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Effects of training on the recovery of full-weight-bearing stepping in the adult spinal cat
EXPERIMENTAL
NEUROLOGY
92,42 l-435 (1986)
Effects of Training on the Recovery of Full-Weight-Bearing Stepping in the Adult Spinal Cat R. G. LOVELY, Department
R. J. GREGOR,
qf Kinesiology
R. R. ROY, AND V. R. EDGERTON’
and Brain Research Institute. Los Angeles, Caijfornia 90024 Received
November
Universiry
oJ‘Cal$ornia.
26. 1985
The effects of ambulatory training on the extent and time course of recovery of weight-bearing-stepping in cats spinalized (T 12-T 13) as adults were investigated. One month after spinal cord transection, 14 of 16 cats were capable of bearing the full weight of their hindquarters with their hind limbs during stepping on a motor-driven treadmill if the tail was pinched or crimped. Of those 14 cats 8 were assigned to a trained and 6 to an untrained group. Trained cats were subjected to 30 min/day of treadmill exercise, 5 days/week. Training was initiated 1 month posttransection and continued until 5 to 7 months posttransection. Daily records were kept on the treadmill speeds used, the time at each speed, and the number of steps that were not full weight bearing. The number of full-weight-bearing steps times treadmill speed was used as a measure of performance. The tail was crimped whenever necessary, but was required less and less as training progressed. Performance plateaus were reached between 25 and 85 days after initiating training (mean = 48 + 22 days). Maximum treadmill speeds increased in untrained cats from 0.075 f 0.042 m/s 1 month posttransection to 0.240 f 0.042 m/s 5 to 7 months posttransection and those of trained cats increased from 0.079 + 0.045 m/s to 0.6 19 f 0.133 m/s during this same period. We conclude that a much larger proportion of adult spinal cats are capable of full-weight-bearing stepping than reported, and that training which emphasizes early tail crimping and complete weight bearing at all times results in marked improvements in the locomotor capacity of the hind limbs. Q 1986 Aademlc press, IK. INTRODUCTION
Kittens spinalized (T 12-T 13) 1 to 2 weeks after birth are capable of supporting the posterior part of their bodies with their hind limbs (full weight Abbreviation: NFW-nonfull-weight-bearing steps. ’ We are indebted to S. Graham, E. Fowler, M. Kuehl. and R. McCoy for their dedication and patience in training the adult spinal cats, and to L. Bomstein for her meticulous attention to the veterinary care of the animals. 421 0014-4886/86 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form mrved
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bearing) during stepping within 3 weeks of spinal cord transection (14, 22. 23, 40). When these kittens have matured to adulthood, full-weight-bearing locomotor capabilities can remain intact with or without training (40). Cats with the spinal cord transected as adults recover motor functions over a longer period (6, 18), and the evidence pertaining to their locomotor capabilities is conflicting. In 1980 Eidelberg et al. (12) reported that adult spinal cats regained a general stepping pattern in the hind limbs within 1 to 6 weeks after cord transection but were incapable of full weight bearing even after 2 months of training. These findings were in agreement with earlier research on spinal dogs which suggested that the spinal cord separated from higher centers was incapable of undergoing changes consistent with learning (7, 27). The work of Asratyan (2) in 1963, however, suggested that the success or failure of a training program in bringing about recovery of motor functions in spinal dogs was related to the quality of nursing care and physical therapy. Indeed, slow recovery from spinal shock (persisting flaccidity) and prevalence of flexor spasms in some paraplegic humans has been associated with decubiti or other skin irritations (15, 24). More recently, Smith et al. (40) studied the influence of a cat’s age at transection and the effects of training on the recovery of weight-bearing locomotion. Based on a nine-point performance rating system, cats with cord transections at 2 weeks of age performed significantly better than those with transections at 12 weeks of age. Four months posttransection, the average treadmill rating of 12-week untrained cats reflected hind limb flexion and extension movements, and some weight bearing with tail pinching, but otherwise dragging of the dorsal surface of the paws on the belt. In contrast with Eidelberg et al. (12), the average treadmill rating of trained 12-week transected cats reflected periodic weight bearing, steady locomotor rhythm, and “good” range of motion. Those authors suggested that the continuation of training beyond 2 months posttransection might be necessary to elicit effects on performance. The locomotor capabilities of adult spinal cats were reassessedby Rossignol et al. (34) who found redevelopment of full-weight bearing in one cat within 3 months of transection, and by Giuliani et al. (19) who reported that 7 of 21 untrained adult spinal cats were capable of full-weight bearing 4 months after transection. In light of the controversies regarding the locomotor capabilities and trainability of adult spinal cats, the effects of training on the extent and time course of recovery of full-weight-bearing locomotion in cats spinalized as adults were investigated. Our methods of training and performance assessment differed from those used previously. Detailed quantitative records were kept on daily treadmill performance of trained cats for 5 to 7 months. At the end of this
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period the treadmill performances of trained and untrained cats were compared. The results indicated that nearly all cats were capable of full-weightbearing stepping, and that training led to substantial improvement in locomotor capabilities. A brief account of some of our observations has been published elsewhere (30). METHODS Transection. Sixteen adult cats underwent surgical transection of the spinal cord after preanesthesia with atropine sulfate (0.9 mg/kg, s.c.) and acepromazine maleate (10 mg/kg, i.m.), and anesthesia with sodium pentobarbital(35 mg/kg, i.p.). The cord was exposed by laminectomy at the level of T 12-T 13. Three drops of lidocaine hydrochloride (2%) were administered through a small incision (1 mm) in the dura and the cord transected with microscissors 1 min later. The cut ends of the cord retracted into the spinal canal (approx 1 cm). A probe was inserted into the canal to verify complete transection. Gelfoam was packed into the space between the cut ends. Surrounding facia was pulled together and sutured (4-O chromic gut) to cover the laminectomized area and the incision closed (4-O Ethilon monofilament nylon). Animal Care. After recovery from anesthesia in an incubator, the cats were transferred to spacious cages (90 X 90 X 190 cm). No more than two cats occupied a cage. The floor of each cage was covered with shredded newspaper which was changed daily. Antibiotics (0.5 ml sterile penicillin G procaine, i.m.) and fluids (100 ml lactated Ringer’s solution s.c.) were administered daily for 4 days following surgery. Bladders and colons were evacuated by gentle manual pressure twice each day for the 1st week and once per day subsequently. Rectal temperatures were recorded daily and weights monitored weekly. All cats groomed themselves rostra1 to the transection and were bathed caudal to the transection whenever necessary. The cats were brushed every day to avoid fur balls and matting. Typically, the cats were lethargic the 1st week following transection, but later engaged in play and moved about readily by pulling themselves forward with their forelimbs. Decubitus ulcers were rare, but when they occurred were successfully treated by cleansing with soap and water, applying hydrogen peroxide (3%) and keeping the area dry with talcum powder. Bladder calculi were more common and alleviated with urine acidifiers (e.g., 120 mg Tribrissen, p.0.). The cats were fed dry food in addition to high-protein canned wet food mixed with water to assure adequate hydration. Testing. One month posttransection, all cats were tested for their ability to bear full weight and generate reciprocal stepping on a motor-driven treadmill.
