Brain Glutamate Receptors and Cocaine Dependence

Objective: Cocaine addiction continues to be an important public health problem with over 1.7 million users in the US alone. Cocaine addiction is characterized by compulsive drug use despite adverse consequences and high rates of relapse during periods of abstinence. Cocaine addiction may be mediated by neuroadaptations in reward-related learning and memory processes in the mesocorticolimbic dopamine system and glutamatergic corticolimbic circuitry. Metabotropic glutamate subtype 5 receptors (mGluR5) likely play essential roles in mediating some of the actions of drugs of abuse. Animal studies have shown that mGluR5 knock-out or blockade reduces self-administration of cocaine and cocaine-induced hyper-locomotion. However, to what extent mGluR5 are involved in the pathophysiology of cocaine addiction in humans is currently unknown, partly due to the lack of suitable methods to reliably quantify mGluR5 in the living human brain. This protocol aims to determine whether the density of mGluR5 in brain is altered in participants with cocaine addiction compared to healthy controls using positron emission tomography (PET) and the recently developed radiotracer for mGluR5, \[18F\]SP203. We also aim to determine whether this density is related to genotype, history of cocaine use, and/or craving for cocaine. Study Population: The study populations will consist of healthy adults with no history of substance abuse and a matched group of healthy current primary cocaine dependent male and female participants (20-55 years old.; N=40/group). Design: Density of mGluR5 will be measured in cocaine dependent participants and healthy adults volunteers with PET and (18(F)SP203, a radioligand with specificity for mGluR5. All participants will undergo genotyping to identify normal or variant mGluR5 gene associated with drug abuse. The intensity of craving for cocaine will be assessed while watching a video about cocaine use. Outcome measures: Density of mGluR5 will be compared between cocaine dependent participants and healthy controls. In addition, correlation among the genetic polymorphism, the craving response, and the density of mGluR5 will be determined.