Graduation Year
2025
Document Type
Campus Only Senior Thesis
Degree Name
Bachelor of Arts
Department
Neuroscience
Reader 1
Sandra Watson
Reader 2
Tom Borowski
Abstract
Previous research has found sex differences in morphine analgesia and in pain responses, leading researchers to believe that pathways involved in pain and analgesia may be sexually dimorphic. One well known way in which female and males systems differ is in their hormonal profile, with females generally having higher levels of estrogen, and males have higher levels of testosterone. The present experiment investigated the role of 17-β-estradiol and testosterone on pain responses to inflammatory pain and morphine analgesia. Because this experiment supplemented another that involved reducing the rats weights, rats in the current experiment were dieted to approximately 85% of their original weight. Gonadectomies were performed on all rats involved (24F, 25M). After surgery, half of the females and males were given oil subcutaneously. Remaining females were administered 17-β-estradiol on a two days on, two days off cycle to mimic the fluctuations of estradiol in the rat estrous cycle. Control females were given oil on the same cycle. Males were administered testosterone daily. Pain responses to inflammatory pain were assessed using the Von Frey assay. Pain responses were assessed before gonadectomy, one week post gonadectomy, and at one and four days after inflammatory pain induction. Inflammatory pain was induced by injecting complete Freund’s adjuvant (CFA) into the ventral subcutaneous area of the left hind paw. Morphine was administered subcutaneously before Von Frey testing after inflammatory pain induction. Paw withdrawal thresholds were difficult to interpret in males because baseline values were inconsistent, and values over time did not change significantly. In females, paw withdrawal thresholds were found to be significant between some groups 24 hours after CFA administration, but these differences were between groups with neither drug nor hormone in common, making them impossible to interpret. Other
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significant results indicated that morphine may have sensitized females given oil and morphine to pain compared to control females and females given estradiol and oil. These results contradict substantial literature indicating that morphine is an effective analgesic agent. These results within the context of literature showing that analgesia can be increased, decreased or remain the same post gonadectomy lead to the conclusion that the gonadectomy paradigm of studying sex hormones itself should be tested in the future.
Recommended Citation
Soberg, Melina, "Sex Hormones on Morphine Analgesia and Allodynia" (2025). Pitzer Senior Theses. 203.
https://scholarship.claremont.edu/pitzer_theses/203
This thesis is restricted to the Claremont Colleges current faculty, students, and staff.