JOURNALOF NEUROPHYSIOLO(;Y Vol. 66, No. 6, Dcccmber 199 1. Pri~td

Fictive Motor Patterns in Chronic Spinal Cats K. G. PEARSON

AND

S. ROSSIGNOL

Centre de Recherche en Sciences Neurologiques, Montreal, Quebec H3C 3J7, Canada SUMMARY

AND

Department

CONCLUSIONS

I. Fictive motor patterns were recorded in hind leg nerves of 10 adult chronic spinal cats (spinalized at T 13). Four of these animals had been trained to step with their hind legs on a treadmill (latespinal animals), whereas the remainder received no training and were examined a short time after spinalization (early-spinal animals). 2. A fictive pattern resembling the locomotor pattern for stepping was evoked in all animals in response to stimulation of the skin of the perineal region. (2-[2,6-Dichloroanilinel-2-imidazo1ine)hydrochloride (Clonidine) at doses ranging from 100 to 500 pg/kg iv facilitated the production of this pattern, particularly in early-spinal animals. 3. The fictive locomotor pattern in late-spinal animals was more complex than that occurring in early-spinal animals. In the latter the pattern consisted of an alternation of activity in flexor and extensor nerves, and changing leg position did not qualitatively alter the pattern, whereas in late-spinal animals the relative durations of the bursts in different flexors were usually not the same, and the pattern of flexor activity was dependent on leg position. 4. Moving the legs from extension to flexion progressively decreased the duration of flexor bursts, increased the cycle period, and decreased the ease with which the pattern could be evoked in both early- and late-spinal animals. 5. 1-P-3,4-Dihydroxyphenylalanine (DOPA)/Isonocotinic acid 2-[(2-benzylcarbamoyl)ethyl]hydrazide(Nialamide) treatment following Clonidine in early-spinal animals increased the complexity of flexor burst activity. This, and other observations, indicates that DOPA and Clonidine do not have strictly identical actions on the locomotor pattern generator. 6. Stimulation of the paws in late-spinal animals produced two patterns of activity distinctly different from the locomotor pattern. One was a short sequence of high-frequency rhythmic activity (at ~8 c/s) in response to gently stimulating one paw with a water jet, and the other was a slow rhythm in flexor nerves in response to squeezing the paw. 7. The main conclusion of this investigation is that three distinctly different fictive motor patterns can be generated in chronic spinal cats depending on the method and site of stimulation. These patterns correspond to three different behaviors (locomotion, paw shake, and rhythmic leg flexion) that can be elicited in behaving chronic spinal cats in response to the same stimuli. We also conclude that the alteration in the locomotor pattern that occurs during recovery of hind leg stepping in chronic spinal cats is in part due to alterations in the properties of the central rhythmgenerating network.

of Physiology,

Universite’ de Montrkal,

tor activity in hind leg muscles is weak and poorly organized, but as recovery progresses the motor pattern evolves to resemble that occurring in normal walking animals ( Barbeau and Rossignol 1987; B&anger et al. 1988; Rossigno1 et al. 1989). During the recovery phase (lasting from 2 to 4 wk) the animal regains plantar foot contact, weight support, and nearly full angular excursions of all joints. At about the same time that stepping has recovered, other rhythmic behaviors can also be elicited, such as air stepping (Giuliani and Smith 1985 ), fast paw shaking [appearing as soon as 48 h posttransection according to Sabin and Smith ( 1984)], and strong flexions in response to squeezing a paw (unpublished observations). Two questions arising from these observations are the following: I ) is the progressive recovery of locomotion reflected in the characteristics of fictive motor patterns generated at different times after spinalization; and 2) can different motor patterns corresponding to the different rhythmic behaviors be elicited in immobilized animals? To gain information related to these questions, we have recorded the fictive motor patterns in hind leg muscle nerves in adult cats that were spinalized at T13 either a few days or a few weeks earlier. Animals in the latter group were trained to step with their hind legs on a treadmill and had regained the ability to produce fast paw shakes when the paw was dipped in water and rhythmic flexions of the limb when the paw was squeezed. Another objective of this investigation was to examine the action of the alpha-2 noradrenergic agonist (2-[2,6Dichloroanilinel-2-imidazoline)hydrochloride (Clonidine) (Anden et al. 1970) on the fictive motor pattern in chronic spinal animals. Clonidine has been shown to initiate stepping in acute spinal animals (Forssberg and Grillner 1973) and modulate stepping in chronic spinal animals (Barbeau et al. 1987). It also abolishes fast paw shaking in chronic spinal animals (Barbeau et al. 1987). Some specific questions we wished to address were as follows: I) can fictive motor patterns related to stepping be elicited reliably when Clonidine is administered a few days after spinalization; 2) what is the effect of Clonidine on the fictive patterns generated in animals that have regained the ability to step with their hind legs on a treadmill; and 3) are the fictive patterns that are generated after the administration of Clonidine the same as those produced by 1-P-3,4-Dihydroxyphenylalanine (L-DOPA)?

