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Peripheral optogenetic stimulation induces whisker movement and sensory perception in head-fixed mice

View Article: PubMed Central - PubMed

ABSTRACT

We discovered that optical stimulation of the mystacial pad in Emx1-Cre;Ai27D transgenic mice induces whisker movements due to activation of ChR2 expressed in muscles controlling retraction and protraction. Using high-speed videography in anesthetized mice, we characterize the amplitude of whisker protractions evoked by varying the intensity, duration, and frequency of optogenetic stimulation. Recordings from primary somatosensory cortex (S1) in anesthetized mice indicated that optogenetic whisker pad stimulation evokes robust yet longer latency responses than mechanical whisker stimulation. In head-fixed mice trained to report optogenetic whisker pad stimulation, psychometric curves showed similar dependence on stimulus duration as evoked whisker movements and S1 activity. Furthermore, optogenetic stimulation of S1 in expert mice was sufficient to substitute for peripheral stimulation. We conclude that whisker protractions evoked by optogenetic activation of whisker pad muscles results in cortical activity and sensory perception, consistent with the coding of evoked whisker movements by reafferent sensory input.

Doi:: http://dx.doi.org/10.7554/eLife.14140.001

No MeSH data available.


Related in: MedlinePlus

Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.(A) Illustration of experiment setup (isoflurane anesthesia, 0.8–1.5%), including chronically implanted microwire array. (B) Example peri-stimulus time histograms (PSTHs; bin size, 10 ms) for one mouse displayed ± 0.5 s relative to stimulation onset. Blue triangles and lines denote onset of 460 nm light stimulation; black triangle and line denotes onset of mechanical whisker stimulation. (C) Example local field potentials (LFPs) from one channel in response to optical whisker pad stimulation of various durations (1–100 ms) and mechanical stimulation of whisker C3. Each trace is the mean of 30 trials. (D) Peak LFP and maximum spike count (mean ± SEM, n = 3 mice), normalized to the maximum response for each channel. The channel that showed the largest response was selected from each mouse. (E) Comparison of LFP response latency for peripheral optical stimulation and mechanical whisker stimulation (shortest latency channel selected for each mouse). Bar graphs show mean (n = 3 mice) and lines connect individual subjects. Mean latency was 17.3 ± 1.0 ms (mean ± SEM) for 20–100 ms optical stimuli and 6.5 ± 0.1 ms (mean ± SEM) for mechanical whisker stimulation. ***p<0.001.DOI:http://dx.doi.org/10.7554/eLife.14140.01010.7554/eLife.14140.011Figure 3—source data 1.Data for Figure 3D.DOI:http://dx.doi.org/10.7554/eLife.14140.011
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fig3: Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.(A) Illustration of experiment setup (isoflurane anesthesia, 0.8–1.5%), including chronically implanted microwire array. (B) Example peri-stimulus time histograms (PSTHs; bin size, 10 ms) for one mouse displayed ± 0.5 s relative to stimulation onset. Blue triangles and lines denote onset of 460 nm light stimulation; black triangle and line denotes onset of mechanical whisker stimulation. (C) Example local field potentials (LFPs) from one channel in response to optical whisker pad stimulation of various durations (1–100 ms) and mechanical stimulation of whisker C3. Each trace is the mean of 30 trials. (D) Peak LFP and maximum spike count (mean ± SEM, n = 3 mice), normalized to the maximum response for each channel. The channel that showed the largest response was selected from each mouse. (E) Comparison of LFP response latency for peripheral optical stimulation and mechanical whisker stimulation (shortest latency channel selected for each mouse). Bar graphs show mean (n = 3 mice) and lines connect individual subjects. Mean latency was 17.3 ± 1.0 ms (mean ± SEM) for 20–100 ms optical stimuli and 6.5 ± 0.1 ms (mean ± SEM) for mechanical whisker stimulation. ***p<0.001.DOI:http://dx.doi.org/10.7554/eLife.14140.01010.7554/eLife.14140.011Figure 3—source data 1.Data for Figure 3D.DOI:http://dx.doi.org/10.7554/eLife.14140.011

