Psychological stress in aged female mice causes acute hypophagia independent of central serotonin 2C receptor activation

RESEARCH ARTICLE Psychological stress in aged female mice causes acute hypophagia independent of central serotonin 2C receptor activation Chinami Matsumoto1, Chihiro Yamada1, Chiharu Sadakane1, Miwa Nahata1, Tomohisa Hattori1*, Hiroshi Takeda2,3 1 Tsumura Research Laboratories, Tsumura & Co., Ibaraki, Japan, 2 Pathophysiology and Therapeutics, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Hokkaido, Japan, 3 Hokkaido University Hospital Gastroenterological Medicine, Sapporo, Hokkaido, Japan a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Matsumoto C, Yamada C, Sadakane C, Nahata M, Hattori T, Takeda H (2017) Psychological stress in aged female mice causes acute hypophagia independent of central serotonin 2C receptor activation. PLoS ONE 12(11): e0187937. https://doi.org/10.1371/journal. pone.0187937 Editor: Eric M Mintz, Kent State University, UNITED STATES Received: March 22, 2017 Accepted: October 27, 2017 Published: November 10, 2017 Copyright: © 2017 Matsumoto et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting Information files. * Abstract Sex differences exist in the activation of the hypothalamic–pituitary–adrenal axis following exposure to stress, and the stress response is further affected by aging. This study was conducted to elucidate the mechanism of hypophagia in aged female mice exposed to stress. Immediately after a stress load, aged female mice exhibited acute hypophagia and a rise in plasma corticosterone levels. The administration of a serotonin 2C receptor (5HT2CR) antagonist suppressed plasma corticosterone but did not affect the reduction in food intake. In contrast, an endogenous ghrelin enhancer, rikkunshito (RKT), significantly inhibited the reduction in food intake. An increase in peripheral acylated ghrelin levels during fasting, which occurs in young mice, was not observed in aged female mice. Moreover, in these mice, significantly increased levels of ghrelin and gastric preproghrelin mRNA expression were observed in the fed status. Moreover, plasma ghrelin levels were elevated by RKT and not by the 5-HT2CR antagonist. In female mice, the hypothalamic non-edited (INI) and partially edited mRNA 5-HT2CR isoforms (VNV, VNI, VSV or VSI) decreased with age, while in male mice, the editing isoform was unchanged by aging or stress. Estrogen receptor α (ERα)-positive cell counts in the arcuate nucleus of young male mice exposed to stress and control aged male mice were increased compared with those in young control mice. In aged male mice exposed to stress, the number of ERαexpressing cells in the paraventricular nucleus were significantly increased compared with those in aged control mice; in female mice, there was no increase in the number of ERαpositive cells. Hypophagia in aged female mice exposed to stress may be independent of 5-HT2CR activation. It seems likely that the mechanisms may be caused by sex dependent, differential regulation in 5-HT2CR mRNA expression, peripheral acylated ghrelin secretion and/or hypothalamic ERα expression. Funding: HT received a research grant from Tsumura & Co. Tsumura & Co. provided support in the form of salaries for authors CM, CY, CS, MN and TH. The specific roles of these authors are articulated in the ’author contributions’ section. This study was funded by Tsumura & Co. Tsumura PLOS ONE | https://doi.org/10.1371/journal.pone.0187937 November 10, 2017 1 / 17 Novelty stress in aged female mice causes acute hypophagia independent of 5-HT2CR & Co. was responsible for the study design, and the collection, analysis and interpretation of data. Competing interests: HT has been received grant supports from Tsumura & Co. CM, CY, CS, MN and TH are employees of Tsumura & Co. This does not alter our adherence to PLOS ONE policies on sharing data and materials. Introduction Adverse life events are associated with the onset and persistence of depression [1], and depression is characterized by feeding abnormalities. In particular, the combination of depression and anorexia may influence morbidity and progressive physical disability among the elderly [2, 3]. Sex differences exist in the activation of the hypothalamic–pituitary–adrenal (HPA) axis following exposure to stress [4–6]. The incidences of major depression [7] and anorexia nervosa [8] are higher in women than in men. In young rodents, the activation of the HPA axis due to stress is greater in females than in males [9] and is regulated by sex hormones [4, 5]. Aging is one of the major factors that affects appetite. Age-related anorexia is more pronounced in males [10, 11]. Furthermore, late-life depression in males is a risk factor for mortality [12, 13]. In addition, aging may even interfere with phenotypes that cause sex differences such as stress. Compared with aged male mice, aged female mice exposed to novelty stress have a milder reduction in food intake after stress, however, the mechanism underlying this observation is unclear [14]. Corticotropin-releasing factor (CRF) and serotonin (5-HT) play important roles in stress responses and the regulation of feeding behavior [15, 16]. The activation of CRF neurons during stress suppresses feeding behavior [17, 18]. CRF production and neuron activation may also be mediated by 5-HT. The serotonin 2C receptor (5-HT2CR), localized on CRF neurons of the hypothalamus, stimulates anxiety [19–21] and negatively regulates food intake [22–25]. The gene expression of 5-HT2CR is increased in the paraventricular nucleus (PVN) of aged male mice [26]. Neural hyperactivity by stimulation of 5-HT2CR in the PVN or amygdala due to exposure to stress suppresses the secretion of the peripheral orexigenic hormone ghrelin, leading to a decrease in food intake. The involvement of 5-HT2CR activation after a stress response in aged female mice is unknown. Excessive, central activation of the 5-HT2CR in aged male mice is caused by increased gene expression [26]. Furthermore, changes in the editing of the 5-HT2CR influence the affinity or signal transduction of the receptor and are involved in neuropsychiatric diseases [27]. Therefore, we examined the influence of aging and sex on changes in the gene expression of the preedited 5-HT2CR. Estrogen regulates food intake, and an ovariectomy increases both and weight gain [4, 28]. The estrogen receptor α (ERα) is widely expressed in the central area of the brain, including the hypothalamus, and negatively controls feeding [29]. The activation of the 5-HT2CR promotes the synthesis of ERα in the dorsal raphe region [30] and hypothalamus [31]. We found that hypophagia in aged male mice exposed to stress may be mediated by the interaction of ERα with 5-HT2CR act (...truncated)