title: Optogenetic analysis of neuronal excitability during global ischemia reveals selective deficits in sensory processing following reperfusion in mouse cortex.
abstract: We have developed an approach to directly probe neuronal excitability during the period beginning with induction of global ischemia and extending after reperfusion using transgenic mice expressing channelrhodopsin-2 (ChR2) to activate deep layer cortical neurons independent of synaptic or sensory stimulation. Spontaneous, ChR2, or forepaw stimulation-evoked electroencephalogram (EEG) or local field potential (LFP) records were collected from the somatosensory cortex. Within 20 s of ischemia, a >90% depression of spontaneous 0.3-3 Hz EEG and LFP power was detected. Ischemic depolarization followed EEG depression with a ∼2 min delay. Surprisingly, neuronal excitability, as assessed by the ChR2-mediated EEG response, was intact during the period of strong spontaneous EEG suppression and actually increased before ischemic depolarization. In contrast, a decrease in the somatosensory-evoked potential (forepaw-evoked potential, reflecting cortical synaptic transmission) was coincident with the EEG suppression. After 5 min of ischemia, the animal was reperfused, and the ChR2-mediated response mostly recovered within 30 min (>80% of preischemia value). However, the recovery of the somatosensory-evoked potential was significantly delayed compared with the ChR2-mediated response (<40% of preischemia value at 60 min). By assessing intrinsic optical signals in combination with EEG, we found that neuronal excitability approached minimal values when the spreading ischemic depolarization wave propagated to the ChR2-stimulated cortex. Our results indicate that the ChR2-mediated EEG/LFP response recovers much faster than sensory-evoked EEG/LFP activity in vivo following ischemia and reperfusion, defining a period where excitable but synaptically silent neurons are present.
authors.affiliation: Department of Psychiatry, Brain Research Centre, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Shangbin
authors.initials: S
authors.lastname: Chen
authors.forename: Majid H
authors.initials: MH
authors.lastname: Mohajerani
authors.forename: Yicheng
authors.initials: Y
authors.lastname: Xie
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Murphy
mesh_terms: D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics; D000075402:Channelrhodopsins; D004195:Disease Models, Animal; D004569:Electroencephalography; D005071:Evoked Potentials / Q000187:drug effects / Q000235:genetics; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005552:Forelimb / Q000294:innervation; D006930:Hyperalgesia / Q000209:etiology*; D066298:In Vitro Techniques; D007511:Ischemia / Q000150:complications* / Q000473:pathology / Q000503:physiopathology; D008164:Luminescent Proteins / Q000235:genetics; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D062308:Optogenetics / Q000379:methods; D010812:Physical Stimulation; D011810:Quinoxalines / Q000494:pharmacology; D015427:Reperfusion Injury; D013779:Tetrodotoxin / Q000494:pharmacology; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D000779:Anesthetics, Local; D001426:Bacterial Proteins; D002352:Carrier Proteins; D000075402:Channelrhodopsins; D018691:Excitatory Amino Acid Antagonists; D008164:Luminescent Proteins; D011810:Quinoxalines; C054562:yellow fluorescent protein, Bacteria; D013779:Tetrodotoxin; C056723:FG 9041; C056639:2-amino-5-phosphopentanoic acid; D014633:Valine