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The treadmill apparatus has been described elsewhere (40) and is shown in Fig. 1. Cats were stabilized by a vest around the chest and shoulder girdle and their forepaws were on a stationary platform (2.5 cm above the belt). The hind limbs were placed on the treadmill belt and allowed to move freely. Trainers assisted the animals in paw placement and pinched or crimped the tail to enhance muscle activation during a IO-min adjustment period. Subsequently, the cats were tested for their ability to perform at least five consecutive full-weight-bearing steps. The highest speed they were able to accommodate was recorded. During these steps the trainer held the tail slack below the level of the hip joints to provide assistance in lateral stability if needed, and tail pinching or crimping to enhance extensor activation. No other assistance was permitted during testing. Two cats which failed the test were retested 1 week later and failed again after 20 min on the treadmill. Training. Eight of the 14 cats capable of full-weight-bearing stepping were selected at random to undergo training on the treadmill 30 min/day, 5 days/ week. Training was initiated 1 month posttransection and continued for 4 to 6 months. The remaining six cats were assigned to an untrained control group. With the exception of treadmill training, this group received the same treatment as the trained group. In addition, the hip, knee, ankle, and metatarsophalangeal joints of these cats were moved passively through their total range of motion once daily. For the trained group, performance records were kept on the treadmill speeds used during each training session, estimates of the step rate at each speed, the number of minutes at a given speed, and the number of nonfullweight-bearing steps (NFW) at each speed. An NIV step was one in which the trainer provided assistance in weight support. During training, the tail was held slack below the level of the hips and became taut only when lateral assistance was required or when a NFW step was taken. Tail pinching or crimping was administered only when needed and reported with the other performance information. The goal of each training session was to achieve full-weight-bearing at the highest speed the animal could accommodate for the duration of the exercise bout. Emphasis was placed on maximizing the number of full-weight-bearing steps taken during an exercise session, rather than on the attainment of a high treadmill speed for a short period. Treadmill speed was not increased unless greater than 95% of the steps were full-weight-bearing. Data Analysis. For each training session, the average treadmill velocity and the total number of full-weight-bearing steps times treadmill velocity were calculated as performance criteria. The latter criterion, which we refer to as the performance index (P), was estimated by: P = 5 Vi(RiTi - Nl), i=l
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where n was the number of speeds used during a session, V was treadmill velocity, R was the step rate (steps per minute), T was the duration (min), and N was the number of NFW steps at each speed (i). The value of this measure for a cat unable to bear full weight during stepping would be zero. Both trained and untrained cats were tested 5 to 7 months posttransection to determine their maximum speed capabilities at that time. RESULTS One Month Posftransection. One month posttransection none of the cats was capable of standing without at least slight tail pinching or crimping. These stimuli elicited vigorous extension of the hind limbs during standing in all cats. Sustained crimping resulted in sustained extension in all but two cats which collapsed unless the point of crimping on the tail was altered continuously. These two cats also failed the test for full-weight-bearing stepping and were not included in either the trained or untrained group. When placed on the treadmill for the first time, all cats dragged their paws forward on the treadmill during the entire swing phase and failed to place their paws on their plantar surfaces at the initiation of the support phase. Trainers assisted the cats by crimping the tail, lifting each limb during its respective swing phase, and placing their paws on the plantar surfaces to initiate the subsequent support phase. Within 3 min, 14 cats were full-weightbearing stepping 75% to 95% of the time with trainer assistance in lateral stability and tail crimping only. Maximum treadmill speeds for these cats at the end of 10 min were 0.05 to 0.15 m/s (Table 1). Sfepping Pattern. Photographs of selected positions during a typical step cycle on the treadmill at 0.6 m/s for a trained cat 6 months posttransection are shown in Fig. 1. This cat and four others developed sufficient lateral stability to locomote for extended periods (i.e., IO to 20 min) without being touched by the trainer. The hip, knee, ankle, and metatarsophalangeal joints extended as the paw made initial contact with the treadmill (Fig. la). The metarsophalangeal joint hyperextended as the load was transferred to the ipsilateral limb (Fig. 1b). Through midstance the level of the pelvis rose as the support paw passed beneath it (Fig. lc). Contralateral paw placement was followed by initiation of the ipsilateral swing phase (Fig. Id). The dorsal surface of the paw was dragged along the treadmill belt through midswing (Fig. le) and then abruptly lifted by flexion of the ankle. knee, and hip (Fig. If). The hind limb joints subsequently extended to return to paw contact (Fig. la). This general pattern was evident at all speeds in both trained and untrained animals. Perfhnance ndth Time. Five trained cats attained plateaus in the maximum average speeds they could accommodate (Fig. 2a-e). Three other cats declined in treadmill speed after reaching a peak (Fig. 2f-h). Declining performance
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TABLE 1 Maximum Treadmill Speeds at I and 5 to 7 Months Posttransection Max speed (m/s) Cat
Group”
SA ED AJ SP LE SH PL KA AD BK BR co TI VE
1 Month
5-7 Months
0.08 0.05 0.05 0.05 0.05 0.05 0.15 0.15 X + SD = 0.079 + 0.045 0.05 0.05 0.05 0.05 0.15 0.10 X f SD = 0.075 _+0.042
0.85 0.65 0.7 0.65 0.4 0.6 0.5 0.6 Xk SD = 0.619 + 0.133 0.15 0.30 NT’ 0.25 0.15 0.35 X f SD = 0.240 k 0.089
’ T = trained, U = untrained. b Not tested.
was due to an increasing frequency of NFW steps which were associated with ankle hyperextension during the stance phase, inability to support body weight, and/or landing on the dorsum of the paw at paw contact. Because the average treadmill speed per session provided no measure of the number of steps that were full-weight-bearing, the number of full-weightbearing steps times treadmill speed (P) also was utilized to monitor performance (Fig. 3). The similarity between these performance index plots and plots of average treadmill speed (Fig. 2) reflects our criteria for increasing the speed: that 95% of the steps at a given speed had to be verifiably full-weightbearing before the speed was increased. The necessity for tail crimping is indicated by the shaded areas of Fig. 3. The darker the shade, the more often tail crimping was necessary. Almost no tail crimping was needed for three cats (Fig. 3a-c) after 6 days of training and for another cat (Fig. 3d) after 5 1 days. One cat regressed from no tail crimping after 4 days to requiring constant tail crimping after 27 days into the training period (Fig. 3g). Other cats required at least some tail crimping periodically throughout training (Fig. 3e, f, h). The average number of days from initiation of training to peak or plateau was 48 -1-22 (SD) for seven of eight cats (Fig. 3a-g). Cat KA was not included in this average due to the presence of several peaks (Fig. 3h).
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160 ms
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FIG. I. Photographs made from high-speed film ( 100 frames/s) of selected positions in the step cycle of an adult spinal cat (treadmill speed = 0.6 m/s: cycle period = 640 ms). A vest around the shoulder girdle and chest restrained the cat’s rostrum. The cat’s forepaws were placed on a platform above (2.5 cm) the moving treadmill belt. A Plexiglas divider removed the possibility of one hind limb stumbling over the other during the swing phase. The tail was slack and, in this sequence, taped to the side of the treadmill to avoid interference with the view of the right hind limb. The positions shown are: (a)-initial treadmill contact, (b&initial posterior movement of the paw, (c)-support phase, (d)-initial ankle flexion, (e)-dragging the paw during the swing phase, and (B-initial extension phase at the ankle.
