Opiates and Monoaminergic Regulation of LH Release in the Rat

Gopalan, Chaya (1988) Opiates and Monoaminergic Regulation of LH Release in the Rat. PhD thesis, University of Glasgow.

Abstract

Monoaminergic regulation of LH release appears to be influenced by the endogenous opioid peptides. Specific opioid receptors exist within the central nervous system and are richly concentrated within the hypothalamus. The present study was undertaken to investigate the effects of specific opiate agonists on hypothalamic monoaminergic activity. In the first set of experiments, various opioid receptor agonists or their antagonist, naloxone, were administered intracerebroventricularly (icv) to short-term orchidectomized rats and blood samples were collected at pre-determined intervals. The animals were decapitated either at 20 minutes or at two-hours post-treatment, and the hypothalamus was surgically isolated. In the second set of experiments, rats were treated with specific opioid receptor agonists, or their antagonist, during the early afternoon of pro-oestrus prior to the preovulatory LH surge. The animals were decapitated after an interval of two hours and the brains removed. Trunk blood was collected for LH measurement by radioimmunoassay. In one group of animals, the whole hypothalamus was dissected out; in another group, specific hypothalamic regions of the hypothalamus were isolated by a micropunch technique. Homogenates of either the whole or of specific hypothalamic regions were prepared and concentrations of noradrenaline (NA), adrenaline (ADR), dopamine (DA), serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) were measured using high performance liquid chromatography coupled to an electrochemical detector. NA and DA turnover rates were estimated by the blockade of the synthesis of these two amines using the enzyme-blocker alpha-methyl-paratyrosine. 5-HT turnover was measured by obtaining the ratio between 5-HT and 5-HIAA. It was observed that the opiates, in general, caused a decrease in NA and 5-HT turnover and an increase in DA turnover in the hypothalamus of the short-term orchidectomized rat. The changes in hypothalamic DA turnover were not consistently associated with changes in LH levels. In the hypothalamic regions studied, opiate agonists either decreased or had no effect on NA turnover whereas the antagonist naloxone had the opposite effect. Surprisingly, DA turnover was increased by both the opiates and by their antagonist, naloxone. 5-HT turnover was significantly decreased by the opiates in most of the regions studied, but was unaffected by naloxone. In conclusion, there exists a heterogenous group of opioid receptors within the hypothalamus which modulate monoamine neurotransmitters controlling LH release.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Neurosciences, Endocrinology
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77774
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77774