The opioid receptor family is comprised of three members: mu, delta and kappa, all of which are G protein coupled receptors, primarily acting through Galphai/o subunits. Clinically, mu opioid receptor (MOR) agonists are used in the treatment of moderate to severe pain. delta opioid receptor (DOR) agonists are being developed as alternative analgesics, since stimulation of this receptor results in fewer adverse side effects. Characterization of behaviourally relevant mu and delta opioid receptors, as well as interactions between them, will provide a better understanding of opioid agonist-induced analgesia. / Although the behavioural knockdown after antisense targeting of MOR has been well characterized, few studies have examined the corresponding in vitro changes. Thus, the first aim of this thesis was to determine the neuroanatomical extent of MOR knockdown after pretreatment with peptide nucleic acid antisense in rats. Antisense pretreatment completely inhibited antinociception by the mu agonist DAMGO, but produced no detectable ex vivo changes in brain or spinal MOR labelling or functional responses. This study suggests that there may be a small, critical population of MORs that mediate antinociceptive responses to agonist. / The second aim of this thesis was to compare the CNS distribution of functional DOR with radioligand binding. DOR labelling was determined autoradiographically using an agonist, ([125I]deltorphin II) and an antagonist ([ 125I]AR-M100613) radioligand. In adjacent tissue sections, functional DORs were detected using deltorphin II-induced [35S]GTPgammaS binding. Overall, radioligand binding did not strongly predict the magnitude of [35S]GTPgammaS responses, and this weak association is possibly explained by a paucity of DORs on the cell surface and/or heterogeneity in G protein receptor coupling. The highest [35S]GTPgammaS responses were found in the basal ganglia, while areas involved with pain perception (spinal cord, brain stem, and periaqueductal grey) possessed low [35S]GTPgammaS responses. / The low deltorphin II-induced [35S]GTPgammaS binding in pain-related areas could explain the moderate degree of antinociception produced by delta agonists relative to their mu counterparts. Thus, the third aim of this thesis was to investigate two pharmacological treatments (short- and long-term morphine pretreatment) that are reported to enhance behavioural responses to delta agonists. As previously observed by others, short-term exposure to morphine resulted in sensitization to spinally administered delta agonists. In contrast, long-term morphine pretreatment resulted in profound tolerance to the antinociceptive and locomotor stimulant effects of deltorphin II. After chronic morphine pretreatment, there was no detectable change in DOR labelling or [35S]GTPgammaS responses in the brain or spinal cord, suggesting that changes in downstream regulators may be responsible for this tolerance.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.85954 |
| Date | January 2005 |
| Creators | Pradhan, Amynah Amir Ali |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Pharmacology and Therapeutics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002261169, proquestno: AAINR21691, Theses scanned by UMI/ProQuest. |
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