The embryonic pineal gland of the chicken as a model for experimental jet lag.

The circadian clock in the chicken pineal model develops before hatching, at around the 17th embryonic day (ED17). By this stage, it runs in synchrony with environmental cues. To address if phase resetting mechanisms are comparable to those of post-hatched chicken, we investigated ED19 stage chicken embryos under 12h light:12h dark (LD), under constant darkness (DD), or under acute 4h phase delay of the LD condition (LD+4). The 24h mRNA-expression patterns of clock gene clock and of clock controlled genes Aanat and hiomt were analyzed with qRT-PCR. Under DD the rhythm of Aanat did not change significantly, however the 24h pattern of hiomt was altered. Clock shows a delayed response to DD with a phase-shift in its rhythm. After the first cycle under LD+4 conditions, the 24h patterns of Aa-nat and hiomt mRNA-s were phase delayed. Clock showed both acute and delayed changes in response to LD+4. These results show that the embryonic chicken pineal gland has a fully functioning clock mechanism, and that it is a good model for phase-change experiments. In addition it demonstrates that only one cycle of altered light schedule is sufficient to trigger changes within the molecular clock mechanisms of the chicken embryonic pineal model.