MnSOD mediated by HSV vectors in the periaqueductal gray suppresses morphine withdrawal in rats

Morphine appears to be the most active metabolite of heroin, therefore, the effects of morphine are important in understanding the ramifications of heroin abuse. Opioid physical dependence (withdrawal response) may have very long-lasting effects on the motivation for reward, including the incubation of cue-induced drug-seeking behavior. However, the exact mechanisms of morphine withdrawal (MW) are not clear yet, and its treatment remains elusive. Periaqueductal gray (PAG) is one of the important sites in the pathogenesis of MW. Here, we used recombinant herpes simplex virus (HSV) vectors that encode the sod2 gene expressing manganese superoxide dismutase (MnSOD) to evaluate its therapeutic potential in MW. Microinjection of HSV vectors expressing MnSOD into the PAG reduced the MW syndrome. MnSOD vectors suppressed the upregulated mitochondrial superoxide, and endoplasmic reticulum (ER) stress markers (glucose related protein 78 (GRP78) and activating transcription factor 6 (ATF6α) in the PAG induced by MW. Immunostaining showed that mitochondrial superoxide, GRP78, and ATF6α were colocalized with neuronal nuclei (NeuN, a neuronal-specific marker), suggesting that they are located in the neurons in the PAG. These results suggest that overexpression of MnSOD by HSV vectors may relieve opioid dependence. This study may provide a novel therapeutic approach to morphine physical withdrawal response.