A genetic kick up the backside?

Switching off a particular gene makes monkeys work harder, new research reveals. The study, carried out by US researchers and described as a 'tour de force' by scientists in the field, sheds light on conditions such as depression, and could eventually lead to new treatments

Monkeys, like humans, concentrate harder on a task when a reward is close at hand. But scientists found that by using gene therapy to block production of the brain chemical dopamine, they  could make monkeys work hard all of the time. The researchers, working at the National Institute of Mental Health, made this discovery by rewarding monkeys upon completion of a task.

The monkeys had to press a lever after a red dot on a screen changed to green. The task was only completed if the monkeys responded quickly, and they had to complete the task several times before being given a reward of a juice drink. As the monkeys completed the tasks, a grey bar on the screen increased in brightness, indicating how near the monkeys were to receiving the reward.

Untreated monkeys took fewer attempts to complete each task the closer they were to being rewarded, and concentrated harder as they got nearer the reward. However, monkeys with a gene switched off completed every task in a small number of attempts, which did not change with the proximity of the incentive.

The researchers switched off the gene, known as D2, using gene therapy. The gene is the blueprint for a receptor that binds to the hormone dopamine, which is known to be important in mental conditions such as depression, obsessive compulsive disorder and mania.

'People who are depressed often feel there is nothing to work for', said Dr Barry Richmond, who led the scientists. 'People with obsessive-compulsive disorder work incessantly; even when they get rewarded they feel they must repeat the task. In mania, people will work feverishly for rewards that aren't worth the trouble of most of us', he explained.

The research, published on 17 August in the journal Proceedings of the National Academy of Sciences, is the first use of gene therapy to silence genes in primates. This method of altering brain chemistry has enormous potential for neurobiological research.