ASSESSMENT OF ENDOGENOUS DOPAMINE RELEASE BY METHYLPHENIDATE CHALLENGE USING I-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 psych ostimulant drug methylphenidate were evaluated by single-photon emissi on tomography (SPET) and constant infusion of iodine-123 iodobenzamide ([I-123]IBZM), a D-2 receptor radioligand that is sensitive to endoge nous DA release. Methylphenidate induced displacement of striatal [I-1 23]IBZM binding, resulting in a significantly decrease in the specific to non-specific [I-123]IBZM uptake ratio (average: 8.6%) in compariso n with placebo (average: -1.9%). Moreover, injection of methylphenidat e induced significant behavioural responses on the following items: ex citement, anxiety, tension, and mannerisms and posturing. The results of this study demonstrate the feasibility of using constant infusion o f [I-123]IBZM and SPET imaging to measure endogenous DA release after methylphenidate challenge and to investigate neurochemical aspects of behaviour.