Differential response of diurnal and nocturnal mammals to prolonged altered light-dark cycle: a possible role of mood associated endocrine, inflammatory and antioxidant system

ABSTRACT

The circadian system maintains internal 24 h oscillation of behavior and physiology, and its misalignment with external light-dark (LD) cycle results in negative health outcomes. In order to elucidate the effect of prolonged constant condition and the differences in the response between nocturnal and diurnal species, we studied the effects of constant light (LL) and constant darkness (DD) on a diurnal (squirrel) and a nocturnal (mouse) rodent species, focusing on the endocrine, inflammatory and antioxidant systems associated with depression-like behavior. Squirrels and mice (n = 10/group) were placed in chronocubicle under 12:12 h LD cycle, LL and DD. After 4 weeks, animals were subjected to sucrose preference test and blood and brain tissues were collected for measuring melatonin, corticosterone, proinflammatory cytokine, tumor necrosis factor-α (TNF-α) and the activity of primary antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD). The results show that in diurnal squirrels, prolonged constant darkness reduced sucrose preference, CAT, and SOD, increased corticosterone and TNF-α levels, but caused no significant change in the melatonin compared to LD condition. In contrast, in nocturnal mice constant darkness caused no significant changes in sucrose preference and corticosterone levels, increased melatonin, CAT and SOD levels but decreased TNF-α levels. Chronic LL caused a similar response in both squirrels and mice: it decreased sucrose preference, melatonin, CAT and SOD levels but increased corticosterone and TNF-α levels. Together, the study demonstrates differential effects of altered light-dark cycle in a diurnal and a nocturnal rodent on interrelated endocrine, inflammatory and antioxidant systems associated with depression-like behavior, with constant light having adverse effects on both species but constant darkness having a negative effect mainly in the diurnal squirrels.

KEYWORDS:

• Diurnal
• nocturnal
• constant light
• constant darkness
• squirrels

Acknowledgements

This research was supported by the UGC (No.6-2/2017/IC to MS) and ISF (grant No. 037261 to NK) within the UGC-ISF/ISF-UGC joint research program framework. CSIR-UGC JRF & SRF to RK (UGC Ref. No. 992/(SC) (CSIR-UGC NET DEC. 2016), CSIR JRF & SRF to VV (File No. 09/013/(0717)/2017-EMR-I) and Departmental facilities of DST-FIST, UGC-CAS and ISLS-BHU is acknowledged. We thank Mr. Punit Kumar for animal handling and their maintenance during the experiment.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

This work was supported by the Israel Science Foundation; University Grants Commission.