Why things we fear become a phobia

Ever wonder just why some people get anxious, or really scared when faced with situations that may not turn out to be dangerous? Well boffins at the European Molecular Biology Laboratory (EMBL) in Italy have unearthed a clue to this question in a new research they conducted on mice.

London, June 4 : Ever wonder just why some people get anxious, or really scared when faced with situations that may not turn out to be dangerous? Well boffins at the European Molecular Biology Laboratory (EMBL) in Italy have unearthed a clue to this question in a new research they conducted on mice.

They have identified a neural circuit that makes mice perceive situations that could be potentially dangerous but not necessarily so, as threatening.

The researchers found that mice, in which a particular receptor for the neurotransmitter serotonin, called 5-Htr1a, was removed, found perceived potentially dangerous situations as big a threat as dangerous ones.

They noted that mice in which the receptor had been removed could not evaluate the true threat of an ambiguous situation, revealed lead researcher, behavioural geneticist Cornelius Gross.

"Mice need this receptor during development. If it is not there during this crucial period, their brains don't get wired up properly, and this affects their relationship with anxiety later in life," Nature quoted him, as saying.

The researchers then reversed the effect by shutting down a particular circuit in the hippocampus, a part of the brain that processes memories, and found that once this was done, the mice responded normally to ambiguous threats.

The boffins shut down the neural circuit using a drug that blocks firing only in neurons called dentate gyrus granule cells, which form part of one of the hippocampus's major neural circuits.

The results show that, as well as memory, the hippocampus assesses risk.

"Shutting down a specific circuit in the hippocampus abolished fear reactions only to ambiguous cues. The pathway must be involved in processing and assessing the value of stimuli. It seems to bias mice to interpret situations as threatening," said Theodoros Tsetsenis who carried out the research in Gross' lab.

Gross said that as the brain's processing of basic, essential emotions such as fear is usually conserved between species, it was very likely that the lack of the receptor in the brain could be the reason why some humans are jumpier than others.

"The human brain is probably wired to evaluate potentially threatening situations in the same way as the mouse," he says.

The research is published in the current issue of Nature Neuroscience.

ANI