The new perspectives of knockout mice and positron emission temography in the development and evaluation of drugs

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Knockout mice and positron emission tomography (PET) are unique methods to evaluate the efficacy of administered drugs in vivo. Using recently-developed new technologies, we developed several new methods to evaluate pharmacological effects in vivo in mice and humans. For studies of knockout mice, we discovered several new functions of the histaminergic neurons. H1 blockers can be used as mild analgesics because histamine-related knockout mice showed reduced nociception to various chemical stimuli and enhanced morphine-induced antinociception. We also demonstrated that pentylenetetrazol-kindling were significantly augmented in histamine H1 receptor knockout mice, histidine decarboxylase deficient mice and mast cell deficient mice, suggesting that chronic treatment of brain-penetrating H1 blockers could develop chronic epilepsy in patients. For the development of PET techniques, specific ^<11>C- or ^<18>F-labelled radiotracers for selective labeling of several receptors were newly synthe … More sized by new synthetic methods. Newly-developed tracers are as follows: ^<11>C-donepezil(acetylcholine esterase inhibitor), ^<18>F-TAK147(acetylcholine esterase inhibitor), ^<18>F-fluorocholine (choline analog), and ^<18>F-fuoroproxytan(histamine H3 antagonist). As a new labeling method, 4-[18F]fluorobenzyl halides and [^<11>C]methyl triflate were synthesized and used to label radioplmramaceuticals. We also developed several new methods of imaging in the human brain using 3-demensional PET system. Our developed PET methods for human neuropharmacology are as follows: Non-invasive measurement of receptor binding parameters; cerebral activation study with H_2^<15>O and 3D-PET; ^<11>C-ligand activation study to measure neurotransmiter release. To understand the brain mechanism of personal characters, we clarified the significant difference in brain processing of emotion by facial expressions in alexithymia using 3D-PET and H_2^<15>O. For neuroreceptor studies, we examined the alternation of histaminergic neurotransmission in depressive and schizophrenic patients. H1 receptor bindings were significantly decreased in brains of both psychiatric diseases. Less