Large intersubject variability in the neurobiologie effects of aging has been noted by several investigators.44,45 These reports, individually limited by small sample sizes, suggest, that aging effects on brain function are likely highly variable, affected by structural brain changes and systemic factors, and may differ between “successful aging” and individuals with substantial medical burden. Alterations in neurotransmitter systems The functional integrity of several neurotransmitter systems is

altered by the aging process. Characterizing the profile of normal aging changes in neurotransmittcrmediated synaptic processes is the foundation upon Inhibitors,research,lifescience,medical which we will come to decipher the biological basis of behavioral and mood alterations accompanying aging. Further, the potential interaction between age effects and neurochemical

disturbances associated with neuropsychiatrie disease states may influence the susceptibility of the elderly to certain neurobehavioral disorders. Our knowledge of the effect of age on neuroreceptor function is primarily Inhibitors,research,lifescience,medical inferred by postmortem studies, with limited and variable regional sampling of the brain, and by animal models, which may not Inhibitors,research,lifescience,medical appropriately represent, human brain aging. In contrast to studies of pathological changes in aging, there are many problems associated with the biochemical study of neurotransmission in humans. These include the effects of postmortem delay, hypoxia, and drug treatment, as well as the fundamental point that the material is removed most often removed following a terminal illness, which may itself influence neurotransmission regardless of the age at which the patient died. Inhibitors,research,lifescience,medical ‘ITtic reader is referred to a comprehensive review

of the subject, Inhibitors,research,lifescience,medical by DeKosky and Palmer.46 With the development of highly selective radioligands for neuroreceptors, transporters, and other markers of neuronal function, it is possible to study the effects of aging and disease on brain neurotransmitter systems in vivo with PET. This approach permits whole-brain quantitative imaging in well-characterized subjects, with the potential for obtaining longitudinal measures. Such work has demonstrated specific aging reductions in dopamine and serotonin (5-hydroxytryptamine [5-HT]) receptor subtypes (Figure 1).47-50 Interestingly, there is evidence that some neuroreceptors first actually increase in density with age, a finding of note in the opiate system.51 PET techniques are desirable relative to neuroendocrine challenge studies, which lack spatial localizing selleck chemical information and physiologic specificity. However, the combination of PET with neuropharmacologic probes is a powerful technique for localizing and quantifying neurotransmitter-mediated function in aging and disease. Figure 1. [18F]Altanserin positron emission tomography (PET) imaging of the 5-hydroxytryptamine (serotonin) type-2A receptor (5-HT2A). Left.