Circadian responses to non-photic treatments in BTBR mice

The BTBR T+ Itpr3tf/J mouse (BTBR) differs from C57BL/6 mice in various circadian parameters, including freerunning period (FRP), circadian responses to light, and prominent circadian responses to scheduled feeding. The circadian system is also sensitive to a host of non-photic cues, which can modify and reset freerunning rhythms as well as modulate responses to other zeitgebers such as light. Here we examine how the BTBR mouse responds to various non-photic treatments. Because activity levels can modulate the FRP, we first examined if the shorter FRP of BTBR mice resulted from their higher activity levels. While overall activity was lower when housed without a running wheel, this did not significantly alter their FRP. When housed in constant light, exposure to a 6 h dark pulse improved the quality of the locomotor rhythms for both BTBR and C57 mice. BTBR mice had significantly smaller phase shifts to midday treatments with either a 3 h sleep deprivation procedure or an injection of the serotonin 1A/7 receptor agonist (±) 8-OH-DPAT than did the comparison C57BL/6J strain. However, BTBR mice did exhibit larger responses to midday refeeding pulses following 18 h food deprivation. Their unique circadian phenotype, particularly their short FRP, makes them a useful model for examining circadian responses in mice.