1. Aged 18 years or older.
2. Must have undergone a screening assessment under protocol 01-M-0254, The Evaluation of Patients with Mood and Anxiety Disorders and Healthy Participants or 17M0181 Recruitment and Characterization of Healthy Research Volunteers for NIMH Intramural Studies.
3. Be healthy based on medical history, physical examination, and laboratory testing.
4. Able to understand and willingness to provide informed consent.
5. Willingness to complete all study procedures including MRI tests.
6. Have had their radial artery pulse checked for the presence of adequate ulnar collateral flow and the absence of any metal or foreign objects in both wrists.
7. Agree to adhere to the lifestyle considerations
EXCLUSION CRITERIA:
An individual who meets any of the following criteria will be excluded from participation in this study:
1. Clinically significant abnormalities on EKG or laboratory testing. This includes CBC and acute care panel (Na, K, Cl, CO2, creatinine, glucose, urea nitrogen).
2. Recent exposure to radiation (i.e., PET from other research) that, when combined with this study, would be above the allowable limits.
3. Inability to lie flat on camera bed for at least two hours, including claustrophobia and weight greater than the maximum for the scanner (500 lbs).
4. HIV infection.
5. Pregnancy or breastfeeding.
6. Must not have substance use disorder or alcohol use disorder.
7. Unable to travel to the NIH.
8. Unable to have an MRI scan (e.g., because of pacemakers or other implanted electrical devices, brain stimulators, dental implants, aneurysm clips (metal clips on the wall of a large artery), metallic prostheses (including metal pins and rods, heart valves, and cochlear implants), permanent eyeliner, implanted delivery pumps, shrapnel fragments, or metal fragments in the eye.
9. Taking medications reported to have significant binding to alpha-1 adrenoceptors, medications that that alter norepinephrine release, or medications that lower blood pressure including antihypertensives, diuretics, or phosphodiesterase-5(PDE-5) inhibitors (e.g. sildenafil, tadalafil, vardenafil) within five elimination halflives prior to any \[11C\]ARMI PET scan.
10. Known hypersensitivity to quinazoline-class medications (e.g., prazosin), defined as any prior allergic or clinically significant adverse reaction requiring discontinuation or medical evaluation.
11. Blood donation within 8 weeks (2 months) before study participation, or unwillingness to avoid blood donation for 8 weeks (2 months) after the study.