A new US study has revealed that teenage mood swings may be explained by biological changes in the adolescent brain.

The research is published in the journal Nature Neuroscience.

Mood swings and anxiety, often caused by stress, are well known characteristics of puberty.

A physiologist at the State University of New York, Sheryl Smith, and her research colleagues experimented on female adolescent mice and showed that their brains respond to stress in a different way to adults and pre-pubescent individuals.

Anxiety is regulated by the brains’s principal inhibitory neurotransmitter, GABA (gamma-amino-butyric-acid) which counteracts the effect of glutamate, an excitatory neurotransmitter in the brain’s limbic system.

Stress causes the release of a steroid known as THP (allopregnanolone) which in adult and pre-pubescent individuals increases the “calming” effect of GABA in the limbic system. However, Smith and her team found that THP had the opposite effect in adolescent mice.

It would appear that THP has two roles, one in the limbic system where it helps to calm things down, and another in the hippocampus where in adolescents it hots things up. The hippocampus is important for emotion regulation.

This paradoxical role of THP, said Smith and her team, is the reason for the adolescent brain behaving differently.

The underlying mechanism appears to be different levels of expression of a type of receptor known as the “alpha4betadelta” GABAA receptor in the hippocampal brain region known as CA1.

In adults and pre-adolescents, the receptors are in low numbers so the overall effect of THP is a calming one.

However, in adolescents, the expression of these receptors is high, so for these individuals the anxiety raising effect of THP in the hippocampus outweighs the calming effect it has in the limbic system.

Smith and her team were able to reverse the puberty effect in the mice by genetically altering the number of receptors.

The net effect is that whatever the teenage person’s reaction to stress is likely to be, whether to cry or be angry, it will be “amplified”. While to adults it may seem like an overreaction, to the teenager it is the only thing they can do, said the researchers.

This study is thought to be the first to suggest an underlying physiological, as opposed to a behavioural-psychological explanation for teenage mood swings.

The researchers said that while the study opens a door to drug development to help counteract the more severe mood swings, their main hope is that it will help teachers, parents and other adults to understand why teenagers have mood swings and why they are hard to control.

“Reversal of neurosteroid effects at alpha4beta2delta GABAA receptors triggers anxiety at puberty.”
Hui Shen, Qi Hua Gong, Chiye Aoki, Maoli Yuan, Yevgeniy Ruderman, Michael Dattilo, Keith Williams and Sheryl S Smith.
Nature Neuroscience Published online: 11 March 2007; doi:10.1038/nn1868.


Written by: Catharine Paddock
Writer: Medical News Today