Abstract
Decrease in natural illumination in fall/winter months causes depressive-like seasonal affective disorders in vulnerable individuals. Obesity is another risk factor of depression. The lethal yellow (AY) mutation causes ectopic expression of agouti protein in the brain. Mice heterozygous for AY mutation (AY/a) are obese compared to their wild-type littermates (a/a). The main aims of the study were to investigate the effects of AY mutation, photoperiod and the interaction between these factors on daily activity dynamics, feeding, locomotor and exploratory activities, anxiety-related and depressive-like behaviors in mild stress condition. Six weeks old mouse males of AY/a and a/a lines were divided into four groups eight animals each and exposed to long- (14 h light and 10 h darkness) or short- (4 h light and 20 h darkness) day conditions for 28 days. Then the behavior of these mice was successively investigated in the home cage, open field, elevated plus-maze and forced swim tests. We did not observed any effect of AY mutation on the general activity, water and food consumption in the home cage; locomotion and exploration in the open field test; anxiety-related behavior in the open field and elevated plus-maze tests. At the same time, AY mutation increased depressive-like immobility time in the forced swim test (F1.28 = 20.03, p = 0.00012). Shortday conditions decreased nocturnal activity in the home cage, as well as locomotion (F1.28 = 16.33, p = 0.0004) and exploration (F1.28 = 16.24, p < 0.0004) in the open field test. Moreover, short-day exposition decreased time spent in the center of the open field (F1.28 = 6.57, p = 0.016) and in the open arms of the elevated plus-maze (F1.28 = 12.08, p = 0.0017) tests and increased immobility time in the forced swim test (F1.28 = 9.95, p = 0.0038). However, no effect of the interaction between AY mutation and photoperiod on immobility time in the forced swim test was observed. Therefore, short-day photoperiod and AY mutation increased depressive-like behavior in the forced swim test by means of different mechanisms.
Highlights
Seasonal alterations of natural illumination in high or moderate latitudes trigger numerous adaptive changes in the nervous system and behavior of all wild animals
The effects of “photoperiod” × “day time” inter action on the daily dynamics of locomotion (F23.552 = 3.42, p < 0.00001) and sleep duration (F23.552 = 6.65, p < 0.00001) were observed. This indicates an influence of photoperiod on the daily dynamics of mouse activity
Mice exposed to long-day conditions were more active (199.54 ± 36.27 m/h in darkness vs 96.69 ± 21.01 m/h in light, p = 0.000018) in the dark-time period, while activity mice exposed to short-day conditions did not differ in the dark- and light-time periods (81.98 ± 36.27 m/h in darkness vs 33.89 ± 21.01 m/h in light, n. s.) (Fig. 1, a)
Summary
Seasonal alterations of natural illumination in high or moderate latitudes trigger numerous adaptive changes in the nervous system and behavior of all wild animals. Humans mainly live at constant illumination, its decrease during fall/ winter months can cause seasonal affective disorders (SAD) or subsyndromal SAD characterized by carbohydrate crav ing, overeating, weight gain, decreased libido, hypersomnia and prominent fatigue (Levitan, 2007) in some vulnerable individuals. Mice lacking leptin receptor are obese and show depressive-like features (Sharma et al, 2010). Another model of hereditary obesity is AY/a mice, heterozygous for lethal yellow (AY ) mutation (Boston et al, 1997; Bazhan et al, 2013)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.