Warm-up. Regardless of the changes in treadmill performance that occurred during the training period, all cats typically required a “warm-up” period (1 to 10 min) before reaching the maximum speeds for a given training session. Most of the tail crimping for a given session occurred during this time. Maximum Treadmill Speed. The maximum treadmill speed increased significantly in both trained and untrained groups between 1 and 5 to 7 months posttransection (Table 1). Untrained cats improved more than threefold, from 0.075 + 0.042 to 0.240 + 0.089 m/s, and trained cats improved nearly eightfold, from 0.079 k 0.045 to 0.6 19 h 0.133 m/s. DISCUSSION Immediate Responses to Training. All cats improved substantially within 3 min of beginning the first training session. Initially cats dragged the paw forward during the entire swing phase and began the support phase on the dorsum of the paw. During this period the trainers attempted to enhance sensory input in several ways to improve motor responses to the moving treadmill belt.
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FIG. 3. The performance index (P) as a function of days from the initiation of training for each trained cat (a-h). The arrows estimate the initiation of plateaus or the occurrence of peaks. Five cats attained plateaus (a-e), and three others reached peaks and then declined in performance (f-h). Bars across the top of each plot indicate the percentage of time during each training session in which the tail was pinched or crimped: solid indicates greater than 75%, cross-hatched means between 10% and 75%. and open means less than 10%.
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First, tail pinching or crimping provided stimuli which promoted the activation of extensor muscles during support and the activation of flexor muscles during the swing phase. Second, the trainers lifted each paw during its respective swing phase and hyperextended the metatarsophalangeal joint to allow appropriate paw placement at the initiation of the subsequent support phase. This assistance may have enhanced the activation of hind limb flexors and digital extensors. Such effects have been demonstrated in the fictive curarized cat in which an ongoing flexion movement reinforced flexor activity and an ongoing extension movement reinforced extensor activity ( 1). Finally, the trainers provided no weight support to the spinal cats to maximize the load on hind limb extensor muscles during the stance phase. With the paw appropriately placed during the stance phase, additional mechanisms became available to heighten reflexive responses which may have aided stepping. Pressure on the plantar surface of the paw for example, loaded the extensor muscles which further facilitated their activation (39). In addition, the diminishing load on extensor muscles and the position of the hip joint at the end of the stance phase may have been important for the initiation of flexor muscle activity and subsequent swing phase (23, 32). The substantial improvement observed during the first training session and the diminished requirement for trainer assistance as time progressed indicate that the effects of therapy were not limited to reflexive responses in the steps in which it was administered. It appears that training effects resulting from sensory stimulation had both immediate and lasting effects on locomotor capability. Capacity for Full- Weight-Bearing Stepping. One month posttransection, 14 of 16 spinal cats were capable of full-weight-bearing stepping if the tail was pinched or crimped. Within the subsequent month, four of the eight cats that received training were capable of full-weight-bearing stepping without this extra stimulus. These results contrast with those of Eidelberg et al. (12) who reported that none of their six cats was capable of full-weight-bearing stepping after 2 months of training. We attribute this disparity to differences in the training apparatus and training techniques. First, Eidelberg’s cats were suspended in a shng such that the hind limbs were never fully loaded. This may have reduced sensory input important for facilitating the activation of extensors during the support phase and the triggering of hip flexion to initiate the swing phase (9, 32). In contrast, we never provided continuous assistance in weight support and occasionally pulled downward on the tail to enhance extensor loading. Second, in Eidelberg’s preparation, the forelimbs were allowed to step freely on the treadmill belt. In our preparation the forelimbs were stationary on a platform and the thorax was restrained by a vest. Movement of the forelimbs in the absence of coordination with hind limb stepping would be expected to
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generate shifts in the loading and positioning of the hind limbs. The inconsistent sensory input resulting from these shifts may have led to muscle activation patterns that were inappropriate for full-weight-bearing stepping. We found that even a subtle movement of the head or shifting of the weight on the forelimbs was sometimes sufficient to disrupt a long sequence of fullweight-bearing steps. Presumably these movements altered the distribution of weight on the hind limbs and subsequent sensory input to the spinal cord. Finally, we applied tail crimping, continuously if necessary, to promote the activation of extensors for support and the activation of flexors for limb recovery during the swing phase. In addition to short-term reflexive influences, tail crimping may have had long-lasting facilitative effects which were helpful in the entrainment of the stepping pattern. Noxious stimuli are known to facilitate certain reflex responses in cats (4 1) and have produced long-lasting heterosynaptic facilitation in sensory pathways of mollusks (4, 5, 29). Smith et al. (40) reported that all their 12-week transected cats that received no training and two of five trained 12-week transected cats were incapable of full-weight-bearing stepping 4 months after transection. Similarly Giuliani et al. (19) reported that only 7 of 2 1 untrained adult spinal cats were capable of full-weight-bearing stepping 4 months after transection. Although our treadmill apparatus was the same as that used by these researchers, our methods of therapy and criteria for measuring performance differed. For example, in the earlier studies no initital assistance in paw placement was provided and the trainers usually gave continuous assistance in weight bearing. Furthermore, in the study by Smith et al., performance was assessed after viewing video tapes of spinal locomotion. They used a nine-point rating scale based on the apparent consistency of weight bearing and appropriateness of paw placement. In the present study however, the trainers provided initial assistance in paw placement, gave no assistance in weight bearing. and administered continuous tail crimping if necessary. Any steps taken that were not full-weight-bearing were not counted using our performance measurement protocol. Our assessment of locomotor capability was made during the training sessions and was based on quantitative data rather than a subjective, nonparametric score. Trained vs. Untrained. Although our results differed with those of Smith et al. (40) on the proportion of adult spinal cats capable of full-weight-bearing stepping, the finding that trained cats performed significantly better than untrained was consistent in both studies. Differences between trained and untrained cats were also apparent in muscle properties in both studies. Some hind limb extensor muscles of trained cats, for example, underwent smaller decreases in wet weight, and maximal tetanic tension and twitch tension after cord transection than those of untrained cats (11, 25, 35, 36). The neural mechanisms which might explain the training effects on performance are obscure. Repeated stimulation is often associated with inhibition
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rather than facilitation of responses. Excitatory postsynaptic potentials from la afferent fibers, for example, can be decreased by use and enhanced by disuse (10, 16, 17, 20, 21). The inhibition of responses after repeated stimulation has also been demonstrated in some reflexes in the chronic spinal cat. Examples include habituation in the flexion withdrawal reflex (41, 43) and also in the responses to touch, heat, and cold (28). The long-term effects of a stimulus, however, do not seem to be a simple function of use or disuse. An afferent stimulus which ordinarily results in posttetanic depression, for example, can cause posttetanic potentiation if the stimulus rate is high enough and the duration of stimulation is long enough (13). In addition, a number of studies suggest that facilitative effects within a given reflex pathway depend on the presence of activity in a parallel sensory pathway. This idea is supported by the findings that long-term habituation in responses to touch, heat, and cold in the chronic spinal cat could be reversed by eliciting reflexes from overlapping receptive modalities (28). Furthermore, lasting facilitative effects on the synapses of a given pathway have been elicited by stimulation of another pathway in mollusks (26, 29, 33). Similarly, longlasting presynaptic facilitation of la afferent fibers has been demonstrated in cat upon stimulation of cutaneous afferent pathways (38). Certainly, in stepping, it seems that a substantial number of sensory pathways may be activated simultaneously at any given point in the step cycle. The facilitative mechanisms exemplified in some reflexes therefore, might be included as potential contributors to the entrainment of stepping. But because stepping is not merely reflexive, and involves pattern-generating circuitry intrinsic to the spinal cord, there are probably other long-lasting facilitative mechanisms involved as well. Although trained cats performed significantly better than untrained cats, both groups improved. This suggests that recovery of motor functions continued beyond 1 month posttransection without therapy. Segmental reflexes (e.g., flexion and crossed extension) and air stepping seem to be fully recovered within 1 month after transection in adult cats (18, 3 I). Weight bearing, however, requires that not only the timing of muscle activation be appropriate for stepping, but that the level of activation in extensors be sufficient to support the weight of the posterior part of the cat. Although 14 of our cats were capable of full-weight-bearing stepping 1 month posttransection without training, they all required tail crimping at that time. It was not until later, (3 to 50 days) that extensors were activated sufficiently to bear full weight without tail crimping. In addition, studies on the static fusimotor system indicate that the response to static muscle stretch may still be depressed after 2 months posttransection (3). Thus, it appears that our cats were still recovering from the effects of spinal cord transection after 1 month posttransection and also that training altered both the time course and the degree of recovery.
