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W2155354145 abstract "Locomotor training of rats held in an upright posture has been used recently to restore locomotion after spinal cord injury. Our results show that the upright posture alone improves locomotor recovery in spinal rats. This improvement is reversed by the removal of cutaneous afferent feedback from the paw, showing that sensory feedback from the foot facilitates the spinal central pattern generator (CPG) for locomotion. 5-HT2 and 5-HT1A/7 agonists improve locomotion in the horizontal posture but can impair locomotion in the upright posture, suggesting that a proper balance of afferent feedback from the foot and 5-HT receptor activation is necessary for optimal locomotor recovery. Our results provide new insights into the organization of the CPG for locomotion and the evolution of hominid bipedalism. The potent effects of cutaneous afferents from the paw revealed here must be taken into account in the design of strategies to restore locomotion after spinal cord injury. Abstract Recent studies on the restoration of locomotion after spinal cord injury have employed robotic means of positioning rats above a treadmill such that the animals are held in an upright posture and engage in bipedal locomotor activity. However, the impact of the upright posture alone, which alters hindlimb loading, an important variable in locomotor control, has not been examined. Here we compared the locomotor capabilities of chronic spinal rats when placed in the horizontal and upright postures. Hindlimb locomotor movements induced by exteroceptive stimulation (tail pinching) were monitored with video and EMG recordings. We found that the upright posture alone significantly improved plantar stepping. Locomotor trials using anaesthesia of the paws and air stepping demonstrated that the cutaneous receptors of the paws are responsible for the improved plantar stepping observed when the animals are placed in the upright posture. We also tested the effectiveness of serotonergic drugs that facilitate locomotor activity in spinal rats in both the horizontal and upright postures. Quipazine and (±)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT) improved locomotion in the horizontal posture but in the upright posture either interfered with or had no effect on plantar walking. Combined treatment with quipazine and 8-OH-DPAT at lower doses dramatically improved locomotor activity in both postures and mitigated the need to activate the locomotor CPG with exteroceptive stimulation. Our results suggest that afferent input from the paw facilitates the spinal CPG for locomotion. These potent effects of afferent input from the paw should be taken into account when interpreting the results obtained with rats in an upright posture and when designing interventions for restoration of locomotion after spinal cord injury. Locomotor recovery after spinal cord injury in animals and humans depends upon the presence of a central pattern generator (CPG) for locomotion in the spinal cord, since the injury interrupts the descending pathways normally responsible for the control of locomotion. Locomotor training is a powerful means of activating the CPG and promoting locomotor recovery after spinal cord injury. Loading of extensor muscles is a major factor contributing to the success of locomotor training in humans (Harkema et al. 1997; Dietz, 1998) and in spinal animals (de Leon et al. 2002; Timoszyk et al. 2002, 2005). The physiological basis for the effect of loading, based on current knowledge of the central actions of proprioceptors, has been reviewed in detail (McCrea & Rybak, 2008; Pearson, 2008). Cutaneous input from the plantar surface of the paw also constitutes afferent input related to loading of the limb, and it is also known to have a potent influence on locomotion in spinal animals (Bouyer & Rossignol, 2003a,b). Recent studies on recovery of locomotor function after spinal cord injury have employed a training method with rats held in a bipedal upright posture. When subjected to a combination of training, epidural stimulation and drug application, such animals recover weight bearing locomotion on a treadmill that can be sustained for long periods (Courtine et al. 2009; Musienko et al. 2011). However, the impact of the upright posture has not been explored, despite the fact that this change in posture, because of its impact on hindlimb loading, has the potential to alter locomotor activity on its own. Therefore, we designed experiments to test the effects of the upright posture alone on locomotor ability of chronic spinal rats. Key elements in recovery of locomotor function drawn from work using rats in an upright posture were the actions of quipazine, a 5-HT agonist acting at 5-HT2A, 5-HT2B and 5-HT2C receptors, and (±)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT), a 5-HT agonist acting at 5-HT1A/7 receptors (Fong et al. 2005; Ichiyama et al. 2008; Courtine et al. 2009, 2011; Musienko et al. 2011). Previous