Rats are nocturnal animals and normally begin their activity slightly after darkness sets in. The rats that had been exposed to alcohol began activities slightly before darkness set in.
When normal rats – or for that matter, humans and other animals – are in situations without environmental cues about day and night, the body’s circadian clock generally drives behaviors on a cycle slightly greater than 24 hours. Untreated animals woke up approximately 20 minutes later each day in the absence of a light-dark cycle. The rats that had been exposed to alcohol consistently became active 30 minutes earlier every day.
In situations when the light-dark cycle was shifted six hours earlier, the “jet lag” equivalent for humans having to shift their body clocks when traveling across different time zones, the rats exposed to alcohol in infancy shifted much more quickly, as they did to 15-minute light pulses. While this may sound good to most traveling humans, it reflects permanent changes that have ramifications on how systems in the body function in relation to each other, says Dr. Earnest.
While the paper, quite rightfully, focuses on implications for Fetal Alcohol Syndrome, I find this study quite intriguing from a very basic biological perspective. Circadian clocks are extremelly non-responsive to chemicals.
Apart from heavy water, lithium and a couple of hormones (e.g., melatonin and estrogen), pharmacological agents (and many have been tested) just do not have any effect on the workings of the clock. Alcohol in adults has no effect.
But this study – and David Earnest is one of the top people in the field – shows large alterations in the clockwork due to DEVELOPMENTAL effects of alcohol. And the alterations are in fundamental properties of the clock: period, phase, and response to phase-shifts of the light-dark cycle. It will be very interesting to see what further research on mechanisms reveals: what is the nature of this effect on a cellular and molecular level.