Extended Data Fig. 6: Spatially targeted photostimulation elicits robust muscle responses.
From: Wireless closed-loop optogenetics across the entire dorsoventral spinal cord in mice
Step 1: Timeline detailing key experiments. Step 2: Post-moterm verification of ChR2 expression. Photographs show the robust expession of ChR2 in the spinal cord and dorsal root ganglia of Thy1-ChR2 mice. ChR2 is expressed in proprioceptive neurons of the dorsal root ganglia, as illustrated with the overlap between ChR2-eYFP with parvalbumin mRNA (HCR). Step 3: Experimental set up to evaluate muscle responses and leg kinematics when delivering single pulses of photostimulation while the mouse is suspended in the air in a robotic body weight support system. Leg movements are reconstructed following one pulse of photostimulation delivered over the rostral versus caudal lumbar spinal cord. Step 4: Associated muscle responses in the iliopsoas and gastrocnemius medialis muscles are shown following one pulse of photostimulation delivered over the rostral versus caudal lumbar spinal cord. Step 5: The bar plot reports the mean range of motion at the knee and hip following photostimulation over the rostral and caudal lumbar spinal cord (n = 10 mice, two-sided unpaired t-test, p= 0.2445 and p = 0.3153 respectively, mean±s.e.m.). Note that the iliopsoas muscle is activated by photostimulation of rostral lumbar segments, as expected based on the anatomical position of the motoneurons innervating this muscle within these spinal segments and pre-motor interneurons, as well as by photostimulation of caudal lumbar segments through the activation of primary afferent fibres embedded in the rostral posterior roots that travel along the spinal cord, in the vicinity of the caudal LED channel. The different location at which photostimulation depolarizes afferent fibers is reflected in the increase in the latency of muscle responses with photostimulation over caudal versus rostral lumbar segments and the clear singluar wave. Step 6: The plots report the area under the curve (AUC) of rectified muscle responses of the illiopsoas and grastrocnemius following photostimulation of the rostral versus caudal lumbar spinal cord with increasing intensity (n = 5 mice, one-way ANOVA, ***, p < 0.0001, mean±s.e.m.).
