Dopamine Responsivity in Gamblers
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About
This study deals with how people decide between rewards of different value. The investigators want to understand how the brain's dopamine system impacts this kind of decision making. The investigators will use a medication, tolcapone, which can temporarily affect the dopamine system.
Full description
Tolcapone increases the effects of dopamine in the brain. Dopamine is a substance that is normally present in the brain. It may increase body movement and may also change a person's ability to process information. Tolcapone stops one's own naturally-released dopamine from being broken down as quickly. The investigators are interested in learning if tolcapone has positive effects on a person's decisions about rewards.
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Inclusion and exclusion criteria
Inclusion Criteria: This behavioral and fMRI study will recruit alcohol drinkers who also participate in gambling activities. Subjects will be selected in an unbiased fashion with respect to gender and ethnicity, as minority representation issues do not interact with any of the hypotheses. To be eligible to participate in the study, the following inclusion criteria must also be met:
- Subject is a healthy volunteer between 18-50 years of age.
- Subject is right handed (important for interpreting MRI activity).
- If female, subject is non-lactating, not pregnant and using a reliable contraception method (i.e. abstinence, intrauterine device, hormonal birth control or barrier method).
- Subject is able to read and speak English.
- Subject is a high school graduate.
- Subject is able and willing to provide written informed consent.
- Subject is able to understand and follow the instructions of the investigator, and understand all ratings scales.
- Subject is in good health.
Exclusion Criteria:
• In order to assess potential contraindications to tolcapone, blood will be tested for routine chemistries including white cell count, red cell count, platelet count, hemoglobin, hematocrit, MCV, MCH, MCHC, RDW, neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Additionally, a hepatic screen will assay total protein, albumin, globulin, A/G ratio, bilirubin (total, direct, and indirect), alkaline phosphatase, AST (SGOT), and ALT (SGPT). Elevation of plasma bilirubin, AST (SGOT), ALT (SGPT), or alkaline phosphatase consistent with liver disease will be grounds for subject exclusion. (Note that ongoing monitoring of liver enzymes will not be necessary, as only a single, counterbalanced dose of tolcapone will be administered to each subject.) Subjects will additionally be urine-screened for illicit drug use and screened for alcohol intoxication via breathalyzer. The 7 drug classes detected include cocaine, amphetamine, methamphetamine, benzodiazepines, THC, opiates & oxycodone. These drugs have been chosen due to their possible interaction with tolcapone and possible cognitive and cardiovascular effects. No identifiers will be put on the test cup and it will be read immediately and discarded by the researcher. Similarly, the results of the breathalyzer will be read and then the test will be discarded. No personal identifiers will be associated with the test results. Subjects who test positive for any of these substances, with the exception of THC, will be excluded from further participation in the study. Subjects who have used any psychoactive drugs (except marijuana) within 2 weeks of the start of the study or more than 10 times in the last year will be excluded from participation in the study.
Subjects will also be excluded if they regularly use medications that affect dopamine levels, or will have used these medications within two weeks of tolcapone administration (such as tolcapone, entacapone, or any of the following: levodopa/carbidopa, amantadine, bromocriptine, pergolide, pramipexole, ropinirole, selegeline, isocarboxazid, phenelzine, tranylcypromine, clozapine, olanzapine, quetiapine, risperidone, ziprasidone, aripiprazole, fluphenazine, haloperidol, perphenazine, pimozide, thiothixene, trifluoperazine, loxapine, molindone, chlorpromazine, mesoridazine, thioridazine, dextroamphetamine, dexmethylphenidate, dextroamphetamine, or methylphenidate).
A licensed health care provider will also conduct a brief physical exam. This exam will search for signs of medical illness, including jaundice or abdominal distension associated with liver disease, that would exclude subjects from participating in the study. Subjects with clinically significant medical or psychiatric illnesses requiring treatment as determined by screening blood tests, medical history, and/or physical exam will not be eligible to participate in the study.
Female subjects will also be screened for pregnancy, as the effects of COMT inhibitors during pregnancy are not adequately known and these compounds can appear in breast milk. (Pregnancy is also a contraindication to MRI scanning). Since subjects may not know they are pregnant, all female subjects recruited to participate in the study will be required to have a urine pregnancy test prior to each session of the study. These requirements will not apply to any female subjects who are post-menopausal.
Active use of substances other than alcohol, tobacco, or marijuana, use of alcohol on the day of the meeting as assessed by breathalyzer testing, reported marijuana use in the 48 hours preceding a testing visit, and/or a positive pregnancy test, will be grounds for exclusion.
For subjects participating in the fMRI, we will administer an extensive questionnaire listing contraindications to MRI scanning. Because the MRI scanner attracts certain metals, subjects who may have metallic objects in their bodies will be excluded. As an additional measure of protection, we will use a hand-held metal detector to screen subjects before entering the scanner. Subjects who experience claustrophobia will also be excluded from participating in the MRI scan.
Known allergy or intolerance to tolcapone or use of an investigational drug within 30 days of the screening visit will be grounds for exclusion.
Trial design
Primary purpose
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Interventional model
Masking
19 participants in 2 patient groups, including a placebo group
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Data sourced from clinicaltrials.gov
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