The neurotransmitter dopamine has been implicated in impulsivity, reward, addiction, and motivation. In the recent paper “Dopaminergic Network Differences in Human Impulsivity” published July 30, 2010 in Science a research team asks if highly impulsive individuals have less midbrain dopamine autoreceptors than those with typical impulse personality traits.
Autoreceptors play an important role in regulating the amount of neurotransmitter that stays in the synapse and for how long. Dopamine autoreceptors clear the synaptic cleft of dopamine neurotransmitter. The research team hypothesized that highly impulsive individuals have less midbrain autoreceptors available for the reuptake of the dopamine neurotransmitter. This would lead to more dopamine initiated spikes (action potentials) following exposure to novel, salient, or rewarding stimuli.
To test their model, the team performed positron emission tomography scans on 32 physically and psychiatrically healthy volunteers using a dopamine receptor (D2 and D3) specific label. Each participant was evaluated for impulse personality traits using the Barratt Impulsiveness Scale. The relative amount of available D2 and D3 dopamine receptors in the striatum was assessed in each volunteer. They also looked at the amount of drug induced dopamine released into the striatum.
They found that individuals displaying more impulsivity traits showed lower amounts of available dopamine autoreceptors in two areas of their brain that send dopamine terminals to the striatum ( specifically the ventral tegmental area and substantia nigra). They also found that individuals displaying more impulsivity traits showed higher amounts of drug induced release of dopamine into the striatum. They went one step further and asked each research subject if they wanted more of the drug that was used to induce the release of dopamine. Individuals with more impulsivity were more likely to want more of the drug.
The results link less midbrain dopamine autoreceptors with more impulsivity and suggest a link between human impulsivity and vulnerability to drug abuse.
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