Project Summary Pain is a complex phenomenon that elicits somatosensory and motor reflexive responses together with marked and long-lasting changes in emotional and autonomic states. While acute pain provides protection from tissue damage, chronic or long-lasting pain, provides no protective function and is often incapacitating. Chronic pain conditions are debilitating to patients, their families, and society by reducing quality of life and creating enormous financial consequences that total more than 630 billion USD annually for the United States of America alone. Neuropathic pain is a type of chronic pain that arises from a lesion or disease affecting the somatosensory system and affects 7-8% of the general population. However, neuropathic pain is poorly responsive to analgesic drugs, including opioids, and alternative therapeutics for treatment are desperately needed. The underlying mechanisms of the development and maintenance of neuropathic pain are poorly understood. A recent wave of high-profile publications implicates the lateral parabrachial nucleus (lPBN) as a sensory hub for pain and aversion. The PBN is, a small, bilateral, pontine brain structure that has long been known to receive alarming, noxious, or threatening homeostatic information such as taste aversion, nociception, or danger cues. Promising preliminary data within the Taylor (UPitt) and Betley (UPenn) laboratories implicate glutamatergic PBN neurons expressing the neuropeptide Y (NPY) Y1 receptor (Npy1r- expressing) in the maintenance of neuropathic pain. First, application of a cool (acetone droplet) or light rub (cotton swab) stimulus to the hindpaw of a mouse following peripheral nerve injury produces significant Fos activation within Npy1r-expressing PBN neurons. Second, pharmacological inhibition of PBNNpy1r-expressing neurons via a selective agonist for the NPY Y1 Gi receptor reduces behavioral symptoms of neuropathic pain, whereas chemogenetic activation of Npy1r-expressing neurons produces conditioned place aversion. Third, application of a heat stimulus produces calcium transients in PBNNpy1r-expressing neurons assessed via in vivo fiber photometry. These observations provide the premise for my central hypothesis that the Npy1r- expressing subset of PBN neurons are necessary for neuropathic pain-like behaviors. Specific Aim 1 will utilize in vivo fiber photometry and in situ hybridization to assess the activation of PBN Npy1r-expressing neurons in both sham and neuropathic animals. Specific Aim 2 will apply both in vivo pharmacology and chemogenetics to inhibit PBN Npy1r-expressing neurons in sham and neuropathic animals to assess their necessity for the behavioral reflexive (mechanical and cold) and affective (conditioned place preference) components of pain. Specific Aim 3 will examine both the anatomy (anatomical tracing) and functional role (inhibitory chemogenetics) of the supraspinal targets of PBNNpy1r-expressing efferent projections to uncover the specific ciruit responsible for both the reflexive and affective components of neuropathic pain.

Project Narrative Neuropathic pain is a debilitating form of chronic pain afflicting millions of patients worldwide but is poorly responsive to current analgesic therapies. Recent preclinical behavioral data implicates the lateral parabrachial nucleus of the brainstem in the maintenance of both the behavioral reflexive and affective components of neuropathic pain. This study uses in vivo and awake moving fiber photometry and in situ fluorescent hybridization, intraparabrachial pharmacology and chemogenetics, and anatomical tracing combined with efferent terminal chemogenetic inhibition to ultimately determine if excitatory lateral parabrachial neurons (those that contain the type 1 receptor for neuropeptide Y) contribute to the behavioral manifestations of neuropathic pain.