title: Plasma corticosterone levels in mouse models of pain.
abstract: BACKGROUND
  Pain markedly activates the hypothalamic-pituitary-adrenal (HPA) axis and increases plasma corticosterone release interfering significantly with nociceptive behaviour as well as the mechanism of action of analgesic drugs.
  
  
  OBJECTIVE
  In the present study, we monitored the time course of circulating corticosterone in two mouse strains (C57Bl/6 and Balb/C) under different pain models. In addition, the stress response was investigated following animal handling, intrathecal (i.t.) manipulation and habituation to environmental conditions commonly used in nociceptive experimental assays. We also examined the influence of within-cage order of testing on plasma corticosterone.
  
  
  RESULTS
  Subcutaneous injection of capsaicin precipitated a prompt stress response whereas carrageenan and complete Freund's adjuvant induced an increased corticosterone release around the third hour post-injection. However, carrageenan induced a longer increased corticosterone in C57Bl/6 mice. In partial sciatic nerve ligation, neuropathic pain model corticosterone increased only in the first days whereas mechanical hypersensitivity remained much longer. Animal handling also represents an important stressor whereas the i.t. injection per se does not exacerbate the handling-induced stress response. Moreover, the order of testing animals from the same cage does not interfere with plasma corticosterone levels in the intrathecal procedure. Animal habituation to the testing apparatus also does not reduce the immediate corticosterone increase as compared with non-habituated mice.
  
  
  CONCLUSIONS
  Our data indicate that HPA axis activation in acute and chronic pain models is time dependent and may be dissociated from evoked hyperalgesia. Therefore, HPA-axis activation represents an important variable to be considered when designing experimental assays of persistent pain as well as for interpretation of data.
authors.affiliation: Department of Neuroscience and Behaviour, Ribeirão Preto School of Medicine, University of São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, SP, 14049-900, Brazil.
authors.forename: M
authors.initials: M
authors.lastname: Benedetti
authors.forename: R
authors.initials: R
authors.lastname: Merino
authors.forename: R
authors.initials: R
authors.lastname: Kusuda
authors.forename: M I
authors.initials: MI
authors.lastname: Ravanelli
authors.forename: F
authors.initials: F
authors.lastname: Cadetti
authors.forename: P
authors.initials: P
authors.lastname: dos Santos
authors.forename: S
authors.initials: S
authors.lastname: Zanon
authors.forename: G
authors.initials: G
authors.lastname: Lucas
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology; D002351:Carrageenan / Q000494:pharmacology; D003345:Corticosterone / Q000097:blood*; D004195:Disease Models, Animal; D005620:Freund's Adjuvant / Q000494:pharmacology; D006185:Habituation, Psychophysiologic / Q000502:physiology; D007030:Hypothalamo-Hypophyseal System / Q000502:physiology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D009437:Neuralgia / Q000097:blood* / Q000139:chemically induced / Q000503:physiopathology*; D009619:Nociceptors / Q000502:physiology; D010913:Pituitary-Adrenal System / Q000502:physiology; D012585:Sciatica / Q000097:blood* / Q000503:physiopathology*; D018689:Sensory System Agents / Q000494:pharmacology; D013045:Species Specificity; D013312:Stress, Physiological / Q000502:physiology
chemical_list: D000276:Adjuvants, Immunologic; D018689:Sensory System Agents; D002351:Carrageenan; D005620:Freund's Adjuvant; D002211:Capsaicin; D003345:Corticosterone