The elucidation of GABAergic functions using glutamate decarboxylase conditional knockout mice

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GABA, a principal inhibitory neurotransmitter mediates inhibitory actions at central nervous system (CNS) synapses. GABA plays important roles in brain functions such as sleep, emotion, perception and movement. GABA is synthesized by glutamate decarboxylase (GAD), which has two isoforms, GAD65 and GAD67. We generated and analyzed GAD65 knockout mice and GAD67 knockout mice. GAD65 knockout mice showed an increase in susceptibility to seizures and changes in emotional behaviors, whereas GAD67 knockout mice died of cleft palate.Because GAD67 conventional knockout mice resulted in a neonatal lethality, we cannot analyze GAD67 gene function in vivo, in particular in adult mice. Therefore, we aimed to develop GAD67 conditional knockout mice using tetracycline-inducible system. The tetracycline-inducible system is composed of (1) the tetracycline-controlled activator (tTA) and (2) tetO promoter to control the transcription of a downstream gene following tTA binding to tetO. We tried to genera … More te GAD67-tTA2 knock-in mice, in which tTA2 was expressed under the control of endogenous GAD67 promoter. The GAD67-tTA2 knock-in mice are necessary for GAD67 conditional knockout mice. We constructed a targeting vecor, electroporated it into ES cells, and screened ES clones by Southern blot analyses. We identified multiple homologous recombinant ES clones. These ES clones will enable us to obtain GAD67-tTA2 knock-in mice.To assess the roles of GABA in taste functions, we analyzed GAD65 knockout mice. Preference/aversion responses to four basic tastes were not different between GAD65 knockout mice and wild-type mice, while GAD65 knockout mice consumed less sucrose-quinine than did wild-type mice. These results suggest that GAD65-generated GABA is not implicated in basic taste functions, but in more complex processing of taste information.GABA is present not only in CNS but also in several nonneuronal tissues. We demonstrated that narrow cells in the epididymis and epithelial cells in the thymic medulla were GABA-positive cells. Less