Fig. 6

Figure 6. th2-Expressing Dopamine Neurons Drive Locomotion by Activating Spinal Projection Neurons in the Mid- and Hindbrain (A) Schematics of the experimental preparation for simultaneous calcium imaging of spinal projection neurons (SPNs) and motor nerve (MN) recordings. SPNs are labeled by backfilling from the spinal cord with the dextran conjugated calcium sensitive dye Cal-590. The red box highlights the brain region expanded in (B). (B) Left: maximum intensity projection image of SPNs in the midbrain and hindbrain. Right: cell bodies of imaged SPNs are outlined. VSN, vestibulospinal neuron. (C) Normalized calcium fluorescence change versus time for identified SPNs shown in (B) during optogenetic stimulation in Tg(th2:GAL4; uas:chr2-eyfp) fish. Uniquely colored traces indicate different neurons within each class. The bottom black trace represents the motor nerve recording; the blue box indicates the photoactivating stimulus, also apparent in the artifactual increase in fluorescence signal for each cell. (D) Whole-cell current clamp recording from a representative nMLF neuron, MeLr, during optogenetic stimulation of th2-expressing neurons with simultaneous motor nerve recording. (D’) An expanded view of the shaded area in the lower panel is shown. (E) Boxplot showing the latency from the photoactivating stimulus onset to the first MeLr action potential. n = 4 fish, 12 trials. (F) Boxplot showing mean firing frequencies of the MeLr in the 500-ms time windows before, during, and immediately after photoactivating stimulation. n = 4 fish, 12 trials. (G) Boxplot showing the latency from the first MeLr action potential to the onset of motor nerve activity. n = 4 fish, 11 trials.