Heterozygous Dcc Mutant Mice Have a Subtle Locomotor Phenotype

Projections of the corticospinal tract in Dcc^+/− and WT mice. A, Schematic drawing of transverse brainstem sections showing a unilateral corticospinal tract axon bundle (gray area) as it projects from the left motor cortex to the contralateral dorsal funiculus. B, BDA tracing of the corticospinal tract of three-month-old WT and Dcc^+/− mice shows no difference in the projection of corticospinal tract axons at the level of the pyramidal decussation.

Dcc^+/− adult mice exhibit normal lateralization of the corticospinal tract. A, Examples of EMG activity of contralateral and ipsilateral TA. A 30-ms train of cathodal pulses (duration 0.2 ms, interval 2.8 ms) was delivered in either the caudal forelimb area or the hindlimb area. Bottom, Higher temporal resolution of the contralateral trace illustrates latency and response (motor spikes raster) measurements. B, left, Threshold for evoking activity in the contralateral BB (BB). Right, Threshold for evoking activity in the contralateral TA. Threshold is defined as motor spikes elicited in at least 50% of trials. C, Thresholds for pairs of hindlimbs (HL; circle) or forelimbs (FL; square). Contralateral is on the x-axis and ipsilateral on the y-axis. D, Success rate (percentage) for evoking an EMG response versus the threshold of the contralateral side. Dashed line indicates the threshold, defined as a success rate of 50%. Data are for pairs of muscle recorded with EMGs. Contralateral is in black and ipsilateral in gray. E, left, Ipsilateral versus contralateral averaged latencies for pairs of muscles recorded with EMGs. Middle, An example of EMG traces to illustrate the delay between contralateral and ipsilateral sides. Right, Boxplot of contralateral to ipsilateral delays. F, Averaged number of motor spikes evoked by ICMS for the contralateral (x-axis) and ipsilateral (y-axis) sides. WT in black and Dcc^+/− in gray; *** P < 0.001.

Locomotor pattern of adult Dcc^+/− and WT mice during treadmill locomotion. A–D, Mean and (E–H) CV of step cycle duration (A, E), swing duration (B, F), stance duration (C, G), and duty cycle of the stance phase (D, H) of WT and Dcc^+/− mice at three different treadmill speeds (15, 20, and 30 cm/s). WT in black and Dcc^+/− in gray; *p < 0.05 and **p < 0.01 (for statistics, see Extended Data Table 4-1).

Swing and stance duration as functions of step cycle duration during treadmill locomotion. Swing (top panels, A, B) and stance (bottom panels, C, D) duration as functions of step cycle duration of WT and Dcc^+/− mice. Note three different treadmill speeds were combined. WT in black and Dcc^+/− in gray.

Bilateral and homolateral interlimb coordination during treadmill locomotion. A–C, Polar plots showing the mean vector for the relationships between left and right forelimbs (A), left and right hindlimbs (C), and between homolateral forelimb and hindlimb (B) of WT (black circles) and Dcc^+/− (gray circles) at treadmill speeds of 15, 20, and 30 cm/s. The position on the polar plot indicates mean phase; the distance from the center of the polar plot indicates strength of the coupling (Rayleigh). Symbols represent individual mice at a treadmill speed of 20 cm/s, vectors represent the mean phase coupling of WT and Dcc^+/− groups at 15, 20, and 30 cm/s. Dashed inner circles represent a Rayleigh value of 0.5. D–F, Phase of the coupling between left and right forelimbs (D), hindlimbs (F), and (E) forelimb-hindlimb as a function of locomotor frequency during treadmill locomotion at 15–30 cm/s. WT in black and Dcc^+/− in gray.

Locomotor gait occurrence during treadmill locomotion. A, Gray-scaled matrixes of the percentage of occurrence of a gait (column) at 15, 20, and 30 cm/s (row) for WT and Dcc^+/− mice. The sum of a row equals 100%. B, Box plots representing the percentage of gait occurrence at 15, 20, and 30 cm/s; ****p < 0.0001.

Dcc protein levels in Dcc^+/− and WT spinal cords. Left, Western blotting of Dcc in embryonic WT and Dcc^+/− spinal cords. Dcc control is a cell lysate overexpressing a Dcc cDNA. Right, Dcc/actin ratio relative to WT (Dcc^+/+); **p < 0.01.

Locomotor pattern and rhythm during neonatal locomotor-like activity. A, B, Examples of L5 and L2 ENG recordings of WT (A) and Dcc^+/− (B) mice on bath application of drugs (8 μm 5HT and 2.5, 5, or 7.5 μm NMDA). C–J, Mean and data of cycle duration (C, G), burst duration (D, H), duty cycle (E, I), and burst amplitude (F, J) of WT and Dcc^+/− L2 (C–F) and L5 (G–J) ENGs at different NMDA concentrations (8 μm 5HT and 2.5, 5, or 7.5 μm NMDA); *p < 0.05 (for statistics, see Extended Data Table 9-1).

Variability in ENG waveforms during neonatal locomotor-like activity. Mean and CVs of cycle duration (A, E), burst duration (B, F), duty cycle (C, G), and burst amplitude (D, H) of WT (black circles) and Dcc^+/− (gray triangles) of L2 (A–D) and L5 (E–H) ENG waveforms at different NMDA concentrations; *p < 0.05 (for statistics, see Extended Data Table 10-1).