INTRODUCTION

Adult cats spinalized at T 13 can regain the ability to step with their hind legs on a treadmill, especially when they are properly exercised (Barbeau and Rossignol 1987; Lovely et al. 1985; Rossignol et al. 1982). Initially the pattern of mo1874

METHODS

Preparation

of spinal animals

The procedure for spinalization and care of the animals were similar to that described by Barbeau and Rossignol ( 1987). Adult

0022~3077/9 1 $1 SO Copyright 63 199 1 The American Physiological Society

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MOTOR

PATTERNS

cats were anesthetized with pentobarbital sodium (Somnotol, 40 mg/ kg), and, under aseptic conditions, the spinal cord was transected at T 13. A urethral catheter was inserted to allow voiding of urine during the first few days after spinalization. Penicillin G ( 300,000 IU ) was administered each day for a fortnight or up to the time of the experimental procedure, whichever was sooner. Fluid and nutritional needs were provided for the first 3 days by subcutaneous injections of 15 ml of a mixture of essential amino acids, B-complex vitamins, and electrolytes (Aminolean, Pharmacentique, Cambridge, Ontario, Canada) in 100 ml lactated Ringer each day. After removal of the urethral catheter, the bladder was emptied twice a day. The animals were caged individually with free access to food and water.

Training

of. spinal animals

Four animals were trained to step with their hind legs on a treadmill. Training commenced 2 days after spinalization. Each training session lasted - 15 min, and one or two sessions were given daily. The cat was held above a treadmill (speed range, O.l0.8 m/s) with its forelegs standing on a platform 3 cm above the treadmill belt. Initially feeble rhythmic hind leg movements were induced by perineal stimulation. Within a week the animals developed good extensor tone and were able to support their weight. Stepping in response to perineal stimulation improved rapidly after this. Bilaterally coordinated stepping with complete weight support of the hindquarters occurred between 2 to 4 wk after spinalization. The quality of stepping, judged by visual observation, varied over time, but in all four animals it was rated as good (periods of regular stepping for > 10 s with the 2 hind legs alternating with complete weight support and plantar foot contact) at the time of the experimental procedure.

Recording offictive motor patterns Ten spinal animals (4 trained and 6 untrained) were used to record the fictive motor patterns. Each animal was anesthetized with a short-lasting steroid anesthetic (Saffan, 1 ml/ kg, a mixture of 9 mg of alphaxalone and 3 mg of alphadolone per ml) and decerebrated by ligating the carotid arteries and either transecting the brain stem or ligating the basilar artery. The latter procedure produced an anemic decerebration (Pollock and Davis 1923). The effectiveness of this procedure was confirmed by examination of the brain at the end of the experiment. A tracheal cannula was inserted, and cannulas were inserted into a jugular vein and a carotid artery to allow the administration of drugs and for monitoring blood pressure, respectively. To record electroneurograms ( ENGs), electrodes were attached to the cut ends of nerves innervating a variety of muscles in both hind legs. Each nerve was exposed and cut close to its insertion into the muscle. A single silver wire (insulated except for -5 mm at the end) was crimped onto the cut end of the nerve, and the uninsulated region of the electrode and - 1 cm of nerve was embedded in silicone-based impression material (Reprosil Light Body, De Trey). This material provided excellent insulation around the nerve and recording electrode. A single indifferent electrode was sewn into a thigh muscle. The skin incisions were closed, and the flexible recording leads ( -50 cm in length) were bundled together and coupled to differential amplifiers. This recording technique allowed the hind legs to be moved over their entire range while maintaining the recordings from the motor nerves. After attachment of the recording electrodes to nerves, the animal was mounted with its head fixed in a stereotaxic holder and its body suspended so as to permit full passive movements of the hind legs. The animals were then immobilized with gallamine triethiodide ( Flaxedil; initially 10 mg/ kg and supplemented as required)

IN SPINAL

1875

CATS

and artificially ventilated. A period of -5 h was allowed for recovery from the anesthetic. Before the administration of any drugs (see below) and after the recovery from the anesthetic, an attempt was made in all animals to elicit fictive motor patterns. A variety of stimulation sites was tried. The most common was to pinch the skin of the perineal region. In late-spinal animals (i.e., those that had been trained to step with their hind legs) relatively modest stimuli initiated rhythmic motor activity. A more intense stimulus was required in earlyspinal animals. Other stimuli consisted of squeezing the paws, pinching the skin of the belly and thighs, gently rubbing the fur on the paws, and squirting a jet of water on the paws. The latter two methods of stimulation were used in attempts to elicit fictive patterns associated with paw shaking. The stimulus duration was usually 1 s. This activity was most elaborate on the stimulated side, although strong activity in some contralateral nerves also appeared. One of the features of this pattern of activity was the coactivation of the ankle flexor TA with the knee extensor vastus lateralis (VL). Another was the double burst of activity in the VL muscle seen here on both sides. Particu-

