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Pathological gambling (PG) has been characterized as a behavioral addiction. Dopamine (DA) has been widely implicated in substance addiction. Positron emission tomography (PET) studies show that compared to controls, subjects (Ss) addicted to alcohol, stimulants or heroin all show decreased DA-D2/D3 receptor availability in the ventral striatum, a brain region crucial for motivation and reinforcement. Although such deficits are not unique to addiction their pervasiveness in addicted Ss suggests that decreased striatal D2/D3 availability may be a hallmark of addiction. If PG is a behavioral addiction, PG Ss should also exhibit decreased striatal D2/D3 availability compared to controls. The proposed study will test this hypothesis by assessing binding of the radioligand PHNO to D2/D3 receptors using PET.
The Incentive-Sensitization Model of addiction asserts that chronic exposure to addictive drugs leads to sensitization of DA systems, as reflected by increased DA release following a standard dose of DA-releasing drug (amphetamine; AMPH). Increased DA release to AMPH in PG Ss vs. controls would be consistent with, although not confirmatory of, sensitization in PG. The proposed study will test this hypothesis by assessing displacement (decreased binding) of PHNO from D2/D3 receptors following 0.4 mg/kg AMPH.
Lower baseline D2/D3 availability correlates with increased subjective reward from a stimulant, methylphenidate in controls, and also predicts greater desire for cocaine in cocaine addicts. Researchers found that PG Ss reported greater subjective reward from AMPH than controls. PG Ss also reported greater Desire to Gamble after AMPH than placebo; controls did not. These findings indirectly support the prediction of lower baseline D2/D3 availability in PG Ss.
Cognitive tasks differentiate PG Ss from controls and operationalize processes (e.g., perseveration) by which DA dysfunction may translate into addictive symptoms. Inclusion of such tasks in the proposed study will enable us to see if DA-based differences (revealed by PET) mediate (i.e., account for) cognitive differences between PG Ss and controls.
Based on SCID and physician’s exam, healthy male PG and control Ss (24/group), matched on age and nicotine dependence will undergo two test sessions. Session 1 will assess: Working Memory, Wisconsin Card Sort, Stop-Signal, Game of Dice, Prepulse Inhibition and Lexical Salience Task performance, along with responses to a Slot Machine game and Self-Report scales (e.g., post-game Desire to Gamble). Session 2 will assess D2/D3 availability with PHNO at baseline and ~2-hr after AMPH (0.4/mg/kg) using PET. Analyses of variance will assess D2/D3 availability. Multiple regression analyses will assess relationships between cognitive task performance and D2/D3 levels. Significant predictors will be entered as covariates in follow-up variance analyses to determine if D2/D3 levels mediate group differences in task performance. Results will reveal if PG parallels substance addictions with respect to D2/D3 availability and could inform preclinical medication development for PG Ss.