Primary Outcome Measures:
- Brain uptake of [11C]PBR28 (measured as distribution volume). [ Time Frame: One brain PET scan in one outpatient visit to NIH per subject. ]
The peripheral benzodiazepine receptor (PBR) is distinct from central benzodiazepine receptors associated with GABAa receptors. Although PBR was initially identified in peripheral organs such as kidneys, endocrine glands and lungs, later studies identified PBR in the central nervous system. In normal conditions, PBR is expressed in low levels in some neurons and glial cells. PBR can be a clinically useful marker to detect neuroinflammation, because activated microglial cells in inflammatory areas express much greater levels of PBR than in microglial cells in resting conditions.
PBR has been imaged with positron emission tomography (PET) using [11C]1-(2-chlorophenyl-N-methylpropyl)-3-isoquinoline carboxamide (PK11195). However, this classical ligand provides low levels of specific signal. Recently we developed a new ligand, N-acetyl-N-(2-methoxybenzyl)-2-phenoxy-5-pyridinamine [11C]PBR28, which showed much greater specific signal than [11C]PK11195 in non-human primates. ln the present protocol we plan to perform a kinetic brain imaging study with [11C]PBR28 in HlV-seronegative controls, HIV-seropositive, non-impaired patients, and HlV-seropositive patients with minor cognitive motor disorder(MCMD). Each subject will recieve a brain-dedicated PET scan with 20 mCi[(11)C]PBR28.