title: The antiepileptic and ictogenic effects of optogenetic neurostimulation of PV-expressing interneurons.
abstract: Parvalbumin (PV)-expressing interneurons exert powerful inhibitory effects on the normal cortical network; thus optogenetic activation of PV interneurons may also possess antiepileptic properties. To investigate this possibility we expressed channelrhodopsin 2 in PV interneurons by locally injecting the Cre-dependent viral vector AAV2/1-EF1a-DIO-ChETA-EYFP into the S1 barrel cortex of PV-Cre mice. Approximately 3-4 wk later recurrent electrographic seizures were evoked by local application of the chemoconvulsant 4-aminopyridine (4-AP); the ECoG and unit activity were monitored with extracellular silicone electrodes; and PV interneurons were activated optogenetically during the ictal and interictal phases. Five- to ten-second optogenetic activation of PV interneurons applied during electrographic seizures (ictal phase) terminated 33.7% of electrographic seizures compared with only 6% during sham stimulation, and the average electrographic seizure duration shortened by 38.7 ± 34.2% compared with sham stimulation. In contrast, interictal optogenetic activation of PV interneurons showed powerful and robust ictogenic effects. Approximately 60% of interictal optogenetic stimuli resulted in electrographic seizure initiation. Single-unit recordings revealed that presumptive PV-expressing interneurons markedly increased their firing during optogenetic stimulation, while many presumptive excitatory pyramidal neurons showed a biphasic response, with initial suppression of firing during the optogenetic pulse followed by a synchronized rebound increase in firing at the end of the laser pulse. Our findings indicated that ictal activation of PV-expressing interneurons possesses antiepileptic properties probably due to suppression of firing in pyramidal neurons during the laser pulse. However, in addition interictal activation of PV-expressing interneurons possesses powerful ictogenic properties, probably due to synchronized postinhibition rebound firing of pyramidal neurons.
authors.affiliation: The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa, Israel; and.
authors.forename: Fadi
authors.initials: F
authors.lastname: Assaf
authors.affiliation: The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa, Israel; and Department of Neurology, Rambam Medical Center, Haifa, Israel y_schiller@yahoo.com.
authors.forename: Yitzhak
authors.initials: Y
authors.lastname: Schiller
mesh_terms: D015761:4-Aminopyridine; D000200:Action Potentials; D000818:Animals; D004195:Disease Models, Animal; D000069280:Electrocorticography; D004827:Epilepsy / Q000503:physiopathology* / Q000628:therapy*; D007395:Interneurons / Q000502:physiology*; D051379:Mice; D008839:Microelectrodes; D062308:Optogenetics; D010320:Parvalbumins / Q000378:metabolism*; D017966:Pyramidal Cells / Q000502:physiology; D012640:Seizures / Q000503:physiopathology / Q000628:therapy; D013003:Somatosensory Cortex / Q000503:physiopathology
chemical_list: D010320:Parvalbumins; D015761:4-Aminopyridine
keywords: epilepsy; interneurons; neocortex; neurostimulation; optogenetics