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Declining Performance. The declining performances observed in three cats (Fig. 3f-h) after attaining a peak and the occasional poor performances observed in three other cats (Fig. 3a, c, d) after reaching plateaus were due to an increased frequency of NFW steps. These steps were associated with lack of metatarsophalangeal joint hyperextension prior to paw contact. ankle hyperextension during the stance phase, or inability to support the hindquarters. Sometimes all three conditions were present. The lack of metatarsophalangeal joint hyperextension prior to paw placement seemed to be due to contractures in the digital flexors rather than a failure to activate the digital extensors. Forceful manipulation was sometimes required by trainers to hyperextend this joint for paw placement. Flexion contractures are common in spinal cord-injured humans and stroke patients (8,42). Joint laxity, spasticity, and hypotonia have also been widely reported in the clinical literature on paraplegia (8, 37) and may have been related to instances of ankle joint hyperextension. Hypotonia in the hind limb extensors seems to have been responsible for the inability to support body weight. Although we made no attempt to quantify the instances of each of these problems in trained and untrained cats, it appeared that they were more prevalent in untrained cats. Although our training regimen in general may have helped to alleviate flexion contractures, joint laxity, spasticity, and hypotonia, it was apparently not sufficient to reverse the progressive dysfunction observed in three of our trained cats. In fact, additional manipulative therapy and treadmill training (7 days/week) administered to one cat (PL; Fig. 3g) was unsuccessful in reversing the trend of declining performance. The occasional poor performances of three other cats may reflect temporary, undiagnosed health maladies such as bladder infections (15, 24) or restlessness and therefore instability of the rostra1 part of the cat. Conclusions. A much larger proportion (87%) of adult spinal cats were capable of full-weight-bearing stepping, regardless of treadmill training, than has been reported (12, 19, 40). In addition, our methods of training which involved continuous tail crimping whenever necessary, and emphasized weight bearing throughout the training period, resulted in marked improvements in the locomotor capacity of the hind limbs.
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3. BAILEY, C. S., J. S. LIEBERMAN, AND R. L. KETCHELL. 1980. Response of muscle spindle primary endings to static stretch in acute and spinal cats. Am. J. Vef. Res. 41: 2030-2036. 4. CAREW, T. J., V. F. CASTELLUCCI,AND E. R. KANDEL. I97 I. An analysis of dishabituation and sensitization of the gill-withdrawal reflex in Aplysia. Int. J. Neurosci. 2: 79-98. 5. CASTELLLJCCGV. F., H. PINSKER, H. I. KUPFERMANN, ANDE. R. KANDEL. 1970. Neuronal mechanisms of habituation and dishabituation of the gill-withdrawal reflex in Aplysia. Science
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6. CHAMBERS, W. W.. C. N. Lru, G. P. MCCOUCH, ANDE. D’AQUILI. 1966. Descending tracts and spinal shock in the cat. Brain 89: 377-390. 7. DEESE, J. E., AND W. M. KELLOGG. 1949. Some new data on the nature of “spinal conditioning.” J. Camp. Psychol. 42: 157-160. 8. DRACHMAN, D. A. 1967. Disorders of tone. Am. J. Physical Med. 46: 525-535. 9. DUYSENS,J., AND K. G. PEARSON. 1980. Inhibition of flexor burst generation by loading ankle extensor muscles in walking cats. Brain Res. 187: 321-332. 10. ECCLES,J. C. 1964. The Physiology ofSynapses. Springer-Verlag, Berlin. 1 I. EDGERTON, V. R., D. J. JOHNSON,L. A. SMITH, K. MURPHY, E. ELDRED, AND J. L. SMITH. 1983. Effects of treadmill exercise on hindlimb muscles of the spinal cat. Pages 435-443 in C. C. KAO, R. P. BUNGE, AND P. J. REIER, Eds., Spinal Cord Reconstruction. Raven Press, New York. 12. EIDELBERG, E., J. L. STORY, B. L. MEYER, AND J. NYSTEL. 1980. Stepping in chronic spinal cats. Exp. Brain Res. 40: 24 I-246. 13. EVARTS, E. V.. AND J. R. HUGHES. 1957. Relation of posttetanic potentiation to subnormality of lateral geniculate potentials. Am. J. Physiol. 188: 238-244. 14. FORSSBERG.H., S. GRILLNER, AND J. HALBERTSMA. 1980. The locomotion of the low spinal cat. I. Coordination within a hindlimb. Acta. Physiol. Stand. 108: 269-28 1. 15. FREEMAN, L. W. 1949. Treatment of paraplegia resulting from trauma to the spinal cord. JAMA.
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18. GIULIANI, C. A., AND J. L. SMITH. 1985. Development and characteristics of airstepping in chronic spinal cats. J. Neurosci. 5: 1276-1282. 19. GIULIANI, C. A., M. C. CARTER, AND J. L. SMITH. 1984. Return of weight supported Iocomotion in adult spinal cats. Sot. Neurosci. Abstr. 10: 632. 20. GOLDBERGER,M. E., AND M. MURRAY. 1974. Restitution of function and collateral sprouting in the cat spinal cord: the deafferented animal. J. Camp. Neural. 158: 37-54. 2 1. COLDRING, J. M., M. KUNO, R. NUNEZ, AND W. D. SNIDER. 1980. Reaction of synapses on motoneurons to section and restoration of peripheral sensory connections in the cat. J. Physiol. (London) 309: 185-198. 22. GRILLNER, S. 1973. Locomotion in the spinal cat. Pages 515-535 in R. B. STEIN, K. G. PEARSON,R. S. SMITH, AND J. B. REDFORD, Eds., Control of posture and locomotion. Plenum, New York. 23. GRILLNER, S., AND S. RO~SIGNOL. 1978. On the initiation of the swing phase of locomotion in chronic spinal cats. Brain Res. 146: 269-277. 24. HEAD, H., AND G. RIDDOCH. 1917. The automatic bladder, excessive sweating, and some other reflex conditions in gross injuries of the spinal cord. Brain 40: 188-263. 25. JOHNSON,D. J., L. A. SMITH, E. ELDRED, AND V. R. EDGERTON. 1982. Exercise-induced changes of biochemical, histochemical and contractile properties of muscle in cordotomized kittens. Exp. Neurol. 76: 414-427.
