Roles of age, gender and gonadal status in opioid antinociception and ingestive behavior in rats.
Item
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Title
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Roles of age, gender and gonadal status in opioid antinociception and ingestive behavior in rats.
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Identifier
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AAI9432344
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identifier
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9432344
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Creator
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Islam, Anita Kazi.
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Contributor
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Mentor: Richard J. Bodnar
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Date
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1994
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Language
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English
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Publisher
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City University of New York.
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Subject
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Biology, Neuroscience | Psychology, Physiological
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Abstract
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Organismic variables appear to modulate various forms of opioid-mediated behaviors. For instance, morphine antinociception is sensitive to gender and aging differences in that its magnitude is greater in male than in female rats, and is lower in older than in younger female rats. Less is known about alterations in opioid-mediated food intake as a function of age and gender. However, a few studies have observed greater sensitivity of opioid modulation of feeding in male than in female animals, and reduced effectiveness of naloxone inhibition of opioid-feeding with aging in males. The present study systematically examined the roles of age, gender, and gonadal status in morphine antinociception on the tail-flick test, and in two forms of opioid-mediated food intake; deprivation-induced and high-fat feeding. Rats were anesthetized and received either sham surgery or gonadectomy at 3 months of age, and tested in separate groups (n = 8-10) at either 6, 12, 18, or 24 mo. of age. Anti-nociceptive efficacy of morphine was assessed at weekly intervals across a dose range of morphine (1-10mg/kg, ip) over a 2 h time course. Following these pain tests the same groups of rats, at this point, 8, 14, 20+ mo. of age, and an additional 4 mo. group, were evaluated at weekly intervals across a dose range of naloxone (.25-5 mg/kg) over a 2 hr. time course, for their sensitivity to naloxone inhibition of food-deprivation-induced food intake, followed by naloxone inhibition of high-fat intake.;Gender differences emerged with age. Whereas intact males and females displayed similar morphine dose-response curves at 6 mo. of age, aging increased antinociceptive sensitivity to morphine in males and decreased sensitivity in females. Moreover, ovariectomy eliminated the age-related decline in morphine responsivity in females, while castration produced little effect. A dissociation was observed between deprivation-induced intake and high-fat intake in terms of age-related, gender-related, and gonadectomy-related alterations in naloxone hypophagia. High-fat intake was most sensitive to organismic factors in their effects on naloxone hypophagia. Aging increased naloxone inhibition of high-fat intake in intact females, but decreased naloxone inhibition in intact males and ovariectomized females. Conversely, aging enhanced naloxone's effects on deprivation-induced intake in males and ovariectomized females. At the highest dose, young intact males were more sensitive to naloxone's inhibitory effects on deprivation intake than were young females.;These results indicate that age and gender interact to alter the efficacy of morphine antinociception and opioid-modulation of food intake in rats, and that ovariectomy but not castration modulates responses of adult rats across the aging process. The ecological relevance of organismic differences in opioid-mediated behavioral process is reviewed in the general discussion.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
