REPRODUCTIVE COMPETENCE IN FEMALE ICR MICE FOLLOWING HIGH FAT DIET AND CONSTANT LIGHT EXPOSURE.pdf
Creators: name: Teeple, Kelsey A
Publisher: name: Purdue University Graduate School
Year: 2023
Subjects: subject: Animal physiology - systems
subject: Reproduction
subject: FOS: Medical biotechnology
subject: Animal growth and development

description: In modern society, continuous light exposure and obesity are increasingly prevalent, especially in women of childbearing age. Circadian, metabolic, and reproductive systems have a complex, inter-regulated relationship. Thus, the disruption of one system likely impedes another. Excessive adiposity and circadian disruption alter normal behavior and physiology and disrupt the endocrine milieu. The overall goal of the studies described in this thesis was to develop and test a model system that could tease apart the influence of prepregnancy obesity and circadian disruption, as well as study the combined effects on female reproductive competence. The first study focuses on the prepregnancy period and aims to determine the effect of high fat diet feeding on diurnal eating pattern, body weight over the four-week period, the body composition at the end of the four-week period, hair corticosterone levels, and circadian fecal corticosterone patterns on female ICR mice. Five-week-old female ICR mice were randomly assigned to control (CON; 10% fat) or high fat (HF; 60%) diets and fed for four weeks to achieve adequate adiposity. During this four-week time period, mice had routine light exposure of 12h light and 12h dark. Feed was weighed at 0600 and 1745 Monday-Friday to determine diurnal feed intake. The mice were weighed on a weekly basis. After four weeks on respective diets, mice were anesthetized with isoflurane to measure crown-rump length to calculate BMI and hair was shaved for corticosterone extraction. Once mice recovered from anesthesia, body composition was measured with EchoMRI. After 1 week on diets, HF mice consumed more (P&lt;0.05) during the day than CON mice, which is typically when mice are inactive. After two weeks on diets, HF mice weighed more (P&lt;0.05) than CON, as well as had higher BMI and percent body fat (P&lt;0.05) than CON after four weeks on diets. After four weeks on diets, HF mice had high hair corticosterone (P&lt;0.05). Sampling feces over a 48h period at the end of the four weeks demonstrated that HF mice had elevated basal corticosterone, attenuated circadian rhythms, and a shift in corticosterone amplitude. The prepregnancy period demonstrated that high fat diets alone alter circadian eating pattern and corticosterone rhythms. The remainder of the study continued the dietary treatments assigned during the prepregnancy period, as well as implemented light conditions to create a 2Χ3 factorial study design. There were three light conditions: 12h light and 12h dark (LD), 24h dim light (L5), or 24h bright light (L100). Mice were moved into experimental light conditions after the observation of a vaginal plug or after 5 days with males. This portion of the study aimed to determine the effect of diet (CON or HF) and light exposure (LD, L5, or L100) on gestation length, number of pups born, milk composition, litter weight on postnatal day 12, as well as dam feed intake, hair corticosterone levels, and plasma prolactin. Continuous light exposure increased gestation length, with L5 (19.1 d ± 0.23) and L100 (18.9 d ± 0.21) having longer gestation lengths (P&lt;0.05) than LD (18.1 d ± 0.25). Diet affected the number of pups born (P&lt;0.05), with HF dams having fewer pups (9.99 ± 0.4) than CON (11.4 ± 0.4). Despite no difference in birth weight of standardized litters (n=8 pus/litter), litters of HF dams weighed more than CON by day 4 postnatal. The greater litter weight of HF dams continued until the end of the study on day 12 of lactation (P&lt;0.05). Light had a tendency to increase litter weight (P=0.07). Diet, light, and stage of reproduction influenced dam feed intake (P&lt;0.05). L100 dams had higher plasma prolactin, as well as final dam and mammary wet weights (P&lt;0.05). Constant light exposure decreased ATP content in the mammary gland (P&lt;0.05) and decreased milk lactose concentration (P&lt;0.05). Pearson’s correlation analysis showed a positive relationship between mammary weight, fat pad weight, BMI, kcal of feed intake, and gestation length (P&lt;0.05). In CON mice, hair corticosterone was negatively correlated with litter weight on lactation day 12. Liver weight was positively correlated with d 12 litter weight in HF mice. Together, these studies demonstrate that feeding high fat diets and continuous light alter maternal behavior and physiology, which may impact offspring health and development, however continuous light may not be the best approach to studying circadian disruption. Elevated maternal plasma prolactin and increased dam weight suggests a long day photoperiod was likely induced, thus potentially mitigating the circadian disruptive effects from constant light. Other model systems should be considered, such as using a chronic jet lag model that changes the light exposure every 3 d.