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Figure 2 Activation of reticulospinal V2a neurons by Gq-coupled bistable rhodopsins. (A) Schematic of experimental devices for induction of swimming behavior and a larva embedded in agarose. The hindbrain region was irradiated with light by using a patterned illuminator. Tail (caudal fin) movements were monitored by a high-speed camera with infrared light. (B) Expression of SpiRh1, SpiRh1[S186F], and channel rhodopsin wide receiver (ChRWR) in hindbrain reticulospinal V2a neurons. 3-dpf (days post fertilization) Tg(vsx2:GAL4FF);Tg(UAS-hsp70l:SpiRh1-Flag-P2A-TagCFP, myl7:mCherry);Tg(UAS:RFP), Tg(vsx2:GAL4FF);Tg(UAS-hsp70l:SpiRh1[S186F]-Flag-P2A-TagCFP, myl7:mCherry);Tg(UAS:RFP) and Tg(vsx2:GAL4FF);Tg(UAS:ChRWR-EGFP);Tg(UAS:RFP) larvae were fixed and stained with anti-Flag or anti-GFP (EGFP, green), and anti-DsRed (RFP, magenta) antibodies. Inset: higher magnification views of the boxed areas showing double-labeled neurons. (C, D, E) Tail movements of 3-dpf Tg larvae expressing SpiRh1 (C), SpiRh1 [S186F] (D), and ChRWR (E) in the reticulospinal V2a neurons after light stimulation. The hindbrain area was stimulated with light (0.4 mW/mm2) of wavelengths of 520 nm (for SpiRh1), 405 nm (for SpiRh1[S186F]), and 470 nm (for ChRWR) for 1 s (for SpiRh1 and SpiRh1[S186F]) or 100 ms (for ChRWR). Typical movies are shown in Figure 2—videos 1–3. Scale bar = 150 μm in (B), 10 μm in the insets of (B).