title: Dendritic calcium nonlinearities switch the direction of synaptic plasticity in fast-spiking interneurons.
abstract: Postsynaptic calcium (Ca2+) nonlinearities allow neuronal coincidence detection and site-specific plasticity. Whether such events exist in dendrites of interneurons and play a role in regulation of synaptic efficacy remains unknown. Here, we used a combination of whole-cell patch-clamp recordings and two-photon Ca2+ imaging to reveal Ca2+ nonlinearities associated with synaptic integration in dendrites of mouse hippocampal CA1 fast-spiking interneurons. Local stimulation of distal dendritic branches within stratum oriens/alveus elicited fast Ca2+ transients, which showed a steep sigmoidal relationship to stimulus intensity. Supralinear Ca2+ events required Ca2+ entry through AMPA receptors with a subsequent Ca2+ release from internal stores. To investigate the functional significance of supralinear Ca2+ signals, we examined activity-dependent fluctuations in transmission efficacy triggered by Ca2+ signals of different amplitudes at excitatory synapses of interneurons. Subthreshold theta-burst stimulation (TBS) produced small amplitude postsynaptic Ca2+ transients and triggered long-term potentiation. In contrast, the suprathreshold TBS, which was associated with the generation of supralinear Ca2+ events, triggered long-term depression. Blocking group I/II metabotropic glutamate receptors (mGluRs) during suprathreshold TBS resulted in a slight reduction of supralinear Ca2+ events and induction of short-term depression. In contrast, blocking internal stores and supralinear Ca2+ signals during suprathreshold TBS switched the direction of plasticity from depression back to potentiation. These data reveal a novel type of supralinear Ca2+ events at synapses lacking the GluA2 AMPA subtype of glutamate receptors and demonstrate a general mechanism by which Ca2+ -permeable AMPA receptors, together with internal stores and mGluRs, control the direction of plasticity at interneuron excitatory synapses.
authors.affiliation: Department Biochemistry, Microbiology and Bio-informatics, Université Laval; Axis of Cellular and Molecular Neuroscience, IUSMQ, Québec, Canada.
authors.forename: Olivier
authors.initials: O
authors.lastname: Camiré
authors.forename: Lisa
authors.initials: L
authors.lastname: Topolnik
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology; D020747:Calcium Channels, T-Type / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology*; D003712:Dendrites / Q000502:physiology*; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005260:Female; D007395:Interneurons / Q000502:physiology*; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008959:Models, Neurological; D009473:Neuronal Plasticity / Q000502:physiology*; D017711:Nonlinear Dynamics; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000502:physiology
chemical_list: D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D015222:Sodium Channels
keywords: calcium; dendrite; interneuron; intracellular release; plasticity; synapse