Neuropharmacology and receptor studies in the elderly.

Functional brain imaging has provided unique and exciting opportunities to strengthen our knowledge of the biologic substrate of the aging brain and neuropsychiatric disorders. Positron emission tomography (PET) is a particularly powerful tool for quantifying the neurobiologic correlates of cognition, mood, and behavior. Initial PET studies of aging, psychiatric disorders, and neurodegenerative disease focused primarily on generalized physiologic parameters such as cerebral blood flow and metabolism, and early neuroreceptor imaging studies relied on relatively nonselective markers. New, selective receptor radioligands now offer a previously inaccessible means to investigate the dynamic relationships among neurochemistry, aging, and psychopathology in vivo. This approach has substantial advantages over peripheral (platelet and cerebrospinal fluid) markers, neuroendocrine challenge studies, animal models, and postmortem receptor binding assays. Advances in tracer kinetic modeling, magnetic resonance imaging facilitated PET image analysis, radiochemistry techniques, instrumentation, and image processing have helped pave the way for increased emphasis on functional imaging studies of neuropsychiatric disorders. The capability to correct PET image data for the confounding effect of cerebral atrophy permits relationships among age-related brain changes and neurobiologic disease mechanisms to be more accurately examined in the elderly.