14 DAY TRIAL // You cannot even remember how you got back home after a night of binge drinking, but a new study reports that had it been only one to two glasses of alcohol, your memory would have been in fact enhanced.
"There are human epidemiological data of others indicating that mild [to] moderate drinking may paradoxically improve cognition in people compared to abstention," said co-author Maggie Kalev, a research fellow in molecular medicine and pathology at the University of Auckland in New Zealand.
"This is similar to a glass of wine protecting against heart disease, however the mechanism is different."
Kalev's team was investigating the role of N-methyl-D-aspartic acid (NMDA) receptors in the neuronal activity of healthy and diseased rats (NMDA receptors are crucial to memory, as they control the strength of synapses (connections) between nerve cells) when they found that memory was boosted when one of its subunits, NR1, was strengthened in the hippocampus (a brain nucleus essential for episodic memory). When discovering this, the researchers reviewed previous tests, which had revealed a connection between alcohol intake and NR1 activation.
"We decided to study if beneficial effects of low-dose alcohol drinking already shown by others could be mediated through the mechanism of increasing NR1 expression. We thought it was worth pursuing, since ethanol drinking is such a common pattern of human behavior." said Kalev.
The team made use of two types of rats: one with an abundance of NR1 subunits in their hippocampi and one in which NR1 was inhibited. Normal rats and those with inhibited NR1 received food containing 0, 2.5 or 5 % alcohol for eight weeks.
"It is hard to relate the alcohol the rats consumed to human quantities, but based on their blood alcohol levels, the 2.5 % ethanol diet was equivalent to a level of consumption that does not exceed [the] legal driving limit. This may be approximately one to two drinks per day for some people or two to three for others, depending upon their size, metabolism or genetic background." said Kalev.
After four weeks of alcohol diet, the rats were checked for cognitive function. One test was of novel object recognition. The animals were out in a cage with two small objects inside for a two-day period. Then, one object was changed with a new toy and rats' memory was assessed by how rapidly they explored the new piece.
In a second test, the animals were taught to expect a shock when they passed from a white compartment to a black one inside the same cage; after a day, the rats were replaced in the cage to test if they were still aware of the black side.
In the case of healthy rats, the animals that ingested moderate alcohol quantities scored better on both tests compared with the abstinent ones. Those with a heavy alcohol intake did not perform well on object recognition (they even had symptoms of neurotoxicity), but they marked better than their abstinent counterparts on the emotional memory test.
"People often drink to 'drown sorrows'. Our results suggest that this could actually paradoxically promote traumatic memories and lead to further drinking, contributing to the development of alcoholism." said Kalev.
Overstimulating the NR1 subunits had the same effects as moderate drinking, whereas inhibiting the NR1 subunits eliminated the effect of low, but steady consumption.
"These findings indicate that the NMDA receptor must be intact for the positive effects of alcohol to manifest," said Kalev. The researchers presume that the NMDA receptor is first stopped by alcohol, boosting the activity of the NR1 subunit as a compensatory reaction (provoking improved cognition).