Project description:For over a millennium, mind-body interactions have fascinated scientists and doctors for their abilities to shape human perceptions of the external world 1,2. Placebo effects are striking demonstrations of mind-body interactions in which, in the absence of any treatment, a positive expectation of pain relief can reduce or even abolish the experience of pain 3–6. However, despite widespread recognition of the strength of placebo effects and their impact on everyday human experience and clinical trials for new analgesics, the neural circuit basis of the placebo effect has remained a mystery. Here, we show that analgesia from the expectation of pain relief is mediated by a distinct population of rostral anterior cingulate cortex (rACC) neurons that project to the pontine nuclei (rACC→Pn), a pair of brainstem pre-cerebellar nuclei with no established function in pain processing. To do this, we created a behavioral assay that models placebo analgesia by conditioning mice to expect pain relief when moving from a chamber with a heated floor to a second chamber. In this assay, an expectation of pain relief induces an analgesic effect that, like placebo analgesia in humans, is mediated by endogenous opioids. Calcium imaging of neural activity in freely moving mice and electrophysiological studies in cingulate cortical brain slices showed that expectations of pain relief boost the activity of rACC→Pn neurons and potentiate neurotransmission in this pathway. Transcriptomic studies of Pn neurons revealed an unusual abundance of opioid receptors in these cells, further suggesting a role in pain modulation. Selective inhibition of either the rACC→Pn pathway or of opioid-receptor-expressing Pn neurons disrupted placebo analgesia and decreased pain thresholds. Finally, a subset of cerebellar Purkinje cells exhibits activity patterns resembling those of rACC→Pn neurons during pain relief expectation, providing cellular-level evidence of a role for the cerebellum in cognitive pain modulation. Altogether, these findings elucidate longstanding mysteries surrounding the placebo effect by identifying a specific neural pathway that mediates expectation-based pain relief. This discovery opens the possibility of targeting this novel pathway with drugs or neurostimulation methods to treat pain. More broadly, our studies provide a framework for investigating the neural circuit basis of other mind-body interactions beyond those involving pain, and point to prefrontocortical-cerebellar communication as a potential basis for such effects.
Project description:For over a millennium, mind-body interactions have fascinated scientists and doctors for their abilities to shape human perceptions of the external world 1,2. Placebo effects are striking demonstrations of mind-body interactions in which, in the absence of any treatment, a positive expectation of pain relief can reduce or even abolish the experience of pain 3–6. However, despite widespread recognition of the strength of placebo effects and their impact on everyday human experience and clinical trials for new analgesics, the neural circuit basis of the placebo effect has remained a mystery. Here, we show that analgesia from the expectation of pain relief is mediated by a distinct population of rostral anterior cingulate cortex (rACC) neurons that project to the pontine nuclei (rACC→Pn), a pair of brainstem pre-cerebellar nuclei with no established function in pain processing. To do this, we created a behavioral assay that models placebo analgesia by conditioning mice to expect pain relief when moving from a chamber with a heated floor to a second chamber. In this assay, an expectation of pain relief induces an analgesic effect that, like placebo analgesia in humans, is mediated by endogenous opioids. Calcium imaging of neural activity in freely moving mice and electrophysiological studies in cingulate cortical brain slices showed that expectations of pain relief boost the activity of rACC→Pn neurons and potentiate neurotransmission in this pathway. Transcriptomic studies of Pn neurons revealed an unusual abundance of opioid receptors in these cells, further suggesting a role in pain modulation. Selective inhibition of either the rACC→Pn pathway or of opioid-receptor-expressing Pn neurons disrupted placebo analgesia and decreased pain thresholds. Finally, a subset of cerebellar Purkinje cells exhibits activity patterns resembling those of rACC→Pn neurons during pain relief expectation, providing cellular-level evidence of a role for the cerebellum in cognitive pain modulation. Altogether, these findings elucidate longstanding mysteries surrounding the placebo effect by identifying a specific neural pathway that mediates expectation-based pain relief. This discovery opens the possibility of targeting this novel pathway with drugs or neurostimulation methods to treat pain. More broadly, our studies provide a framework for investigating the neural circuit basis of other mind-body interactions beyond those involving pain, and point to prefrontocortical-cerebellar communication as a potential basis for such effects.
