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Immunomodulating effects of morphine microinjected into periaqueductal gray
Aim:
To study the effects of morphine on immune system through rat brain periaqueductal gray (PAG).
Methods:
Three hours after microinjection of morphine through the implanted steel tubes to PAG, splenic cytokines interleukin 2 (IL-2), interleukin 6 (IL-6), tumor necrosis factor (TNF), and natural killer cells (NK) activity were measured.
Results:
Microinjection of morphine (0.5 microL, 3672 ng) into PAG region had no influence on IL-6 and TNF-alpha (production of splenic macrophages, suppressed the natural killer cell (NK) activity and enhanced T-lymphocyte functions, including concanavalin A (Con A)-induced T-cell proliferation, IL-2 and TNF-beta production. Both the suppressive and stimulating actions were blocked by PAG preinjection of the mu opioid receptor antagonist naloxone (0.5 microL, 1 microgram), which alone showed the contrary effect to morphine.
Conclusion:
Morphine affected immunofunctions through opioid receptors in PAG, and the influences on various immunocompetent cells were different.