Maternal separation as a risk factor for aggravation of neuropathic pain in later life in mice

•Infant maternal separation (MS) induces emotional impairment in mice.•This emotional impairment is related to augmentation of neuropathic pain in adulthood.•Antidepressant-treated MS mice do not exhibit augmentation of allodynia.•Activation of microglia contributes to heightened pain sensitivity in MS mice. Psychological stresses such as social loss and separation during childhood induce hardship, referred to as emotional pain. These experiences are well-documented risk factors for the development of physical pain in adulthood. However, the underlying neuronal mechanisms of this exacerbation of pain are largely unknown, and consequently there is no effective pharmacotherapy. In this study, we sought to determine whether infant maternal separation (MS) contributes to aggravation of neuropathic pain in adult mice. MS increased anxiety- and depression-like behavioral responses to adult stress. In MS animals, chronic constriction injury (CCI) heightened the sensory dimension of chronic pain relative to that of control mice. However, MS mice treated with fluoxetine for 4 weeks after MS did not exhibit augmentation of allodynia, and their emotional response was attenuated. Microglia were more abundant in the spinal cord in MS/CCI mice than in control/CCI mice. These results suggest that emotional impairment is related to augmentation of neuropathic pain, and that dysfunction of microglial activation contributes to heightened pain sensitivity.