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Cheng KT.


Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.
2005 Dec 20 [updated 2008 Mar 10].


4-(2´-Methoxyphenyl)-1-[2´-(N-2´´-pyridinyl)-p-[18F]fluorobenzamido]ethylpiperazine (p-[18F]MPPF) is a radioligand developed for positron emission tomography (PET) imaging of serotonin-1A (5-HT1A) receptors in the central nervous system (1). It is a selective 5-HT1A radiotracer labeled with 18F, a positron emitter with a physical t½ of 110 min (2). The serotonin (5-hydroxytryptamine (5-HT)) neurotransmission system consists mainly of neurons in the brainstem, with nerve tracts extending from these neurons to many areas of the brain and spinal cord (3). During firing, the neurons release 5-HT, a neurotransmitter that is involved in the modulation of various important physiologic functions and behavior, such as thermoregulation, cardiovascular function, aggressive and sexual behavior, mood, appetite, and the sleep–wake cycle. The effects of 5-HT are mediated by as many as seven classes of receptor populations (5-HT1 to 5-HT7), many of which also contain several subtypes. There are five receptor subtypes within the G protein–coupled 5-HT1 receptor family, and the 5-HT1A subtype is located primarily in the limbic forebrain (the hippocampus, entorhinal cortex, and septum). 5-HT1A appears to function both as a presynaptic (somatodendritic) autoreceptor in the raphe nuclei and as a postsynaptic receptor in the terminal fields. This receptor subtype is involved in the modulation of emotion and the function of the hypothalamus, and is implicated in the pathogenesis of anxiety, depression, hallucinogenic behavior, motion sickness, dementia, schizophrenia, and eating disorders. Many psychiatric drugs modulate serotonergic transmission or specifically target the 5-HT1A receptors. Many compounds have been radiolabeled and studied for visualization and quantification of these receptors by PET or single-photon emission computed tomography (SPECT). WAY 100635 has been developed as a highly selective, silent antagonist (possessing no intrinsic agonist activity) of 5HT1A receptors at both pre- and postsynaptic sites. Zhuang et al. (4, 5) first developed a series of arylpiperazine-benzamido derivatives and 4-(2´-methoxyphenyl)-1-[2´-[N-(2´´-pyridinyl)-p-iodobenzamido]ethyl]piperazine ([125I]MPPI), which appeared to selectively bind to the 5-HT1A receptors in vitro and in vivo. Their studies showed that various benzoyl substituents affected the inhibition constant (Ki) of the compound. Zhuang et al. (4) also synthesized a fluoro analog, p-MPPF, that displayed a high binding affinity for 5-HT1A receptors and acted as a receptor antagonist in vivo. In 1994, Shiue et al. (6) synthesized p-[18F]MPPF for PET studies of 5-HT1A receptors in humans.

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