demonstrations of the efficacy of 5-HT agonists and grafts of 5-HT neurons for the restoration of locomotion in the absence of any other intervention have been carried out in spinal rodents (Feraboli-Lohnherr et al. 1999; Gimenez y Ribotta et al. 2000; Schmidt & Jordan, 2000; Sławińska et al. 2000; Hochman et al. 2001; Antri et al. 2002, 2003, 2005; Landry & Guertin, 2004; Majczyński et al. 2005; Landry et al. 2006) and spinal cats (Barbeau & Rossignol, 1990; Brustein & Rossignol, 1999) walking in the normal horizontal posture. Any changes in the response to 5-HT that might occur when the animals are held in the upright posture have not been assessed. We report here that the upright posture alone dramatically improves locomotion in spinal rats. Reducing afferent feedback derived from the hindlimbs during air-stepping or after anaesthesia of the hindpaw showed that the facilitation of plantar stepping that occurs in rats in the upright posture is due largely to afferent feedback from the plantar surface of the paw. Moreover, in contrast to the horizontal posture, the ability of 5-HT receptor activation to improve locomotor capability in animals placed in the upright posture was altered. Experiments were performed on female Wistar Albino Glaxo (WAG) rats (Charles River) (10 spinal and 5 intact). In the case of spinal animals, the experiments were commenced 10 weeks after spinal cord injury. All surgical and experimental procedures were conducted with care to minimize pain and discomfort of animals with the approval of the First Local Ethics Committee in Poland, according to the principles of experimental conditions and laboratory animal care of the European Union and the Polish Law on Animal Protection, and of the University of Manitoba Animal Care Committee, in accordance with the guidelines of the Canadian Council on Animal Care. All the procedures used in this study conform to the principles of UK regulations, as described in Drummond (2009). We performed complete transection of the spinal cord using surgical procedures described in detail in previous papers (Sławińska et al. 2000; Majczyński et al. 2005). Briefly, in ten 3-month-old WAG rats under deep anaesthesia (isofluorane, 2% plus Butomidor, 0.05 mg (kg body weight (b.w.))−1), and under sterile conditions, a laminectomy of the Th8 vertebrae was performed. The spinal cord was completely transected at the thoracic level Th9/10. To prevent the possibility of axonal regrowth through the cavity of the lesion, 2–3 mm of spinal cord tissue was aspirated using a glass pipette. Then the muscles and fascia overlying the paravertebral muscles were closed in layers using sterile sutures, and the skin was closed with stainless-steel surgical clips. After surgery, the animals received a non-steroidal anti-inflammatory and analgesic treatment (s.c., Tolfedine, 0.4 mg (100 g b.w.)−1), and during the following 8 days, the animals were given antibiotics (s.c. Baytril, 0.5 mg (100 g b.w.)−1 and gentamycin, 0.2 mg (100 g b.w.)−1). During this postoperative period, the bladder was emptied manually twice a day until the voiding reflex was re-established. When the data collection was completed the animals were killed by i.p. injection of an overdose of pentobarbital (150 mg kg−1). Then the spinal cords were inspected to confirm that the transection was complete. Ten weeks after spinal cord transection the animals were anaesthetized with Equithesin (i.p. 0.35 ml (100 g b.w.)−1)) and bipolar EMG recording electrodes were implanted in the soleus (Sol) and tibialis anterior (TA) muscles of both hindlimbs. The electrodes were made of Teflon-coated stainless-steel wire (0.24 mm in diameter; AS633, Cooner Wire, Chastworth, CA, USA). The tips of the electrodes with 1–1.5 mm of the insulation removed were pulled through a cutaneous incision at the back of the animal, and each of the hook electrodes was inserted into the appropriate muscle, where it was secured by a suture. The distance between the tips of electrodes was 1–2 mm. The ground electrode was placed under the skin on the back of the animal at some distance from hindlimb muscles. A custom-made connector with the other ends of the wires fixed to it, covered with dental cement (SpofaDental) and silicone (3140 RTV, Dow Corning), was secured to the back of the animal. A wire loop left under the skin on the back of the animal prevented the electrodes from being pulled out from the muscles during movements. The incisions on the hindlimbs were closed. To prevent infection animals were treated by single dose of antibiotic (s.c. Baytril, 0.5 mg (100 g b.w.)