M65 - The Effect of Chronic Stress on Weight And Hypothalamic Insulin And Melanocortin 4 Receptors In Young And old Female Mice

Abstract

Background Chronic stress (CS) has a deleterious effect on several physiological systems, among them cognition, memory and the regulation of appetite and weight. In humans, stress can cause weight gain in some people, but weight loss in others. Weight loss, mainly in advanced ages, is a major health concern. The exact mechanism is unknown; however, chronic psychological and social stressors are considered among the main contributing factors. The central site for appetite regulation is located in the hypothalamus. Insulin enters the central nervous system (CNS) in proportion to its plasma level and start a cascade that controls food intake. Activation of Melanocortin 4 receptors (MC4R) on neurons in the paraventricular hypothalamic nucleus (PVN), decreases food intake while elevating energy utilization The present study was designed to gain a mechanistic understanding of the age-related effects of chronic stress on weight and to try to explore for the mechanisms of weight change in the context of chronic stress in mice. Methods 62 female C57BL/6JRccHsd mice aged 3 months (young) and 20-23 months (old) were used in this study . Mice were housed in groups of 4-5 . Food and water were provided ad libitum. Old and young mice were divided into equally sized subgroups that underwent a chronic stress (CS) regimen or were maintained under regular animal facility conditions (Control). Mice were weighed once weekly. Mice were sacrificed, hypothalami were dissected and mRNA was extracted. To measure the expression of IR and MC4R, real time PCR (rtPCR) was used. Results Old mice were more vulnerable to the effects of chronic stress on weight than young mice. Two way ANOVA with repeated measures comparing changes in body weight from baseline (i.e. before onset of stress protocol) until after eight concessive weeks of CS revealed a significant age by time interaction (F [2,58] = 11.126, p=0. 009). Ins-R expression in the hypothalamus was quantified by rtPCR in young vs. very old female mice subject to CS or control conditions. A 2-way ANOVA with age and treatment as independent variables yielded a significant main effect of treatment (F[1,18]=5, p=0.038). MC4R expression in the hypothalamus was quantified by rtPCR in young vs. very old female mice subjected to CS or control conditions. A 2-way ANOVA with age and treatment as independent variables yielded a strong, highly-significant main effect of age (F[1,23]=23.4, p Discussion In the present study, we compared four groups of female mice: young and old control mice versus young and old mice in CS conditions. We found that female mice lost weight under CS conditions significantly more than the rest of the groups. We hypothesized that a change in the mRNA expression of Ins-R and MC4R, will indicate for the mechanism of weight loss in that group. The results indicate that there is an increase in hypothalamic Ins-R expression under CS without regard to age. This result in itself is novel and in view of the paucity of knowledge that exists regarding the role of insulin in the CNS. The expression of MC4R did not show any significant interaction with CS exposure, but there was a significant rise in expression in old mice versus young mice. This may imply that in old age, CRH neurons in the PVN are more sensitive to anorexigenic signals than in young age.