Opioids are powerful and effective drugs used for pain management, but their therapeutic usage is limited due to their side effects. Therefore, obtaining an extensive understanding of the pharmacological properties that underlie the actions of these drugs is much needed. Efficacy is the extent to which an agonist can stimulate the activity of the receptor it interacts with, and many studies have claimed to determine the efficacy of a wide range of opioid agonists. However, these opioids reportedly appear to be full agonists in some studies but seem to be partial agonists in others. Discrepancies from previous findings hamper the determination of accurate measurements of the efficacy of these drugs. As such, several assays focus on different aspects of opioid receptor signaling to deduce how efficacious these drugs may be. In this study, we focus on the μ-opioid receptor (MOR) as agonists that act on it represent the majority of clinically used opioids. We take advantage of a unique cellular model that captures the differential activation of each Gαi/o/z protein on top of measuring the relative efficacies of each tested opioid agonist. Using various cell-based assays, we demonstrate that these can be tools used to directly look at the interaction between the receptor and its effectors through the coupling of inhibitory heterotrimeric G proteins. The distinctions between each functional readout reveal insights about the nature of each established system, highlighting their advantages as well as their limitations. Key details about the mechanistic basis of inhibitory G protein activation are also uncovered. Precise determination of the efficacy of opioids could ultimately impact the understanding of opioid-mediated neuromodulation, as further links can be made between this important pharmacological parameter and the extent in which it induces analgesia and limits the side effects typically associated with opioid intake.

<p>Localization and subtype distribution of the receptors for neurotensin and opiods in canine small intestine was studied by the radioligand binding technique.</p> <p>Extensive dissection procedure was developed to separate a) longitudinal muscle (LM) layer containing myenteric plexus (MP), b) the circular muscle (CM) layer containing the deep muscular plexus (DMP) and c) the submucosa containing the submucous plexus (SMP).</p> <p>Purified membranes were prepared from the LM, MP, CM, DMP and SMP by differential and the density gradient centrifugation and using the markers 5'-nucleotidase (for smooth muscle plasma membranes), NADPH cytochome C reductase (for endoplasmic reticulum), cytochrome C oxidase (for mitochondrial membranes), specific binding of [^3H]saxitoxin for the neuronal membranes and the content of the vasoactiev intestinal polypeptide immunoreactive material as a measure of intact synaptosomes.</p> <p>The fractions enriched in the membranes from LM, CM, DMP, MP and SMP were used to study the distribution and properties of neurotensin receptors using [^125]Tyr^3-neurotensin and of opioid receptors using [^3H]diprenorphine, [^3H]etorphine and [^3H]ethylketocyclazocine.</p> <p>Neurotensin receptors were confined to the CM, DMP and SMP. These receptors has the similar affinity and recognition properties at their high affinity sites (Kd 0.1 - 0.2 nM). The low affinity receptors on the DMP were of lower affinity than their CM counterparts (Kd 40 nM vs 3nM). The receptors on the CM differed from those on the DMP in their radiation target size (mw - 190, 000 da on the CM and - 120, 000 da. on the DMP). Reduced disulfide bridges were required for the binding to both the CM and DMP neurotensin receptors. However, in vitro, the excitation, but not the inhibition, of the circular muscle strips to added neurotensin was abolished on reduction of the disulfide bonds.</p> <p>Opioid receptors were present on the DMP, MP and SMP but not on any smooth muscle. The receptors on all the three plexuses had similar affinity for the non-selective opioid ligand ([3H]diprenorphine (Kd - 0.1 - 0.2 nM). Both the DMP and MP contained -40-45% 5-subtypes of opioid receptors as assessed in competition studies. All three plexuses contained similar porportion of k-subtype (10-15%), assessed by competition studies with dynorphin [1-13] and U-50488H, and confirmed by saturation experiments with [^3H]ehtylketocyclazocine with or without sheilded 5-receptors. Ionic regulation of these receptors was similar to those observed for the opioid receptors in other systems.</p> <p>Therefore the action of neurotensin on the motility of the canine small intestine may be the combined result of the its action on the smooth muscle and on the modulation of the release of other mediators presynaptically at the DMP level. The action of opioids on the motility is probably through the modulation of the release of other mediatorset the DMP and MP level: direct action of opioids on the smooth muscle is not supported by the present studies.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.

The thirteen essays in this collection center on the narrator's shifting relationship to opioid painkillers and other drugs. The narrator and protagonist, Amy, begins using opioids recreationally with her boyfriend Ryan, an opiate addict who initiates Amy's drug use. Years after the couple breaks up, Amy's childhood headaches return as migraines and transform into chronic daily headaches, which she relieves with oxycodone (and sometimes other drugs). The narrative chronicles Amy's relationship with Ryan and her iatrogenic dependence on narcotic painkillers, detoxification, return to opioids following a year spent "clean," and the ways in which her headache treatment regimen shapes her relationship to her family, friends, various medical personnel, and her own embodied subjectivity. / MFA

The Mu Opioid Receptor (MOR) is a G protein-coupled receptor (GPCR) important for pain regulation. Opioid agonists have long been the most effective treatment for most types of pain; however, this class of drugs is highly problematic due to the combination of several dangerous side effects like addiction, tolerance, and respiratory depression. Recently, a dramatic rise in opioid prescriptions has led to a nationwide opioid epidemic. Efforts to develop novel opioids with improved therapeutic profiles have led to work suggesting that MOR signaling through G proteins leads to analgesia while signaling through arrestin leads to respiratory depression and tolerance. However, more recent work has raised questions about which aspects of arrestin signaling and function contribute to these side effects. Additionally, the overall complexity of arrestin function especially with regard to trafficking at the cell membrane has recently come in to clearer view. Here, we use single-molecule tracking to describe membrane diffusion behavior of single MORs before and after agonist treatment in heterologous cells. By tracking individual MORs, we have revealed cell-context specific rules for MOR immobilization and endocytosis and shown that these processes depend on receptor density as well as the local availability of arrestin molecules.

Graduation date: 1996

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

No description available.

published_or_final_version / abstract / Biochemistry / Master / Master of Philosophy

No description available.