Article Figures & Data
Figures
- Figure 1.
Motor pattern generation for walking in neonatal rat (3-7 d of age) spinal cord. A1, Electromyographic recordings of right forelimb (r. fore.) and bilateral hindlimb (l. and r. hind.) extensor muscles (ext.) during overground locomotion. A2, Phase diagram showing a single normalized locomotor cycle with onset and offset (±SEM as horizontal lines) of extensor EMG activity expressed as a percentage (5 animals). B, C, In vitro spinal cord preparation used to study coordination between spinal rhythm-generating circuitry during spontaneous (B1) and pharmacologically induced (C1) fictive locomotion. Extracellular recordings were made simultaneously from indicated cervical (C) and lumbar (L) ventral roots. In C1, stable episodes of fictive locomotion were evoked by perfusion of a saline containing serotonin (5-HT; 10-5 m), NMA (10-5 m), and DA (10-4 m). B2, C2, Phase diagrams (as in A2) illustrating “fictive gaits” corresponding to walking during spontaneous (B2; from 1 preparation) and pharmacologically induced (C2; from 18 preparations) rhythmicity. E, Extensor; F, flexor; r, right; l, left.
- Figure 2.
Effect of isotonic sucrose blockade of thoracic cord segments on cervical and lumbar locomotor rhythmicity. A, Left, Schematic of experimental procedure. Middle, Raw extracellular and integrated activity from cervical (bilateral C8) and lumbar (bilateral L2) ventral roots during 5-HT/NMA/DA-induced fictive locomotion. Right, Respective autocorrelograms of rectified data recorded from right C8 and right L2 ventral roots and cross-correlation between homolateral C8 and L2 activity showing an in-phase relationship (indicated by a positive cross-correlation coefficient at lag 0) in control conditions. Correlograms were computed from 120 to 190 s of activity and are superimposed with 95% (±2 SEM) confidence intervals (dashed lines). B, Loss of rostrocaudal coordination after sucrose block of thoracic segments (schematic to the left). Same presentation as in A. Note that, despite decoupling (indicated by near flat cross-correlogram), both cervical and lumbar generators continued to operate at regular (see autocorrelograms) and similar (see Fig. 3A) frequencies. C, Recovery of control in-phase anteroposterior coordination after removal of sucrose blockade. C, Cervical ventral root; L, lumbar ventral root.
- Figure 3.
Histograms of combined lumbocervical locomotor cycle periods (mean values ± SEM) in intact cord (open bars) and of independent lumbar and cervical periods (filled bars) during reversible sucrose blockade of thoracic cord (A) and after cord (at T7) transection (B). As indicated by the schematics at the left, A is from the same experiments as in Figure 2 and B is from a different series of experiments. Numbers of measured preparations are indicated in parentheses. ★p < 0.05. NS, Not significantly different.
- Figure 4.
Ability of lumbar generators to drive cervical locomotor rhythmicity. A, Raw extracellular and integrated cervical (bilateral C8) and lumbar (bilateral L2) ventral root activity from the same preparation during application of 5-HT/NMA/DA to the whole cord (A1; control conditions) and to the spinal region caudal to T10 (A2), caudal to T3 (A3), and then rostral to T10 (A4). Dashed lines below each integrated trace indicate zero levels of background activity corresponding to tonic discharge. B, Histograms illustrating the relationship between preparations (proportions indicated in parentheses) producing fictive cervical locomotion during caudal pharmacological activation and thoracic barrier position. C, Cervical ventral root; L, lumbar ventral root.
- Figure 5.
Caudorostral influence from lumbar to cervical generators in the absence of caudal synaptic inhibition. A1, B1, C1, Top, Schematics of experimental procedures; bottom, raw (upper) and integrated (lower) ventral root activity at cervical (bilateral C8) and lumbar (bilateral L2) levels during 5-HT/NMA/DA perfusion to the whole cord (A1) and (B1) when the spinal region caudal to T7 is additionally bathed with BIC (0.25 × 10-5 m) and STR (0.25 × 10-5 m). C1, Same saline conditions as in B1 but after additional sucrose blockade of axonal conduction through thoracic spinal segments. A2, B2, C2, Cross-correlograms (corresponding to A1, B1, C1, respectively) showing strict alternation (A2, control conditions) and then synchronization (B2, during lumbar BIC plus STR application) between bilateral ventral roots at both lumbar (L2) and cervical (C8) levels. C2, Cross-cord cervical alternation was restored by thoracic cord conduction block, although the lumbar roots continued to burst in synchrony. Each cross-correlogram was computed from 120 to 190 s of activity; dashed lines indicate 95% (±2 SEM) confidence interval. Autocorrelograms occurring under BIC/STR are added as insets in B2 and in the bottom of C2. A3, B3, C3, Mean cross-correlation coefficients (±SEM) of left-right motor root activity at cervical (C) and lumbar (L) levels under control saline (A3), during caudal blockade of synaptic inhibition (B3), and after additional thoracic conduction block (C3). Numbers of preparations are indicated in parentheses. ★★p < 0.01; ★★★p < 0.001. NS, Not significantly different.
- Figure 6.
Involvement of ascending lumbar excitation in bilateral cervical alternation and caudorostral coordination. A1, B1, C1, Ventral root activity at cervical (bilateral C8) and lumbar (bilateral L2) levels during 5-HT/NMA/DA perfusion to the whole cord (A1), after a midsagittal lesion extending from C1 to T7 (B1), and when BIC plus STR was additionally applied to the cord anterior to T7 (C1). A2, B2, C2, Corresponding cross-correlograms illustrating left-right cervical (C8 vs C8) and caudorostral (homolateral L2 vs C8) coordinations in control conditions (A2), after sagittal cervicothoracic lesion (B2), and then after rostral BIC plus STR application (C2). Sample size, 120-190 s. Dashed lines indicate 95% (±2 SEM) confidence interval. D, Mean cross-correlation coefficients (±SEM) of right versus left cervical ventral root bursts (D1) and homolateral L2 versus C8 (D2) motor bursts under the three different experimental conditions. Note that left-right alternation persisted at the cervical level despite longitudinal cord section and pharmacological blockade of cervical synaptic inhibition. Numbers of preparations are indicated in parentheses. ★★p < 0.01; ★★★p < 0.001. NS, Not significantly different.
- Figure 7.
Lack of effect of blockade of cervical synaptic inhibition on bilateral lumbar rhythmicity. A1, B1, Ventral root activity at cervical (bilateral C8) and lumbar (bilateral L2) levels during 5-HT/NMA/DA perfusion of the whole cord (A1) and when BIC plus STR is added rostrally to T7. A2, B2, Cross-correlograms showing coordination between bilateral ventral roots at C8 and L2 levels in control conditions (A2) and after rostral BIC plus STR application (B2). Note that left and right lumbar rhythmicity continues to alternate while cervical activity becomes bilaterally synchronized. C, Mean cross-correlation coefficients (±SEM) of right versus left motor root activity. Numbers of preparations are indicated in parentheses. ★p < 0.05; ★★★p < 0.001.
- Figure 8.
Summary of central spinal pathways contributing to interlimb coordination in quadrupedal locomotion. See Discussion for an explanation. EXT, Extensor; FLE, flexor; T, thoracic segment.
