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MU-opioid receptor-knockout mice: role of μ-opioid receptor in morphine mediated immune functions

1998; Elsevier BV; Volume: 61; Issue: 1-2 Linguagem: Inglês

10.1016/s0169-328x(98)00212-5

1872-6941

Sabita Roy, Roderick A. Barke, Horace H. Loh,

Pain Mechanisms and Treatments

The role of the μ-opioid receptor in immune function was investigated using μ-opioid receptor knockout mice (MOR-KO). Morphine modulation of several immune functions, including macrophage phagocytosis and macrophage secretion of TNF-α, was not observed in the MOR-KO animals, suggesting that these functions are mediated by the classical μ-opioid receptor. In contrast, morphine reduction of splenic and thymic cell number and mitogen-induced proliferation were unaffected in MOR-KO mice, as was morphine inhibition of IL-1 and IL-6 secretion by macrophages. These latter results are consistent with morphine action on a naloxone insensitive morphine receptor, a conclusion supported by previous studies characterizing a nonopioid morphine binding site on immune cells. Alternatively, morphine may act either directly or indirectly on these cells, by a mechanism mediated by either delta or kappa opioid receptors.