−1). EMG recordings started 3–5 days after electrode implantation. Electrode position in the muscles was verified visually after the animals were killed. The hindlimb locomotor pattern was investigated 3–4 months after spinal cord transection with the animals placed on a moving treadmill (treadmill speed 5–10 cm s−1) in either a horizontal or an upright posture (Fig. 2A). For the horizontal posture the rats were manually positioned with their forelimbs on a platform above the treadmill and their hindlimbs touching the moving belt. For the upright posture, the rat was manually held above the treadmill belt in a vertical position with the hindlimbs touching the moving belt. In intact rats the EMG activity of hindlimb muscles was investigated during spontaneous locomotor movement on a treadmill. In order to obtain sustained locomotion with horizontal posture without pauses in the intact animals, the treadmill speed was kept at 20 cm s−1. In the upright posture the intact animals were unwilling to sustain locomotor activity at speeds above 10 cm s−1, and so these trials were done at 5–10 cm s−1. Manual stimulation of the tail was used to elicit locomotor-like hindlimb movements in the spinal rats. Stimulation of tail or perineal area afferents is routinely used for eliciting locomotion in cases of complete spinal cord transection (Meisel & Rakerd, 1982; Pearson & Rossignol, 1991; Sławińska et al. 2000; Majczyński et al. 2005; Rossignol et al. 2006; Lev-Tov et al. 2010). We adopted it as a suitable method for comparing locomotion in the horizontal and upright postures. The tail was stimulated in an attempt to induce weight support and stepping movements as previously described in spinal rats in the horizontal posture (Sławińska et al. 2000; Majczyński et al. 2005). In the upright posture the spinal rats were held above the treadmill by an experimenter who adjusted body weight support and tail stimulation to obtain the best hindlimb walking pattern. The EMG activity of two muscles, the extensor soleus (Sol) and the flexor tibialis anterior (TA), of both hindlimbs was simultaneously digitized and stored on a computer (3 kHz sampling frequency) as previously described (Sławińska et al. 2000; Liu et al. 2009). The EMG activity was simultaneously recorded with synchronized video recordings, thus enabling the further off-line analysis of precisely verified portions of EMG activity related to the best locomotor performance in every animal. EMG amplitude was determined from filtered (band pass 0.1–1 kHz), integrated (20 Hz) and rectified EMG records of 10–30 consecutive steps. Peak amplitude, burst duration and burst area were determined using Winnipeg Spinal Cord Research Centre custom analysis programs (http://www.scrc.umanitoba.ca/doc/). The locomotor pattern was analysed using polar plots to determine the coordination between flexor and extensor muscles on the two sides, as well as left–right coordination among the muscles of the left and right sides, as previously described (Liu et al. 2009). The analysis of the relationships between the EMG burst duration and step cycle duration was performed using the regression line method. The correlation coefficients from the polar plots and the slopes from regression line analysis from EMG recordings in pre-drug conditions were then compared to those obtained after the drug applications using Student's paired t test. The normal distribution of the data was confirmed using a Shapiro–Wilk test. For comparison of the EMG cycle or burst duration as well as the peak amplitude and area expressed as a ratio of the control values (Fig. 3) the non-parametric Wilcoxon's test was used. Spinal rats placed in the upright posture (n= 6) display near-normal locomotor patterns A, the same rat in the horizontal posture (upper panel) and the upright posture (lower panel) is depicted. C, the relationships between the step cycle durations and burst durations for the left and right TA and Sol muscles. F, bar graph showing that the slopes of this relationship differ significantly between the horizontal and upright posture trials (Student's paired t test). D and E, polar plots illustrating the interlimb (D) and intralimb (E) coordination changes that occur when the animals is placed in the upright posture (lower panel) compared to the horizontal posture (upper panel). G, bar graph showing the mean angle (a, ±SD) of polar plots for the left–right TA (l-r) and for the right Sol–right TA (r S-T) relationships. H, bar graph demonstrating the mean correlation coefficients (r, ±SD) for the left–right TA (l-r) and for the right Sol–right TA (r S-T) relationships, indicating a highly significant increase in r for inter- and intralimb coordination in the upright posture trials. Student’t test: *P < 0.05, **P < 0.005, ***P < 0.0005. Changes in mean ± SD cycle duration, peak amplitude, burst duration and burst area established on the basis of EMG recordings from soleus (Sol) and tibialis anterior (TA) muscles of both hindlimbs during locomotion in the horizontal and upright postures in different experimental conditions Each bar is the mean of 4–6 spinal rats and 5 experiments from intact rats taken from 10–30 consecutive steps in both hindlimbs during rhythmic movements in a particular experimental condition. The means in A are expressed as the percentage of that obtained during locomotor trials in the horizontal posture. The means in B are expressed as the percentage of the values obtained during trials in the upright posture. 