(240) Estrous Cycle and Sex Differences in Referred and Visceral Sensitivity in Rodents

• Published in: The journal of pain Vol. 20; no. 4; pp. S34 - S35
• Main Authors: Gonzalez, S. Martinez, Carrasquillo, Y.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.04.2019
• ISSN: 1526-5900; 1528-8447
• DOI: 10.1016/j.jpain.2019.01.161

Women are more sensitive to pain and make up most of the patients suffering from chronic pathological pain conditions, particularly pelvic and gastrointestinal disorders. Despite this prevalence, most preclinical studies in rodents have focused on males due to the potential variability that the estrous cycle stage might add when studying female subjects. The failure to account for sex differences and the estrous cycle effects in pain leaves unanswered important questions regarding mechanisms driving pain-related behaviors and limits our ability to translate preclinical findings to clinical applications. Therefore, a systematic evaluation of potential differences between sexes and/or across the estrous cycle in pain thresholds and in rodent models of visceral pain is warranted. In the present study, we used Von Frey filaments to measure abdominal and paw sensitivity to tactile stimulation and the intracolonic capsaicin model of visceral pain to measure visceral sensitivity. Pain-related behaviors were compared between male and female mice across the different stages of the estrous cycle. Our results demonstrate that abdominal sensitivity to tactile stimulation is strongly dependent on the phase of the estrous cycle, with mice in metestrous/diestrous (M/D) exhibiting significantly greater responses to abdominal stimulation compared to those in proestrous/estrous (P/E). Responses to abdominal stimulation in male mice were similar to females in M/D and were significantly differently from females in P/E. Interestingly, the sex and estrous cycle differences were specific to the abdomen as no significant differences in paw sensitivity were observed between males and females or across the estrous cycle. Quantification of pain-related behaviors following intracolonic injection of capsaicin further revealed that female mice display significantly higher nociceptive responses to intracolonic capsaicin, compared to males. Altogether, our results indicate that sex and the estrous cycle are important biological variables to be considered when studying abdominal and visceral sensitivity in mice.