Prostaglandin E 2 (PGE 2 ) couples to stimulation of adenylyl cyclase through two distinct G protein-coupled receptors designated EP2 and EP4. Although they have similar affinities for PGE 2 , the EP 2 and EP4 receptors have distinct structural characteristics. EP2 is a 358-amino-acid protein with short third intracellular loop and C-terminal domains, whereas EP4 consists of 488 amino acids with a long third intracellular loop and a long cytoplasmic tail. The ability of the HA epitope-tagged receptors to undergo PGE 2 -induced internalization was examined by enzyme-linked immunosorbent assay and immunofluorescence microscopy after expression in human embryonic kidney 293 cells. The EP2 receptor did not internalize, whereas the EP4 receptor underwent rapid internalization. Truncation of the EP4 receptor after amino acid 350, which removes 138 residues, abolished internalization. Truncation after amino acid 369 markedly attenuated internalization, whereas truncation after amino acid 383 had little effect. Serine and threonine residues in the region 350 to 383 were mutated to determine their role in internalization. The mutants S370-382A, a fulllength receptor containing six serine-to-alanine mutations in the region 370 to 382, and S354-369A, containing four serine mutations and one threonine mutation in the region 350 to 370, both internalized to the same extent as the wild-type. A further mutant, designated S354-382A, containing amino acid substitutions S354A, S359A, S364A, S366G, T369A, S370A, S371A, S374A, S377A, S379A, and S382A, also internalized to the same extent as the wild-type. We conclude that the C terminus of the EP4 receptor is involved in internalization; however, serine and threonine residues do not seem to be involved. PGE 2 is an important autocrine mediator in the cardiovascular and other systems (Campbell and Halushka, 1996). PGE 2 is a potent vasodilator in the microvasculature, although it may also cause constriction at selected sites. It causes a fall in systemic blood pressure and an increase in blood flow to the heart; it increases blood flow to the kidneys, leading to increased diuresis, natriuresis, and kaluresis, and causes secretion of renin from the renal cortex. PGE 2 exerts its actions through four distinct G protein-coupled receptors, designated EP1, EP2, EP3, and EP4, that are encoded by different genes (for a review, see Negishi et al., 1995). The EP1 receptor couples to phospholipase C, the EP2 and EP4 receptors couple to stimulation of adenylyl cyclase, and the EP3 receptor couples to inhibition of adenylyl cyclase.EP2 and EP4 receptors are widely distributed; both receptors are found in uterus, spleen, and lung; the EP4 receptor is also present in small intestine, thymus, pancreas, leukocytes, and kidney (Regan et al., 1994;Katsuyama et al., 1995). There are no selective EP receptor antagonists that can be used in studies to functionally distinguish the two receptors. However, the selective EP2 receptor agonist butaprost is not active at the EP4 receptor (Regan et al.,...

Chronic administration of cocaine has been shown to attenuate the functional capacity of delta opioid receptors to inhibit adenylyl cyclase activity. Abuse and withdrawal from cocaine in humans is associated with increases in anxiety and depression. Since recent research supports the role of delta opioid receptors in anxiety-and depression-like behaviors in rodents, we hypothesized that functional desensitization of delta opioid receptors contributes to anxiety-and depression-like behavioral phenotypes following short-term withdrawal from chronic administration of cocaine. To test this hypothesis, delta opioid receptor signaling and behaviors were evaluated 24 h after 14 days of bingepattern cocaine administration (15 mg/kg three times daily at 1 h intervals) in male Sprague Dawley rats. Results showed that the inhibition of adenylyl cyclase by delta opioid receptor agonists was attenuated in the frontal cortex, nucleus accumbens and caudate putamen 24 h after cessation of cocaine administration. One day withdrawal from chronic administration of cocaine resulted in increased anxiety-and depression-like behaviors as measured by the elevated plus maze and the force swim test respectively, and no change in locomotor activity. The anxiety-and depression-like behaviors were dose-dependently reduced by acute administration of the selective delta opioid receptor agonist, SNC80. These results demonstrate that early withdrawal from cocaine resulted in increased anxiety and depression, which accompanies the desensitization of delta opioid receptor function. Furthermore, cocaine-induced anxiety-and depression-like behaviors were reversible by the delta opioid receptor agonist SNC80.

Aside from reduced respiratory depression, G-protein[FIGURE DASH]biased agonists such as oliceridine may reduce opioid maladaptations and enhance the quality of surgical recovery.

Perioperative pain management is a unique challenge in patients undergoing spine surgery due to the increased incidence of both pre-existing chronic pain conditions and chronic postsurgical pain. Peri-operative planning and counseling in spine surgery should involve an interdisciplinary approach that includes consideration of patient-level risk factors, as well as pharmacologic and nonpharmacologic pain management techniques. Consideration of psychological factors and patient focused education as an adjunct to these measures is paramount in developing a personalized perioperative pain management plan. Understanding the currently available body of knowledge surrounding perioperative opioid management, management of opioid use disorder, regional/neuraxial anesthetic techniques, ketamine/lidocaine infusions, non-opioid oral analgesics, and behavioral interventions can be useful in developing a comprehensive, multi-modal treatment plan among patients undergoing spine surgery. Although many of these techniques have proved efficacious in the immediate postoperative period, long-term follow-up is needed to define the impact of such approaches on persistent pain and opioid use. Future techniques involving the use of precision medicine may help identify phenotypic and physiologic characteristics that can identify patients that are most at risk of developing persistent postoperative pain after spine surgery.

BACKGROUND: Persistent use of prescription opioids beyond the period of surgical recovery is a large part of a public health problem linked to the current opioid crisis in the United States. However, few studies have been conducted to examine whether morphine reward is influenced by acute pain and injury. METHODS: In a mouse model of incisional injury and minor trauma, animals underwent conditioning, extinction, and drug-primed reinstatement with morphine to examine the rewarding properties of morphine in the presence of acute incisional injury and drug-induced relapse, respectively. In addition, we sought to determine whether these behaviors were influenced by kappa opioid receptor signaling and measured expression of prodynorphin messenger RNA in the nucleus accumbens and medial prefrontal cortex after conditioning and before reinstatement with morphine and incisional injury. RESULTS: In the presence of incisional injury, we observed enhancement of morphine reward with morphine-conditioned place preference but attenuated morphine-primed reinstatement to reward. This adaptation was not present in animals conditioned 12 days after incisional injury when nociceptive sensitization had resolved; however, they showed enhancement of morphine-primed reinstatement. Prodynorphin expression was greatly enhanced in the nucleus accumbens and medial prefrontal cortex of mice with incisional injury and morphine conditioning and remained elevated up to drug-primed reinstatement. These changes were not observed in mice conditioned 12 days after incisional injury. Further, kappa opioid receptor blockade with norbinaltorphimine before reinstatement reversed the attenuation induced by injury. CONCLUSIONS: These findings suggest enhancement of morphine reward as a result of incisional injury but paradoxically a protective adaptation with incisional injury from drug-induced relapse resulting from kappa opioid receptor activation in the reward circuitry. Remote injury conferred no such protection and appeared to enhance reinstatement.