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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.

Silasi G, Boyd JD, Ledue J, Murphy TH - Front Neural Circuits (2013)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, University of British Columbia Vancouver, BC, Canada ; Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

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.

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Automated quantification of evoked movements during light based motor mapping.(A,B) The head of the anesthetized mouse is stabilized with a head-fixing assembly consisting of a stainless steel (ER2) post, a 4/40 threaded nut and an articulating arm. The mouse is positioned with its limbs freely hanging in a natural posture. (C,D) Accelerometers are attached to each forelimb and the analog voltage signals are rotated into a frame of reference that aligns all of the acceleration due to gravity into the vertical (Z) axis. (D) The magnitude of acceleration averaged over a 30 ms period (gray shaded region) was used to construct motor maps based on peak acceleration (E) as well as movement direction in the vertical or horizontal planes (F).
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Figure 1: Automated quantification of evoked movements during light based motor mapping.(A,B) The head of the anesthetized mouse is stabilized with a head-fixing assembly consisting of a stainless steel (ER2) post, a 4/40 threaded nut and an articulating arm. The mouse is positioned with its limbs freely hanging in a natural posture. (C,D) Accelerometers are attached to each forelimb and the analog voltage signals are rotated into a frame of reference that aligns all of the acceleration due to gravity into the vertical (Z) axis. (D) The magnitude of acceleration averaged over a 30 ms period (gray shaded region) was used to construct motor maps based on peak acceleration (E) as well as movement direction in the vertical or horizontal planes (F).

Mentions: Following chronic window implantation mice were allowed to recover for at least 5 weeks. LBMM was carried out three times for each mouse at weekly intervals, with the exception of two mice, where the last map was generated 1 month after the second map. For each mapping session, mice were anesthetized with an IP injection of ketamine (60 mg/kg) and xylazine 10 mg/kg) and supplemental doses of ketamine alone were delivered as needed to maintain anesthesia. Anesthetic depth was determined by monitoring spontaneous whisking and the toe-pinch withdrawal reflex (Tandon et al., 2007). The mice were placed on a custom made baseplate equipped with an articulating arm (ThorLabs, Newton, NJ, USA; Product: TRB1) for stabilizing the head, and an elevated platform to support the body of the mouse. Body temperature was maintained via a heating pad placed underneath the animal and controlled by a rectal thermometer. The head of the mouse was connected to the articulating arm on the base plate via the setscrew next to the chronic window (Figures 1A,B). To achieve greater stability at this connection, a 4/40 nut was first threaded onto the setscrew, followed by a stainless-steel threaded ER2 post (ThorLabs, Newton, NJ, USA; Product: ER2). The nut was then tightened firmly (upward) against the ER2 post (as opposed to tightening downward against the dental cement on the head). This configuration stabilized the head without directly applying torque or pressure.


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.

Silasi G, Boyd JD, Ledue J, Murphy TH - Front Neural Circuits (2013)

Automated quantification of evoked movements during light based motor mapping.(A,B) The head of the anesthetized mouse is stabilized with a head-fixing assembly consisting of a stainless steel (ER2) post, a 4/40 threaded nut and an articulating arm. The mouse is positioned with its limbs freely hanging in a natural posture. (C,D) Accelerometers are attached to each forelimb and the analog voltage signals are rotated into a frame of reference that aligns all of the acceleration due to gravity into the vertical (Z) axis. (D) The magnitude of acceleration averaged over a 30 ms period (gray shaded region) was used to construct motor maps based on peak acceleration (E) as well as movement direction in the vertical or horizontal planes (F).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3722499&req=5

Figure 1: Automated quantification of evoked movements during light based motor mapping.(A,B) The head of the anesthetized mouse is stabilized with a head-fixing assembly consisting of a stainless steel (ER2) post, a 4/40 threaded nut and an articulating arm. The mouse is positioned with its limbs freely hanging in a natural posture. (C,D) Accelerometers are attached to each forelimb and the analog voltage signals are rotated into a frame of reference that aligns all of the acceleration due to gravity into the vertical (Z) axis. (D) The magnitude of acceleration averaged over a 30 ms period (gray shaded region) was used to construct motor maps based on peak acceleration (E) as well as movement direction in the vertical or horizontal planes (F).
Mentions: Following chronic window implantation mice were allowed to recover for at least 5 weeks. LBMM was carried out three times for each mouse at weekly intervals, with the exception of two mice, where the last map was generated 1 month after the second map. For each mapping session, mice were anesthetized with an IP injection of ketamine (60 mg/kg) and xylazine 10 mg/kg) and supplemental doses of ketamine alone were delivered as needed to maintain anesthesia. Anesthetic depth was determined by monitoring spontaneous whisking and the toe-pinch withdrawal reflex (Tandon et al., 2007). The mice were placed on a custom made baseplate equipped with an articulating arm (ThorLabs, Newton, NJ, USA; Product: TRB1) for stabilizing the head, and an elevated platform to support the body of the mouse. Body temperature was maintained via a heating pad placed underneath the animal and controlled by a rectal thermometer. The head of the mouse was connected to the articulating arm on the base plate via the setscrew next to the chronic window (Figures 1A,B). To achieve greater stability at this connection, a 4/40 nut was first threaded onto the setscrew, followed by a stainless-steel threaded ER2 post (ThorLabs, Newton, NJ, USA; Product: ER2). The nut was then tightened firmly (upward) against the ER2 post (as opposed to tightening downward against the dental cement on the head). This configuration stabilized the head without directly applying torque or pressure.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychiatry, University of British Columbia Vancouver, BC, Canada ; Brain Research Centre, University of British Columbia Vancouver, BC, Canada.

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.

Show MeSH
Related in: MedlinePlus