アストロサイトに発現するヒスタミン代謝酵素は自発行動量と覚醒状態を制御する

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  • Astrocytic histamine <i>N</i>-methyltransferase controls locomotor activity and vigilance state

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<p>Brain histamine plays a role as a neurotransmitter in the regulation of various brain activities. Previously, we demonstrated that histamine N-methyltransferase (HNMT), a histamine-metabolizing enzyme, controls brain histamine concentration and brain functions. However, it is still unknown whether neuronal Hnmt or astrocytic Hnmt contributes to the regulation of histaminergic system. Here, we phenotyped astrocytes-specific Hnmt knockout (cKO) mice to elucidate the role of Hnmt in astrocytes. First, we made cKO mice by crossing Hnmt flox mice and Gfap-Cre mice which expressed Cre recombinase in astrocytes. Although Hnmt expression in the cKO cerebellum was decreased, brain histamine concentrations in the cKO brain homogenates was not significantly different from those of control mice. In behavioral tests, locomotor activity of cKO mice in novel environment and in their home cages were decreased during the dark phase. Anxiety- and depression-like behaviors were not changed by Hnmt deletion in astrocytes. Sleep analysis showed that the power density of delta frequency was increased in cKO mice, indicating the lower cortical activation of cKO mice. These results demonstrate that astrocytic Hnmt is important for locomotor activity and vigilance state, although the impact of Hnmt in astrocytes on histamine concentration was limited.</p>

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