Behavioral and genetic dissection of a XXXX model for @entity1442 .

@entity1 @entity19 @entity1442 @entity53837 @entity36992
STUDY OBJECTIVE: The adaptive value of the endogenous circadian clock arises from its ability to synchronize (i.e., entrain) to external light-dark (LD) cycles at an appropriate phase. Studies have suggested that advanced circadian phase alignment might result from shortening of the period length of the clock. Here we explore mechanisms that contribute to an early activity phase in @entity36992 ( @entity36992 ) @entity19 . METHODS: We investigated circadian rhythms of wheel-running activity in C57BL/6J (B6), @entity36992 and 2 strains of B6. @entity36992 congenic @entity19 , which carry @entity36992 segments introgressed in a B6 genome. RESULTS: When entrained, all @entity36992 @entity19 initiate daily activity several hours earlier than normal @entity19 . This difference could not be explained by alterations in the endogenous period, as activity onset did not correlate with period length. However, the photic phase-shifting responses in these @entity19 were phase-lagged by 3 hours relative to their activity. Attenuated light masking responses were also found in @entity36992 @entity19 , which allow for activity normally inhibited by light. A previously identified quantitative trait locus (QTL), @entity53837 , which contributes to the early activity trait, was confirmed and refined here using two B6. @entity36992 congenic strains. Surprisingly, these B6. @entity36992 @entity19 exhibited longer rather than shorter endogenous periods, further demonstrating that the advanced phase in these @entity19 is not due to alterations in period. CONCLUSIONS: @entity36992 @entity19 have an advanced activity phase similar to @entity1 @entity1442 . This advanced phase is not due to its shorter period length or smaller light-induced phase shifts, but appears to be related to both light masking and altered coupling of the circadian pacemaker with various outputs. Lastly, a QTL influencing this trait was confirmed and narrowed using congenic @entity19 as a first step toward gene identification.
