Abstract
The aim of this study was to analyse the circadian behavioural responses of mice carrying a functional knockout of the Per3 gene
(𝑃𝑒𝑟3−/−) to different light : dark (L : D) cycles. Male adult wild-type (WT) and 𝑃𝑒𝑟3−/− mice were kept under 12-hour light : 12-
hour dark conditions (12L : 12D) and then transferred to either a short or long photoperiod and subsequently released into total
darkness. All mice were exposed to both conditions, and behavioural activity data were acquired through running wheel activity and
analysed for circadian characteristics during these conditions. We observed that, during the transition from 12L : 12D to 16L : 8D,
𝑃𝑒𝑟3−/− mice take approximately one additional day to synchronise to the new L : D cycle compared to WT mice. Under these long
photoperiod conditions, 𝑃𝑒𝑟3−/− mice were more active in the light phase. Our results suggest that 𝑃𝑒𝑟3−/− mice are less sensitive
to light. The data presented here provides further evidence that Per3 is involved in the suppression of behavioural activity in direct
response to light.