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The role of the hypothalamic-pituitary-adrenal axis in the susceptibility to adjuvant-induced polyarthritis in the rat /

The hypothalamic-pituitary-adrenal (HPA) axis, a system activated by stress, is traditionally considered to affect the susceptibility to chronic pain via effects on peripheral processes. This study investigates whether the HPA axis contributes to the development of chronic pain in an animal model via direct effects on central pain mechanisms. / First, correlations between pain processes and the susceptibility to chronic pain in an animal model that is correlated with HPA-axis function were examined. The results show that, in the Fischer rat, the amount of pain suppression observed during the formalin interphase depression is negatively correlated with susceptibility to polyarthritis. Since the formalin interphase depression mechanisms are within the central nervous system, the results suggest a role for central pain mechanisms in the development of polyarthritis. / Hypophysectomy inhibits the development of adjuvant-induced arthritis. To test whether hypophysectomy inhibits adjuvant-induced polyarthritis via central pain mechanisms, the analgesic effect of hypophysectomy was examined in the formalin test. The results show that hypophysectomy specifically prolongs the formalin interphase depression, further supporting that the underlying central pain suppression mechanisms are associated with resistance to adjuvant-induced polyarthritis. / Corticotropin-releasing factor (CRF) was then investigated as a possible underlying mechanism of the effects of hypophysectomy. Peripheral injection of CRF into inflamed tissue affects pain mechanisms unrelated to the susceptibility to adjuvant-induced polyarthritis. However, central and intravenous administration of CRF preferentially affect the formalin interphase depression mechanisms. The observed dose-response relationships indicate that these effects are due to direct actions of CRF within the central nervous system. / In conclusion, the results strongly suggest that the HPA axis modulates the susceptibility to adjuvant-induced polyarthritis via direct effects on supraspinal pain suppression mechanisms. Thus, the HPA axis may contribute to the development of chronic pain syndromes associated with HPA-axis abnormalities, such as rheumatoid arthritis and fibromyalgia, via effects on pain mechanisms within the central nervous system.

Identiferoai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36631
Date January 2000
CreatorsLariviere, William R.
ContributorsMelzack, Ronald (advisor)
PublisherMcGill University
Source SetsLibrary and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada
LanguageEnglish
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Formatapplication/pdf
CoverageDoctor of Philosophy (Department of Psychology.)
RightsAll items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated.
Relationalephsysno: 001764165, proquestno: NQ64597, Theses scanned by UMI/ProQuest.

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