Hippocampal theta rhythm and its coupling with gamma oscillations require fast inhibition onto parvalbumin-positive interneurons

• Published in: Proceedings of the National Academy of Sciences - PNAS 2009-03, Vol.106 (9), p.3561-3566
• Main Authors: Wulff, Peer, Ponomarenko, Alexey A, Bartos, Marlene, Korotkova, Tatiana M, Fuchs, Elke C, Bähner, Florian, Both, Martin, Tort, Adriano B.L, Kopell, Nancy J, Wisden, William, Monyer, Hannah
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal; Behavioral neuroscience; Biological Sciences; Brain; Cells; Electrophysiology; Hippocampus; Hippocampus - drug effects; Hippocampus - metabolism; Interneurons; Interneurons - drug effects; Interneurons - metabolism; Mice; Models, Neurological; Neurons; Oscillation; Parvalbumins - pharmacology; Patch-Clamp Techniques; Protein Subunits - metabolism; Pyramidal cells; Receptors; Receptors, GABA-A - metabolism; Rodents; Studies; Synapses - drug effects; Synapses - metabolism; T lymphocytes; Theta Rhythm; Time Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0813176106

Hippocampal theta (5-10 Hz) and gamma (35-85 Hz) oscillations depend on an inhibitory network of GABAergic interneurons. However, the lack of methods for direct and cell-type-specific interference with inhibition has prevented better insights that help link synaptic and cellular properties with network function. Here, we generated genetically modified mice (PV-Δγ₂) in which synaptic inhibition was ablated in parvalbumin-positive (PV+) interneurons. Hippocampal local field potential and unit recordings in the CA1 area of freely behaving mice revealed that theta rhythm was strongly reduced in these mice. The characteristic coupling of theta and gamma oscillations was strongly altered in PV-Δγ₂ mice more than could be accounted for by the reduction in theta rhythm only. Surprisingly, gamma oscillations were not altered. These data indicate that synaptic inhibition onto PV+ interneurons is indispensable for theta- and its coupling to gamma oscillations but not for rhythmic gamma-activity in the hippocampus. Similar alterations in rhythmic activity were obtained in a computational hippocampal network model mimicking the genetic modification, suggesting that intrahippocampal networks might contribute to these effects.