In hippocampal CA1 area, the dendrites of PCs express voltage-gated Ca 2+ and sodium (Na +) channels and NMDA receptors. Due to methodological limitations, our current knowledge about the functional organization of dendritic Ca 2+ signals stems mostly from experiments on glutamatergic principal cells (PCs Regehr and Tank, 1990 Markram and Sakmann, 1994 Schiller et al., 1997 Golding et al., 2002 Losonczy and Magee, 2006 Sheffield and Dombeck, 2015 Sheffield et al., 2017). It may have different spatial and temporal ranges of action, and can exert various functions from induction of synaptic plasticity and local tuning of neuronal firing to the regulation of the expression of genes involved in neurodegenerative processes ( Verkhratsky, 2005 Higley and Sabatini, 2008 Camiré and Topolnik, 2012 Camiré et al., 2012 Topolnik, 2012). Calcium (Ca 2+) signaling represents an important aspect of dendritic integration. Neuronal dendrites exhibit a large variety of voltage- and ligand-gated ion conductances and, therefore, may operate as independent signaling devices ( Branco and Häusser, 2011). Thus, these data indicate that while animal locomotion is associated with widespread Ca 2+ elevations in interneuron dendrites that may reflect regenerative activity, local CaTs that may be related to synaptic activity become apparent during animal quiet state. As such, spreading regenerative CaTs dominated in dendrites during locomotion, whereas both spreading and localized Ca 2+ signals were seen during immobility. Despite overall variability in dendritic Ca 2+ transients (CaTs) across different cells and dendritic branches, we report consistent behavior state-dependent organization of Ca 2+ signaling in interneurons. Here, we used two-photon Ca 2+ imaging in mouse hippocampal CA1 interneurons to reveal Ca 2+ signal patterns in interneuron dendrites during animal locomotion and immobility. However, little is still known about dendritic Ca 2+ activity in interneurons during different behavioral states. High resolution imaging techniques allowed examining somatic Ca 2+ signals and, accordingly, the recruitment of hippocampal interneurons in awake behaving animals. Hippocampal inhibitory interneurons exhibit a large diversity of dendritic Ca 2+ mechanisms that are involved in the induction of Hebbian and anti-Hebbian synaptic plasticity. Department of Biochemistry, Microbiology and Bio-informatics, Faculty of Science and Engineering, Neuroscience Axis, CHU de Québec Research Center (CHUL), Laval University, Québec, PQ, Canada.Ruggiero Francavilla, Vincent Villette †, Olivier Martel and Lisa Topolnik *
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