Neonatal Alcohol Exposure Differentially Alters Clock Gene Oscillations Within the Suprachiasmatic Nucleus, Cerebellum, and Liver of Adult Rats

Jan 25, 2008Alcoholism, clinical and experimental research

Early alcohol exposure changes daily gene rhythms differently in the brain’s clock center, movement system, and liver of adult rats

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Abstract

Neonatal alcohol exposure may alter circadian gene expression rhythms in adult rats.

In the suprachiasmatic nucleus (SCN), cerebellum, and liver, clock genes Per1, Per2, Cry1, Bmal1, and Rev-erbalpha exhibited oscillation with peak-to-trough differences of 2- to 9-fold in control groups.
Control animals showed peak expression of Per1, Per2, Cry1, and Rev-erbalpha during the subjective day, while Bmal1 peaked during the subjective night.
In alcohol-exposed rats, Cry1 expression in the SCN was significantly dampened compared to control groups.
Per2 expression in the cerebellum and liver of alcohol-treated rats was phase-advanced, peaking during the mid-subjective day.
These findings suggest that neonatal alcohol exposure may disrupt the temporal regulation of key molecular components in the circadian clock.

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BACKGROUND: In rats, alcohol exposure during the period of rapid brain growth produces long-term changes in the free-running period, photoentrainment and phase-shifting responses of the circadian rhythm in wheel-running behavior. To determine whether these alterations in circadian behavior are associated with permanent damage to the circadian timekeeping mechanism or reconfiguration of its molecular components, we examined the long-term effects of neonatal alcohol exposure on clock gene rhythms in the pacemaker located in the suprachiasmatic nucleus (SCN) and in other brain or peripheral tissues of adult rats.

METHODS: Artificially reared male rat pups were exposed to alcohol (4.5 g/kg/d) or isocaloric milk formula (gastrostomy control; GC) on postnatal days 4 to 9. At 3 months of age, animals were exposed to constant darkness and then SCN, cerebellum, and liver tissue were harvested at 6-hour intervals for subsequent analysis of Period1 (Per1), Per2, Cryptochrome1 (Cry1), Bmal1, and Rev-erbalpha mRNA levels by quantitative PCR.

RESULTS: In the SCN, cerebellum and liver, Per1, Per2, Cry1, Bmal1, and Rev-erbalpha expression oscillated with a similar amplitude (peak-to-trough differences of 2- to 9-fold) and phase in the suckle control (SC) and GC groups. These clock gene rhythms in control animals were marked by peak expression of Per1, Per2, Cry1, and Rev-erbalpha during the subjective day and of Bmal1 during the subjective night. The EtOH group was distinguished by altered rhythms in the expression of specific clock genes within the SCN, cerebellum and liver. In EtOH-treated rats, the SCN rhythm in Cry1 expression was strongly damped and the Per2 rhythms in the cerebellum and liver were phase-advanced such that peak expression occurred during the mid-subjective day.

CONCLUSIONS: These results demonstrate alcohol exposure during the brain growth spurt alters the circadian regulation of some molecular components of the clock mechanism in the rat SCN, cerebellum, and liver. The observed alterations in the temporal configuration of essential "gears" of the molecular clockworks may play a role in the long-term effects of neonatal alcohol exposure on the regulation of circadian behavior.

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Neonatal Alcohol Exposure Differentially Alters Clock Gene Oscillations Within the Suprachiasmatic Nucleus, Cerebellum, and Liver of Adult Rats

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