Gastric vagal afferents (GVAs) play an important role in the regulation of food intake . GVAs exhibit circadian rhythmicity in response to mechanical stimuli allowing time of day specific satiety signalling . Disruption of the circadian clock is associated with increased risk of obesity . We aimed to investigate the effect of disrupting the light cycle on GVA satiety signalling in health and high fat diet (HFD)-induced obesity.
C57BL/6 male mice (8wks old) were fed a standard mouse chow (SLD; 14% energy from fat) or HFD (60% energy from fat) ad libitum for 12 weeks. After 4 weeks on the respective diets they were placed into 2 groups/diet: 1) maintained in a normal light cycle environment (NL-mice; lights on 0600 to 1800); and 2) exposed to a rotating light cycle (RL-mice; 3 days lights on 0600 to 1800; 4 days lights on 1800 to 0600) for 8wks. In vitro GVA recordings  were taken at 3 hour intervals starting at 1800.
The HFD-mice gained significantly more weight than SLD-mice and the HFD/RL mice gained significantly more weight than the HFD/NL mice (SLD/NL-mice: 8.19±0.2g; SLD/RL-mice: 9.01±0.2g; HFD/NL-mice: 20.63.±0.6g; HFD/RL-mice: 22.49±0.6g). SLD/NL-mice exhibited circadian oscillations in GVA mechanosensitivity with peaks at 1200 and troughs at 0000hr. Consistent with these results, food intake was greater during the dark phase (2.59±0.1g) compared to the light phase (0.53±0.1g: P<0.001) in SLD/NL-mice. Circadian rhythmicity in GVA mechanosensitivity and food intake was lost in SLD-RL, HFD-RL and HFD-NL-mice.
In conclusion, rotating the light cycle and/or HFD feeding abrogates circadian rhythmicity of GVA satiety signalling and alters feeding behaviour.
Supported by NH&MRC (APP1046289)