Test-retest Reproducibility of [11C]PHNO PET Using the Constant Infusion Paradigm

Inclusion Criteria: * men and women, aged 18-55 years * who are able to read and write * who are able to give voluntary written informed consent * have no current uncontrolled medical condition such as neurological, cardiovascular, endocrine, renal, liver, or thyroid pathology * have no history of a neurological or psychiatric disorder, e.g., no DSMIV Axis 1 diagnosis in 2 preceding years, except nicotine dependence in smokers) * drink less than 21 drinks/week for women and less than 35 drinks per week for men * have not used marijuana in the past 30 days and have not met criteria for dependence in the past 2 years * do not suffer from claustrophobia or any MRI contradictions * nonsmokers (smoked \< 40 cigarettes in lifetime with urinary cotinine levels 0-30 ng/mL both at intake evaluation and on scan day) * smokers (smoked at least 10 cigarettes/day for at least one year with an FTND\>3, urine cotinine \>150 ng/mL and CO \>12 ppm at intake) Exclusion Criteria: * psychosis * presence of acute or unstable medical or neurological illness. Subjects will be excluded from the study if they present with any history of serious medical or neurological illness or if they show signs of a major medical or neurological illness on examination or lab testing including history of seizures, head injury, brain tumor, heart, liver or kidney disease, eating disorder, diabetes. * regular use of any psychotropic drugs including anxiolytics and antidepressants and other over-the-counter medicat…