Mentions: We next investigated whether peripheral optogenetic stimulation evoked neural activity in S1 by implanting 8-channel microwire arrays in S1 of Emx1-Cre;Ai27D mice. After one week of recovery, we recorded local field potentials (LFPs) and multiunit spiking activity in three anesthetized mice (isoflurane 0.8–1.5%) in response to peripheral optogenetic stimulation (Figure 3A). To account for potential differences in the locations of the arrays in S1, we analyzed signals from the channel with the shortest latency in each mouse. Spiking activity and LFP amplitude increased with the duration of peripheral optogenetic stimulation (Figure 3B,C). Plotting the responses normalized to the maximum response in each mouse indicated that spike count and LFP amplitude increase steeply with light pulse duration from 1–20 ms, and moderately between 20–100 ms (Figure 3D). We used a brief mechanical deflection of the whisker to compare S1 response timing. While the active whisker protraction evoked by optogenetic stimulation provides qualitatively distinct activation of sensory input compared with passive mechanical deflection, this experiment allowed us to determine the relative latencies of S1 responses. The spike number and LFP amplitude evoked by peripheral optogenetic stimulation were on average similar to those evoked by mechanical whisker deflection (peak spike number per stimulus in 10 ms bin: 3.5 ± 0.2 mechanical, 3.2 ± 1.1 optical; LFP peak amplitude: −168.5 ± 24.7 µV mechanical, 159.66 ± 45.1 µV optical). In one mouse, the largest responses observed to peripheral optogenetic stimulation were 5.8 spikes/stimulus and −267.5 µV peak LFP amplitude (129.3 ± 16.3% of the LFP amplitude evoked by mechanical whisker stimulation; values were 54.0 ± 7.6%, and 68.4 ± 2.6% in two other mice). Notably, the response latency determined from LFP recordings was 10.8 ± 0.1 ms longer for peripheral optogenetic stimulation compared to mechanical whisker stimulation (p<1x10-5 in n = 3/3 mice; paired t-tests; 13–39 trials per mouse) (Figure 3C, inset; Figure 3E). These results suggest that the longer latency in S1 for peripheral optogenetic stimulation can likely be attributed to the 11.9 ± 0.8 ms delay associated with the initiation of evoked whisker movement (Figure 2B; value from 9.3 mW intensity), and that sensory signals arrive rapidly in S1once whisker movement is initiated. These results are consistent with our histological data suggesting that ChR2 is expressed in muscle and absent from sensory nerve (Figure 1C; Figure 1—figure supplement 2).10.7554/eLife.14140.010Figure 3.Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.