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AND SPINAL CAT
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E. R., AND L. TAUC. 1965. Heterosynaptic facilitation in neurones of the abdominal ganglion of Aplysia depilans. J. Physiol. (London) 181: I-27. 27. KELLOGG, W. M., J. DEESE,N. H. PF~ONKO, ANDM. FEINBERG.1947. An attempt to condition the chronic spinal dog. J. Exp. Psycho/. 37: 99-I 17. 28. KOZAK, W., W. V. MACFARLANE, R. WESTERMAN. 1962. Long-lasting reversible changes in the reflex responses of chronic spinal cats to touch, heat, and cold. Nature 193: 17 l173. 29. KUPFERMANN. H. I.. V. F. CASTELLUCCI,H. PINSKER,AND E. R. KANDEL. 1970. Neuronal correlates of habituation and dishabituation of the gill-withdrawal reflex in Aplwia. Science 26. KANDEL,
167: 1743-1745.
LOVELY, R. G.. R. J. GREGOR, R. R. ROY, AND V. R. EDGERTON. 1985. Training effectson the recovery of full weight-bearing stepping in adult spinal cats. Sot. Neurosci. Abstr. 11: 1101. 31. MCCOUCH, G. P. 1947. Reflex development in the chronically spinal cat and dog. J. Neu30.
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32. PEARSON,K. G.. AND J. DUYSENS. 1976. Function of segmental reflexes in the control of stepping in cockroaches and cats. Pages 519-538 in R. M. HERMAN. S. GRILLNER, P. STEIN, AND D. G. STUART, Eds.. Neural Control of Locomotion, Vol. 18. Plenum, New York. 33. PINSKER,H., H. I. KUPFERMANN, V. F. CASTELLUCCI,ANDE. R. KANDEL. 1970. Habituation and dishabituation of the gill-withdrawal reflex in Apysia. Science 167: 1740- 1742. 34. ROSSIGNOL.S., H. BARBEAU, AND J. PROVENCHER.1982. Locomotion in the adult chronic spinal cat. Sot. Neurosci. Abstr. 8: 163. 35. ROY. R. R., R. D. SACKS,K. M. BALDWIN, M. SHORT, AND V. R. EDGERTON. 1984. Interrelationships of contraction time, V,, and myosin ATPase after spinal transection. J. Appl. Physiol. 56: 1594- 160 I. 36. ROY, R. R., R. J. GREGOR, R. L. LOVELY, K. M. BALDWIN, AND V. R. EDGERTON. 1985. Long term exercise effectson the mechanical properties of the soleus muscle in adult spinal cats. Sot. Neurosci. Abstr. 11: I 101. 37. RUCH, T. C. 1965. Transection of the human spinal cord: the nature of higher control. In T. C. RUCH, H. D. PATTON, J. W. WOODBURY, AND A. L. TOWE, Eds., Neurophysiology, 2nd ed. Saunders, Philadelphia. 38. RUDOMIN, P., R. NUNEZ, J. MADRID, AND R. E. BURKE. 1974. Primary afferent hyperpolarization and presynaptic facilitation of la afferent terminals induced by large cutaneous fibers. J. Neurophysiol. 37: 4 13-429. 39. SHERRINGTON,C. S. 19 10. Flexion reflex of the limb, crossed extension reflex stepping and standing. J. Physiol. (London) 40: 28- 12 I. 40. SMITH, J. L., L. A. SMITH. R. F. ZERNICKE, AND M. HOY. 1982. Locomotion in exercised and nonexercised cats cordotomized at two or twelve weeks of age. E.up. Neural. 76: 393413. 41.
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NEUROLOGY
92,42 l-435 (1986)
Effects of Training on the Recovery of Full-Weight-Bearing Stepping in the Adult Spinal Cat R. G. LOVELY, Department
R. J. GREGOR,
qf Kinesiology
R. R. ROY, AND V. R. EDGERTON’
and Brain Research Institute. Los Angeles, Caijfornia 90024 Received
November
Universiry
oJ‘Cal$ornia.
26. 1985
The effects of ambulatory training on the extent and time course of recovery of weight-bearing-stepping in cats spinalized (T 12-T 13) as adults were investigated. One month after spinal cord transection, 14 of 16 cats were capable of bearing the full weight of their hindquarters with their hind limbs during stepping on a motor-driven treadmill if the tail was pinched or crimped. Of those 14 cats 8 were assigned to a trained and 6 to an untrained group. Trained cats were subjected to 30 min/day of treadmill exercise, 5 days/week. Training was initiated 1 month posttransection and continued until 5 to 7 months posttransection. Daily records were kept on the treadmill speeds used, the time at each speed, and the number of steps that were not full weight bearing. The number of full-weight-bearing steps times treadmill speed was used as a measure of performance. The tail was crimped whenever necessary, but was required less and less as training progressed. Performance plateaus were reached between 25 and 85 days after initiating training (mean = 48 + 22 days). Maximum treadmill speeds increased in untrained cats from 0.075 f 0.042 m/s 1 month posttransection to 0.240 f 0.042 m/s 5 to 7 months posttransection and those of trained cats increased from 0.079 + 0.045 m/s to 0.6 19 f 0.133 m/s during this same period. We conclude that a much larger proportion of adult spinal cats are capable of full-weight-bearing stepping than reported, and that training which emphasizes early tail crimping and complete weight bearing at all times results in marked improvements in the locomotor capacity of the hind limbs. Q 1986 Aademlc press, IK. INTRODUCTION
Kittens spinalized (T 12-T 13) 1 to 2 weeks after birth are capable of supporting the posterior part of their bodies with their hind limbs (full weight Abbreviation: NFW-nonfull-weight-bearing steps. ’ We are indebted to S. Graham, E. Fowler, M. Kuehl. and R. McCoy for their dedication and patience in training the adult spinal cats, and to L. Bomstein for her meticulous attention to the veterinary care of the animals. 421 0014-4886/86 $3.00 Copyright 0 1986 by Academic Press, Inc. All rights of reproduction in any form mrved
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bearing) during stepping within 3 weeks of spinal cord transection (14, 22. 23, 40). When these kittens have matured to adulthood, full-weight-bearing locomotor capabilities can remain intact with or without training (40). Cats with the spinal cord transected as adults recover motor functions over a longer period (6, 18), and the evidence pertaining to their locomotor capabilities is conflicting. In 1980 Eidelberg et al. (12) reported that adult spinal cats regained a general stepping pattern in the hind limbs within 1 to 6 weeks after cord transection but were incapable of full weight bearing even after 2 months of training. These findings were in agreement with earlier research on spinal dogs which suggested that the spinal cord separated from higher centers was incapable of undergoing changes consistent with learning (7, 27). The work of Asratyan (2) in 1963, however, suggested that the success or failure of a training program in bringing about recovery of motor functions in spinal dogs was related to the quality of nursing care and physical therapy. Indeed, slow recovery from spinal shock (persisting flaccidity) and prevalence of flexor spasms in some paraplegic humans has been associated with decubiti or other skin irritations (15, 24). More recently, Smith et al. (40) studied the influence of a cat’s age at transection and the effects of training on the recovery of weight-bearing locomotion. Based on a nine-point performance rating system, cats with cord transections at 2 weeks of age performed significantly better than those with transections at 