Investigating the role of dorsal raphe nucleus enkephalin neurons in motivational and affective behaviors during chronic pain - PROJECT SUMMARY The primary goal of this NRSA F32 proposal is to determine the contribution of endogenous opioids in dorsal raphe nucleus to motivational and affective dysregulation during chronic pain. Chronic pain is a complex disease state which is associated with comorbidities such as depression, anxiety, and increased risk of suicide. However, the primary target of analgesic research has been peripheral and spinal sensory mechanisms despite emotional unpleasantness being a key feature of the human pain experience. Exogenous opioids are the gold standard for pain relief but are associated with many negative side effects. The endogenous opioid system is well known to powerfully modulate both analgesia and affective and motivational neural circuits. It is therefore essential to understand how this system may be contributing to the emotional component of chronic pain states. Historically, dorsal midbrain nuclei such as dorsal raphe nucleus (DRN) and adjacent periaqueductal grey have been shown to be important sites of opioid action. However, the specific role of opioid peptides within the DRN during chronic pain has not been characterized despite studies showing opioid activity here can also powerfully modulate pain and motivated behaviors. Preliminary data from our lab indicate that CRISPR-Cas9 disruption of preproenkephalin (PENK) in DRN enhances aversion. Specifically, DRNPENK knockdown increases allodynia following a mild acute pain state and decreases time spent investigating an aversive odor. This increase in aversion is similar to behavioral changes observed in chronic pain states. Therefore, the goal of this NRSA F32 is to determine how DRNPENK contributes to the motivational and affective behavioral dysfunction resulting from chronic pain. First in Aim 1, we will use dual-color 1-photon endoscopic imaging to examine how enkephalinergic and non-enkephalinergic neurons encode evoked and non-evoked pain as well as motivational behaviors before and after the development of chronic pain. In Aim 2 we will determine whether suppression of DRNPENK neuron activity elicits a pain-like phenotype in naïve animals using designer receptors exclusively activated by designer drugs (DREADDs). Finally, in Aim 3 we will test the therapeutic potential of activating DRNPENK in a chronic pain state. We will use DREADDs to activate DRNPENK neurons both with and without CRISPR-Cas9 disruption of enkephalin peptide to specifically interrogate the function of this peptide in chronic pain-induced behavioral dysregulation. Together, these studies will provide insight into the role of endogenous opioids within a unique dorsal midbrain nucleus on motivational and affective behavioral dysregulation during chronic pain. This will lead to a better understanding of chronic pain pathophysiology and more effective potential neurochemical targets for therapeutic intervention.
