title: An Optogenetic Approach for Investigation of Excitatory and Inhibitory Network GABA Actions in Mice Expressing Channelrhodopsin-2 in GABAergic Neurons.
abstract: To investigate excitatory and inhibitory GABA actions in cortical neuronal networks, we present a novel optogenetic approach using a mouse knock-in line with conditional expression of channelrhodopsin-2 (ChR2) in GABAergic interneurons. During whole-cell recordings from hippocampal and neocortical slices from postnatal day (P) 2-P15 mice, photostimulation caused depolarization and excitation of interneurons and evoked barrages of postsynaptic GABAergic currents. Excitatory/inhibitory GABA actions on pyramidal cells were assessed by monitoring the alteration in the frequency of EPSCs during photostimulation of interneurons. We found that in slices from P2-P8 mice, photostimulation evoked an increase in EPSC frequency, whereas in P9-P15 mice the response switched to a reduction in EPSC frequency, indicating a developmental excitatory-to-inhibitory switch in GABA actions on glutamatergic neurons. Using a similar approach in urethane-anesthetized animals in vivo, we found that photostimulation of interneurons reduces EPSC frequency at ages P3-P9. Thus, expression of ChR2 in GABAergic interneurons of mice enables selective photostimulation of interneurons during the early postnatal period, and these mice display a developmental excitatory-to-inhibitory switch in GABA action in cortical slices in vitro, but so far show mainly inhibitory GABA actions on spontaneous EPSCs in the immature hippocampus and neocortex in vivo
  
  
  
  We report a novel optogenetic approach for investigating excitatory and inhibitory GABA actions in mice with conditional expression of channelrhodopsin-2 in GABAergic interneurons. This approach shows a developmental excitatory-to-inhibitory switch in the actions of GABA on glutamatergic neurons in neocortical and hippocampal slices from neonatal mouse pups in vitro, but also reveals inhibitory GABA actions in the neonatal mouse neocortex and hippocampus in vivo.
authors.affiliation: Institut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U-901, 13273 Marseille, France, Aix-Marseille University, 13273 Marseille, France, and Laboratory of Neurobiology, Kazan Federal University, 420008 Kazan, Russia roustem.khazipov@inserm.fr guzelvaleyeva@yahoo.com.
authors.forename: Guzel
authors.initials: G
authors.lastname: Valeeva
authors.affiliation: Institut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U-901, 13273 Marseille, France, Aix-Marseille University, 13273 Marseille, France, and.
authors.forename: Thomas
authors.initials: T
authors.lastname: Tressard
authors.affiliation: Laboratory of Neurobiology, Kazan Federal University, 420008 Kazan, Russia.
authors.forename: Marat
authors.initials: M
authors.lastname: Mukhtarov
authors.affiliation: Institut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U-901, 13273 Marseille, France, Aix-Marseille University, 13273 Marseille, France, and.
authors.forename: Agnes
authors.initials: A
authors.lastname: Baude
authors.affiliation: Institut de Neurobiologie de la Méditerranée, Institut National de la Santé et de la Recherche Médicale U-901, 13273 Marseille, France, Aix-Marseille University, 13273 Marseille, France, and Laboratory of Neurobiology, Kazan Federal University, 420008 Kazan, Russia roustem.khazipov@inserm.fr guzelvaleyeva@yahoo.com.
authors.forename: Rustem
authors.initials: R
authors.lastname: Khazipov
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D000075402:Channelrhodopsins; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D018682:GABA Agents / Q000494:pharmacology; D059330:GABAergic Neurons / Q000187:drug effects* / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism; D018698:Glutamic Acid / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000254:growth & development; D066298:In Vitro Techniques; D053444:Inhibitory Postsynaptic Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D019579:Neocortex / Q000166:cytology / Q000254:growth & development; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D062308:Optogenetics; D018408:Patch-Clamp Techniques; D055366:Synaptic Potentials / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
chemical_list: D000075402:Channelrhodopsins; D018683:Excitatory Amino Acid Agents; D018682:GABA Agents; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005968:Glutamate Decarboxylase; C401141:glutamate decarboxylase 2
keywords: ChR2; GABA; cortex; hippocampus; inhibition; interneurons; optogenetics; patch clamp