Figure 5.

MLR neurons with spinal projections regulate body extension

(A) Approach to target the optogenetic inhibitor stGtACR2 into MLR>SC neurons for loss-of-function (LOF) experiments (n = 13).

(B) Left: snapshots from video analysis of rearing mouse just before laser onset (0 s) to +200 ms after laser onset, with one intermediate frame (snout: yellow). Right: Cartoon representation of body contraction effect induced by optogenetic LOF of MLR>SC neurons during rearing.

(C) DeepLabCut tracking of snout position upon optogenetic inhibition of MLR>SC neurons (white points before stimulation; orange to yellow points from 0 to 500 ms of laser stimulation), showing single trials (left) and normalized snout trajectory over all trials and mice (right) (n = 13).

(D) Average (±SEM) of normalized body length (red) of rearing mice and single mouse averages (gray) upon optogenetic inhibition (blue window) of MLR>SC neurons and reliability of laser-induced decrease in average body length (0.5 being chance level) in mice expressing stGtACR2 (LOF, n = 13) or GFP (Ctrl, n = 5) in MLR > SC neurons.

(E) Average (±SEM) of locomotor speed upon closed loop optogenetic inhibition (blue window, red line) of MLR>SC neurons during locomotion and control trials with no laser stimulation (black line) with single-mouse averages of the two conditions and reliability of locomotor speed decrease (n = 13), compared to the reliability of occurrence of the same phenotype in control mice upon light application (n = 5).

(F) Approach used to target the optogenetic activator ReaChR into MLR>SC neurons for gain-of-function (GOF) experiments (n = 10 mice).

(G) Left: snapshots from video analysis of stationary mouse just before laser onset (0 s) to +200 ms after laser onset, with one intermediate frame. Snout, head base, forelimbs, hindlimbs, body center, genital, and tail base are marked through DeepLabCut analysis. Right: cartoon representation of the body extension effect induced by optogenetic GOF of MLR>SC neurons in stationary mice.

(H) DeepLabCut tracking of body part position upon optogenetic activation of MLR>SC neurons through laser application (white points before stimulation; orange to yellow points from 0 to 500 ms of laser stimulation), showing single trials (left) and normalized body part trajectories over all trials and mice (right) (n = 10; compared to n = 5 control mice).

(I) Average (±SEM) of normalized body length (green) of stationary mice and single-mouse averages (gray) upon optogenetic activation (blue window) of MLR>SC neurons and reliability of laser induced increase in body length (n = 10) compared to the probability of observing an increase in body length in control mice upon light application (n = 5).

(J) Binned average path length (±SEM) for head (average of snout and head base), forelimbs (FL; average of left and right forelimb), and hindlimbs (HL; average of left and right hindlimb) for stationary mice upon laser application (blue window) to MLR>SC neurons for optogenetic activation (n = 10).

(K) Graph depicting probability above baseline levels (baseline: application of a 0-mW laser with same closed-loop protocol) to initiate at least one cycle of four limb stepping after body stretching upon optogenetic activation of MLR>SC neurons (n = 10) and light application in control mice (n = 5). Stimulations were performed when mice were sedentary with all four paws on ground in an unrestrained open field environment.

See also Figure S6.

∗p ≤ 0.05 ∗∗p ≤ 0.01.