12 weeks of age. Four months posttransection, the average treadmill rating of 12-week untrained cats reflected hind limb flexion and extension movements, and some weight bearing with tail pinching, but otherwise dragging of the dorsal surface of the paws on the belt. In contrast with Eidelberg et al. (12), the average treadmill rating of trained 12-week transected cats reflected periodic weight bearing, steady locomotor rhythm, and “good” range of motion. Those authors suggested that the continuation of training beyond 2 months posttransection might be necessary to elicit effects on performance. The locomotor capabilities of adult spinal cats were reassessedby Rossignol et al. (34) who found redevelopment of full-weight bearing in one cat within 3 months of transection, and by Giuliani et al. (19) who reported that 7 of 21 untrained adult spinal cats were capable of full-weight bearing 4 months after transection. In light of the controversies regarding the locomotor capabilities and trainability of adult spinal cats, the effects of training on the extent and time course of recovery of full-weight-bearing locomotion in cats spinalized as adults were investigated. Our methods of training and performance assessment differed from those used previously. Detailed quantitative records were kept on daily treadmill performance of trained cats for 5 to 7 months. At the end of this
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period the treadmill performances of trained and untrained cats were compared. The results indicated that nearly all cats were capable of full-weightbearing stepping, and that training led to substantial improvement in locomotor capabilities. A brief account of some of our observations has been published elsewhere (30). METHODS Transection. Sixteen adult cats underwent surgical transection of the spinal cord after preanesthesia with atropine sulfate (0.9 mg/kg, s.c.) and acepromazine maleate (10 mg/kg, i.m.), and anesthesia with sodium pentobarbital(35 mg/kg, i.p.). The cord was exposed by laminectomy at the level of T 12-T 13. Three drops of lidocaine hydrochloride (2%) were administered through a small incision (1 mm) in the dura and the cord transected with microscissors 1 min later. The cut ends of the cord retracted into the spinal canal (approx 1 cm). A probe was inserted into the canal to verify complete transection. Gelfoam was packed into the space between the cut ends. Surrounding facia was pulled together and sutured (4-O chromic gut) to cover the laminectomized area and the incision closed (4-O Ethilon monofilament nylon). Animal Care. After recovery from anesthesia in an incubator, the cats were transferred to spacious cages (90 X 90 X 190 cm). No more than two cats occupied a cage. The floor of each cage was covered with shredded newspaper which was changed daily. Antibiotics (0.5 ml sterile penicillin G procaine, i.m.) and fluids (100 ml lactated Ringer’s solution s.c.) were administered daily for 4 days following surgery. Bladders and colons were evacuated by gentle manual pressure twice each day for the 1st week and once per day subsequently. Rectal temperatures were recorded daily and weights monitored weekly. All cats groomed themselves rostra1 to the transection and were bathed caudal to the transection whenever necessary. The cats were brushed every day to avoid fur balls and matting. Typically, the cats were lethargic the 1st week following transection, but later engaged in play and moved about readily by pulling themselves forward with their forelimbs. Decubitus ulcers were rare, but when they occurred were successfully treated by cleansing with soap and water, applying hydrogen peroxide (3%) and keeping the area dry with talcum powder. Bladder calculi were more common and alleviated with urine acidifiers (e.g., 120 mg Tribrissen, p.0.). The cats were fed dry food in addition to high-protein canned wet food mixed with water to assure adequate hydration. Testing. One month posttransection, all cats were tested for their ability to bear full weight and generate reciprocal stepping on a motor-driven treadmill.
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AL.
The treadmill apparatus has been described elsewhere (40) and is shown in Fig. 1. Cats were stabilized by a vest around the chest and shoulder girdle and their forepaws were on a stationary platform (2.5 cm above the belt). The hind limbs were placed on the treadmill belt and allowed to move freely. Trainers assisted the animals in paw placement and pinched or crimped the tail to enhance muscle activation during a IO-min adjustment period. Subsequently, the cats were tested for their ability to perform at least five consecutive full-weight-bearing steps. The highest speed they were able to accommodate was recorded. During these steps the trainer held the tail slack below the level of the hip joints to provide assistance in lateral stability if needed, and tail pinching or crimping to enhance extensor activation. No other assistance was permitted during testing. Two cats which failed the test were retested 1 week later and failed again after 20 min on the treadmill. Training. Eight of the 14 cats capable of full-weight-bearing stepping were selected at random to undergo training on the treadmill 30 min/day, 5 days/ week. Training was initiated 1 month posttransection and continued for 4 to 6 months. The remaining six cats were assigned to an untrained control group. With the exception of treadmill training, this group received the same treatment as the trained group. In addition, the hip, knee, ankle, and metatarsophalangeal joints of these cats were moved passively through their total range of motion once daily. For the trained group, performance records were kept on the treadmill speeds used during each training session, estimates of the step rate at each speed, the number of minutes at a given speed, and the number of nonfullweight-bearing steps (NFW) at each speed. An NIV step was one in which the trainer provided assistance in weight support. During training, the tail was held slack below the level of the hips and became taut only when lateral assistance was required or when a NFW step was taken. Tail pinching or crimping was administered only when needed and reported with the other performance information. The goal of each training session was to achieve full-weight-bearing at the highest speed the animal could accommodate for the duration of the exercise bout. Emphasis was placed on maximizing the number of full-weight-bearing steps taken during an exercise session, rather than on the attainment of a high treadmill speed for a short period. Treadmill speed was not increased unless greater than 95% of the steps were full-weight-bearing. Data Analysis. For each training session, the average treadmill velocity and the total number of full-weight-bearing steps times treadmill velocity were calculated as performance criteria. The latter criterion, which we refer to as the performance index (P), was estimated by: P = 5 Vi(RiTi - Nl), i=l
