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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

Absence of ChR2/tdTomato expression in vibrissal nerve fibers of EMX-cre;Ai27D mice.(A) Example images of two whisker follicles in an Emx1-Cre;Ai27D mouse. Expression of ChR2/tdTomato was present in intrinsic muscle (m.) surrounding the follicle, but was not observed in nerve fibers innervating the follicle. (B).Example images of two whisker follicles in a parvalbumin (PV)-Cre;Ai27D mouse. In contrast to the Emx1 results, PV mice showed a profusion of ChR2/tdTomato expression in follicular nerves, consistent with previous results (Sakurai et al., 2013). Dotted curved lines indicate the interior or the cavernous sinus. Arrowheads indicate ChR2/tdTomato expression in nerve fibers and/or nerve endings at the whisker shaft (s) and base (b). Images below are from single focal planes (not z-projections) at boxed regions. Each image in A and B is a maximum z-projection of 20 focal planes at 1 µm spacing in coronal sections. Scale bar, 50 µm.DOI:http://dx.doi.org/10.7554/eLife.14140.005
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fig1s2: Absence of ChR2/tdTomato expression in vibrissal nerve fibers of EMX-cre;Ai27D mice.(A) Example images of two whisker follicles in an Emx1-Cre;Ai27D mouse. Expression of ChR2/tdTomato was present in intrinsic muscle (m.) surrounding the follicle, but was not observed in nerve fibers innervating the follicle. (B).Example images of two whisker follicles in a parvalbumin (PV)-Cre;Ai27D mouse. In contrast to the Emx1 results, PV mice showed a profusion of ChR2/tdTomato expression in follicular nerves, consistent with previous results (Sakurai et al., 2013). Dotted curved lines indicate the interior or the cavernous sinus. Arrowheads indicate ChR2/tdTomato expression in nerve fibers and/or nerve endings at the whisker shaft (s) and base (b). Images below are from single focal planes (not z-projections) at boxed regions. Each image in A and B is a maximum z-projection of 20 focal planes at 1 µm spacing in coronal sections. Scale bar, 50 µm.DOI:http://dx.doi.org/10.7554/eLife.14140.005

Mentions: We performed histological analysis to determine if these results could be explained by expression of ChR2 in muscles that control different types of whisker movements (Dörfl, 1982; Hill et al., 2008; Haidarliu et al., 2015). Indeed, analysis of the native fluorescence of the ChR2/tdTomato fusion protein in sections of the whisker pad revealed tdTomato expression in intrinsic and extrinsic whisker pad muscles (Figure 1C). Intrinsic muscles appeared on both superior and inferior sides of the follicle in coronal sections, and on the rostral side in transverse sections (Figure 1C1, C2), consistent with their sling-like morphology (Dörfl, 1982; Haidarliu et al., 2010). No fluorescence was evident in the infraorbital (sensory) nerve (Figure 1—figure supplement 2). Comparison of fluorescence intensity indicated the highest intensity in intrinsic sling muscles, followed by the deep extrinsic retractor muscle (pars maxillaris superficialis and pars maxillaris profunda of M. nasolabialis profundus), and lastly the superficial extrinsic protractor muscle (the pars media superior and pars media inferior of M. nasolabialis profundus,) (F(2,6) = 57.66, p=0.0001, repeated measures ANOVA followed by paired contrasts; p=0.0004 comparing external extrinsic and intrinsic, p=0.0086 comparing external extrinsic and internal extrinsic, p=0.0341 comparing intrinsic and internal extrinsic; n=4 follicles from one mouse) (Figure 1D). These results indicate that light-evoked whisker movements in Emx1-Cre;Ai27D mice arise from activation of ChR2 expressed in extrinsic and intrinsic whisker pad muscles.


Peripheral optogenetic stimulation induces whisker movement and sensory perception in head-fixed mice
Absence of ChR2/tdTomato expression in vibrissal nerve fibers of EMX-cre;Ai27D mice.(A) Example images of two whisker follicles in an Emx1-Cre;Ai27D mouse. Expression of ChR2/tdTomato was present in intrinsic muscle (m.) surrounding the follicle, but was not observed in nerve fibers innervating the follicle. (B).Example images of two whisker follicles in a parvalbumin (PV)-Cre;Ai27D mouse. In contrast to the Emx1 results, PV mice showed a profusion of ChR2/tdTomato expression in follicular nerves, consistent with previous results (Sakurai et al., 2013). Dotted curved lines indicate the interior or the cavernous sinus. Arrowheads indicate ChR2/tdTomato expression in nerve fibers and/or nerve endings at the whisker shaft (s) and base (b). Images below are from single focal planes (not z-projections) at boxed regions. Each image in A and B is a maximum z-projection of 20 focal planes at 1 µm spacing in coronal sections. Scale bar, 50 µm.DOI:http://dx.doi.org/10.7554/eLife.14140.005
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fig1s2: Absence of ChR2/tdTomato expression in vibrissal nerve fibers of EMX-cre;Ai27D mice.(A) Example images of two whisker follicles in an Emx1-Cre;Ai27D mouse. Expression of ChR2/tdTomato was present in intrinsic muscle (m.) surrounding the follicle, but was not observed in nerve fibers innervating the follicle. (B).Example images of two whisker follicles in a parvalbumin (PV)-Cre;Ai27D mouse. In contrast to the Emx1 results, PV mice showed a profusion of ChR2/tdTomato expression in follicular nerves, consistent with previous results (Sakurai et al., 2013). Dotted curved lines indicate the interior or the cavernous sinus. Arrowheads indicate ChR2/tdTomato expression in nerve fibers and/or nerve endings at the whisker shaft (s) and base (b). Images below are from single focal planes (not z-projections) at boxed regions. Each image in A and B is a maximum z-projection of 20 focal planes at 1 µm spacing in coronal sections. Scale bar, 50 µm.DOI:http://dx.doi.org/10.7554/eLife.14140.005
Mentions: We performed histological analysis to determine if these results could be explained by expression of ChR2 in muscles that control different types of whisker movements (Dörfl, 1982; Hill et al., 2008; Haidarliu et al., 2015). Indeed, analysis of the native fluorescence of the ChR2/tdTomato fusion protein in sections of the whisker pad revealed tdTomato expression in intrinsic and extrinsic whisker pad muscles (Figure 1C). Intrinsic muscles appeared on both superior and inferior sides of the follicle in coronal sections, and on the rostral side in transverse sections (Figure 1C1, C2), consistent with their sling-like morphology (Dörfl, 1982; Haidarliu et al., 2010). No fluorescence was evident in the infraorbital (sensory) nerve (Figure 1—figure supplement 2). Comparison of fluorescence intensity indicated the highest intensity in intrinsic sling muscles, followed by the deep extrinsic retractor muscle (pars maxillaris superficialis and pars maxillaris profunda of M. nasolabialis profundus), and lastly the superficial extrinsic protractor muscle (the pars media superior and pars media inferior of M. nasolabialis profundus,) (F(2,6) = 57.66, p=0.0001, repeated measures ANOVA followed by paired contrasts; p=0.0004 comparing external extrinsic and intrinsic, p=0.0086 comparing external extrinsic and internal extrinsic, p=0.0341 comparing intrinsic and internal extrinsic; n=4 follicles from one mouse) (Figure 1D). These results indicate that light-evoked whisker movements in Emx1-Cre;Ai27D mice arise from activation of ChR2 expressed in extrinsic and intrinsic whisker pad muscles.

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