BACKGROUND: Premenstrual syndrome (PMS) is a disruptive physiological condition affecting a phenomenal 90% of women worldwide. The most common symptoms include anxiety and mood swings. Despite this, PMS continues to be a poorly understood disorder, due to a lack of an appropriate animal model of menstruation. We recently discovered the spiny mouse has a menstrual cycle; the first report of a rodent with natural menstruation1.
AIM: To determine whether spiny mice exhibit behavioural changes across their menstrual cycle.
METHODS: We performed daily vaginal lavage on virgin spiny mice (6-8 months old). At each stage of the menstrual cycle (early follicular, late follicular, early luteal, late luteal, early menstrual and late menstrual), females were randomly subjected to Open Field (OF), Novel Object Recognition (NORT), Social Interaction (SI) and Elevated Plus Maze (EPM) tests to assess exploration and social behaviours. The late luteal and early menstrual phases were designated pre-menstrual phases. Repeated tests were conducted on cycling (n=11) and ovariectomised control (n=5) females. Results are mean ± STD with statistical significance set to p<0.05.
RESULTS: Cycling females in their early menstrual phase travelled significantly less distance in the outer zone of the OF arena (13.3 ± 9.0 m) than females in their early luteal phase (22.3 ± 9.9m) and at significantly reduced velocities (40.2 ± 10.5mm/s and 78.8 ± 31.0mm/s, respectively). These females also travelled less distance in the EPM open arms (3.2 ± 2.8m and 7.0 ± 5.5m, respectively). No differences were observed in NORT or SI, or compared to controls.
SIGNIFICANCE: Spiny mice, during the early menstrual phase of their cycle travel less distance, at lower velocities compared to females in the early luteal phase. This is the first report of cycle variability in behaviour in spiny mice. The timing suggests that spiny mice may exhibit premenstrual syndrome.