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Includes bibliographical references (leaves 308-327) / xxviii, 356 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 2004?

We investigated the role of metabotropic glutamate receptors (mGluRs), and related intracellular second messengers, in the development of morphine tolerance and dependence. The mGluRs are divided into three groups: group I mGluRs are positively coupled to phosphatidylinositol (PI) hydrolysis, while group II and III mGluRs are negatively coupled to cyclic adensoine-3$ sp prime$,5$ sp prime$-monophosphate (cAMP) production. Opioid receptors are also coupled to these same systems, and have been shown to elicit changes in these messenger systems during chronic treatment. / We showed that chronic intracerebroventricular (i.c.v.) administration of selective group II and III mGluR antagonists concurrently with subcutaneous (s.c.) morphine significantly reduced the severity of precipitated withdrawal symptoms. Conversely, acute i.c.v. injection of a selective group II mGluR antagonist just prior to the precipitation of withdrawal significantly exacerbated the severity of abstinence symptoms. In addition, acute i.c.v. injection of a selective group II mGluR agonist just prior to the precipitation of withdrawal significantly reduced abstinence symptoms. From these results we hypothesized that chronic opioid treatment may induce a desensitization of group II mGluRs. / We also demonstrated that chronic i.c.v. infusion of a selective group I mGluR antagonist concurrently with s.c. morphine significantly attenuated the precipitated withdrawal syndrome. In addition, we showed that chronic i.c.v. antagonism of $ delta$-opioid receptors with a highly selective antagonist also decreased the development of morphine dependence, as well as tolerance. Since both group I mGluRs and $ delta$-opioid receptors are positively coupled to PI hydrolysis, further evidence for a role of products of PI hydrolysis in the development of morphine dependence was obtained when we showed that selective chronic inhibition of protein kinase C (PKC) activation, as well as selective chronic inhibition of intracellular Ca$ sp{2+}$ release, concurrently with morphine treatment significantly reduced the severity of abstinence symptoms. Thus, compensatory changes usually elicited by chronic opioid treatment may be counteracted by antagonizing receptors positively coupled to PI hydrolysis, as well as by inhibiting products of PI hydrolysis. / In the General Discussion, we propose a model based on the possible interaction of mGluRs and opioid receptors, via related intracellular second messengers, to explain the development of morphine dependence.

It was hypothesized that a metabolite of morphine, morphine-3-glucuronide (M3G), contributes to the expression of symptoms seen during withdrawal from morphine. To test this hypothesis, the behaviors observed during precipitated withdrawal from morphine and sufentanil were compared. Sufentanil was chosen because, like morphine, it acts primarily at the mu opioid receptor, but has different metabolites. Differences in the abstinence syndromes produced by the two drugs may therefore be attributable to the actions of metabolites, rather than the primary opioid actions of morphine and sufentanil. Although there were some differences in the occurrence of symptoms, morphine and sufentanil withdrawal were very similar. Therefore, the evidence was inconclusive as to the contribution of metabolites during withdrawal. / Systemic administration of M3G alone and in combination with morphine produced no withdrawal-like behaviors. However, when these drugs were given centrally, withdrawal-like behaviors were observed in conjunction with seizures. The seizures were not attenuated by naloxone (but were alleviated by an anti-convulsant), indicating that they were not mediated by opioid receptors. The behaviors resembled those seen by previous investigators following high doses of morphine. The results suggest that M3G may play a role in the toxic effects of high doses of morphine.

The present studies used the classical method of serial transections of the neuraxis to examine the neural mechanisms of injury-produced pain and morphine analgesia in the formalin test. The results showed that the behavioral response that follows formalin injection is complete within the brainstem, whereas telencephalic structures are critical for morphine to produce analgesia. In contrast, when the tail flick test, a model of noninjurious pain was used, both the behavioral response, and analgesia, were intact in the brainstem transected rat, in keeping with the current model of analgesia for this test. Brain areas classically associated with pain processing were not sufficient for morphine to produce analgesia in the formalin test. Instead, the amygdala, part of the emotion-mediating limbic system, was critical. It is argued that the formalin test may be a model of "dissociative" analgesia, in which reduction of the negative affective consequences of the pain plays a major role.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 85-101). / Microfiche. / xvi, 101 leaves, bound ill. 29 cm

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / While opioids are the most effective and widely used class of drug for the management of moderate to severe pain, their use may be limited by adverse effects that are unpleasant and potentially dangerous. Research is increasingly directed towards strategies to improve the use of opioids in pain management, investigating methods by which the analgesia afforded by an opioid may be enhanced, while minimising adverse effects. One approach that has produced promising findings in animal studies and some clinical reports is the combination of an opioid agonist and "ultra-low" (nanomole) doses of an opioid antagonist. A recent animal study reported that antinociception may be significantly enhanced with the combination of the partial opioid agonist/antagonist buprenorphine and ultra-low doses of the antagonist naloxone. The central aim of the studies described herein was to investigate the effect of this drug combination on response to experimental nociceptive stimuli and the incidence and severity of adverse effects among healthy volunteers. The first study established normative responses to two commonly used nociceptive tests, the cold pressor and electrical stimulation tests, in 100 healthy volunteers. The effect of buprenorphine on nociceptive test performance had not previously been determined, therefore a dose-ranging study of buprenorphine was conducted to establish a doseresponse relationship. The subsequent two studies investigated the effect of a range of buprenorphine:naloxone IV dose ratios (5:1, 10:1, 12.5:1, 15:1, 20:1 and 25:1) on nociception and adverse effects among healthy volunteers. These studies are the first to investigate the combination of buprenorphine and ultra-low dose antagonist in humans, and the first to assess the agonist:antagonist combination in an experimental model of human nociception. Antinociception was significantly enhanced with the combination of buprenorphine and naloxone in the 12.5:1 and 15:1 ratios. Moreover, this enhanced antinociception occurred without a simultaneous increase in adverse effects and indeed with a reduction in the severity of some effects. An agent that produces greater analgesia and reduces adverse effects has the potential to overcome some of the barriers that limit the use of opioids in pain management. The current findings indicate that further investigation of this drug combination is warranted. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1177227 / Thesis (Ph.D.) -- University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 2005

Thesis (Ph. D.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 140-173).

Thesis (M. Phil.)--University of Hong Kong, 1997. / Cover title. Includes bibliographical references (leaves 108-124).

Thesis (Ph. D.)--University of Chicago, Committee on Neurobiology, August 1999. / Includes bibliographical references. Also available on the Internet.