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  • Title: Pain behavior and spinal cell activation due to carrageenan-induced inflammation in two inbred rat strains with differential hypothalamic-pituitary-adrenal axis reactivity.
    Author: Juif PE, Anton F, Hanesch U.
    Journal: Physiol Behav; 2012 Feb 28; 105(4):901-8. PubMed ID: 22115949.
    Abstract:
    Lewis (LEW) and Fischer (FIS) inbred rats were used to study the relationship of hypothalamic-pituitary-adrenal (HPA) axis reactivity with inflammation-related pain behavior. LEW rats are susceptible to the development of autoimmune and chronic inflammatory disorders, whereas FIS rats are resistant. Since contradictory data have previously been collected under conditions of acute inflammation, we investigated the onset and maintenance of thermal and mechanical hyperalgesia and spinal activation of neurons and glia cells in a model of ongoing inflammation in both strains. Hind paw volumes and mechanical and thermal pain thresholds were measured prior to and during one week after intraplantar injection of carrageenan. The activation of nociceptive neurons (FosB), astroglia (GFAP) and microglia (OX-42) in the spinal cord of segments L5/L6 was assessed using immunohistochemistry. Inflammation increased paw volume, pain sensitivity and cell activation in both strains. FIS rats were more sensitive to sensory stimulation and developed a more severe edema on day 1, but recovered faster up to day 7 than LEW rats. At that time a higher amount of activated nociceptive neurons and corticosterone was seen in FIS rats, but microglial activation was more pronounced in LEW rats. Our results suggest a biphasic role of the HPA axis in pain behavior and spinal cell activation associated with ongoing inflammation. In the acute stage, the stronger reaction in FIS rats might be explained by an activating effect of corticosteroids on neutrophil function. Under ongoing inflammatory conditions the immunosuppressive actions of corticosteroids may dominate and lead to a quicker recovery of paw volume and pain sensitivity in FIS rats.
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