Sart 1 s Records showing that leg position influences the relative burst durations in St and Sart in an early-spinal animal that had been treated with DOPA after the administration of 4-AP and Clonidine. With the hind legs flexed (top tracm) the bursts in St and Sart were short and similar in duration. Moving the legs to a pendant position ( middk traces) caused the burst durations in Sart to increase and become distinctly longer than the bursts in St. With the legs fully extended (bottom trams) the bursts in both St and Sart were similar in duration and longer than those generated when the legs were flexed. FIG.

8.

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1882

K. G.

PEARSON

AND

S. ROSSIGNOL

HB6026

I I

iSart

iSart . ITA

.

ITA

coSart

-

COTA itl

coTA

100 ms

6

1s

PHASE FIG. 9. High-frequency fictive motor pattern recorded in hind leg nerves of a late-spinal animal (n innocuous stimulus (jet of water) to the ipsilateral paw. This pattern of activity was recorded in treatment. The /~fi pund shows a complete “fictive fast paw-shake” sequence of 12 cycles, whereas the average activity of these 12 cycles obtained by triggering on iSart. Because of variability in the timing within the cycle, some temporal features of the pattern were lost in the averages, such as the weak bursts the double bursts of activity in iVL and COVL. Nevertheless, the averaged data do illustrate the overlap VL. The 100-ms time base at the bottom right is derived from the mean cycle duration.

tion with either a stimulation of the paw or the perineal region, respectively. The second fictive pattern elicited by stimulation of the paw consisted of intense and relatively long-duration bursts TABLE

1.

I 3 3 4 5 6 7 8 All cats

60) in response to an the absence of drug right panel shows the of individual bursts of activity in iSt and of activity in TA and

in ipsilateral flexor nerves. This pattern, shown here (Fig. 11) for the same cat as in Figs. 9 and 10, occurred in response to maintained squeezing of a paw, here identified as contralateral to maintain consistency between the three

Churuc’teristicsof’fti.57 . . puw shakesin cut pwpurutions Intact

Cat

1 :o

015 OF CYCLE

Duration,

883 700 726.7

784

ms

+ 304 (6) r!I 100 (3) + 141 (5)

+ 221 (11)

Fictive

Spinal Frequency,

Hz

8.6 + 1.8 (48) 13.6 & 1.9 (30) 9.0 AI 1.5 (36)

10.3 + 2.9 (1 14)

Duration, 981 1,02 1 1,000 1,160

ms

-t278(11) + 269 (8) + 565 (2) + 254 (8)

1,043 IL 28 1 (29)

Frequency, 8.5 10.6 8.8 9.4

?I + + III

1.5 2.0 1.6 1.6

Hz (94) (79) (18) (82)

9.4 + 2.2 (273)

Duration,

ms

Frequency,

1,442 + 383 (5) 1,480 + 961 (2) 426 + 151 (3)

7.6 5.5 8.5

965 (1) 812 k 189 (6) 1,029 IL 534 (16)

5.33 IL 0.9 7.7 IL 1.5 7.4 + 1.9

Hz

+ 1.8 (55) + 1.28 (15) k 2.0 (13)

(5) (33) (116)

Values are means t SD; number of sequences for duration and number of cycles for frequency are in parentheses. The duration refers to the mean total duration of all the sequences of fast paw shake measured in one cat. The frequency was obtained by measuring the duration of all the cycles in all the sequences.

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MOTOR

PATTERNS

IN

SPINAL

1883

CATS

Hi36026

I

iSart

iSart

I ITA

I ITA

coSart

coSart

#

coTA

I

100 ms Is

0

0.5

1 .o

PHASE OF CYCLE FIG. 10. Fictive motor pattern recorded in hind leg nerves of a late-spinal animal in response to pinching the skin of the perineum. Same animal as in Fig. 8. Lqft panel: -6 c of 1 long sequence. Right panel: averaged data of 33 cycles in that sequence. In this animal the durations of the bursts in all flexors (St, Sart, and TA) were similar (compare with Fig. 3).

patterns obtained in the same cat. The most notable features of the pattern elicited by paw squeezing were the relative long durations of the flexor bursts ( 500- 1,000 ms) and the absence of any obvious pattern in the relative durations of the bursts in different nerves. Although extensor nerves on the stimulated side could be reciprocally active during this rhythm, they normally remained silent. Bursts of activity could also occur in motor nerves on the other side, but, if they did, they were most prominent in extensor nerves. Thus this pattern had no resemblance to that elicited by perineal stimulation. This rhythm was observed in all latespinal animals with and without Clonidine, and in all earlyspinal animals that had been treated with Clonidine. This fictive rhythm is likely the basis for the production of rhythmic flexion movements of a hind leg of a chronic spinal cat in response to squeezing the paw. DISCUSSION

