Project Summary:Many patients suffer from chronic pain in the absence of identifiable injury. Such pains are termed functionaland include irritable bowel syndrome temporomandibular joint disorder fibromyalgia migraine and others. Forreasons that are not understood almost all functional pain syndromes (FPS) are female prevalent. FPS patientsexperience pain-free interictal periods punctuated by attacks of pain. The frequency of attacks is predictive ofrisk of chronification. Pain episodes thus produce a priming effect establishing a state of increased vulnerabilityto future attacks likely reflecting peripheral and central sensitization. FPS patients commonly identify stress asa key trigger of pain. Repeated stress may thus promote vulnerability and pain in a sexually dimorphic fashion.We have developed an injury-free rodent model of FPS based on hyperalgesic priming with repeated stress.Hyperalgesic priming produces a pain-free state of increased vulnerability that has been termed latentsensitization (LS). Following induction of LS normally subthreshold triggers can produce pain attacks modelingthe interictal and ictal periods of FPS. We will use this model to test the novel hypothesis that repeated stressactivates kappa opioid receptor (KOR) signaling in the hypothalamus resulting in release of prolactin (PRL) anddysregulation of prolactin receptor (PRLR) isoform expression selectively in female nociceptors. PRL signalsthrough homodimers of PRLR long and short (i.e. PRLR-L and PRLR-S) isoforms that respectively regulatetranscription and pain. Repeated stress down-regulates PRLR-L promoting female-selective pain throughstress-induced PRL/PRLR-S signaling. The balance of PRLR isoforms may therefore tune female nociceptorsto promote LS and pain from normally subthreshold stimuli.We will use genetic and chemogenetic manipulations along with anatomical neurochemicalelectrophysiological pharmacological and behavioral studies in male and female mice to evaluate the role ofdorsal root ganglion (DRG) PRLR-L down-regulation and stress-related hypothalamic KOR activation asessential mechanisms of LS and stress-related pain in females. Aim 1 will establish the effects of repeatedstress on hypothalamic KOR signaling and PRL release. Aim 2 will establish a potential causal relationship ofrepeated stress or hypothalamic KOR activation on DRG PRLR isoform expression neural excitability LS andstress-related pain. Aim 3 will determine if KOR antagonists DA agonists or a PRL antibody will prevent LS andFPS-like pain selectively in females.The proposed studies will characterize a previously unknown stress-related neuroendocrine link betweenhypothalamic KOR and PRL/PRLR signaling to promote female selective functional pain. Importantly thesestudies will advance knowledge about previously unknown biological mechanisms and may unravel mechanismsfor therapeutic interventions allowing improved therapy of FPS in women.