The mechanisms involved in morphine tolerance are poorly understood. It was reported that calcitonin gene-related peptide (CGRP) immunoreactivity was increased in the spinal dorsal horn during morphine tolerance and an in vitro repetitive morphine treatment was able to mimic the in vivo results by inducing increases in CGRP- and substance P (SP)-immunoreactive (IR) neurons in cultured dorsal root ganglia (DRG). The aim of this study was to validate the DRG cell culture model by establishing which subtypes of opioid receptors are involved in the induction of CGRP and SP in cultured rat DRG neurons and to examine the signaling pathway involved in the induction of the neuropeptides following repetitive opiate treatments. / Following treatment with any of the three opioid agonists [mu; DAMGO, delta; DPDPE, kappa; U50488H], the number of CGRP- and SP-IR neurons increased significantly, in a concentration-dependent manner. Double-immunofluorescence staining showed that the three opioid receptors were colocalized with both of the pain-related neuropeptides. Protein kinase C (PKC)-IR was found to be significantly increased following a repetitive treatment with DAMGO. Double-immunofluorescence staining showed the colocalization of PKCalpha with CGRP or SP in cultured DRG neurons. Moreover, a combined treatment of the opioid with a PKC inhibitor was able to block the effects of the opioid on increased CGRP-like IR. / In conclusion, the data suggests that the three opioid receptors may be involved in the induction of CGRP and SP observed following chronic exposure to opiates and that PKC probably plays a role in the signaling pathway leading to the upregulation. These findings further validate the DRG cell culture as a suitable model to study intracellular pathways that govern changes seen following repetitive opioid treatments.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.32758 |
| Date | January 2001 |
| Creators | Belanger, Serge. |
| Contributors | Quirion, Remi (advisor) |
| 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 | Master of Science (Department of Pharmacology & Therapeutics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001861980, proquestno: MQ78830, Theses scanned by UMI/ProQuest. |
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