100% represents the mean value obtained in the control situation for each analysed index (white bar). The black bar on the left represents results obtained during locomotor trials of intact rats in the upright posture in comparison to the horizontal posture (A) and in the horizontal posture in comparison to the upright posture (B). For example, in the case of the cycle duration index, the mean cycle duration of intact rats in the upright posture is longer than that obtained during locomotor trials in the horizontal posture. Similarly, the grey bars represent the means obtained in spinal rats, showing that the cycle duration increases significantly when going from the horizontal to the upright posture (A), and decreases when going from upright to the horizontal posture (B). The orange bar represents the means of each index for air-stepping. C and D, pharmacological treatments induce different effects on locomotor movements recorded in the horizontal and upright postures. The values after treatment are expressed as a percentage of the values measured from locomotor trials taken before the pharmacological treatment. Abbreviations: U, upright posture; H, horizontal posture; air step, air-stepping; Quip, quipazine (0.1–0.25 mg kg−1i.p.); 8-OH, 8-OH-DPAT (0.1–0.4 mg kg−1i.p.); Lido, lidocaine injections into the hindpaw bilaterally (0.05 ml, one medial and one lateral in each paw); BLD, both Quip and 8-OH-DPAT, low dose (0.1 mg kg−1). Wilcoxon's non-parametric test: *P < 0.05, **P < 0.02, ***P < 0.01. Three months after spinal cord transection, treadmill locomotion was tested approximately twice per week, as previously described (Majczyński et al. 2005). The testing periods were kept as short as possible (less than 5 min on the treadmill on any given test) to minimize training effects. We established the quality of plantar stepping based upon EMG analysis. The features that we used to characterize plantar stepping were (1) sustained soleus activity throughout the stance phase, (2) soleus burst duration related to step cycle duration, (3) brief TA activity of consistent duration, (4) consistent intra- and interlimb coordination with highly significant correlation coefficients, and (5) weight support detected by the experimenter. Tests were conducted with the experimenter manually placing the animal in the horizontal or the upright posture (see videos). Hindlimb movement was induced by tail pinching. Tests were conducted at treadmill speeds of 5 and 10 cm s−1 for all cases involving spinal rats. To determine the role of afferent input from the hindlimb on their locomotor ability, the spinal rats were tested on a treadmill before and after the hindpaw anaesthesia using bilateral injections of lidocaine (2%, Polfa). Two injections (0.05 ml) were made into the foot pad of each hindpaw, one medial and one lateral. This served to temporarily block cutaneous feedback from the plantar surface of the paw. In order to reduce the afferent feedback from loading the hindlimb, locomotor trials evoked by tail stimulation were conducted during air-stepping. In this case, the animal was held in the upright posture with its hindpaws pendent. To determine the effects of serotonergic agonists on the hindlimb locomotor abilities on a treadmill we started from evaluation of the pre-drug baseline performance. Then the evaluation of hindlimb movements was carried out at 15–30 min intervals after drug injection (i.e. when the maximal effect of the drugs administration was usually observed). The effects were assessed at all time intervals after drug application with the animals held for 60 s in the horizontal posture, then in the upright posture at two treadmill speeds (5 and 10 cm s−1). Experiments using different drug applications performed on a single animal were separated by at least 72 h to prevent drug interactions. In order to prevent any possible effect of training on the time course of recovery, locomotor performance was tested no more frequently than twice a week, and each test was limited to 5 min. duration. The following agonists of 5-HT2 and 5-HT7 receptors were used with i.p. administration in the volume 0.1–0.2 ml per 100 g of body weight: quipazine (5-HT2 agonist; Sigma-Aldrich) 0.25 mg kg−1 (dissolved in saline with 10% of propylene glycol); 8-OH-DPAT (5-HT7 and 5-HT1A agonist; Sigma-Aldrich) 0.2–0.4 mg kg−1 (dissolved in saline). During the combined treatment, both drugs were applied with the dose 0.1 mg kg−1 with a 20 min delay in between (the quipazine i.p. injection was followed by the 8-OH-DPAT i.p. applications). First we determined the effects of the two postures on the locomotor capability of untrained intact rats. Figure 1 shows the very similar pattern of EMG activity recorded in both postures from hindlimb muscles of intact rats during voluntary locomotion on the treadmill, and provides baseline data for comparison with the locomotor patterns obtained in spinal rats in this study. The presence