Are the monoamines involved in shaping conduct ...( Antisocial and aggressive behaviours...)

Antisocial and aggressive behaviours represent a widespread and expensive social problem. Recent research has convincingly shown that there is a strong interaction between genetic inheritance and environment for development of personality and behaviour. It appears to be common knowledge that childhood maltreatment often causes psychiatric problems (e.g. depression or anxiety) or behavioural problems (e.g. aggression or antisocial behaviour) later in life. The risk for such a development is, however, different between individuals and can to a large extent be explained by genetic factors. The identification of neural mechanisms underlying human personality and temperament seems to be promising due to their considerable importance as highly heritable risk mediators for aggressive behaviour, criminal activity, as well as somatic and psychiatric disorders (Buckholtz et al., 2008; Buckholtz & Meyer-Lindenberg, 2008; Nilsson et al., 2006).

MAOs: key molecules for personality and behaviour

Monoamine oxidases (MAOs) are two enzymes (MAO-A and MAO-B) which inactivate the so called monoamine transmitter substances serotonin, noradrenalin and dopamine. The brain systems which utilise those transmitters are of great importance for the fine-tuning of personality traits, as well as state-dependent features such as mood, appetite, attention, etc. MAOs are present in almost all cells in the body, however, naturally, it is the activities of MAOs in the brain that are of major interest in relation to personality and behaviour.

In association with a complete lack of MAO-A, as in mice in which the MAO-A gene has been knocked out, and in a Dutch family with a dysfunction of this gene, aggressiveness has been reported (Brunner, 1996). In the Dutch family aggressiveness was also combined with arson and cases of rape indicating a lack of impulse control. Extensive search for more families with this abnormality has, however, been negative.

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