Imaging endogenous dopamine competition with [11C]raclopride in the human brain.

This study images dopamine release in response to a neurochemically specific challenge with the psychostimulant drug methylphenidate. Changes in synaptic dopamine induced by methylphenidate were evaluated with positron emission tomography and [11C]raclopride, a D2 receptor radioligand that is sensitive to endogenous dopamine. Methylphenidate significantly decreased striatal [11C]raclopride binding. The decrease was variable and was negatively correlated with age. Mood and anxiety at baseline, were also correlated with methylphenidate-induced DA changes. This strategy provides a tool to investigate the responsiveness of the dopamine system in the normal and diseased human brain and to investigate the neurochemical correlates of behavior.