Articles: chronic-pain.
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Microglia take on an altered morphology during chronic opioid treatment. This morphological change is broadly used to identify the activated microglial state associated with opioid side effects, including tolerance and opioid-induced hyperalgesia (OIH). Microglia display similar morphological responses in the spinal cord after peripheral nerve injury (PNI). ⋯ After PNI, we identify an early proliferative transcriptional event across models that precedes the upregulation of histological markers of microglial activation. However, we found no proliferative transcriptional response associated with opioid-induced microglial activation, consistent with histological data, indicating that the number of microglia remains stable during morphine treatment, whereas their morphological response differs from PNI models. Collectively, these results establish the diversity of pain-associated microglial transcriptomic responses and point towards the targeting of distinct insult-specific microglial responses to treat OIH, PNI, or other central nervous system pathologies.
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Humans use cannabinoid drugs to alleviate pain. As cannabis and cannabinoids are legalized in the United States for medicinal and recreational use, it has become critical to determine the potential utilities and harms of cannabinoid drugs in individuals living with chronic pain. Here, we tested the effects of repeated ∆9-tetrahydrocannabinol (THC) vapor inhalation on thermal nociception and mechanical sensitivity, in adult male and female Wistar rats using a chronic inflammatory pain model (ie, treated with complete Freund's adjuvant [CFA]). ⋯ These data provide a foundation for future work that will explore the cells and circuits underlying the antihyperalgesic effects of THC vapor inhalation in individuals with chronic inflammatory pain. PERSPECTIVE: Cannabinoids are thought to have potential utility in the treatment of chronic pain, but few animal studies have tested the effects of chronic THC or cannabis in animal models of chronic pain. We tested the effects of repeated THC vapor inhalation on chronic pain-related outcomes in male and female animals.