Assessment of endogenous dopamine release by methylphenidate challenge using iodine-123 iodobenzamide single-photon emission tomography

This double-blind, placebo-controlled study assessed pharmacologically induced endogenous dopamine (DA) release in healthy male volunteers (n=12). Changes in endogenous DA release after injection of the psychostimulant drug methylphenidate were evaluated by single-photon emission tomography (SPET) and constant infusion of iodine-123 iodobenzamide (¹²³I]IBZM), a D₂ receptor radioligand that is sensitive to endogenous DA release. Methylphenidate induced displacement of striatal ¹²³I]IBZM binding, resulting in a significantly decrease in the specific to non-specific ¹²³I]IBZM uptake ratio (average: 8.6%) in comparison with placebo (average: –1.9%). Moreover, injection of methylphenidate induced significant behavioural responses on the following items: excitement, anxiety, tension, and mannerisms and posturing. The results of this study demonstrate the feasibility of using constant infusion of ¹²³I]IBZM and SPET imaging to measure endogenous DA release after methylphenidate challenge and to investigate neurochemical aspects of behaviour.