Pain doesn’t feel the same at every hour of the day. Many people notice their pain is worse at night or first thing in the morning, but we don’t yet understand why. One major clue is our body clock which times daily rhythms in hormones, immune responses, and brain activity. Another key factor is sex: more women than men suffer from chronic pain, with males and females often experiencing pain differently.

Yet most treatments ignore these differences. Our project asks a focused question: do daily changes in pain come from sex hormones (like estrogen or testosterone), from sex chromosomes (XX or XY), or both? Early work from our team shows that after a nerve injury, male but not female mice have pain that rises and falls across the day, and their brain immune cells (microglia) change shape and activity in step with these rhythms. We propose now using a new experimental paradigm that separates sex chromosomes from sex hormones to help determine what biological signals truly drive the clock-like pattern of pain and immune cell activity. We will profile microglia across the day to define the activity states these cells enter when pain is high versus low (i.e., day vs. night), and how those states differ in males and females. We will also map how microglia “talk” with nearby cells in the spinal cord where pain is processed over time, using advanced tools that read the activity of hundreds of genes in intact tissue.

This work can point to treatments that are timed for maximum benefit with fewer side effects by revealing when, and in whom, specific pain pathways change. In the long run, this work brings us closer to personalized and “right time for the right patient” approaches for chronic pain and related neuroimmune conditions like Alzheimer’s and MS.