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 Ͼ90% depression of spontaneous 0.3-3 Hz EEG and LFP power was detected. Ischemic depolarization followed EEG depression with a ϳ2 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 (Ͼ80% of preischemia value). However, the recovery of the somatosensory-evoked potential was significantly delayed compared with the ChR2-mediated response (Ͻ40% 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.

Chloride Cotransporters as a Molecular Mechanism underlying Spreading Depolarization-Induced Dendritic Beading

“…To confirm this observation, we calculated the power spectrum amplitude (mV 2 /Hz) in the 0.3-3 Hz band of DC EEG activity that is typical for urethane anesthesia (Mohajerani et al, 2010). DC EEG recordings were analyzed by selecting homologous 3 min segments during the periodic activity reported in urethane-anesthetized mice (Clement et al, 2008;Pagliardini et al, 2013). The power spectrums of EEG signals were similar before control SD and before the third SD at 135 Ϯ 7 min of drug application (n ϭ 6 mice, p ϭ 0.63), indicating no significant drug-induced effects on cortical function.…”

“…During SD, the interstitial space shrinks dramatically (Pérez-Pinzó n et al, 1995;Mazel et al, 2002), reflecting abrupt cytotoxic edema manifested by profound neuronal swelling and dendritic beading with spine loss (Takano et al, 2007;Murphy et al, 2008;Risher et al, 2012) and attendant synaptic failure and neuronal damage (Somjen, 2001;Douglas et al, 2011;Chen et al, 2012). It appears that the transient or terminal nature of SD-induced dendritic beading depends on the metabolic status of the tissue invaded by this SD Risher et al, 2010;Sword et al, 2013).…”

Optogenetic neuronal stimulation promotes functional recovery after stroke

“…Optogenetic approaches have been used in rodents to probe neuronal circuits for several neurological/neurodegenerative diseases, including Parkinson disease (30) and epilepsy (31). Recent studies have also used optogenetics to map functional organization after stroke (32)(33)(34)(35). The safety and efficacy of using optogenetics in nonhuman primates has also been characterized (29,36).…”

Optogenetic Approaches to Target Specific Neural Circuits in Post-stroke Recovery

“…Optogenetic approaches have also been used to study cortical excitability within hours after stroke [150][151][152]. Anenberg et al [150] used optogenetics to investigate cortical excitability and motor output in a ministroke model generated by occlusion of arterioles in the motor cortex.…”