To date, there has been only one detailed analysis of the characteristics of fictive motor patterns in spinal cats (Grillner and Zangger 1979). This earlier study was done in acute spinal cats after the administration of DOPA and Nialamide. Numerous other studies using DOPA / Nialamide-treated spinal cats have confirmed and extended

many of the basic findings of Grillner and Zangger’s study (Andersson and Grillner 198 1; Baker et al. 1984; Conway et al. 1987; Dubuc et al. 1987; Schmidt et al. 1988). Although some features of the fictive patterns in acute spinal DOPA / Nialamide animals are qualitatively similar to features occurring during stepping in intact animals, e.g., a relatively short burst of activity in flexor digitorum longus nerves during the flexor phase (Schmidt et al. 1988)) many features differ from those seen during normal stepping. For example, the bursts in St are usually very long and comparable in duration with bursts in other flexors, and double bursting in St, Sart, and rectus femoris (RF) nerves has never been reported following DOPA / Nialamide treatment. However, additional administration of 4-AP (which by itself does not initiate rhythmicity ) can lead to relatively short St bursts and to double bursting in St and RF nerves (Dubuc et al. 1986). Thus, with the appropriate drug treatment, the acutely isolated cord has the capacity to generate complex motor patterns. One of the questions we wished to answer in this investigation was whether similar patterns of activity could be generated in chronic spinal cats in the absence of drugs. Surprisingly little information is available on the characteristics of fictive motor patterns in chronic spinal cats. In fact, there have been only two brief reports

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1884

K. G. PEARSON AND S. ROSSIGNOL HB6026

II II

iSt

iSt jI I I

iSart

iSart I I I I I I I I

.

ITA -

iTA 1I I

. IVL I

iVL

I I I I

cost

I I I

coSart coTA

I I

COVL H

COVL ! 100 ms

I 0.5 PHASE OF CYCLE FIG. 1 1. Fictive motor pattern recorded in hind leg nerves of a late-spinal animal in response to squeezing the contralatera1 (right) paw. Same animal as in Figs. 8 and 9. L&panel: records for a single sequence. Right panel: averaged data for 8 cycles. In this animal COVL was activated weakly in-phase with the flexor bursts. IS

(Baker et al. 1984; Grillner and Zangger 1974) that fictive motor patterns can be generated in chronic spinal cats in the absence of drug treatment, and there has been no analysis of the characteristics of these patterns. In this study we have found that the characteristics of these patterns depend on the site and method of stimulation and on leg position. Furthermore, our data indicate that the fictive patterns in response to perineal stimulation increase in complexity with time after spinalization, thus suggesting that functional recovery of stepping in chronic spinal cats depends to some extent on slow modifications of the properties of the spinal pattern-generating network. Finally, we have demonstrated that the alpha-2 noradrenergic agonist Clonidine strongly facilitates the generation of the fictive patterns in response to perineal stimulation, and that DOPA administration following Clonidine can alter the pattern in earlyspinal animals. In the following discussion we consider each of these factors separately. Recovery of thejctive

pattern for stepping

It is well known that it is difficult to elicit rhythmic motor activity in hind leg motor nerves immediately after transection of the spinal cord. Only extreme mechanical stimula-

r 0

1 1 .o

tion [e.g., sectioning the cord (Graham Brown 19 1 1 )] or drug treatment [e.g., DOPA / Nialamide ( Grillner and Zangger 1979)] will produce fictive patterns. Thus there is a recovery of the capacity to centrally generate rhythmic motor activity after spinalization, but the time course and details of this recovery have not been established. Although an analysis of recovery was not the main objective of this study, we did observe that fictive motor activity related to stepping can be evoked in the absence of drug treatment within a few days of spinalization and that the ease with which this activity can be evoked is considerably higher some weeks after spinalization. One of the most interesting observations of this study was that the fictive pattern without drugs in late-spinal animals was more complex than the pattern in animals a few days after spinalization. The most obvious difference we observed was in the characteristics of the flexor bursts. In early-spinal animals, bursts in St and Sart were virtually identical (Fig. 1). On the other hand, in late-spinal animals there were usually clear differences in the duration of the bursts in St and Sart, and the relative durations of the bursts in different flexors could be easily altered by changing the position of the legs (Figs. 5 and 6). From these observations we conclude that two separate events occur during the re-

