Chronic pain-induced emotional dysfunction is associated with astrogliosis due to cortical delta-opioid receptor dysfunction.

It has been widely recognized that chronic pain could cause physiological changes at supraspinal levels. The delta-opioidergic system is involved in antinociception, emotionality, immune response and neuron-glia communication. In this study, we show that mice with chronic pain exhibit anxiety-like behavior and an increase of astrocytes in the cingulate cortex due to the dysfunction of cortical delta-opioid receptor systems. Using neural stem cells cultured from the mouse embryonic forebrain, astrocyte differentiation was clearly observed following long-term exposure to the selective delta-opioid receptor antagonist, naltrindole. We also found that micro-injection of either activated astrocyte or astrocyte-conditioned medium into the cingulate cortex of mice aggravated the expression of anxiety-like behavior. Our results indicate that the chronic pain process promotes astrogliosis in the cingulate cortex through the dysfunction of cortical delta-opioid receptors. This phenomenon may lead to emotional disorders including aggravated anxiety under chronic pain-like state.