Swim Stress-Induced Analgesia in CXBK Mice: Roles of Gender, Gonadectomy, and Estrogen Replacement
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1996
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Haverford College. Department of Psychology
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Thesis
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Award
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eng
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Haverford users only
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Abstract
CXBK mice, an inbred strain, have 30% fewer opiate receptors than outbred mice. CXBK male mice have previously exhibited only non-opioid (naloxone-insensitive), NMDA (MK-801-sensitive) mediated swim stress-induced analgesia (SSIA), following a forced swim in 20°C water. Outbred Swiss-Webster mice have previously exhibited sex differences in the NMDA mediation of non-opioid SSIA. The purpose of the present study was: (1) to examine the existence of sex differences in the NMDA mediation of non-opioid SSIA in CXBK mice, following a 20°C forced swim; (2) to examine the effects of gonadectomy and estrogen replacement therapy on the sex differences, if they do exist in these inbred CXBK mice. Results indicated that there were no sex differences in the NMDA mediation of non-opioid SSIA in CXBK mice. In both male and female CXBK mice, non-opioid analgesia (naloxone-insensitive) was not mediated by the NMDA receptor (MK-801-insensitive) in SSIA after a forced 20°C swim. MK-801 did alter basal nociception in both males and females, indicating the presence of NMDA receptors in CXBK mice. Females showed significantly lower baseline hot-plate latencies than males, and estrogen replacement therapy for as few as 6 days significantly attenuated non-opioid SSIA in females. The results of this study suggest that although female and male CXBK mice possess NMDA receptors, these receptors are not involved in non-opioid SSIA. These overall findings are discussed in terms of: (1) the possible serotonin mediation of non-opioid SSIA in CXBK mice; and (2) the possible interaction of estrogen and the hypothalamic-pituitary-adrenal (HPA) axis to attenuate non-opioid SSIA in CXBK female mice.