Patient description: The patient is a 35-year-old woman with myasthenia gravis, class IIa. She complains of diplopia and fatigue and weakness that affects mainly her upper limbs. She had a positive anti-AChR antibody test, and her single fiber electromyography (SFEMG) was positive. She takes pyridostigmine 60 mg three times a day. But she still has some symptoms that interfere with her job. She is a research coordinator and has 3 children. Her 70-year-old father has hypertension. She does not smoke or use illicit drugs. She drinks alcohol occasionally at social events. Her physical exam and lab studies were not remarkable for any other abnormalities. BP: 110/75 Hgb: 11 g/dl WBC: 8000 /mm3 Plt: 300000 /ml Creatinine: 0.5 mg/dl BUN: 10 mg/dl Beta hcg: negative for pregnancy

Clinical trial eligibility criteria: eligible ages (years): 18.0-50.0,  Schizophrenia Age: Subjects will be male and female volunteers aged 18 to 50 years. Contact: All subjects must have a stable point of contact and must agree to participate in one PET study and one MRI scan. Smoking group: must smoke at least 10 cigarettes per day for at least the last year. They should have experience with abstaining from smoking for at least 48 h. Nonsmoking group: Subjects in the non-smoking group must be nonsmokers or have smoked less than 100 cigarettes in their lifetime and have ceased smoking at least two years before the start of the study. Diagnosis: Each volunteer will have a diagnosis of schizophrenia using DSMIV criteria. Each subject will have the following information available for diagnostic consideration: Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I), a general psychiatric interview for past illness characteristics and family history, information from 2-3 months of independent clinician observation including current detailed mental status evaluations using the Brief Psychiatric Rating Scale (BPRS), Schedule for the Assessment of Positive and Negative Symptoms (SAPS/SANS), and Schedule for Deficit Syndrome (SDS). An assessment of impulsivity will also be done (Patton, 1995). Comorbidity: No subject with a current axis I diagnosis other than schizophrenia will be allowed. No subject with known claustrophobia will be allowed. Medications: Study participants will continue to take their antipsychotic medications that they have been taking for at least 3 months prior to the study. Haldol, risperidone and olanzapine will be allowed because of their lack of significant effect on the density of beta2* nACh receptors after prolonged administration to rats (Haldol; Breese et al., 2000; risperidone and olanzapine; personal communication, Mukhin, also SFN abstract)  Weight: Anyone weighing more than 300 lbs is excluded from the study. The purpose of this is the weight limit of the PET scanner. History of Drug Abuse: Participants reporting current or having a significant history of illicit drug abuse will be excluded from the study. Subjects may use moderate amounts of alcohol and caffeine and smoke an occasional marijuana cigarette, but must not be dependent on alcohol, caffeine or marijuana. No alcohol or marijuana for at least 72 hours prior to scanning. No smoking for 48 hrs before the PET scan. Current Medication Use: Participants will continue to use their prescription medications. The following hypertension medications will be exclusionary: Indapamide, spironolactone, clonidine, guanfacine, methyldopa, propranolol. Over the counter medications are not exclusionary, however, subjects will not be allowed to use over the counter medications in the week prior to their PET scan. CNS disease: History of known structural brain abnormalities (e.g., neoplasm, subarachnoid cysts), cerebrovascular disease, infectious disease (e.g., abscess), history of head trauma (defined as documented loss of consciousness for 5 min or greater), history of seizures as an adult, sleep apnea. Cardiovascular, pulmonary, or systemic disease: Untreated hypertension known arrhythmia, symptomatic or known coronary artery disease; history of endocarditis, cerebral embolism, obstructive pulmonary disease, asthma, active tuberculosis, known endocrine disease (derangements in adrenal, thyroid, bone or reproductive function) known chronic renal or hepatic dysfunction, known HIV seropositive, known current autoimmune disease involving the CNS, type I diabetes mellitus. Subjects with type II diabetes mellitus will be allowed if their Hb A1C is less than 7. Special considerations for female subjects. Female participants who are planning to become pregnant, currently pregnant or nursing will not be allowed to participate in this study because of potential damage to the fetus or baby from the radiation. In addition, women of child bearing age who are sexually active are required to use an effective form of birth control for the duration of the study. Effective forms of birth control 1. hormonal contraceptives (birth control pills, injectable hormones, vaginal ring hormones), 2. surgical sterility (tubal ligation or hysterectomy) 3. IUD 4. Diaphragm with spermicide 5. Condom with spermicide Female subjects will be given a serum pregnancy test (quantitative beta HCG) within 24 hours of the PET study. Menstrual cycle phase or sex has not been shown to affect receptor availability (Cosgrove et al., 2007). Radiation exposure: Any subject who has participated in any research studies in which he/she received a radiation exposure that would result in combination with the present study, in a total effective radiation exposure (from research studies) exceeding 5.0 rem in a year. Children under the age of 18 will be excluded to avoid unnecessary exposure to radiation to these populations. Presence in body of metallic implants or materials that could be moved by the magnet of the MRI scanner: pacemakers, surgical implants, aneurysm clips, dental braces, bullet(s) or other metallic materials