Project description:Background. Inter- and intra-individual fluctuations in pain intensity pose a major challenge to treatment efficacy, with a majority perceiving their pain relief as inadequate. Recent preclinical studies have identified circadian rhythmicity as a potential contributor to these fluctuations and therapeutic target. Methods. We therefore sought to determine the impact of these rhythms in people with chronic low back pain (CLBP) through a detailed characterization, including questionnaires to evaluate biopsychosocial characteristics, ecological momentary assessment (7-day e-diaries at 8:00/14:00/20:00) to assess pain fluctuations, and intra-day blood transcriptomics (8:00/20:00) to identify genes/pathways of interest. Results. While most individuals displayed constant or variable/mixed pain phenotypes, a distinct subset had daily fluctuations of increasing pain scores (>30% change in intensity over 12-hours in ≥4/7 days). This population had no opioid users, better biopsychosocial profiles, and differentially expressed transcripts relative to other pain phenotypes. The circadian-governed neutrophil degranulation pathway was particularly enriched among arhythmic individuals; the link between neutrophil degranulation and opioid use was further confirmed in a separate CLBP cohort. Conclusion. Our findings identify pain rhythmicity and the circadian expression of neutrophil degranulation pathways as indicators of CLBP outcomes, which may help provide a personalized approach to phenotyping biopsychosocial characteristics and medication use. This highlights the need to better understand the impact of circadian rhythmicity across chronic pain conditions.
Project description:Opioid pain-relief and adverse outcomes differ between individuals. We show that runt-related transcription factor 1 (Runx1) is a determinant of opioid responses in humans and rodents and modulates the microglial transcriptome. Electron microscopy and single-cell RNA-sequencing revealed that deletion of Runx1 from microglia produces distinct ultra-structural and transcriptomic signatures. Microglia Runx1-deficient mice have reduced morphine potency, despite having no prior opioid exposure and normal nociceptive thresholds. These mice required greater amounts of post-operative morphine and displayed robust morphine-induced hyperalgesia and exacerbated withdrawal. In humans, genome-wide linkage analyses (GWAS) revealed variations within the Runx1 gene is associated with inter-individual differences in perioperative opioid requirement and opioid withdrawal severity. Identification of Runx1 susceptibility genotypes has implications for individualizing opioid pain management and determining risk of opioid dependence.
Project description:In settings of heightened pain sensitivity, such as following peripheral nerve injury (PNI) or opioid-induced hyperalgesia (OIH), microglia take on an activated phenotype. Functional studies have suggested that microglia activated by PNI or chronic opioids then engage common mechanisms to facilitate pain. Here we conducted RNA sequencing of acutely isolated spinal cord microglia to comprehensively interrogate commonality between PNI and OIH. By combining our results with meta-analysis of published datasets, we identify transcriptional signatures of microglial reactivity that differ between PNI models over time, opioid exposure, or CNS pathology, despite similar histological outcomes. Collectively, these results reveal a discrepancy between histological markers of activation and transcriptional response, and provide a resource of pain-associated microglial transcriptomes that caution against a universal signature of microglia activation.
Project description:In settings of heightened pain sensitivity, such as following peripheral nerve injury (PNI) or opioid-induced hyperalgesia (OIH), microglia take on an activated phenotype. Functional studies have suggested that microglia activated by PNI or chronic opioids then engage common mechanisms to facilitate pain. Here we conducted RNA sequencing of acutely isolated spinal cord microglia to comprehensively interrogate commonality between PNI and OIH. By combining our results with meta-analysis of published datasets, we identify transcriptional signatures of microglial reactivity that differ between PNI models over time, opioid exposure, or CNS pathology, despite similar histological outcomes. Collectively, these results reveal a discrepancy between histological markers of activation and transcriptional response, and provide a resource of pain-associated microglial transcriptomes that caution against a universal signature of microglia activation.
Project description:Chronic pain affects 20-30% of the population and imposes a significant socio-economic burden as it is often accompanied by substantial emotional comorbidities such as anxiety and depression. Yet, the mechanisms underlying the interactions between the sensory and emotional aspects of chronic pain remain poorly understood. Here, we investigated the role of FKBP51, a regulator of the stress response, in mediating both sensory and emotional symptoms of chronic pain. Inhibition of FKBP51, via genetic deletion or pharmacological blockade, in persistent joint pain reduced fast-onset sensory, functional and activity-related symptoms, as well as late anxio-depressive comorbidities. FKBP51 inhibition after the establishment of the hypersensitive state provided only temporary symptoms relief, while acute inhibition at disease onset protected from the full development of sensory and anxio-depressive symptoms for up to 6 months. Our results also indicated that early pain symptoms could predict the late sensory and emotional outcomes of chronic pain. RNA sequencing of spinal cord tissue revealed that late FKBP51 inhibition transiently altered nociceptive genes associated with mechanical hypersensitivity. In contrast, early inhibition persistently downregulated the Naaa gene, a key regulator of the transition to chronic pain, and reorganized spinal cilia. Our results indicate that early FKBP51 inhibition after injury can persistently reduce chronic pain and prevent the onset of associated emotional comorbidities by modulating critical spinal neurobiological pathways that play pivotal roles in the transition to chronic pain.