Figure 3.

Optogenetic Stimulation of Brainstem Locomotor Circuits

(A) Schematic representation of PPN optogenetic stimulation experiments. After injection of AAV5-CaMKIIa-hChR2(H134R)-EYFP in PPN (top), animals were implanted with an optic fiber in PPN and tetrodes in HDB and MEC (bottom), in order to record activity of speed cells in the latter regions in response to PPN stimulation.

(B) Left: sagittal immunofluorescence photomicrograph of the brainstem of one representative ChR2-expressing animal (rat number shown in top left corner) implanted with an optic fiber in PPN (YFP expression in ChR2 neurons in magenta). The anatomical boundary of PPN (white dashed line) was defined with ChAT immunofluorescence staining (cyan). White arrows indicate tip of optic fiber. Right: increases of average running speed during PPN optogenetic stimulation (laser on, blue window) for the animal identified on the left. Gray line represents mean ± SEM running speed for all laser-on periods during one stimulation session.

(C) Individual (gray) and group-average (orange) running speed between baseline (−5 to 0 s, before laser onset) and stimulation (0 to 5 s, after laser onset) epochs for the 13 ChR2-expressing animals that responded with increases in running speed (speed values of each animal averaged over seven to ten stimulation sessions).

(D) Same as in (B), but for one of four animals that displayed reduced locomotion or freezing during PPN stimulation.

^∗∗p < 0.01 and ^∗∗∗p < 0.001, Wilcoxon signed-rank test between baseline and stimulation epochs. Scale bars: 500 μm.