Figure 2. The axons of position-encoding (claw) proprioceptors are not suppressed during active leg movements.
(A) Experimental setup for two-photon calcium imaging from VNC neurons and 3D leg tracking of the left front leg of tethered flies on a treadmill.
(B) Computational models of FeCO proprioceptors translating time courses of joint angles into time courses of calcium signals. The activation functions were fitted to calcium signals measured during passive leg movement.
(C) Top: Confocal image of position-encoding claw axons in the VNC. The black box indicates the imaging region. Green: GFP; gray: neuropil stain (nc82). A: anterior; L: lateral. Bottom: Mean tdTomato signal within the imaging region during an example trial.
(D) Example trial of two-photon calcium imaging of claw axons and behavior tracking on the treadmill.
(E) Cross-correlation coefficient between predicted and measured calcium signals per trial at a time lag of zero. The black line shows the median. The black dot marks the trial shown in (D). n: number of trials; N: number of flies.
(F) Median predicted and measured calcium signals as a function of the median femur-tibia angle for individual resting bouts. Bouts are 1 ≥ s in duration. The black and green line indicate the mean calcium signals in bins of 10°. The dashed blue line indicates the resting angle at which activity is minimal.The blue rectangle indicates the range of resting angles analyzed in (G). The plot on top shows a kernel density estimation of the femur-tibia angles during resting. The solid blue line indicates the most frequent femur-tibia angle (mode of the distribution). n: number of resting bouts; N: number of flies.
(G) Predicted and measured calcium signals aligned to the transitions into and out of movement. Movement includes walking and grooming. Thin lines show animal means, thick lines show mean of means, shadings show standard error of the mean. n: number of transitions; N: number of flies.