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MOTOR

PATTERNS

covery of locomotor function in spinal cats. The first is an increase in the excitability of the rhythm-generating network (indicated by the ease with which rhythmicity could be evoked in late-spinal animals), and the second is a modification of the circuits that establish the temporal characteristics of the pattern (indicated by the more complex pattern of flexor activity). One explanation for the dual nature of recovery is that there is a progressive enhancement of transmission in various afferent pathways (namely from the skin of the perineum) to increase excitability, and a slow modification of the pattern-generating network to alter details of the fictive pattern. Whatever the mechanism is for recovery, it seems unlikely that it is due to recovery from shock after cord transection because the fictive rhythms are difficult to evoke many days after spinalization. The relatively slow recovery over the course of weeks suggests that processes such as sprouting, competition, and so on are involved. Indeed Goldberger and Murray ( 1982) have presented anatomic evidence to indicate that these processes do occur. One point that should be kept in mind is that all our late-spinal animals had been trained to step with their hind legs on a treadmill. Thus one possibility is that training is a factor in the emergence of the fictive pattern. To distinguish between an effect of training from an intrinsic recovery process will require a comparison of fictive patterns in trained and untrained groups of late-spinal animals. l@ct

of. tonic sensory input One of the most consistent findings of this investigation was that the position of the hind legs strongly influenced the fictive pattern elicited by perineal stimulation. Flexion of the legs shortened the durations of the flexor bursts, increased the cycle period, and sometimes prevented the rhythm from being generated. The rhythm was most easily generated when the legs were extended. More subtle features of the patterns were also sometimes influenced by leg position. For example, in late-spinal animals the relative durations of the bursts in St, Sart, and TA were often not the same when the legs were held in a position close to midway between full flexion and full extension (Fig. 8) but were similar when the legs were flexed (short burst durations) or extended (long burst durations). Do these observations have any relevance to the problem of understanding how afferent input regulates the motor pattern during stepping? Our data suggest that during the stance phase there is a progressive facilitation of the network for generating flexor bursts. It is therefore conceivable that this facilitation is scaled so as to lead to the production of a flexor burst when the leg is extended and so lead to the transition from stance to swing. A similar conclusion was reached from studies on the effect of extending the hip in acute DOPAtreated cats ( Andersson and Grillner 1983 ). Efect of Clonidine and DOPA on theJictive patterns . Previous work has shown that stepping of the hind legs can be induced in acute spinal adult cats after the administration of Clonidine (Forssberg and Grillner 1973), and that Clonidine can facilitate hind leg stepping in chronic spinal animals (Barbeau et al. 1987 ). Consistent with these

IN

SPINAL

CATS

1885

observations was our finding that Clonidine greatly potentiated the ease with which the fictive pattern for stepping could be elicited. In all 10 of our experimental animals, Clonidine in doses within the range of 100-500 pg/ kg allowed robust and sustained rhythmicity to be generated in response to perineal stimulation. An interesting aspect of the effect of Clonidine was that it did not influence the detailed structure of the fictive pattern, i.e., the pattern generated before Clonidine was strengthened but not altered. DOPA / Nialamide treatment after Clonidine also facilitated the generation of the locomotor pattern, usually leading to spontaneous rhythmicity. In addition, however, DOPA often altered the details of the timing of activity in flexor nerves ( Fig. 8) and hence qualitatively altered the fictive pattern. Whereas double bursting in St and Sart was not seen in early-spinal with Clonidine only, it was occasionally seen after DOPA in early-spinal and in two out of four late-spinal cats. This is in agreement with other observations in mesencephalic immobilized preparations (Perret and Cabelguen 1980) and acute spinal cats treated with DOPA (Dubuc et al. 1986; Schmidt et al. 1989) in which double bursting in St nerves or two depolarizations per cycle have been reported. The observation that the details of the patterns may be different after Clonidine and DOPA, together with the fact that DOPA usually gave spontaneous rhythmicity whereas high concentrations of Clonidine did not (at least in the early stages), suggests that the receptor sites activated by these two drugs on the central pattern-generating network are not identical. Whereas the action of Clonidine is exerted on noradrenergic alpha-2 receptors, it is not clear how L-DOPA acts on noradrenergic receptors in the chronically spinalized animal. L-DOPA is thought to act on noradrenergic receptors through the synthesis of noradrenaline after an uptake by noradrenergic terminals. Because these terminals have degenerated after 1 or 2 wk (Anden et al. 1964; Magnusson 1973), other sites of action must be postulated especially after 1 mo (see Anden et al. 1964). One possibility as discussed in Rossignol et al. ( 1986) is an action on dopaminergic receptors after an extraneuronal decarboxylation within the spinal cord (Bartholini et al. 1967). Fictive patterns and their relation to behavior One of the main results of this study was that at least three distinctly different patterns of motor activity can be generated in chronic spinal cats depending on the method and site of stimulation. The pattern we analyzed in most detail was evoked by pinching of the skin of the perineal region. This pattern was characterized by brisk reciprocal bursts of activity in flexor and extensor nerves, with the period of activity being longer in extensors than in flexors, and an alternation of activity in homonymous motor nerves in the two legs (Figs. 1 and 3). The duration of the flexor phase in this fictive pattern corresponds fairly closely to the duration of the flexor activity in walking animals in both magnitude and dependence on cycle period (Fig. 2). As shown in Fig. 6, which illustrates the cycle period as a function of hip angle, the period of these rhythmic sequences ranged from -500 to 1,500 ms, which would

