The role of delta opioid receptors in trigeminovascular pain

点击翻译按钮获取中文摘要

Project Summary/Abstract Over 2 million people in the United States suffer from prescription drug abuse of opioid analgesics. One of the leading causes for the prescription of opioids is for the treatment of trigeminovascular pain (migraine); and the majority of these treatments target the µ opioid receptor. These µ agonists have poor efficacy for trigeminovascular pain, contribute to the progression of pain from an episodic to chronic state, and serve as an entry point to prescription drug abuse. Drugs that selectively activate the δ opioid receptor have distinct properties which make them promising alternatives to currently used µ-based therapies. We have recently developed a novel model of trigeminovascular pain, using the known human migraine trigger nitroglycerin (NTG). Chronic intermittent treatment with NTG results in acute and chronic hyperalgesia, which is inhibited by δ agonists. In addition, we have also shown that the δ agonist SNC80 can inhibit cortical spreading depression, a “gold standard” model of aura associated with trigeminovascular pain. The continued development of δ agonists for migraine depends upon a better understanding of where and how δ agonists inhibit trigeminovascular pain and related symptoms. δ opioid receptors are expressed in several central and peripheral regions that are important in pain processing, and emotional modulation. Which δORs are anatomically important for regulating trigeminovascular pathophysiology is currently unknown. A goal of this proposal will be to determine the role of central vs. peripheral δ opioid receptors in the development and treatment of trigeminovascular pain. For this purpose, we will use novel conditional knockout (cKO) mice with δ opioid receptors deleted in specific central and peripheral regions. We will examine the effects of these specific knockouts in the NTG model of trigeminovascular pain and negative affect, and on cortical spreading depression. We will also explore the mechanism by which δ agonists inhibit trigeminovascular pain. The neuropeptide, calcitonin gene related peptide (CGRP) plays a pivotal role in the induction and maintenance of trigeminovascular pain, primarily through the peripheral afferents projecting from the trigeminal ganglia. A further aim of this proposal will be to determine the expression of δORs on CGRP-expressing ganglia, as well as changes in CGRP release, when animals are naïve, in trigeminovascular pain, and chronically treated with δ agonists. Together, these studies will provide a deeper insight into how δORs affect trigeminovascular pain, thus enhancing the development of novel therapeutic compounds for this disorder.