Researchers at University of Maryland in Baltimore have found that when newborn female rats are given a substance mimicking cannabis, their brains become more masculine - as does their behaviour.
Margaret McCarthy and colleagues also found that females had a smaller endocannabinoid system, involving brain receptors that react to cannabis, reports New Scientist.
They also injected a chemical that allowed them to see cell division in brain tissue. To find out how these changes affected rats' behaviour, the team also studied the playing habits of the pups after four weeks.
Without treatment, female rats played 30 to 40 per cent less than males. But females that were given cannabinoid compounds had cell proliferation rates and play behaviour similar to those of males.
"Play behaviour is similarly sex-specific in humans. The ultimate goal is now to find out whether the neurological underpinnings of this behaviour, which we are beginning to understand in this study, are similar in humans," said McCarthy.
Javier Fernandez Ruiz from the Complutense University in Madrid, Spain, however, that the study describes is a physiological process in the brains of rats. And since it didn't use a plant-derived cannabinoid, or higher doses to reflect the fact that mouse metabolism is quicker than humans, no conclusions can be made about the effects of conventional cannabis on human babies.
The study is published in Proceedings of the National Academy of Sciences.