The passages given below are followed by a set of questions. Choose the most…

The passages given below are followed by a set of questions. Choose the most appropriate answer to each question.

A new US study has warned that adolescents who take performance-enhancing anabolic steroids are more likely to have adverse neural and behavioural consequences, like aggression and moodiness because of the steroids' effect on the underdeveloped brain and the nervous system. The study, by Northeast University in the US, centred around a brain chemical called serotonin which is linked to mood. Lower levels of serotonin are associated with depression and aggression. For the study, experiments were carried out on a strain of Syrian hamsters. This breed has similar neurological circuitry to humans, so experts felt it might be a good model for humans in this respect. The hamsters were given a high dose of anabolic steroids over the course of a month- which corresponds to 5 years, repeated dosage in humans. The researchers found that the hamsters were more aggressive than those not given steroids and these aggressive tendencies were mellowed if Prozac- a drug which boosts serotonin “uptake”-was given. However, subsequent analysis showed significantly lower than normal serotonin levels in the neural connections of the hamster’s brains. This suggests there may be a longer-term effect of taking steroids while the brain is still developing. Professor Richard Melloni, who helped run the study, was quoted as saying by BBC: “We know testosterone or steroids affect the development of serotonin nerve cells, which, in turn, decreases serotonin availability in the brain. The serotonin neural system is developing during adolescence and the use of anabolic steroids during this critical period appears to have immediate neural and behavioural consequences.”

The thrust area of the research mentioned in the passage was ________