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1886

K. G. PEARSON AND S. ROSSIGNOL

correspond in an intact animal walking on a treadmill to speeds of 1.O-0.2 m/s, respectively (Halbertsma 1983). All of these characteristics indicate that this pattern is the basis for stepping in spinal animals. This is consistent with the fact that pinching the skin of the perineum is the most effective stimulus for eliciting stepping in spinal animals walking on a treadmill (Carter and Smith 1986b; Forssberg et al. 1980; Giuliani and Smith 1985). However, it should be noted that the pattern of burst activity in flexor nerves evolved with time in these fictive preparations and that the changes observed largely matched those seen in chronic spinal cats walking on a treadmill at different stages of chronicity (Barbeau and Rossignol 1987). In early-spinal animals the durations of the fictive bursts in all flexor nerves were usually similar and rather long compared with the late-spinal cats (short St bursts were, however, sometimes produced by Nialamide / LDOPA treatment after Clonidine; Fig. 8). These longer periods of flexor activity correspond well to the long St EMG bursts seen in early stage after spinalization (Barbeau and Rossignol 1987, 199 1) and are consistent with the fact that the kinematic parameters of locomotion at this stage are not yet well developed. On the other hand, a pattern of flexor activity (short St, long Sart, delayed TA) resembling the stepping pattern of chronic spinal cats on a treadmill was often seen in latespinal fictive preparations (Fig. 3). Double bursting in St could also be seen, as is the case for the walking spinal cat ( Fig. 7 ). It should be noticed that the delay usually seen in intact cats between the onset of St and the onset of Sart is not seen in chronic spinal cats walking on the treadmill nor in the fictive preparation. The pattern of flexor muscle discharge was more unstable than in a walking animal and could be strongly influenced by leg position. The second pattern we observed consisted of a high-frequency ( 5- 11 c/s) burst of activity in flexor and extensor nerves in response to innocuous stimulation of the ipsilatera1 paw (Fig. 9). This pattern was only observed in latespinal animals that had not been treated with Clonidine. This pattern is undoubtedly associated with paw shaking: it is evoked only in late-spinal animals by the same stimuli that give paw shaking in behaving cats. It occurs mainly ipsilateral to the site of stimulation, and the relative timing of activity in different motor nerves resembles that seen during paw shaking. In particular, as shown by Smith et al. ( 1985 ) by the characteristic synergy consisting in a coactivation of VL, a knee extensor, and TA, an ankle flexor is preserved after paralysis. Recently Koshland and Smith ( 1989a) have reported similar patterns generated in chronic spinal cats after deafferentation. They also observed a reduction in the rhythm frequency from 10.2 Hz in the control to 8 Hz after deafferentation. In our series the intact cat rhythm was at 10.3, the spinal at 9.4, and the fictive at 7.4. Thus our results confirm the existence of a central pattern generator for paw shaking and also suggest that afferent feedback plays a role in determining the frequency of the pattern. This is also consistent with the observation of Prochazka et al. ( 1989) who have shown that altering the afferent feedback by adding weights to the paw during fast paw shake in the intact cat leads to a reduction

