For crayfish at least, a more sociable life makes booze work quicker. When crayfish were put in water containing a little alcohol, the ones who had been kept on their own over the preceding week took longer to show signs of alcohol exposure – such as tail flips – than those who had been living with others of their kind.
The researchers then implanted tiny electrodes in the neurons that drive the tail-flip behaviour. They found that in crayfish exposed to alcohol, the intensity of the electrical signal needed to trigger a tail flip was lower – and it dropped further and more quickly in the animals that had had company than in the isolated ones.
“This clearly shows a socially induced change in their reaction to alcohol,” says neuroscientist Jens Herberholz at the University of Maryland in College Park.
His team chose to study crayfish because it has long been known that their social status affects their behaviour, and also because exposing the animals to alcohol has obvious effects. At first they stand tall on fully extended legs in an aggressive pose, then start to tail flip and finally end up on their back unable to right themselves.
So why is this response affected by being solitary or in company? It seems the social environment affects the receptors on nerve cells that respond to neurotransmitters like serotonin, which in turn changes how alcohol affects nerves.
The next step is to figure out what is changing on the cellular and molecular level when the animals are kept isolated, Herberholz says. “Do the receptors change on this neuron when the crayfish are with their buddies or by themselves? What types of receptors change?”
He speculates that a similar mechanism could be at work in humans: people who are socially isolated may have to drink more alcohol to achieve the same level of intoxication.
A link between social isolation and an animal’s response to alcohol has been noted in several species of mammal, says Boris Tabakoff, a behavioural geneticist at the University of Colorado in Denver. But this study goes further by linking the altered response to changes in specific neurons, he says.