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CAT
425
where n was the number of speeds used during a session, V was treadmill velocity, R was the step rate (steps per minute), T was the duration (min), and N was the number of NFW steps at each speed (i). The value of this measure for a cat unable to bear full weight during stepping would be zero. Both trained and untrained cats were tested 5 to 7 months posttransection to determine their maximum speed capabilities at that time. RESULTS One Month Posftransection. One month posttransection none of the cats was capable of standing without at least slight tail pinching or crimping. These stimuli elicited vigorous extension of the hind limbs during standing in all cats. Sustained crimping resulted in sustained extension in all but two cats which collapsed unless the point of crimping on the tail was altered continuously. These two cats also failed the test for full-weight-bearing stepping and were not included in either the trained or untrained group. When placed on the treadmill for the first time, all cats dragged their paws forward on the treadmill during the entire swing phase and failed to place their paws on their plantar surfaces at the initiation of the support phase. Trainers assisted the cats by crimping the tail, lifting each limb during its respective swing phase, and placing their paws on the plantar surfaces to initiate the subsequent support phase. Within 3 min, 14 cats were full-weightbearing stepping 75% to 95% of the time with trainer assistance in lateral stability and tail crimping only. Maximum treadmill speeds for these cats at the end of 10 min were 0.05 to 0.15 m/s (Table 1). Sfepping Pattern. Photographs of selected positions during a typical step cycle on the treadmill at 0.6 m/s for a trained cat 6 months posttransection are shown in Fig. 1. This cat and four others developed sufficient lateral stability to locomote for extended periods (i.e., IO to 20 min) without being touched by the trainer. The hip, knee, ankle, and metatarsophalangeal joints extended as the paw made initial contact with the treadmill (Fig. la). The metarsophalangeal joint hyperextended as the load was transferred to the ipsilateral limb (Fig. 1b). Through midstance the level of the pelvis rose as the support paw passed beneath it (Fig. lc). Contralateral paw placement was followed by initiation of the ipsilateral swing phase (Fig. Id). The dorsal surface of the paw was dragged along the treadmill belt through midswing (Fig. le) and then abruptly lifted by flexion of the ankle. knee, and hip (Fig. If). The hind limb joints subsequently extended to return to paw contact (Fig. la). This general pattern was evident at all speeds in both trained and untrained animals. Perfhnance ndth Time. Five trained cats attained plateaus in the maximum average speeds they could accommodate (Fig. 2a-e). Three other cats declined in treadmill speed after reaching a peak (Fig. 2f-h). Declining performance
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TABLE 1 Maximum Treadmill Speeds at I and 5 to 7 Months Posttransection Max speed (m/s) Cat
Group”
SA ED AJ SP LE SH PL KA AD BK BR co TI VE
1 Month
5-7 Months
0.08 0.05 0.05 0.05 0.05 0.05 0.15 0.15 X + SD = 0.079 + 0.045 0.05 0.05 0.05 0.05 0.15 0.10 X f SD = 0.075 _+0.042
0.85 0.65 0.7 0.65 0.4 0.6 0.5 0.6 Xk SD = 0.619 + 0.133 0.15 0.30 NT’ 0.25 0.15 0.35 X f SD = 0.240 k 0.089
’ T = trained, U = untrained. b Not tested.
was due to an increasing frequency of NFW steps which were associated with ankle hyperextension during the stance phase, inability to support body weight, and/or landing on the dorsum of the paw at paw contact. Because the average treadmill speed per session provided no measure of the number of steps that were full-weight-bearing, the number of full-weightbearing steps times treadmill speed (P) also was utilized to monitor performance (Fig. 3). The similarity between these performance index plots and plots of average treadmill speed (Fig. 2) reflects our criteria for increasing the speed: that 95% of the steps at a given speed had to be verifiably full-weightbearing before the speed was increased. The necessity for tail crimping is indicated by the shaded areas of Fig. 3. The darker the shade, the more often tail crimping was necessary. Almost no tail crimping was needed for three cats (Fig. 3a-c) after 6 days of training and for another cat (Fig. 3d) after 5 1 days. One cat regressed from no tail crimping after 4 days to requiring constant tail crimping after 27 days into the training period (Fig. 3g). Other cats required at least some tail crimping periodically throughout training (Fig. 3e, f, h). The average number of days from initiation of training to peak or plateau was 48 -1-22 (SD) for seven of eight cats (Fig. 3a-g). Cat KA was not included in this average due to the presence of several peaks (Fig. 3h).
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(al
Oms
(b)
(d)
430 ms
(e) 500 ms
RECOVERY,
20 ms
AND SPINAL CAT
(c)
(f)
427
160 ms
600 ms
FIG. I. Photographs made from high-speed film ( 100 frames/s) of selected positions in the step cycle of an adult spinal cat (treadmill speed = 0.6 m/s: cycle period = 640 ms). A vest around the shoulder girdle and chest restrained the cat’s rostrum. The cat’s forepaws were placed on a platform above (2.5 cm) the moving treadmill belt. A Plexiglas divider removed the possibility of one hind limb stumbling over the other during the swing phase. The tail was slack and, in this sequence, taped to the side of the treadmill to avoid interference with the view of the right hind limb. The positions shown are: (a)-initial treadmill contact, (b&initial posterior movement of the paw, (c)-support phase, (d)-initial ankle flexion, (e)-dragging the paw during the swing phase, and (B-initial extension phase at the ankle.
Warm-up. Regardless of the changes in treadmill performance that occurred during the training period, all cats typically required a “warm-up” period (1 to 10 min) before reaching the maximum speeds for a given training session. Most of the tail crimping for a given session occurred during this time. Maximum Treadmill Speed. The maximum treadmill speed increased significantly in both trained and untrained groups between 1 and 5 to 7 months posttransection (Table 1). Untrained cats improved more than threefold, from 0.075 + 0.042 to 0.240 + 0.089 m/s, and trained cats improved nearly eightfold, from 0.079 k 0.045 to 0.6 19 h 0.133 m/s. DISCUSSION Immediate Responses to Training. All cats improved substantially within 3 min of beginning the first training session. Initially cats dragged the paw forward during the entire swing phase and began the support phase on the dorsum of the paw. During this period the trainers attempted to enhance sensory input in several ways to improve motor responses to the moving treadmill belt.
428
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430
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AL.
