Effects of bright light therapy on neuroinflammatory and neuroplasticity markers in a diurnal rodent model of Seasonal Affective Disorder

Abstract

Background

Bright light therapy (BLT) is widely used for treating Seasonal Affective Disorder (SAD). However, the neural mechanisms underlying the therapeutic effects of BLT remain largely unexplored. The present study used a diurnal rodent (Nile grass rats; Arvicanthis niloticus) to test the hypothesis that the therapeutic effects of BLT could be, in part, due to reduced neuroinflammation and/or enhanced neuroplasticity. Our previous research has demonstrated that compared to grass rats housed in a summer-like daytime bright light condition (1000 lux), those housed in a winter-like daytime dim light condition (50 lux) showed increased depression- and anxiety-like behaviours, as well as impaired sociosexual behaviours and spatial memory, similar to what is observed in patients suffering from SAD.

Materials and Methods

In the present study, male and female grass rats were housed under the winter-like dim daytime light condition (lights on 600–1800 hr, 50 lux). The experimental groups received daily 1-h early morning BLT from 0600-0700 using full-spectrum light (10,000 lux), while the control groups received narrowband red light (λmax, 780 nm). Following 4 weeks of treatment, the expression of several neuroinflammatory or plasticity markers was examined in the medial prefrontal cortex (mPFC), basolateral amygdala (BLA), and the CA1 of the dorsal hippocampus.

Results

For the neuroinflammatory markers, BLT reduced TNF-α in the BLA of females, and upregulated CD11b in the mPFC and IL6 in the BLA in males. For the neuroplasticity markers, BLT downregulated BDNF in the CA1 and TrkB in all three brain regions in females but upregulated BDNF in the BLA and CA1 in males.

Conclusions

These results indicate that the therapeutic effects of BLT on sleep, mood, and cognition may be attributed in part to mechanisms involving neuroinflammation and neuroplasticity in corticolimbic brain regions. Moreover, these effects appear to vary between sexes.

Keywords:

• Amygdala
• bDNF
• CD11b
• cortex
• depression
• daylight
• hippocampus
• tNF
• α IL6
• TrkB

Author contributions

AC, JSL, and LY designed the study and wrote the manuscript. AC, KL-D, and CV conducted the experiments and analyzed data. All authors have approved the final version of the paper for submission.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data supporting the findings of this study are viewable within the article’s figures and will be made available in spreadsheet form upon request made to the corresponding author.

Additional information

Funding

This research was supported by the NIH grant R01MH111276 to JSL and LY. This content is solely the responsibility of the authors and does not necessarily represent the official views of the funding agency.