Dim light at night provokes depression-like behaviors and reduces CA1 dendritic spine density in female hamsters

Tracy A. Bedrosian, Laura K. Fonken, James C. Walton, Abraham Haim, Randy J. Nelson

Research output: Contribution to journalArticlepeer-review

Abstract

The prevalence of major depression has increased in recent decades; however, the underlying causes of this phenomenon remain unspecified. One environmental change that has coincided with elevated rates of depression is increased exposure to artificial light at night. Shift workers and others chronically exposed to light at night are at increased risk of mood disorders, suggesting that nighttime illumination may influence brain mechanisms mediating affect. We tested the hypothesis that exposure to dim light at night may impact affective responses and alter morphology of hippocampal neurons. Ovariectomized adult female Siberian hamsters (Phodopus sungorus) were housed for 8 weeks in either a light/dark cycle (LD) or a light/dim light cycle (DM), and then behavior was assayed. DM-hamsters displayed more depression-like responses in the forced swim and the sucrose anhedonia tests compared with LD-hamsters. Conversely, in the elevated plus maze DM-hamsters reduced anxiety-like behaviors. Brains from the same animals were processed using the Golgi-Cox method and hippocampal neurons within CA1, CA3, and the dentate gyrus were analyzed for morphological characteristics. In CA1, DM-hamsters significantly reduced dendritic spine density on both apical and basilar dendrites, an effect which was not mediated by baseline cortisol, as concentrations were equivalent between groups. These results demonstrate dim light at night is sufficient to reduce synaptic spine connections to CA1. Importantly, the present results suggest that night-time low level illumination, comparable to levels that are pervasive in North America and Europe, may contribute to the increasing prevalence of mood disorders.

Original languageEnglish
Pages (from-to)1062-1069
Number of pages8
JournalPsychoneuroendocrinology
Volume36
Issue number7
DOIs
StatePublished - Aug 2011
Externally publishedYes

Bibliographical note

Funding Information:
This work was supported by US-Israeli Binational Science Foundation Grant 2005-337 (RJN and AH). This funding agency had no further role in study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Keywords

  • Depression
  • Females
  • Hippocampus
  • Light pollution
  • Phodopus sungorus
  • Plasticity

ASJC Scopus subject areas

  • Endocrine and Autonomic Systems
  • Psychiatry and Mental health
  • Biological Psychiatry
  • Endocrinology
  • Endocrinology, Diabetes and Metabolism

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