiliation: Department of Psychology, P404 Duff Roblin Bldg, 190 Dysart Rd, University of Manitoba, Winnipeg, MB R3T 2N2, Canada. Electronic address: hrodgers@mix.wvu.edu.
authors.forename: Helen M
authors.initials: HM
authors.lastname: Rodgers
authors.forename: Suadi
authors.initials: S
authors.lastname: Liban
authors.forename: Linda M
authors.initials: LM
authors.lastname: Wilson
mesh_terms: D000375:Aging; D000704:Analysis of Variance; D000818:Animals; D001835:Body Weight / Q000187:drug effects / Q000235:genetics; D004326:Drinking / Q000187:drug effects; D005260:Female; D020738:Leptin / Q000008:administration & dosage*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese / Q000235:genetics; D009765:Obesity / Q000503:physiopathology*; D010146:Pain / Q000188:drug therapy* / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects / Q000235:genetics
chemical_list: D020738:Leptin
keywords: Aging; B6.Cg-lep(ob); B6.V-lep(ob); Diabetes; Leptin; Nociception; Obesity; Pain; ob/ob