A severely stressful episode can kill off new nerve cells in the brain and may ultimately lead to depression, research suggests.

Scientists from Rosalind Franklin University have discovered that considerable stress can reduce the chances of cells surviving in the hippocampus part of the brain. The hippocampus is associated with learning, memory and emotion and a loss of cells in this part of the brain could have a devastating impact.

The tests, conducted on rats, initially revealed that bullied rodents are able to generate new nerve cells in the hippocampus. These cells are unlikely to survive, however, leaving the animals with fewer neurons to process emotions.

To arrive at their conclusions, scientists placed a young rat in a cage with two older rats for 20 minutes. The older rats predictably bullied the younger creature, causing its stress hormone levels to soar six times higher than normal.

Analysis of the rat's brain tissue revealed that, contrary to previous theories, stress does not hamper the ability to generate new cells in the hippocampus. After a week, however, only a third of the new cells had managed to survive, which may open up new avenues for the prevention and treatment of depression.

"If we can keep these new nerve cells alive, we might be able to forestall or prevent the types of depressive symptoms that might normally occur," Daniel Peterson, a researcher at the university, told Reuters.

Interestingly, the scientists believe that the cells typically die 24 hours after the stressful incident occurs. This may indicate that there is an opportunity to salvage the cells in this intervening period, if the correct technologies or therapies are discovered.

While bullying is the most immediately obvious source of severe stress, similar symptoms also arise in the workplace because of impossible workloads and pressure to meet deadlines or targets. Psychologist Saqib Saddiq investigated the stresses associated with a number of professions in 2006 and concluded that librarians suffer more stress than police officers, firefighters and teachers.

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