title: Hormonal and molecular effects of restraint stress on formalin-induced pain-like behavior in male and female mice.
abstract: 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 60min following formalin injection and mechanical hypersensitivity was evaluated 120 and 180min post-injection. Restraint stress altered formalin-induced spontaneous behaviors in male and female mice and formalin-induced mechanical hypersensitivity in male mice. To assess molecular indices of SIA, tissue samples from the CeA and blood samples were collected at the 180min time point. Restraint stress prevented formalin-induced increases in extracellular signal regulated kinase 2 (ERK2) phosphorylation in the male CeA, but no changes associated with pERK2 were seen with formalin or restraint in females. Sex differences were also seen in plasma corticosterone concentrations 180min post injection. These results demonstrate sex-based differences in behavioral, molecular, and hormonal indices of acute stress in mice that extend for 180min after stress and noxious stimulation.
authors: Biology Department, Swarthmore College, Swarthmore, PA 19081, United States; Department of Biological Sciences and Chronic Pain Research Consortium, Duquesne University, Pittsburgh, PA 15219, United States.
authors: Caela C
authors: CC
authors: Long
authors: Department of Biological Sciences and Chronic Pain Research Consortium, Duquesne University, Pittsburgh, PA 15219, United States.
authors: Katelyn E
authors: KE
authors: Sadler
authors: Department of Biological Sciences and Chronic Pain Research Consortium, Duquesne University, Pittsburgh, PA 15219, United States. Electronic address: kolberb@duq.edu.
authors: Benedict J
authors: BJ
authors: Kolber
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003345:Corticosterone / Q000097:blood*; D004195:Disease Models, Animal; D005260:Female; D005404:Fixatives / Q000633:toxicity; D005557:Formaldehyde / Q000633:toxicity; D006930:Hyperalgesia / Q000503:physiopathology / Q000534:rehabilitation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010146:Pain / Q000139:chemically induced / Q000378:metabolism* / Q000534:rehabilitation*; D010147:Pain Measurement; D010812:Physical Stimulation / Q000009:adverse effects; D012149:Restraint, Physical / Q000379:methods*; D012727:Sex Characteristics; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
chemical_list: D005404:Fixatives; D005557:Formaldehyde; C535148:Mapk1 protein, mouse; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D003345:Corticosterone
keywords: Acute restraint; Central nucleus of the amygdala; Pain; Sex differences; Stress-induced analgesia