in frequency of the shake or that atypical feedback produced by immobilization of different joints may lead also to a decrease in paw-shake frequency (Koshland and Smith 1989b). The third fictive rhythm we observed was elicited in response to squeezing a paw (Fig. 11). This rhythm consisted of long-duration bursts in all ipsilateral flexor nerves, and only weak or no activity in ipsilateral extensor and contralateral motor nerves. Again, this rhythm can be associated with a distinct behavior in chronic spinal cats, namely strong rhythmic flexions of a hind leg when the paw is squeezed (we refer to this as the paw-squeeze response). The flexor bursts generated in this rhythm were distinctly different from those generated in response to perineal stimulation in three respects: the durations were longer for the same cycle period, the durations were more strongly dependent on cycle period, and burst durations in St were usually longer than the burst durations in Sart. Our finding of three distinct fictive patterns corresponding to three very different behaviors (stepping, paw shaking, paw-squeeze response) is consistent with the notion that the basic motor patterns for rhythmic movements are established by central networks independent of phasic sensory feedback. An important problem now is to determine the extent to which these motor patterns for the different behaviors are generated by different interneuronal circuits. One extreme view would be that the same interneuronal network is involved in all three patterns, and which pattern is expressed simply depends on how the network is activated. The opposite extreme would be that there are three entirely separate networks. Resolving this issue will require recording from interneurons in the cord, a task that is quite feasible. One indication that paw-shaking and stepping patterns might depend on separate circuits is that paw shaking can be superimposed on stepping (Carter and Smith 1986b; Giuliani and Smith 1985 ). It would be interesting to establish whether the simultaneous expression of both patterns can occur in immobilized chronic spinal cats. This work was supported by a grant from the Canadian Medical Research Council to the Group in Neurological Sciences. Special thanks to J. Provencher for efficient help with experiments and computer analyses and to D. Cyr for the photographic work. Thanks to Dr. Hughes Barbeau and Dr. Marc Belanger for participation in some experiments. Present address of K. G. Pearson: Dept. of Physiology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada. Address for reprint requests: S. Rossignol, Centre de Recherche en Sciences Neurologiques, Dept. of Physiology, Universite de Montreal, PO Box 6 128, Station A, Montreal, Quebec H3C 357, Canada. Received 11 October 1990; accepted in final form 13 July 199 1. REFERENCES N. E., HAGGENDAL, J., MAGNUSSON, T., AND ROSENGREN, E. The time course of disappearance of noradrenaline and 5hydroxytryptamine in the spinal cord after transection. Ac*ta Physiol. Stand. 62: 115-l 18, 1964. ANDEN, N. E., CORRODI, H., FUXE, K., HOKFELT, B., RYDIN, C., AND SVENSSON, T. Evidence for a central noradrenaline receptor stimulation by Clonidine. L$> Sci. 9: 5 13-523, 1970. ANDERSSON, 0. AND GRILLNER, S. Peripheral control of the cat’s step cycle. I. Phase dependent effects of ramp-movements of the hip during ‘fictive locomotion.’ Acta PhJjsiol. Stand. 113: 89- 102, 198 1. ANDEN,

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MOTOR

PATTERNS

0. AND GRILLNER, S. Peripheral control of the cat’s step cycle. II. Entrainment of the central pattern generators for locomotion by sinusoidal hip movements during fictive locomotion. Acta Physio/. Stand. 118: 229-239, 1983. BAKER, L. L., CHANDLER, S. H., AND GOLDBERG, L. J. L-Dopa-induced locomotor-like activity in ankle flexor and extensor nerves of chronic and acute spinal cats. Exp. Neurol. 86: 5 15-526, 1984. BARBEAU, H., JULIEN, C., AND ROSSIGNOL, S. The effects of clonidine and yohimbine on locomotion and cutaneous reflexes in the adult chronic spinal cat. Brain Res. 437: 83-96, 1987. BARBEAU, H. AND ROSSIGNOL, S. Recovery of locomotion after chronic spinalization in the adult cat. Brain Res. 4 12: 84-95, 1987. BARBEAU, H. AND ROSSIGNOL, S. Initiation and modulation of the locomotor pattern in the adult chronic spinal cat by noradrenergic, serotonergic and dopaminergic drugs. Brain Res. 546: 250-260, 199 1. BARTHOLINI, G., BATES, H. M., BUCKARD, W. P., AND PLETSCHER, A. Increase of cerebral catecholamine caused by 3-4 dihydroxyphenylalanine after inhibition of peripheral decarboxylase. Nature Lond. 215: ANDERSSON,

852-853, B~LANGER,

1967.

M., DREW, T., AND ROSSIGNOL, S. Spinal locomotion: a comparison of the kinematics and the electromyographic activity in the same animal before and after spinalization. Acta Biol. Hung. 39: 15 l154, 1988. CARTER, M. C. AND SMITH, J. L. Simultaneous control of two rhythmical behaviors. I. Locomotion with paw-shake response in normal cat. J. Neurophysio/. 56: 17 1- 183, 1986a. CARTER, M. C. AND SMITH, J. L. Simultaneous control of two rhythmical behaviors. II. Hindlimb walking with paw-shake response in spinal cat. J. Neurophysiol. 56: 184- 195, 1986b. CONWAY, B. A., HULTBORN, H., AND KIEHN, 0. Proprioceptive input resets central locomotor rhythm in the spinal cat. Exp. Brain Res. 68: 643-656, 1987. DUBUC, R., ROSSIGNOL,

