Sustained morphine exposure alters spinal NMDA receptor and astrocyte expression and exacerbates chronic pain behavior in female rats.

Introduction: Sustained opioid use has long-term negative impacts on future pain experience, particularly in women. This study aimed to investigate the underlying spinal neurobiology of this clinical observation in an experimental model of joint pain.

Objectives: In this study, we tested the hypothesis that sustained opioid treatment exacerbates chronic pain responses and alters spinal cord dorsal horn astrogliosis and the expression of GluN2B-containing N-methyl-d-aspartate receptors in female rats.

Anxiety enhances pain in a model of osteoarthritis and is associated with altered endogenous opioid function and reduced opioid analgesia.

Introduction: Negative affect, including anxiety and depression, is prevalent in chronic pain states such as osteoarthritis (OA) and associated with greater use of opioid analgesics, potentially contributing to present and future opioid crises.

Objectives: We tested the hypothesis that the interaction between anxiety, chronic pain, and opioid use results from altered endogenous opioid function.

Methods: A genetic model of negative affect, the Wistar-Kyoto (WKY) rat, was combined with intra-articular injection of monosodium iodoacetate (MIA; 1 mg) to mimic clinical presentation.