Figure 3. Effects of light pulse duration on a heterogeneous SST interneuron population.
(A–E) Sst-Cre+/−; ROSA26LSL-tdTomato animals express the tdTomato reporter in SST-positive interneurons, which display heterogeneous morphologies (scale bars, 50 μM). (F) Sst-Cre+/−; ROSALSL-ChR2-EYFP mice display diffuse expression of ChR2-EYFP throughout the cortex (scale bar, 1 mm). Inlay shows zoomed image of ChR2-expressing SST cortical interneurons (scale bar, 100 μM). (G) Steady firing of a regular-spiking ChR2-expressing SST cortical interneuron in response to brief light pulses (20 Hz, 10 ms pulse width). (H) Prolonged light pulse duration (20 Hz, 49 ms pulse width) leads to depolarization block in regular-spiking SST cortical interneurons. (I) Moderate current injection (30 pA) leads to steady firing of regular-spiking SST cortical interneurons expressing ChR2. (J) High current injection (100 pA) results in depolarization block of regular-spiking ChR2-expressing SST cortical interneurons. (K) Steady firing of a fast-spiking SST cortical interneuron in response to brief light pulse stimulation (20 Hz, 10 ms pulse width). (L) Prolonged light pulse duration (20 Hz, 49 ms pulse width) leads to robust firing in fast-spiking SST cortical interneurons. (M) Current injection (120 pA) leads to steady firing of fast-spiking SST interneurons. (N) High current injection (500 pA) results in robust firing of fast-spiking SST cortical interneurons.