Date of Award

Spring 2016

Document Type

Restricted Thesis

Terms of Use

© 2016 Caela C. Long. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Biology Department

First Advisor

Kathleen King Siwicki


The evolutionary advantages to the suppression of pain during a stressful event (stress-induced analgesia (SIA)) are obvious, yet the reasoning behind sex-differences in the expression of this pain reduction are not. The different ways in which males and females integrate physiological stress responses and descending pain inhibition are unclear. A potential supraspinal modulator of stress-induced analgesia is the central nucleus of the amygdala (CeA). This limbic brain region is involved in both the processing of stress and pain; the CeA is anatomically and molecularly linked to regions of the hypothalamic pituitary adrenal (HPA) axis and descending pain network. The CeA exhibits sex-based differences in response to stress and pain that may differentially induce SIA in males and females. Here, sex-based differences in behavioral and molecular indices of SIA were examined following noxious stimulation. Acute restraint stress in male and female mice was performed prior to intraplantar injections of formalin, a noxious inflammatory agent. Spontaneous pain-like behaviors were measured for 60 min following formalin injection and mechanical hypersensitivity was evaluated 180 min post-injection. Restraint stress decreases centrally mediated formalin-induced spontaneous behavior and formalin-induced mechanical hypersensitivity. To assess molecular indices of SIA, tissue samples from the CeA and blood samples were collected at the 180 min time point. Restraint stress prevents formalin-induced extracellular signal regulated kinase 1/2 phosphorylation in the male CeA, but not in the female. In male mice, restraint and formalin injection significantly increased blood corticosterone concentrations 180 min post injection compared to naïve and non-restrained formalin-injected males. These results demonstrate sex-based differences in behavioral, molecular, and hormonal indices of acute stress in mice that extend for 180 min after stress and noxious stimulation.