Calcium Dynamics in Dendrites of Hippocampal CA1 Interneurons in Awake Mice

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. High resolution imaging techniques allowed examining somatic Ca(2+) signals and, accordingly, the recruitment of hippocampal interneurons in awake behaving animals. However, little is still known about dendritic Ca(2+) activity in interneurons during different behavioral states. 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. 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. As such, spreading regenerative CaTs dominated in dendrites during locomotion, whereas both spreading and localized Ca(2+) signals were seen during immobility. 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.