Improved methods for chronic light-based motor mapping in mice: automated movement tracking with accelerometers, and chronic EEG recording in a bilateral thin-skull preparation

Abstract

Optogenetic stimulation of the mouse cortex can be used to generate motor maps that are similar to maps derived from electrode-based stimulation. Here we present a refined set of procedures for repeated light-based motor mapping in ChR2-expressing mice implanted with a bilateral thinned-skull chronic window and a chronically implanted electroencephalogram (EEG) electrode. Light stimulation is delivered sequentially to over 400 points across the cortex, and evoked movements are quantified on-line with a three-axis accelerometer attached to each forelimb. Bilateral maps of forelimb movement amplitude and movement direction were generated at weekly intervals after recovery from cranial window implantation. We found that light pulses of ~2 mW produced well-defined maps that were centered approximately 0.7 mm anterior and 1.6 mm lateral from bregma. Map borders were defined by sites where light stimulation evoked EEG deflections, but not movements. Motor maps were similar in size and location between mice, and maps were stable over weeks in terms of the number of responsive sites, and the direction of evoked movements. We suggest that our method may be used to chronically assess evoked motor output in mice, and may be combined with other imaging tools to assess cortical reorganization or sensory-motor integration.

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…Consistent with this idea, we have demonstrated the persistence of cortical motif structure derived from both infraslow and slow spontaneous activity in both anaesthetized and quiet awake states 27 . The advent of increasingly sensitive genetically encoded voltage indicators (GEVI) 55,56 may permit future studies whereby longduration awake state recordings may more readily be facilitated in combination with less invasive chronic imaging window preparations 57,58 . In addition, this strategy is advantaged by cell type-specific expression of the genetically encoded voltage indicators and the potential to minimize contaminating nonneuronal signals through a noise gain equalization of Förster resonance energy transfer signals 55 .…”

Intact skull chronic windows for mesoscopic wide-field imaging in awake mice

“…The preparation we describe here evolved from previous work where the skull thinning technique originally developed for two-photon imaging (Drew et al, 2010;Yoder and Kleinfeld, 2002) was expanded to create a bilateral preparation to facilitate optogenetic stimulation in both hemispheres (Silasi et al, 2013). In contrast to full craniectomies, where a piece of the skull is removed (Ricardo and Carlos, 2008), skull-thinning preparations are less invasive, reducing inflammation and gliosis (Xu et al, 2007).…”

“…In addition to the Metabond adhesive used here and in other studies (Hira et al, 2009), chronic windows may also be created with clear-drying OrthoJet adhesive (Guo et al, 2015) or with cyanoacrylate based adhesives (Yang et al, 2010). Although we anticipate there to be slight differences between materials (such as drying time during surgery), all three of these adhesives have been used for some form transcranial imaging or optogenetic stimulation in mice (Drew et al, 2010;Hilton et al, 2016;Silasi et al, 2013;Vanni and Murphy, 2014;Yang et al, 2010).…”

“…Several research groups began to take advantage of the semi-transparent nature of the mouse skull by generating large, bi-hemispheric windows through either the intact (Guo et al, 2014), or partially thinned skull (Silasi et al, 2013). Although retraction of the skin alone can have some unwanted effects, such as significant brain cooling in anesthetized mice (Kalmbach and Waters, 2012), the reduced invasiveness offered by transcranial windows has made this the preparation of choice in a number of imaging applications (Cang et al, 2005;Yang et al, 2010;Yoder and Kleinfeld, 2002) including wide-field imaging of hemodynamic signals in anesthetized preparations (Kalchenko et al, 2014;White et al, 2011), and targeted photostimulation in awake (Hira et al, 2009) or behaving mice (Hira et al, 2015).…”

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).…”