Optogenetic induction of cortical spreading depression in anesthetized and freely behaving mice

Abstract

Cortical spreading depression, which plays an important role in multiple neurological disorders, has been studied primarily with experimental models that use highly invasive methods. We developed a relatively non-invasive optogenetic model to induce cortical spreading depression by transcranial stimulation of channelrhodopsin-2 ion channels expressed in cortical layer 5 neurons. Light-evoked cortical spreading depression in anesthetized and freely behaving mice was studied with intracortical DC-potentials, multi-unit activity and/or non-invasive laser Doppler flowmetry, and optical intrinsic signal imaging. In anesthetized mice, cortical spreading depression induction thresholds and propagation rates were similar for invasive (DC-potential) and non-invasive (laser Doppler flowmetry) recording paradigms. Cortical spreading depression-related vascular and parenchymal optical intrinsic signal changes were similar to those evoked with KCl. In freely behaving mice, DC-potential and multi-unit activity recordings combined with laser Doppler flowmetry revealed cortical spreading depression characteristics comparable to those under anesthesia, except for a shorter cortical spreading depression duration. Cortical spreading depression resulted in a short increase followed by prolonged reduction of spontaneous active behavior. Motor function, as assessed by wire grip tests, was transiently and unilaterally suppressed following a cortical spreading depression. Optogenetic cortical spreading depression induction has significant advantages over current models in that multiple cortical spreading depression events can be elicited in a non-invasive and cell type-selective fashion.

The CGRP receptor antagonist BIBN4096 inhibits prolonged meningeal afferent activation evoked by brief local K+ stimulation but not cortical spreading depression-induced afferent sensitization

“…Future studies that use the CSD paradigm to study related trigeminal responses and their underlying mechanisms thus should be conscientious about the CSD induction method used. The use of less invasive methods that induce CSD remotely, such as optogenetics, 31 which may not influence meningeal afferents responsiveness per se may provide a better choice to study mechanisms of CSD-related meningeal nociception and its involvement in migraine headache.…”

Spreading depolarizations trigger caveolin‐1–dependent endothelial transcytosis

“…The amplitude and duration at half-amplitude of the first CSD in each hemisphere were measured. In a separate cohort we induced CSDs non-invasively through intact skull using transgenic mice expressing channelrhodopsin-2 (Thy1-ChR2-YFP) in neurons as previously described (Chung et al, 2018; Houben et al, 2016). Briefly, the skull was exposed by midline scalp incision and cleared of connective tissue.…”

Brainstem activity, apnea, and death during seizures induced by intrahippocampal kainic acid in anaesthetized rats

“…Mice with two epilepsyrelated genetic modifications develop brainstem spreading depolarization following induced seizures, 8 as does a familial hemiplegic migraine mutation. Anesthesia in mice delays the lethal apnoea and spreading depolarization, 10 but does not change the threshold, amplitude, and propagation rate of cortical spreading depolarization, 42 from which we conclude that while the timing of apnea and spreading depolarization may be slowed by anesthesia, the fundamental pathophysiology is likely preserved. Our DC recordings from the brainstem of wild-type rats show that the DC shift in pre-Bötzinger always follows the cessation of airflow at the onset of terminal apnea, whether obstructive or central, which is inconsistent with spreading depolarization causing apnea.…”

“…Precise timing is crucial and needs to relate airflow (not only respiratory effort) to spreading depolarization or other neural pathophysiology. Anesthesia in mice delays the lethal apnoea and spreading depolarization, 10 but does not change the threshold, amplitude, and propagation rate of cortical spreading depolarization, 42 from which we conclude that while the timing of apnea and spreading depolarization may be slowed by anesthesia, the fundamental pathophysiology is likely preserved.…”