MODULATION OF INTRATHECAL MORPHINE-INDUCED IMMUNOSUPPRESSION BY MICROINJECTION OF NALOXONE INTO PERIAQUEDUCTAL GRAY

AIM: To study the involvement of opioid receptor of periaqueductal gra y (PAG) and hypothalamic-pituitary-adrenal (HPA) axis in the effect of intrathecal morphine on immune function. METHODS: Rat splenic natural killer (NK) cell activity was determined by a europium release assay; the concanavalin A-induced splenic IL-2 production, TNF-beta activity , and serum TNF-alpha level were determined by colorimetric thiazolyl blue tetrazolium bromide (MTT) and gentian violet assay, and serum cor ticotrophin ( ACTH) level by radioimmunological method after intrathec al injection of morphine and FAG microinjection of naloxone. RESULTS: Intrathecal morphine inhibited splenic NK cell activity, IL-2 producti on, TNF-beta activity, and increased in serum ACTH level. Microinjecti on of naloxone 1 mu g into FAG partially antagonized the inhibition of NK cell activity and the elevation of serum ACTH level by morphine. C ONCLUSION: The opioid receptor of FAG involved in the suppression of N K cell activity by intrathecal morphine, which was accompanied by an a ctivation of HPA axis.