Automated light-based mapping of motor cortex by photoactivation of channelrhodopsin-2 transgenic mice

Abstract

Traditionally, mapping the motor cortex requires electrodes to stimulate the brain and define motor output pathways. Although effective, electrode-based methods are labor-intensive, potentially damaging to the cortex and can have off-target effects. As an alternative method of motor mapping, we photostimulated transgenic mice expressing the light-sensitive ion channel channelrhodopsin-2 in predominantly layer-5 output cortical neurons. We report that optical stimulation of these neurons in vivo using a stage scanning laser system resulted in muscle excitation within 10-20 ms, which can be recorded using implanted electromyogram electrodes or by a noninvasive motion sensor. This approach allowed us to make highly reproducible automated maps of the mouse forelimb and hindlimb motor cortex much faster than with previous methods. We anticipate that the approach will facilitate the study of changes in the location and properties of motor maps after skilled training or damage to the nervous system.

Optogenetic Analysis of Neuronal Excitability during Global Ischemia Reveals Selective Deficits in Sensory Processing following Reperfusion in Mouse Cortex

“…The beam was positioned over the somatosensory cortex as determined by stereotaxic coordinates. Laser output ϳ1 mW premeasured with a power meter (Thorlabs) was triggered by a transistor-transistor logic pulse of 5 ms duration for each photostimulation (Arenkiel et al, 2007;Ayling et al, 2009). The power was ϳ700 mW/mm 2 at brain surface.…”

“…For experiments (n ϭ 4) involving glutamate receptor antagonists, DNQX (200 M) and APV (500 M) (Sigma) were dissolved in ACSF and applied to the craniectomy. Experiments (n ϭ 3) using tetrodotoxin (TTX; 30 M, Sigma) used local microinjection within the craniotomy, and were performed under ketamine-xylazine anesthesia using a similar collimated laser delivery system (Ayling et al, 2009) with 10 ms laser pulses.…”

“…Electrophysiological measurements involving direct antidromic neuronal stimulation may be difficult to employ and interpret in vivo. Here, we selectively examine neuronal excitability during the period beginning with the induction of ischemia and extendingafterreperfusionusingtransgenicmice[B6.Cg-Tg(Thy1-COP4/EYFP)18Gfng/J] expressing channelrhodopsin-2 (ChR2) in predominantly layer 5 cortical pyramidal neurons (Arenkiel et al, 2007;Wang et al, 2007;Ayling et al, 2009). ChR2 is a directly light-gated nonselective cation channel, which when expressed in neurons can transduce light energy into neural activity (Nagel et al, 2003;Boyden et al, 2005;Miesenböck, 2009).…”

Principles of designing interpretable optogenetic behavior experiments

“…Light-receptive molecules have been reported to exist in brains of the vertebrates (Okano et al 1994;Blackshaw and Snyder 1999;Koyanagi et al 2013). Light may have other effects on experiments, such as causing photoelectric artifacts on neural recording electrodes (Ayling et al 2009;Han et al 2009). Light may also distract the animal, perhaps eliciting increased locomotion (Godsil and Fanselow 2004) or encouraging the use of a visual distractor to mask the optogenetic stimulus (Huber et al 2008).…”

Resistance of Optogenetically Evoked Motor Function to Global Ischemia and Reperfusion in Mouse in Vivo

“…Light-based optogenetic motor mapping methodology has been described previously 9 (for details see the Supplementary Information).…”