[123] 5-I-A-85380

This study will use single photon emission computed tomography, or SPECT (see below), to examine brain nicotine receptors in evaluating the role of a chemical called acetylcholine in memory and other problems in Parkinson's disease (PD). Acetylcholine acts by binding to these nicotine receptors.
Healthy normal volunteers and patients with Parkinson's disease 40 years of age and older, with or without dementia, may be eligible for this study. Candidates will be screened with physical and neurological examinations, a pen and paper test of memory and other mental functions, blood tests, and, for women of childbearing potential, a pregnancy test. Patients with cognition problems will have more intensive mental function tests.
All participants will undergo the following procedures:
Magnetic resonance imaging (MRI): This test uses a strong magnetic field and radio waves to show structural and chemical changes in the brain. During the scan, the subject lies on a table in a narrow cylinder (the scanner). The time required in the scanner is about 1 hour, during which the subject is asked to lie very still for 10 to 15 minutes at a time. He or she can speak with a staff member via an intercom system at all times during the procedure.
SPECT: This nuclear medicine test produces a picture of the receptors in the brain. On the night before the scan, the day of the scan, and for 4 days after the scan, subjects take an oral dose of potassium iodide to protect the thyroid gland from the radioactive tracer used in the SPECT procedure. (People allergic to potassium iodide will take potassium perchlorate instead.) Before the scan, small radioactive markers containing 99Tc are glued to the subject's head. Two catheters (thin, flexible tubes) are placed in veins in the arms to inject the radioactive tracer [123I]5-I-A-85380 and to draw blood samples. Another catheter is placed in an artery in the wrist to draw arterial blood samples. During the scan, the subject lies on a bed with his or her head held still with a head holder. The scans are taken over a 6-hour period after injection of [123I]5-I-A-85380. An electrocardiogram, respiration, and blood pressure measures are taken before the tracer is injected, then 5 minutes after the injection, and again 30 to 60 minutes after the injection. Blood and urine samples are collected 5 to 6 hours after starting the scan. Participants are asked to urinate at least every 2 hours for 12 hours after injection of [123I]5-I-A-85380 to decrease radiation exposure.

The purpose of this study is to use brain imaging technology to examine the role of certain brain chemicals in individuals with Alzheimer's disease (AD) and in healthy volunteers.
Cognitive dysfunction in people with AD is thought to arise from decreased chemical activity in specific parts of the brain. Decreases in alpha4beta2 nicotinic acetycholine receptors (nAChRs) have been found in the brains of people who died with AD; however, the status of this receptor system in living brains remains unclear. This study will use single photon emission computed tomography (SPECT) to study this receptor system in people with AD who have mild to moderate dementia and in healthy volunteers. In addition, this study will examine the relationship between cognitive dysfunction and nAChR deficits in the brains of individuals with AD.
Participants with AD will have four clinic visits; healthy volunteers will have three visits. At Visit 1, participants will undergo a medical history, physical examination, and laboratory tests. Healthy volunteers will have a Mini-Mental State Examination (MMSE) cognitive function test. Participants with AD will have a MMSE and measurement of the severity of their dementia.
During Visit 2, participants will undergo a magnetic resonance imaging (MRI) scan of the brain.
At Visit 3, participants will undergo SPECT imaging.
Only participants with AD will participate in Visit 4. During this visit, cognitive testing will be performed.