Genetic Effects on Dopamine Response to an Opiate

Study Summary

Background: \- Small differences in genes may alter responses to drugs. One gene that has different forms is the mu opioid receptor gene. People with one form of this gene are more sensitive to alcohol. People with a different form are sometimes more sensitive to pain. Morphine and other prescription pain pills produce pain relief by acting at the mu opioid receptor. Researchers want to see the effect of morphine on brain reward and subjective effects. Morphine is a strong but short-acting pain medication that is sometimes used for anesthesia during surgery. Objectives: \- To compare the effect of morphine on brain measures of dopamine release using imaging. Eligibility: \- Individuals between 21 and 55 years of age who have previously taken pain pills prescribed to treat pain from a medical or dental procedure. Design: * This study has a screening phase and a study phase. The screening phase involves one or two visits of 5 to 6 hours. The study phase consists of 4 study visits. Each study visit will take about 8 hours. * Participants will be screened with a medical and psychiatric history and physical exam. They will be asked about drinking and drug-taking history, and any family history of alcoholism or drug abuse. Blood, urine, and breath samples will be collected. * During the first study visit, an MRI scan may be performed, questionnaires completed, and a blood sample collected for genetic testing. * During study visit 2, participants will test their pain sensitivity by placing one hand in cold water. Pupil diameter will be measured after the sensitivity test. After a blood sample is taken, participants will receive the morphine or a salt solution. The sensitivity test and pupil diameter test will be repeated. Final blood samples will be collected. A brief physical exam will also be performed. * During study visits 3 and 4, participants will receive morphine or a salt solution during a PET scan. Questionnaires to assess subjective effects will be adminis

Primary Outcome

Binding potential measured using regions-of-interest analysis of PET data. Parametric Binding Potential (BPND) images were obtained using the Simple Reference Tissue Model 2 (SRTM2), with cerebellum as the reference region. BPND is computed in units of mCi/ml reflecting the radioactivity (milliCuries or mCi) per unit volume (milliliters or ml) in specific brain regions. Reduction in raclopride binding is attributed to competition with endogenous dopamine, and has been shown to be proportional to

Interventions

• DRUG Placebo
• DRUG Morphine