of plantar paw placement and weight supported stepping is evident in the images taken from videos of the same animal in the two postures (Fig. 1A). Regular and well-coordinated EMG patterns in the soleus (Sol) and tibialis anterior (TA) muscles bilaterally are illustrated for the two postures (Fig. 1B). Rectified and filtered EMG records taken from the raw EMGs illustrated in Fig. 1B were normalized to the step cycle, taking the onset of activity in the right (r) TA as the onset of the cycle, then overlaid, with the first cycle repeated to emphasize the repetitive activity of muscles during locomotion. These plots show left–right and flexor–extensor coordination over the same step cycles displayed in the raw EMG records. The stance phase was characterized by sustained activity of the soleus muscles throughout the period when the TA muscles were inactive, so that weight support persisted throughout the stance phase (Fig. 1B). The relationships between the step cycle durations and burst durations for the left and right TA and Sol muscles established for different animals are illustrated in Fig. 1C. In both the horizontal posture (upper panel) and the upright posture (lower panel) the extensor EMG systematically increased in duration as the step cycle duration increased. The slopes of this relationship did not differ significantly between the horizontal and upright posture trials (Fig. 1F; Student's paired t test; P > 0.05). Polar plots show intra- and interlimb coordination in the two postures. Interlimb coordination (Fig. 1D and H) was decreased in the upright posture, so that stance was initiated earlier (Fig. 1E), and the swing phase was slightly shortened (Fig. 1B and G). There were significant changes in cycle duration, soleus EMG burst duration, TA burst duration and peak EMG amplitude (see Fig. 3A and B). In the upright posture the animals used longer steps with prolonged bursts in extensor muscles and shortened bursts in flexor muscles bilaterally, thereby minimizing the amount of time the limb was off the treadmill surface. EMG analysis of locomotor patterns of intact rats (n= 5) in horizontal and upright postures A, plantar paw placement and weight supported stepping is evident in the video frames of the same animal in the two postures. B, well-coordinated EMG patterns in the soleus (Sol) and tibialis anterior (TA) muscles bilaterally are illustrated for the two postures. Rectified and filtered EMG records are normalized to the step cycle, taking the onset of activity in the right TA as the onset of the cycle and show left–right and flexor–extensor coordination over the same step cycles displayed in the raw EMG records. l, left; r, right. C, the relationships between the step cycle durations and burst durations for the left and right TA and Sol muscles. F, bar graph showing the slopes (±SD) of this relationship. The darker green bar is the mean slope from the horizontal posture trials in left soleus muscle (l Sol), while the lighter green bar represents the trials in the upright posture. Dark (horizontal) and light (upright) grey represent the slopes of right soleus muscle (r Sol), and dark and light blue and red represent left tibilalis anterior muscle (l TA) and right tibialis anterior muscle (r TA), respectively. D and E, polar plots showing the relationships between the onset of r TA activity and either the contralateral TA or the ipsilateral extensor (r Sol). The 0 position on the polar plot corresponds to the onset of activity in the right TA muscle, and the positions of the filled circles (orange) indicate the times of onset of activity in the left TA (interlimb coordination, D) or the onset of activity in the right Sol (intralimb coordination, E). The black bars in D demonstrate the average time of onset (angle, a) of activity in the contralateral l TA for each animal, and the length of each bar is a measure of the strength of the relationship (correlation, r) between the right TA and left TA times of onset. The positions of the red bars represent the mean angle and their lengths represent correlation. The polar plots in E show the same relationships for intralimb coordination, with the times of onset of ipsilateral Sol activity plotted in relation to the times of onset of the ipsilateral r TA. The bar graph in G demonstrates the means (±SD) of the angle of the left–right TA (l-r) and of the right Sol – right TA (r S-T) relationships (relative timing of the onsets for the two muscles represented in each polar plot in the two postures, a). The dark green bars represent the angle in the horizontal posture (a in H) and the light green represent the angles in the upright posture (a in U). The bar graph in H shows the means (±SD) of the correlation coefficient (r) between the times of onset of activity in both left–right and flexor–extensor EMG comparisons for the two postures. The black bars represent r in the horizontal posture (r in H) and the grey bars represent r in the upright posture (r in U). Student’t test: *P < 0.05, **P < 0.005, P < 0.0005. There is ample reason to suppose the upright posture should have an impact on the locomotor capacity of animals with spinal cord transection. Sensory feedback from load receptors in muscles of the hindlimb (Timoszyk et al. 2005; Pearson, 2008) and cutaneous receptors from the plantar surface of the hindpaw (Duysens & Pearson, 1976; Bouyer & Rossignol, 2003a,b) can facilitate locomotion, and even lead to the initiation of stepping (Giszter et al. 2007). A comparison of locomotion in the horizontal posture (Video 1) with the same animal in the upright posture (Video 2) demonstrates that there is a dramatic effect of loading the hindlimbs. Rats with complete spinal cord transections (Th9/10), when placed in the horizontal posture, responded to tail pinch with rhythmic EMG activity that was poorly coordinated, resulting in failure of plantar foot placement, prolonged extension and failure to produce a normal swing phase of the locomotor cycle (Video 1, Fig. 2B, upper panel). When the same animal was placed in the upright posture, tail pinch led to sustained bouts of locomotion with successful plantar foot placement, weight support, and near-normal swing and stance phases of locomotion (Fig. 2B, lower panel). The EMG pattern was dramatically improved in the upright posture (Fig. 2B, lower panel), with near-normal intra- and interlimb coordination. The timing of bursts of EMG activity (Fig. 2B) in the extensor Sol changed from a brief burst of activity that occurred irregularly after the flexor TA burst, and sometimes overlaps with it when the rats were in the horizontal position, to sustained activity throughout the period between the bursts of activity in TA (stance phase), with no co-active periods. The relationships between the step cycle durations and burst durations for the left and right TA and Sol muscles is illustrated in Fig. 2C. In the horizontal position (Fig. 2C, upper panel) the extensor EMG did not systematically increase in duration as the step cycle duration increased, whereas the relationship between extensor burst duration and step cycle duration became more normal (see Fig. 1C) when the same animals were placed in the upright posture (Fig. 2C, lower panel). The bar graph in Fig. 2F shows that the slopes of this relationship differed significantly between the horizontal and upright posture trials. Moreover, interlimb and intralimb coordination improved significantly in the upright posture (Fig. 2H). Polar plots illustrate the interlimb (Fig. 2D) and intralimb (Fig. 2E) coordination changes that occurred when the animals were placed in the upright posture compared to the horizontal posture. The bar graph in Fig. 2H shows correlation coefficients (r) for the left–right TA and for the right Sol–right TA relationships, which were significantly increased in the upright posture. As shown in Fig. 3A and B the mean cycle duration was significantly prolonged in the upright posture, due to a marked increase in soleus burst duration. Peak amplitude was unchanged in Sol but significantly reduced in TA. Comparable changes occurred in burst area for both muscles. Thus the activation of hindlimb load receptors in the upright posture facilitates and prolongs Sol activity while decreasing TA activity in spinal rats. Taken together, these results demonstrate that the upright posture alone dramatically improves coordination and weight support to restore plantar stepping in chronic spinal animals without any interventions other than tail stimulation. The improved locomotion of spinal rats in the upright posture might be attributable to the influence of load receptors, including cutaneous receptors on the foot pads and proprioceptors in joints, muscles and tendons. Load receptors in muscles of the rat (Timoszyk et al. 2005) and cat (Duysens & Pearson, 1980; Conway et al. 1987; Pearson et al. 1992; Guertin et al. 1995) hindlimb or cutaneous receptors from the plantar surface of the hindpaw in spinal cats (Duysens & Pearson, 1976; Bouyer & Rossignol, 2003a,b) can facilitate locomotion. Denervation of cutaneous nerves of the hindpaw of spinal cats eliminated the recovery of locomotion after spinal cord injury that could not be overcome by extensive training (Bouyer & Rossignol, 2003b). We used two strategies to test the contribution from these afferents to the upright posture: first we tested air-stepping induced by tail stimulation of a rat held in the upright posture with its hindpaws pendent, a procedure that removes force feedback from both proprioceptors and cutaneous receptors on the hindpaw (Fig. 4). In order to target the plantar cutaneous receptors only and maintain the contributions of the proprioceptors, we tested the effects of local anaesthesia of the cutaneous receptors of the foot pads (" @default.
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W2155354145 title "The upright posture improves plantar stepping and alters responses to serotonergic drugs in spinal rats" @default.
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