Acetylcholine, Tobacco Smoking, Genes and Nicotinic Receptors

* Magnetic resonance image. Within approximately two weeks of the PET study, anatomical MRIs will be acquired at the Yale University MRI Center. Subjects will be taken through a ferromagnetic metal detector before entering the scan room. The purpose of the MRI scan is to direct the region of interest placement on the lower resolution PET images. The T1 weighted images will be acquired on a 3 Tesla Siemens Scanner. There will also be an additional resting state scan with subjects in the scanner, eyes open, fixating on a cross. * Physostigmine challenge Physostigmine will be administered as follows. Glycopyrrolate, a cholinergic antagonist that does not have central side-effects, will be administered prior to physostigmine challenge to block physostigmine peripheral side-effects (e.g. nausea). Subjects will receive 200 mcg /ml x 1 ml of glycopyrrolate through an IV. Physostigmine administered i.v. has a short half life of 20 min with peak plasma levels 20-30 min post administration. The same dose of physostigmine will be administered as in the preliminary data: 1.5 mg/hr for 1 hr. Vital signs, including systolic and diastolic blood pressure, heart rate and respiration rate, will be monitored before physostigmine and then at 10, 20, 30, 60 min after the beginning of the infusion and then hourly until the end of the study day. Subjects will be questioned before, during, and after physostigmine challenge about potential adverse reactions typical to this medication (nausea, upset stomach, etc., as in Risks section). \[If there is a significant and persistent drop in subjects' heart rate (\>15% for at least 1 min), the IV physostigmine infusion will be stopped but the subject will continue to be monitored and will be discharged at the discretion of the study doctor. In emergency situation, PET center protocol will be followed accordingly (on file with HIC). * Amphetamine challenge On PHNO PET days, subjects will have a baseline PHNO scan and then will receive amphetamine by mouth (0.5mg/kg). Approximately 2.5 hours after amphetamine administration, subjects will be scanned with PHNO again. * Positron emission tomography PET scans may be performed on the High Resolution Research Tomograph (HRRT, 2-3 mm resolution) or another similar camera. Venous catheters will be used for i.v. administration of the radiotracer, venous blood sampling of AChE activity, and for the administration of glycopyrrolate and physostigmine. A radial artery catheter will be inserted by an experienced physician before the PET scan to draw arterial blood samples for metabolite analysis and for determination of the fraction of plasma radioactivity unbound to protein. At the beginning of scan, the subject's head will be immobilized and a transmission scan will be obtained for attenuation correction. PET scans will be acquired using bolus or bolus to infusion administration of up to 10 millicuries of NCFHEB or PHNO. Dynamic images of radioactivity concentration are reconstructed with corrections for attenuation, normalization, random events, scatter, and deadtime. Subject motion is corrected automatically on an event-by-event basis with the Vicra motion tracking system. Vital signs (blood pressure, pulse and respiration) are collected prior to and during each PET scan. Urine pregnancy test will be again administered on the PET scan day prior to the initiation of any imaging procedures. Smoking abstinence, when appropriate, will also be confirmed for smoking subjects prior to PET scanning. PET scanning will then proceed as following for each aim: Aim 1. Subjects will be asked to come to the PET center on two separate days to participate in one NCFHEB PET scan each time to assess test retest reproducibility of binding parameters measured with the radiotracer. Aim 2. Subjects will participate in one PET scan day. Aim 3. Subjects from Aim 2 who are able to continue smoking abstinence will be asked to come back for another PET scan after about 6-8 weeks of smoking abstinence. Aim 4. Baseline NCFHEB PET imaging will be conducted followed by administration of physostigmine. Preferably, this will be done on the same day. However, at times there is not enough radiotracer or subject is not able to tolerate a longer scan day. Therefore, some subjects may complete the study over two separate days (preferably within 1 month apart based on the availability of PET scanning times and subject's schedule). Aim 5. Baseline NCFHEB PET imaging will be conducted followed by administration of physostigmine. Preferably, this will be done on the same day. However, at times when there is not enough radiotracer or when a subject is not able to tolerate a longer scan day. Therefore, some subjects may complete the study over two separate days (preferably within 1 month apart based on the availability of PET scanning times and subject's schedule). Control subjects may participate in more than 1 aim. For example, nonsmoking subjects may complete Aim 1 and if chose, participate in Aim 4. Thus, subjects may participate in up to 4 PET scans for this protocol. Aim 7. Subjects from Aim 4 will be asked to participate in 2 PHNO PET scans and amphetamine administration.