title: Decreased daytime illumination leads to anxiety-like behaviors and HPA axis dysregulation in the diurnal grass rat (Arvicanthis niloticus).
abstract: The impact of ambient light on mood and anxiety is best exemplified in seasonal affective disorder, in which patients experience depression and anxiety in winter when there is less light in the environment. However, the brain mechanisms underlying light-dependent changes in affective state remain unclear. Our previous work revealed increased depression-like behaviors in the diurnal Nile grass rat (Arvicanthis niloticus) housed in a dim light-dark (dim-LD) cycle as compared to the controls housed in a bright light-dark (bright-LD) condition. As depression is often comorbid with anxiety and is associated with dysregulation of the body's stress response system, the present study examined the anxiety-like behaviors as well as indicators of the hypothalamic-pituitary-adrenal (HPA) axis functioning in the grass rats. Animals housed in dim-LD showed increased anxiety-like behaviors compared to bright-LD controls, as revealed by fewer entries and less time spent at the center in the open field test and more marbles buried during the marble-burying test. Following the marble-burying test, dim-LD animals showed higher plasma corticosterone (CORT) levels and hippocampal Fos expression. Although the daily CORT rhythm was comparable between bright-LD and dim-LD groups, the day/night variation of corticotropin-releasing hormone mRNA expression in the paraventricular nucleus was diminished in dim-LD animals. In addition, glucocorticoid receptor and mineralocorticoid receptor mRNA expression were higher in the hippocampus of dim-LD animals. The results suggest that in diurnal species, reduced daytime illumination can lead to increased anxiety-like behaviors and altered HPA axis functioning, providing insights into the link between decreased environmental illumination and negative emotion.
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA. Electronic address: ikenotom@msu.edu.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Ikeno
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA. Electronic address: deatssea@msu.edu.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Deats
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA. Electronic address: solerjoe@msu.edu.
authors.forename: Joel
authors.initials: J
authors.lastname: Soler
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA; Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA. Electronic address: lonstein@msu.edu.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Lonstein
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, MI 48824, USA; Neuroscience Program, Michigan State University, East Lansing, MI 48824, USA. Electronic address: yanl@msu.edu.
authors.forename: Lily
authors.initials: L
authors.lastname: Yan
mesh_terms: D000818:Animals; D001008:Anxiety Disorders / Q000209:etiology / Q000503:physiopathology*; D002940:Circadian Rhythm / Q000502:physiology; D003345:Corticosterone / Q000097:blood; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D004195:Disease Models, Animal; D006624:Hippocampus / Q000378:metabolism*; D006799:Housing, Animal; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism*; D008027:Light; D008029:Lighting; D008297:Male; D009043:Motor Activity / Q000502:physiology; D051189:Murinae; D010913:Pituitary-Adrenal System / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D018161:Receptors, Mineralocorticoid / Q000378:metabolism
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D018161:Receptors, Mineralocorticoid; D003346:Corticotropin-Releasing Hormone; D003345:Corticosterone
keywords: Anxiety; Corticosterone; Corticotropin-releasing hormone; Hippocampus; Hypothalamic-pituitary-adrenal axis; Seasonal affective disorder