Peripheral optogenetic stimulation induces whisker movement and sensory perception in head-fixed mice
Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.(A) Illustration of experiment setup (isoflurane anesthesia, 0.8–1.5%), including chronically implanted microwire array. (B) Example peri-stimulus time histograms (PSTHs; bin size, 10 ms) for one mouse displayed ± 0.5 s relative to stimulation onset. Blue triangles and lines denote onset of 460 nm light stimulation; black triangle and line denotes onset of mechanical whisker stimulation. (C) Example local field potentials (LFPs) from one channel in response to optical whisker pad stimulation of various durations (1–100 ms) and mechanical stimulation of whisker C3. Each trace is the mean of 30 trials. (D) Peak LFP and maximum spike count (mean ± SEM, n = 3 mice), normalized to the maximum response for each channel. The channel that showed the largest response was selected from each mouse. (E) Comparison of LFP response latency for peripheral optical stimulation and mechanical whisker stimulation (shortest latency channel selected for each mouse). Bar graphs show mean (n = 3 mice) and lines connect individual subjects. Mean latency was 17.3 ± 1.0 ms (mean ± SEM) for 20–100 ms optical stimuli and 6.5 ± 0.1 ms (mean ± SEM) for mechanical whisker stimulation. ***p<0.001.DOI:http://dx.doi.org/10.7554/eLife.14140.01010.7554/eLife.14140.011Figure 3—source data 1.Data for Figure 3D.DOI:http://dx.doi.org/10.7554/eLife.14140.011
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fig3: Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.(A) Illustration of experiment setup (isoflurane anesthesia, 0.8–1.5%), including chronically implanted microwire array. (B) Example peri-stimulus time histograms (PSTHs; bin size, 10 ms) for one mouse displayed ± 0.5 s relative to stimulation onset. Blue triangles and lines denote onset of 460 nm light stimulation; black triangle and line denotes onset of mechanical whisker stimulation. (C) Example local field potentials (LFPs) from one channel in response to optical whisker pad stimulation of various durations (1–100 ms) and mechanical stimulation of whisker C3. Each trace is the mean of 30 trials. (D) Peak LFP and maximum spike count (mean ± SEM, n = 3 mice), normalized to the maximum response for each channel. The channel that showed the largest response was selected from each mouse. (E) Comparison of LFP response latency for peripheral optical stimulation and mechanical whisker stimulation (shortest latency channel selected for each mouse). Bar graphs show mean (n = 3 mice) and lines connect individual subjects. Mean latency was 17.3 ± 1.0 ms (mean ± SEM) for 20–100 ms optical stimuli and 6.5 ± 0.1 ms (mean ± SEM) for mechanical whisker stimulation. ***p<0.001.DOI:http://dx.doi.org/10.7554/eLife.14140.01010.7554/eLife.14140.011Figure 3—source data 1.Data for Figure 3D.DOI:http://dx.doi.org/10.7554/eLife.14140.011
Mentions: We next investigated whether peripheral optogenetic stimulation evoked neural activity in S1 by implanting 8-channel microwire arrays in S1 of Emx1-Cre;Ai27D mice. After one week of recovery, we recorded local field potentials (LFPs) and multiunit spiking activity in three anesthetized mice (isoflurane 0.8–1.5%) in response to peripheral optogenetic stimulation (Figure 3A). To account for potential differences in the locations of the arrays in S1, we analyzed signals from the channel with the shortest latency in each mouse. Spiking activity and LFP amplitude increased with the duration of peripheral optogenetic stimulation (Figure 3B,C). Plotting the responses normalized to the maximum response in each mouse indicated that spike count and LFP amplitude increase steeply with light pulse duration from 1–20 ms, and moderately between 20–100 ms (Figure 3D). We used a brief mechanical deflection of the whisker to compare S1 response timing. While the active whisker protraction evoked by optogenetic stimulation provides qualitatively distinct activation of sensory input compared with passive mechanical deflection, this experiment allowed us to determine the relative latencies of S1 responses. The spike number and LFP amplitude evoked by peripheral optogenetic stimulation were on average similar to those evoked by mechanical whisker deflection (peak spike number per stimulus in 10 ms bin: 3.5 ± 0.2 mechanical, 3.2 ± 1.1 optical; LFP peak amplitude: −168.5 ± 24.7 µV mechanical, 159.66 ± 45.1 µV optical). In one mouse, the largest responses observed to peripheral optogenetic stimulation were 5.8 spikes/stimulus and −267.5 µV peak LFP amplitude (129.3 ± 16.3% of the LFP amplitude evoked by mechanical whisker stimulation; values were 54.0 ± 7.6%, and 68.4 ± 2.6% in two other mice). Notably, the response latency determined from LFP recordings was 10.8 ± 0.1 ms longer for peripheral optogenetic stimulation compared to mechanical whisker stimulation (p<1x10-5 in n = 3/3 mice; paired t-tests; 13–39 trials per mouse) (Figure 3C, inset; Figure 3E). These results suggest that the longer latency in S1 for peripheral optogenetic stimulation can likely be attributed to the 11.9 ± 0.8 ms delay associated with the initiation of evoked whisker movement (Figure 2B; value from 9.3 mW intensity), and that sensory signals arrive rapidly in S1once whisker movement is initiated. These results are consistent with our histological data suggesting that ChR2 is expressed in muscle and absent from sensory nerve (Figure 1C; Figure 1—figure supplement 2).10.7554/eLife.14140.010Figure 3.Extracellular recordings of S1 activity in response to optogenetic whisker pad stimulation.

View Article: PubMed Central - PubMed

ABSTRACT

We discovered that optical stimulation of the mystacial pad in Emx1-Cre;Ai27D transgenic mice induces whisker movements due to activation of ChR2 expressed in muscles controlling retraction and protraction. Using high-speed videography in anesthetized mice, we characterize the amplitude of whisker protractions evoked by varying the intensity, duration, and frequency of optogenetic stimulation. Recordings from primary somatosensory cortex (S1) in anesthetized mice indicated that optogenetic whisker pad stimulation evokes robust yet longer latency responses than mechanical whisker stimulation. In head-fixed mice trained to report optogenetic whisker pad stimulation, psychometric curves showed similar dependence on stimulus duration as evoked whisker movements and S1 activity. Furthermore, optogenetic stimulation of S1 in expert mice was sufficient to substitute for peripheral stimulation. We conclude that whisker protractions evoked by optogenetic activation of whisker pad muscles results in cortical activity and sensory perception, consistent with the coding of evoked whisker movements by reafferent sensory input.

Doi:: http://dx.doi.org/10.7554/eLife.14140.001

No MeSH data available.


Related in: MedlinePlus