Figure 4. Optogenetic activation of Sst+ or Pvalb+ interneurons.

(a) Schematic of optogenetic manipulation in ChR2/Sst mice in which blue light directly activates Sst+ cells (cyan cells). (b) Rasters of tone-evoked action potentials for a representative suppressed unit without (top) and with (bottom) activation of Sst+ cells. The black sine wave represents the duration of the sound, the cyan bar represents the duration and power of the light, and the yellow bar indicates the response period used to construct FTCs. (c) FTCs (mean ± SEMs) derived from tone-evoked firing rates (FRs) without (black) and with (red) activation of Sst+ cells for the representative unit in (b). Inset shows unit waveforms on trials without (black) and with (red) activation of Sst+ cells. (d) Distribution of the ratio of light-on to light-off FRs during the response period in ChR2/Sst mice for frequency tuned units. Red bars indicate units with significantly suppressed FRs (n = 64 of 97 units), grayish red bars indicate units with no significant change in FR (n = 19 of 97 units), and cyan bars with red outline indicate units with significantly increased FRs (n = 14 of 97 units). (e–h) As (a–b), but in ChR2/Pvalb mice, in which blue light directly activates Pvalb+ cells (e). (f,g) show the rasters and FTCs of a representative suppressed unit with and without activation of Pvalb+ cells. In (h), blue bars indicate units with significantly suppressed FRs (n = 62 of 103 units), grayish blue bars indicate units with no significant change in FR (n = 20 of 103 units), and cyan bars with blue outline indicate units with significantly increased FRs (n = 19 of 103 units).

DOI: http://dx.doi.org/10.7554/eLife.18383.013

Figure 4—figure supplement 1. ChR2(GFP) co-localizes with somatostatin in ChR2/Sst mice and with parvalbumin in ChR2/Pvalb mice.

(a) Immunostaining of a brain slice from a ChR2/Sst mouse. (Left) Grayscale image of GFP stain. (Middle) Grayscale image of somatostatin stain. (Right) Merged image of GFP (green) and somatostatin (red) stains. Magenta arrows indicate three examples of putative Sst+ cells. Note that red and green somata mostly overlap. Scale bars are 50 microns. (b) Immunostaining of a brain slice from a ChR2/Pvalb mouse. (Left) Grayscale image of GFP stain. (Middle) Grayscale image of parvalbumin stain. (Right) Merged image of GFP (green) and parvalbumin (red) stains. Magenta arrows indicate three examples of putative Pvalb+ cells. Note that red and green somata mostly overlap. Scale bars are 50 microns.

DOI: http://dx.doi.org/10.7554/eLife.18383.014

Figure 4—figure supplement 2. Interneuron activation decreases firing rates and increases signal to noise ratio.

(a) An example unit’s mean firing rate (FR) ± SEMs relative to sound onset, without (black) and with (red) activation of Sst+ interneurons. The black sine wave represents the duration of the sound, the green bar represents the duration and power of the light, the orange bar indicates the 50 ms time period used to calculate spontaneous FR, and the yellow bar indicates the 50 ms response period used to calculate tone-evoked FR. (b) Same as (a), but of an example unit recorded from a ChR2/Pvalb mouse without (black) and with (blue) activation of Pvalb+ interneurons. (c) The spontaneous firing rate (FR) (calculated as average spikes/second in the 50 ms before the stimulus) with versus without light for each tuned unit whose sound-evoked FR was increased by light. Left: ChR2/Sst, n = 64 units; right: ChR2/Pvalb, n = 62 units. (d) Spontaneous rate ratio (defined as light-on FR divided by light-off FR) for the units in (a). Activation of Sst+ interneurons decreases the spontaneous rate ratio (signrank p=1.1 × 10⁻¹¹), as does activation of Pvalb+ interneurons (signrank p=5.1 × 10⁻¹¹), but these ratios are not different from each other (ranksum p=0.56). (e) Same as (c), but for sound-evoked FRs (calculated as average spikes/second in the 50 ms after response onset). (f) Sound-evoked rate ratio for the units in (e). Activation of Sst+ interneurons decreases the sound-evoked rate ratio (signrank p=3.5 × 10⁻¹²), as does activation of Pvalb+ interneurons (signrank p=7.6 × 10⁻¹²), but these ratios are not different from each other (ranksum p=0.76). (g) Same as (c), but for baseline-subtracted sound-evoked FRs (defined as evoked FR minus spontaneous FR). (h) Baseline-subtracted sound-evoked ratio for the units in (g). Activation of Sst+ interneurons decreases the baseline-subtracted sound-evoked ratio (signrank p=2.2 × 10⁻¹⁰), as does activation of Pvalb+ interneurons (signrank p=7.6 × 10⁻¹²), but these ratios are not different from each other (ranksum p=0.31). (i) Same as (c), but for signal to noise ratio (SNR: defined as sound-evoked FR divided by spontaneous FR). (j) SNR ratio for the units in (i). Activation of Sst+ interneurons increases SNR ratio (signrank p=5.2 × 10⁻¹²), as does activation of Pvalb+ interneurons (signrank p=1.6 × 10⁻¹¹), but these ratios are not different from each other (ranksum p=0.20).

DOI: http://dx.doi.org/10.7554/eLife.18383.015