First, tail pinching or crimping provided stimuli which promoted the activation of extensor muscles during support and the activation of flexor muscles during the swing phase. Second, the trainers lifted each paw during its respective swing phase and hyperextended the metatarsophalangeal joint to allow appropriate paw placement at the initiation of the subsequent support phase. This assistance may have enhanced the activation of hind limb flexors and digital extensors. Such effects have been demonstrated in the fictive curarized cat in which an ongoing flexion movement reinforced flexor activity and an ongoing extension movement reinforced extensor activity ( 1). Finally, the trainers provided no weight support to the spinal cats to maximize the load on hind limb extensor muscles during the stance phase. With the paw appropriately placed during the stance phase, additional mechanisms became available to heighten reflexive responses which may have aided stepping. Pressure on the plantar surface of the paw for example, loaded the extensor muscles which further facilitated their activation (39). In addition, the diminishing load on extensor muscles and the position of the hip joint at the end of the stance phase may have been important for the initiation of flexor muscle activity and subsequent swing phase (23, 32). The substantial improvement observed during the first training session and the diminished requirement for trainer assistance as time progressed indicate that the effects of therapy were not limited to reflexive responses in the steps in which it was administered. It appears that training effects resulting from sensory stimulation had both immediate and lasting effects on locomotor capability. Capacity for Full- Weight-Bearing Stepping. One month posttransection, 14 of 16 spinal cats were capable of full-weight-bearing stepping if the tail was pinched or crimped. Within the subsequent month, four of the eight cats that received training were capable of full-weight-bearing stepping without this extra stimulus. These results contrast with those of Eidelberg et al. (12) who reported that none of their six cats was capable of full-weight-bearing stepping after 2 months of training. We attribute this disparity to differences in the training apparatus and training techniques. First, Eidelberg’s cats were suspended in a shng such that the hind limbs were never fully loaded. This may have reduced sensory input important for facilitating the activation of extensors during the support phase and the triggering of hip flexion to initiate the swing phase (9, 32). In contrast, we never provided continuous assistance in weight support and occasionally pulled downward on the tail to enhance extensor loading. Second, in Eidelberg’s preparation, the forelimbs were allowed to step freely on the treadmill belt. In our preparation the forelimbs were stationary on a platform and the thorax was restrained by a vest. Movement of the forelimbs in the absence of coordination with hind limb stepping would be expected to
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generate shifts in the loading and positioning of the hind limbs. The inconsistent sensory input resulting from these shifts may have led to muscle activation patterns that were inappropriate for full-weight-bearing stepping. We found that even a subtle movement of the head or shifting of the weight on the forelimbs was sometimes sufficient to disrupt a long sequence of fullweight-bearing steps. Presumably these movements altered the distribution of weight on the hind limbs and subsequent sensory input to the spinal cord. Finally, we applied tail crimping, continuously if necessary, to promote the activation of extensors for support and the activation of flexors for limb recovery during the swing phase. In addition to short-term reflexive influences, tail crimping may have had long-lasting facilitative effects which were helpful in the entrainment of the stepping pattern. Noxious stimuli are known to facilitate certain reflex responses in cats (4 1) and have produced long-lasting heterosynaptic facilitation in sensory pathways of mollusks (4, 5, 29). Smith et al. (40) reported that all their 12-week transected cats that received no training and two of five trained 12-week transected cats were incapable of full-weight-bearing stepping 4 months after transection. Similarly Giuliani et al. (19) reported that only 7 of 2 1 untrained adult spinal cats were capable of full-weight-bearing stepping 4 months after transection. Although our treadmill apparatus was the same as that used by these researchers, our methods of therapy and criteria for measuring performance differed. For example, in the earlier studies no initital assistance in paw placement was provided and the trainers usually gave continuous assistance in weight bearing. Furthermore, in the study by Smith et al., performance was assessed after viewing video tapes of spinal locomotion. They used a nine-point rating scale based on the apparent consistency of weight bearing and appropriateness of paw placement. In the present study however, the trainers provided initial assistance in paw placement, gave no assistance in weight bearing. and administered continuous tail crimping if necessary. Any steps taken that were not full-weight-bearing were not counted using our performance measurement protocol. Our assessment of locomotor capability was made during the training sessions and was based on quantitative data rather than a subjective, nonparametric score. Trained vs. Untrained. Although our results differed with those of Smith et al. (40) on the proportion of adult spinal cats capable of full-weight-bearing stepping, the finding that trained cats performed significantly better than untrained was consistent in both studies. Differences between trained and untrained cats were also apparent in muscle properties in both studies. Some hind limb extensor muscles of trained cats, for example, underwent smaller decreases in wet weight, and maximal tetanic tension and twitch tension after cord transection than those of untrained cats (11, 25, 35, 36). The neural mechanisms which might explain the training effects on performance are obscure. Repeated stimulation is often associated with inhibition
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rather than facilitation of responses. Excitatory postsynaptic potentials from la afferent fibers, for example, can be decreased by use and enhanced by disuse (10, 16, 17, 20, 21). The inhibition of responses after repeated stimulation has also been demonstrated in some reflexes in the chronic spinal cat. Examples include habituation in the flexion withdrawal reflex (41, 43) and also in the responses to touch, heat, and cold (28). The long-term effects of a stimulus, however, do not seem to be a simple function of use or disuse. An afferent stimulus which ordinarily results in posttetanic depression, for example, can cause posttetanic potentiation if the stimulus rate is high enough and the duration of stimulation is long enough (13). In addition, a number of studies suggest that facilitative effects within a given reflex pathway depend on the presence of activity in a parallel sensory pathway. This idea is supported by the findings that long-term habituation in responses to touch, heat, and cold in the chronic spinal cat could be reversed by eliciting reflexes from overlapping receptive modalities (28). Furthermore, lasting facilitative effects on the synapses of a given pathway have been elicited by stimulation of another pathway in mollusks (26, 29, 33). Similarly, longlasting presynaptic facilitation of la afferent fibers has been demonstrated in cat upon stimulation of cutaneous afferent pathways (38). Certainly, in stepping, it seems that a substantial number of sensory pathways may be activated simultaneously at any given point in the step cycle. The facilitative mechanisms exemplified in some reflexes therefore, might be included as potential contributors to the entrainment of stepping. But because stepping is not merely reflexive, and involves pattern-generating circuitry intrinsic to the spinal cord, there are probably other long-lasting facilitative mechanisms involved as well. Although trained cats performed significantly better than untrained cats, both groups improved. This suggests that recovery of motor functions continued beyond 1 month posttransection without therapy. Segmental reflexes (e.g., flexion and crossed extension) and air stepping seem to be fully recovered within 1 month after transection in adult cats (18, 3 I). Weight bearing, however, requires that not only the timing of muscle activation be appropriate for stepping, but that the level of activation in extensors be sufficient to support the weight of the posterior part of the cat. Although 14 of our cats were capable of full-weight-bearing stepping 1 month posttransection without training, they all required tail crimping at that time. It was not until later, (3 to 50 days) that extensors were activated sufficiently to bear full weight without tail crimping. In addition, studies on the static fusimotor system indicate that the response to static muscle stretch may still be depressed after 2 months posttransection (3). Thus, it appears that our cats were still recovering from the effects of spinal cord transection after 1 month posttransection and also that training altered both the time course and the degree of recovery.
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Declining Performance. The declining performances observed in three cats (Fig. 3f-h) after attaining a peak and the occasional poor performances observed in three other cats (Fig. 3a, c, d) after reaching plateaus were due to an increased frequency of NFW steps. These steps were associated with lack of metatarsophalangeal joint hyperextension prior to paw contact. ankle hyperextension during the stance phase, or inability to support the hindquarters. Sometimes all three conditions were present. The lack of metatarsophalangeal joint hyperextension prior to paw placement seemed to be due to contractures in the digital flexors rather than a failure to activate the digital extensors. Forceful manipulation was sometimes required by trainers to hyperextend this joint for paw placement. Flexion contractures are common in spinal cord-injured humans and stroke patients (8,42). Joint laxity, spasticity, and hypotonia have also been widely reported in the clinical literature on paraplegia (8, 37) and may have been related to instances of ankle joint hyperextension. Hypotonia in the hind limb extensors seems to have been responsible for the inability to support body weight. Although we made no attempt to quantify the instances of each of these problems in trained and untrained cats, it appeared that they were more prevalent in untrained cats. Although our training regimen in general may have helped to alleviate flexion contractures, joint laxity, spasticity, and hypotonia, it was apparently not sufficient to reverse the progressive dysfunction observed in three of our trained cats. In fact, additional manipulative therapy and treadmill training (7 days/week) administered to one cat (PL; Fig. 3g) was unsuccessful in reversing the trend of declining performance. The occasional poor performances of three other cats may reflect temporary, undiagnosed health maladies such as bladder infections (15, 24) or restlessness and therefore instability of the rostra1 part of the cat. Conclusions. A much larger proportion (87%) of adult spinal cats were capable of full-weight-bearing stepping, regardless of treadmill training, than has been reported (12, 19, 40). In addition, our methods of training which involved continuous tail crimping whenever necessary, and emphasized weight bearing throughout the training period, resulted in marked improvements in the locomotor capacity of the hind limbs.
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