Yan Li1, Connie Sánchez1, Maria Gulinello2 Estrogen withdrawal induces depression-like behavior, cognitive dysfunction and temperature dysregulation in a rodent model of perimenopausal symptoms Yan Li1, Connie Sánchez1, Maria Gulinello2 1 Lundbeck Research USA, Paramus, NJ; 2 Albert Einstein College of Medicine, Yeshiva University, Bronx, NY 614.17 Results Introduction The perimenopausal period is accompanied by a range of symptoms including hot flushes, depression and cognitive dysfunctions, due to the rapid fluctuation of estrogens. Although depression-like behavior has been demonstrated in several rodent models of perimenopause, few of these models have characterized functional changes in more than one relevant behavioral domain. In the current study, we assessed depression-like behavior, cognitive function and temperature regulation in a rodent model of perimenopause that is easy to implement. 1. Estrogen withdrawal induces depression-like behavior: increased immobility in forced swim test 3. Estrogen withdrawal induces social memory deficits, which is not due to a lack of social preference. A. Individual periods B. Cumulative (9min) A. Social memory B. Social preference Methods Female gonadally intact Sprague Dawley rats (10 weeks of age) were group housed with ad libitum access to tap water (control) or to water containing 20ug/ml beta-estradiol for 3 weeks (2mg/kg per day), followed by abrupt cessation of estradiol (estrogen withdrawal – EWD). A behavioral test battery was conducted on day1 and day2 after EWD. Studies were approved by the Lundbeck Institutional Animal Care and Use Committee. Forced Swim test (on Day 1 of withdrawal): Rats were placed into a tank of 23˚C water (20cm diameter, 30cm deep) for 10 minutes. The amount of immobility (no movement other than necessary to keep afloat) was manually measured using stopwatches for 3minute time bins, excluding the first minute of the trial. Results were expressed as % immobility: duration of floating (sec) x100/180. Temperature (on Day 1 of withdrawal): Tail surface temperature was measured at 3 time points using a thermo-couple thermometer (Type K): before forced swim test, immediately after forced swim test, and after 10min recoverying under a heat lamp post forced swim test. Social preference and memory test (on Day 2 of withdrawal): Rats were allowed to freely explore an object or an ovariecotomized conspecific stimulus animal for 10 minutes. After a 25min of retention period, rats were allowed to explore the same testing arena, now the object is replaced by another ovariectomized stimulus animal. The amount of exploration were scored manually using stopwatches. Social preference score= exploration(sec) STIMULUS RAT x100/exploration(sec) STIMULUS RAT+OBJECT from trial one. Social memory score= exploration (sec) NEW STIMULUS RAT x100/ exploration (sec) NEW+FAMILIAR STIMULUS RAT from trial two. Object placement test (on Day 1 of withdrawal): Rats were allowed to freely explore an open field with two identical object and high contrast visual cues for 7 minutes (Trial 1). After a retention period of 8 minutes, rats were returned to the same open field for 3 minutes (Trial 2), now with one object moved to a new location. Preference score= exploration(sec) RELOCATED OBJECT/total exploration (sec) in Trial 2. Novel object recognition (on Day 2 of withdrawal): Rats were allowed to freely explore an open field with two identical objects and high contrast visual cues for 4 minutes (Trial 1). After a retention period of 45 minutes, rats were returned to the same open field for 3 minutes (Trial 2), now with one object replaced by a novel object. Preference score= exploration(sec) NOVEL OBJECT/total exploration (sec) in Trial 2. Statistical analysis: Repeated measure or student t-tests were used to analyze the results with p<0.05 considered significant. Repeated measure EWD effect F(1,26)=6.58, p<0.05 t=2.57, df=26, p<0.05 t=-3.48, df=19, p<0.01 Difference not significant No significant difference in locomotor activity measured as total track length in an open field (control: 3318±140cm, EWD: 3060±122 cm). 2. Estrogen withdrawal induces dysregulation in temperature : increased basal temperature and slower recovery from cold exposure. 4. Estrogen withdrawal does not induce deficits in other types of memory tests (visuospatial or recognition memory). A. Visuospatial memory B. Recognition memory A. Basal temperature B. Temperature recovery t=3.88, df=22, p<0.01 t=-2.48, df=22, p<0.05 Difference not significant Difference not significant Conclusion Similar to perimenopausal women, estrogen withdrawal in intact rats induces depression-like behavior, temperature dysregulation and memory deficits, which may be useful to study the pathophysiology and treatments for perimenopausal symptoms.