Platelet MAO and personality--function and dysfunction.

Research on the association between platelet monoamine oxidase (MAO) activity and personality traits, such as sensation seeking and impulsiveness, is reviewed with an emphasis on early history and current situation. The effects of MAO-inhibiting compounds in cigarette smoke for the interpretation of this association are discussed and recent results confirming a true association between platelet MAO activity and personality and vulnerability, for e.g. type 2 alcoholism are presented. From a clinical point of view, the link between platelet MAO activity, which is highly genetically regulated and is stable in the individual, and personality traits, has had its greatest impact on the understanding of the nature of constitutional factors making individuals vulnerable, for e.g. substance abuse and other forms of sociopathic behaviour. The molecular mechanisms underlying the association between platelet MAO and behaviour are discussed and evidence that common transcriptional factors, e.g. within the AP-2 family, regulating both the expression of platelet MAO and components of the central monoaminergic systems, such as synthesising enzymes, receptors and transporters, are presented. A hypothesis is put forward, that such common transcription factors may not directly regulate platelet MAO expression, but rather mitochondrial density, or outer mitochondrial membrane surface.

Smoking only explains part of the associations between platelet monoamine oxidase activity and personality.

Platelet monoamine oxidase (MAO) activity has been shown to be inversely associated with personality traits such as sensation seeking, impulsiveness and extraversion. Those personality traits have also been linked to vulnerability for substance abuse, e.g. tobacco smoking and early onset or "type 2" alcoholism. Compounds in cigarette smoke have been shown to be inhibitors of MAO, which has led several authors to claim that there is no association between alcoholism, which is the most studied psychiatric condition, and platelet MAO if the effect of smoking is removed. With regard to the association between personality and platelet MAO, authors have in general been cautious. In the present paper we describe a number of results which show that there is such an association, both in clinical series if the effect of smoking is removed and in series where smoking have never taken place. A cornerstone in this regard is the significant association between platelet MAO activity and both behaviour/personality, voluntary alcohol intake and biochemical measures of CNS serotonergic activity in non-human primates. Strong evidence that the regulation of platelet MAO activity takes place on a transcriptional level with an involvement of transcription factors, likely to also regulate central monoaminergic activity, are presented.