The intrahypothalamic distribution of mu, delta and kappa opioid receptor types was examined by in vitro radioautography using the opioid ligands $ sp{125}$I-FK-33 824, $ sp{125}$I-DTLET and $ sp{125}$I-DPDYN, respectively as selective markers. The density and distribution of these receptors in the hypothalamus of normal rats was then compared to that of rats injected with estradiol valerate in order to verify the location of the described increase in $ sp3$H-naloxone binding and to identify the specific opioid receptor type involved. Analysis of opioid receptor changes following long-term exposure to estradiol revealed that mu opioid binding densities were significantly increased in the medial preoptic area of EV-treated animals. Delta and kappa opioid binding densities were unchanged in the medial preoptic area although a slight decrease in delta sites was observed in the suprachiasmatic nucleus. Hypothalamic $ beta$-endorphin concentrations were concomitantly decreased in EV-treated animals, suggesting that observed increases in mu opioid binding were due to a compensatory up-regulation of receptors secondary to loss of $ beta$-endorphin input from the arcuate nucleus. To confirm this interpretation, mu opioid receptor binding was measured in the MPOA of animals treated with monosodium glutamate, which destroys the arcuate nucleus. Results indicated that mu opioid receptor binding densities were inversely proportional to hypothalamic $ beta$-endorphin concentrations in the same animals supporting the existence of a causal relationship between chronic reductions in hypothalamic $ beta$-endorphin concentrations and mu opioid receptor upregulation in the medial preoptic area. / To further document the decreased concentrations of $ beta$-endorphin in the hypothalamus of EV-treated animals, light microscopic immunocytochemistry for $ beta$-endorphin was performed in colchicine treated control and EV-injected rats. Eight weeks following EV treatment, a 60% decrease in the total number of $ beta$-endorphin-immunoreactive neurons was detected in the arcuate nucleus, while neuron numbers for nearby neuronal populations were unchanged. These results were confirmed in biochemical experiments demonstrating reduced hypothalamic $ beta$-endorphin concentrations in the absence of changes in neuropeptide-Y and met-enkephalin in EV-treated rats as compared to controls. Cell counts performed in Nissl-stained material using unbiased stereological methods revealed a reduction in the total number of neurons in the EV-treated group as compared to controls. Furthermore, the estimated number of neurons lost ($ sim$3500) corresponded precisely with the total number of $ beta$-endorphin neurons lost ($ sim$3600) as estimated using quantitative immunocytochemistry. Together, these findings strongly suggest that $ beta$-endorphin neurons are selectively destroyed following long-term exposure to estradiol. Results demonstrated that EV-treated animals co-treated with vitamin E displayed hypothalamic $ beta$-endorphin concentrations similar to controls. In addition, these animals maintained regular estrous cycles and displayed normal ovarian morphology. These findings suggest that estradiol-induced neurotoxicity of $ beta$-endorphin neurons involves the production of free radicals and further supports the notion that the loss of these neurons is important to the induction of chronic anovulation and polycystic ovaries resulting after EV treatment. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41015 |
| Date | January 1992 |
| Creators | Desjardins, G. Clarissa (Gina Clarissa) |
| Contributors | Beaudet, Alain (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 | Doctor of Philosophy (Department of Anatomy.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001319728, proquestno: NN87850, Theses scanned by UMI/ProQuest. |
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