Identifying the Neurodevelopmental Differences of Opioid Withdrawal

Pannexin-1 channel inhibition alleviates opioid withdrawal in rodents by modulating locus coeruleus to spinal cord circuitry

Opioid withdrawal is a liability of chronic opioid use and misuse, impacting people who use prescription or illicit opioids. Hyperactive autonomic output underlies many of the aversive withdrawal symptoms that make it difficult to discontinue chronic opioid use. The locus coeruleus (LC) is an important autonomic centre within the brain with a poorly defined role in opioid withdrawal. We show here that pannexin-1 (Panx1) channels expressed on microglia critically modulate LC activity during opioid withdrawal. Within the LC, we found that spinally projecting tyrosine hydroxylase (TH)-positive neurons (LCspinal) are hyperexcitable during morphine withdrawal, elevating cerebrospinal fluid (CSF) levels of norepinephrine. Pharmacological and chemogenetic silencing of LCspinal neurons or genetic ablation of Panx1 in microglia blunted CSF NE release, reduced LC neuron hyperexcitability, and concomitantly decreased opioid withdrawal behaviours in mice. Using probenecid as an initial lead compound, we designed a compound (EG-2184) with greater potency in blocking Panx1. Treatment with EG-2184 significantly reduced both the physical signs and conditioned place aversion caused by opioid withdrawal in mice, as well as suppressed cue-induced reinstatement of opioid seeking in rats. Together, these findings demonstrate that microglial Panx1 channels modulate LC noradrenergic circuitry during opioid withdrawal and reinstatement. Blocking Panx1 to dampen LC hyperexcitability may therefore provide a therapeutic strategy for alleviating the physical and aversive components of opioid withdrawal.

A single dose of ketamine relieves fentanyl-induced-hyperalgesia by reducing inflammation initiated by the TLR4/NF-κB pathway in rat spinal cord neurons

A large amount of clinical evidence has revealed that ketamine can relieve fentanyl-induced hyperalgesia. However, the underlying mechanism is still unclear. In the current study, a single dose of ketamine (5 mg/kg or 10 mg/kg), TAK-242 (3 mg/kg), or saline was intraperitoneally injected into rats 15 min before four subcutaneous injections of fentanyl. Results revealed that pre-administration of ketamine alleviated fentanyl-induced hyperalgesia according to hind paw-pressure and paw-withdrawal tests. High-dose ketamine can reverse the expression of toll-like receptor-dimer (d-TLR4), phospho- nuclear factor kappa-B (p-NF-κB, p-p65), cyclooxygenase-2 (COX-2), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) 1 d after fentanyl injection in the spinal cord. Moreover, fentany-linduced-hyperalgesia and changes in the expression of the aforementioned proteins can be attenuated by TAK-242, an inhibitor of TLR4, as well as ketamine. Importantly, TLR4, p-p65, COX-2, and IL-1β were expressed in neurons but not in glial cells in the spinal cord 1 d after fentanyl injection. In conclusion, results suggested that a single dose of ketamine can relieve fentanyl-induced-hyperalgesia via the TLR4/NF-κB pathway in spinal cord neurons.

Buprenorphine reduces somatic withdrawal in a mouse model of early-life morphine exposure

The rising prevalence of early-life opioid exposure has become a pressing public health issue in the U.S. Neonates exposed to opioids in utero are at risk of experiencing a constellation of postpartum withdrawal symptoms commonly referred to as neonatal opioid withdrawal syndrome (NOWS). Buprenorphine (BPN), a partial agonist at the mu-opioid receptor (MOR) and antagonist at the kappa-opioid receptor (KOR), is currently approved to treat opioid use disorder in adult populations. Recent research suggests that BPN may also be effective in reducing withdrawal symptoms in neonates who were exposed to opioids in utero. We sought to determine whether BPN attenuates somatic withdrawal in a mouse model of NOWS. Our findings indicate that the administration of morphine (10mg/kg, s.c.) from postnatal day (PND) 1-14 results in increased somatic symptoms upon naloxone-precipitated (1mg/kg, s.c.) withdrawal. Co-administration of BPN (0.3mg/kg, s.c.) from PND 12-14 attenuated symptoms in morphine-treated mice. On PND 15, 24h following naloxone-precipitated withdrawal, a subset of mice was examined for thermal sensitivity in the hot plate test. BPN treatment significantly increased response latency in morphine-exposed mice. Lastly, neonatal morphine exposure elevated mRNA expression of KOR, and reduced mRNA expression of corticotropin-releasing hormone (CRH) in the periaqueductal gray when measured on PND 14. Altogether, this data provides support for the therapeutic effects of acute low-dose buprenorphine treatment in a mouse model of neonatal opioid exposure and withdrawal.

Future Newborns with Opioid-Induced Neonatal Abstinence Syndrome (NAS) Could Be Assessed with the Genetic Addiction Risk Severity (GARS) Test and Potentially Treated Using Precision Amino-Acid Enkephalinase Inhibition Therapy (KB220) as a Frontline Modality Instead of Potent Opioids

In this nonsystematic review and opinion, including articles primarily selected from PubMed, we examine the pharmacological and nonpharmacological treatments of neonatal abstinence syndrome (NAS) in order to craft a reasonable opinion to help forge a paradigm shift in the treatment and prevention of primarily opioid-induced NAS. Newborns of individuals who use illicit and licit substances during pregnancy are at risk for withdrawal, also known as NAS. In the US, the reported prevalence of NAS has increased from 4.0 per 1000 hospital births in 2010 to 7.3 per 1000 hospital births in 2017, which is an 82% increase. The management of NAS is varied and involves a combination of nonpharmacologic and pharmacologic therapy. The preferred first-line pharmacological treatment for NAS is opioid therapy, specifically morphine, and the goal is the short-term improvement in NAS symptomatology. Nonpharmacological therapies are individualized and typically focus on general care measures, the newborn-parent/caregiver relationship, the environment, and feeding. When used appropriately, nonpharmacologic therapies can help newborns with NAS avoid or reduce the amount of pharmacologic therapy required and the length of hospitalization. In addition, genetic polymorphisms of the catechol-o-methyltransferase (COMT) and mu-opioid receptor (OPRM1) genes appear to affect the length of stay and the need for pharmacotherapy in newborns with prenatal opioid exposure. Therefore, based on this extensive literature and additional research, this team of coauthors suggests that, in the future, in addition to the current nonpharmacological therapies, patients with opioid-induced NAS should undergo genetic assessment (i.e., the genetic addiction risk severity (GARS) test), which can subsequently be used to guide DNA-directed precision amino-acid enkephalinase inhibition (KB220) therapy as a frontline modality instead of potent opioids.

Understanding Opioid Actions, Pain and Analgesia: A Tribute to Dr. Gavril Pasternak

This special issue is a tribute to our mentor, colleague and friend, Gavril W. Pasternak, MD, PhD. Homage to the breadth and depth of his work (~ 450 publications) over a 40 career in pharmacology and medicine cannot be captured fully in one special issue, but the 22 papers collected herein represent seven of the topics near and dear to Gav's heart, and the colleagues, friends and mentees who held him near to theirs. The seven themes include: (1) sites and mechanisms of opioid actions in vivo; (2) development of novel analgesic agents; (3) opioid tolerance, withdrawal and addiction: mechanisms and treatment; (4) opioid receptor splice variants; (5) novel research tools and approaches; (6) receptor signaling and crosstalk in vitro; and (7) mentorship. This introduction to the issue summarizes contributions and includes formal and personal remembrances of Gav that illustrate his personality, warmth, and dedication to making a difference in patient care and people's lives.