Effects of Morphine on Behavioral and CNS Inflammatory Responses in GP120 Mice Under Immunocompetent vs. Immunodeficient Conditions

Abstract

Abstract HIV-associated neurocognitive disorder is a common complication of HIV infection, whose development is known to be facilitated by inflammation and exacerbated by morphine. In this study, we infected HIV gp120tg mice with LP-BM5 (a murine retrovirus that can cause systemic immunodeficiency in susceptible mouse strains) to examine morphine’s effect on gp120 in both immunocompetent and immunodeficient conditions. Specifically, we examined the expression of a series of inflammation-related molecules in the brain via qRT-PCR as well as the animals’ learning/memory function using spontaneous alternation T-maze. Morphine treatment (2×25mg pellets) did not significantly affect the development of immunodeficiency induced by LP-BM5 and all brain regions examined (hippocampus, striatum, and frontal lobe) had detectable LP-BM5 viral gag genes. Morphine notably reduced the performance of gp120tg+ mice in the T-maze assay when 2-minute retention was used, regardless of LP-BM5 treatment. Without LP-BM5 treatment, morphine increased hippocampal expression of CCL2, CCL5, CXCL10, IL-12 p40, TNFα, and IFNγ, while it decreased the expression of IL-6, arginase-1, IFNα and IFNβ. For mice who were subjected to LP-BM5 treatment, hippocampal expression of CCL2, CCL5, CXCL10, IL-12p40, and IL-1β were decreased by morphine, while CCL4, TNFα, IFNγ, iNOS, arginase-1 and IFNβ were increased by morphine. Further, expression of the mu opioid receptor was upregulated by morphine without LP-BM5, yet down-regulated by morphine with LP-BM5 treatment. Altogether, the effects of morphine are complex and dependent on the immune status of the host, which will be further elucidated in the future studies. (Supported by NIH/NIDA R21DA044886 (PI, Cao))