Involvement of substance P and central opioid receptors in morphine modulation of the CHS response

Morphine administration prior to challenge with the antigen 2,4-dinitro-flu orobenzene increases the contact hypersensitivity (CHS) response in rats. T he present study extended these findings by showing that central, but not s ystemic, administration of N-methylnaltrexone antagonized the morphine-indu ced enhancement of the CHS response. The importance of the neuroimmune medi ator substance P was shown via the attenuation of the morphine-induced enha ncement following both systemic and topical administration of the NK-1 anta gonist WIN51,708. Taken together, the findings of the present study provide new data showing that central opioid receptors and peripheral substance P are involved in the morphine-induced enhancement of the CHS response. (C) 2 001 Elsevier Science B.V. All rights reserved.