Student Theses and Dissertations

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

McEwen Laboratory


Opiates are important regulators of reproductive function in the rat, potently inhibiting gonadotropin secretion. However, the role of opiates in the control of lordosis, hormone-dependent female sexual behavior, is less clear. While opiate agonists inhibit lordosis, antagonists do not consistently facilitate behavior. The purpose of the present experiments was to further investigate opiate regulation of lordosis, and to examine the role of other neurotransmitter systems in the actions of opiates. The opiate antagonist naltrexone was found to facilitate lordosis in estrogen-primed rats. Naltrexone facilitated behavior was compared to the facilitation of behavior by progesterone. The medial preoptic area (POA) was found to be important in the actions of naltrexone. The role of serotonergic systems in the opiate regulation of lordosis was examined. Lesions of hypothalamic serotonergic terminals blocked the inhibition of behavior by morphine. Naltrexone increased the rate of norepinephrine turnover, but decreased the rate of serotonin turnover in the POA. These changes were not seen in other areas of the brain. Both naltrexone and morphine increased the rate of serotonin synthesis in the POA. The dissociation between the rates of serotonin synthesis and turnover is discussed. Opiate regulation of serotonin turnover was indirectly assessed by examining changes in serotonin receptors after treatment with opiates.Opiates might be regulating serotonin release by actions at opiate receptors on serotonergic terminals in the POA. Levels of opiate receptors were measured after selective serotonergic lesions. Mu and delta opiate receptors in the POA were decreased after the lesion, suggesting that opiate receptors are located on serotonin terminals, and providing a neuroanatomical basis for opiate regulation of serotonin turnover.The work presented here extends previous investigations of opiate regulation of lordosis. There is evidence that two previously described systems, serotonin and endogenous opiates, may be working in concert to regulate behavior.


A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy

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