Expression pattern of clock under acute phase-delay of the light/dark cycle in the chicken pineal model

Effect of monochromatic light on circadian rhythmic expression of clock genes in the hypothalamus of chick

To clarify the effect of monochromatic light on circadian clock gene expression in chick hypothalamus, a total 240 newly hatched chickens were reared under blue light (BL), green light (GL), red light (RL) and white light (WL), respectively. On the post-hatched day 14, 24-h profiles of seven core clock genes (cClock, cBmal1, cBmal2, cCry1, cCry2, cPer2 and cPer3) were measured at six time points (CT 0, CT 4, CT 8, CT 12, CT 16, CT 20, circadian time). We found all these clock genes expressed with a significant rhythmicity in different light wavelength groups. Meanwhile, cClock and cBmal1 showed a high level under GL, and followed a corresponding high expression of cCry1. However, RL decreased the expression levels of these genes. Be consistent with the mRNA level, CLOCK and BMAL1 proteins also showed a high level under GL. The CLOCK-like immunoreactive neurons were observed not only in the SCN, but also in the non-SCN brain region such as the nucleus anterior medialis hypothalami, the periventricularis nucleus, the paraventricular nucleus and the median eminence. All these results are consistent with the auto-regulatory circadian feedback loop, and indicate that GL may play an important role on the circadian time generation and development in the chick hypothalamus. Our results also suggest that the circadian clock in the chick hypothalamus such as non-SCN brain region were involved in the regulation of photo information.

Role of monochromatic light on daily variation of clock gene expression in the pineal gland of chick

The avian pineal gland is a master clock that can receive external photic cues and translate them into output rhythms. To clarify whether a shift in light wavelength can influence the circadian expression in chick pineal gland, a total of 240 Arbor Acre male broilers were exposed to white light (WL), red light (RL), green light (GL) or blue light (BL). After 2weeks light illumination, circadian expressions of seven core clock genes in pineal gland and the level of melatonin in plasma were examined. The results showed after illumination with monochromatic light, 24h profiles of all clock gene mRNAs retained circadian oscillation, except that RL tended to disrupt the rhythm of cCry2. Compared to WL, BL advanced the acrophases of the negative elements (cCry1, cCry2, cPer2 and cPer3) by 0.1-1.5h and delayed those of positive elements (cClock, cBmal1 and cBmal2) by 0.2-0.8h. And, RL advanced all clock genes except cClock and cPer2 by 0.3-2.1h, while GL delayed all clock genes by 0.5-1.5h except cBmal2. Meanwhile, GL increased the amplitude and mesor of positive and reduced both parameters of negative clock genes, but RL showed the opposite pattern. Although the acrophase of plasma melatonin was advanced by both GL and RL, the melatonin level was significantly increased in GL and decreased in RL. This tendency was consistent with the variations in the positive clock gene mRNA levels under monochromatic light and contrasted with those of negative clock genes. Therefore, we speculate that GL may enhance positive clock genes expression, leading to melatonin synthesis, whereas RL may enhance negative genes expression, suppressing melatonin synthesis.

Expression of Clock genes in the pineal glands of newborn rats with hypoxic-ischemic encephalopathy

Clock genes are involved in circadian rhythm regulation, and surviving newborns with hypoxic-ischemic encephalopathy may present with sleep-wake cycle reversal. This study aimed to determine the expression of the clock genes Clock and Bmal1, in the pineal gland of rats with hypoxic-ischemic brain damage. Results showed that levels of Clock mRNA were not significantly changed within 48 hours after cerebral hypoxia and ischemia. Expression levels of CLOCK and BMAL1 protein were significantly higher after 48 hours. The levels of Bmal1 mRNA reached a peak at 36 hours, but were significantly reduced at 48 hours. Experimental findings indicate that Clock and Bmal1 genes were indeed expressed in the pineal glands of neonatal rats. At the initial stage (within 36 hours) of hypoxic-ischemic brain damage, only slight changes in the expression levels of these two genes were detected, followed by significant changes at 36–48 hours. These changes may be associated with circadian rhythm disorder induced by hypoxic-ischemic brain damage.

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.