S., AND LAMARRE, Y. The effectsof 4-aminopyridine on the spinal cord: rhythmic discharges recorded from the peripheral nerves. Brain Res. 369: 243-259, 1986. FORSSBERG, H. AND GRILLNER, S. The locomotion of the acute spinal cat injected with clonidine i.v. Brain Res. 50: 184- 186, 1973. FORSSBERG, H., GRILLNER, S., AND HALBERTSMA, J. The locomotion of the low spinal cat. I. Coordination within a hindlimb. Acta Physiol. Stand. 108: 269-28 1, 1980. GIULIANI, C. A. AND SMITH, J. L. Development and characteristics of air stepping in chronic spinal cats. J. Neurosci. 5: 1276- 1282, 1985. GOLDBERGER, M. AND MURRAY, M. Lack of sprouting and its presence after lesions of the cat spinal cord. Brain Res. 24 1: 227-239, 1982. GRAHAM BROWN, T. The intrinsic factors in the act of progression in the mammal. Proc. R. Sot. Lond. B Biol. Sci. 85: 278-289, 19 1 1. GRILLNER, S. The effect of L-Dopa on the spinal cord-relation to locomotion and the half-center hypothesis. In: Neurobiology of‘ Vertebrate Locomotion, edited by S. Grillner, P. S. G. Stein, D. G. Stuart, H. Forssberg, and R. M. Herman. London: Macmillan, 1986, p. 269-277. GRILLNER, S. AND ZANGGER, P. Locomotor movements generated by the deafferented spinal cord (Abstract). Acta Physiol. Stand. 9 1: 38-39A, 1974. GRILLNER, S. AND ZANGGER, P. On the central generation of locomotion in the low spinal cat. Exp. Brain Res. 34: 24 1-26 1, 1979. HALBERTSMA, J. M. The stride cycle of the cat: the modelling of locomo-

IN

SPINAL

CATS

1887

tion by computerized analysis of automatic recordings. Acta Ph.ysiol. Stand. Suppl. 52 1, 1983. HOFFER, J. A., LOEB, G. E., SUGANO, N., MARKS, W. B., O’DONOVAN, M. J., AND PRATT, C. A. Cat hindlimb motoneurons during locomotion. III. Functional segregation in Sartorius. J. Neuroph-ysiol. 57: 554-562, 1987. KOSHLAND,

G. F. AND SMITH, J. L. Mutable and immutable features of paw-shake responses after hindlimb deafferentation in the cat. J. Neurophysiol. 62: 162- 173, 1989a. KOSHLAND, G. F. AND SMITH, J. L. Paw-shake responses with joint immobilization: EMG changes with atypical feedback. Exp. Brain Res. 77: 36 l-373, 1989b. LOVELY, R. G., GREGOR, R. J., ROY, R. R., AND EDGERTON, V. R. Effects of training on the recovery of full weight bearing stepping in adult spinal cat. Exp. Neurol. 92: 42 l-435, 1986. MAGNUSSON, T. Effect of chronic transection on dopamine, noradrenaline and 5-hydroxytryptamine in the rat spinal cord. Naunyn-Schmiedeberg’s Arch. Pharmacol. 278: 13-22, 1973. PERRET, C. AND CABELGUEN, J.-M. Main characteristics of the hindlimb locomotor cycle in the decorticate cat with special reference to bifunctional muscles. Brain Res. 187: 333-352, 1980. POLLOCK, L. J. AND DAVIS, L. Studies in decerebration. I. A method of decerebration. Arch. New-o/. PLsychiatry 10: 39 l-398, 1923. PROCHAZKA, A., HULLIGER, M., TREND, P., LLEWELLYN, M., AND DURMULLER, N. Muscle afferent contribution to control of paw shakes in normal cats. J. NeurophysioZ. 6 1: 550-562, 1989. ROSSIGNOL, S., BARBEAU, H., AND JULIEN, C. Locomotion of the adult chronic spinal cat and its modification by monoaminergic agonists and antagonists. In: Development and Plasticity qfthc Mammalian Spinal Cord, edited by M. Goldberger, A. Gorio, and M. Murray. Fidia Research Series III, Padua, Italy: Liviana Press, 1986, p. 323-345. ROSSIGNOL, S., BARBEAU, H., AND PROVENCHER, J. Locomotion in the adult chronic spinal cat. Sot. Neurosci. Abstr. 8: 163, 1982. ROSSIGNOL, S., BELANGER, M., BARBEAU, H., AND DREW, T. Assessment of locomotor functions in the adult chronic spinal cat. In: Con/erence Proceedings. Criteria .fi,r Assessing Recovery of Function: Behavioral Methods, edited by M. Brown and M. E. Goldberger. American Paralysis Association, 1989, p. 62-65. SABIN, C. AND SMITH, J. L. Recovery and perturbation of paw-shake responses in spinal cats. J. Neurophysiol. 5 1: 680-688, 1984. SCHMIDT, B. J., MEYERS, D. E. R., FLESHMAN, J. W., TOKURIKI, M., AND BURKE, R. E. Phasic modulation of short latency cutaneous excitation in flexor digitorum longus motor nerves during fictive locomotion. Exp. Brain Res. 7 1: 568-578, 1988. SCHMIDT, B. H., MEYERS, D. E. R., TOKURIKI, M., AND BURKE, R. E. Modulation of short latency cutaneous excitation in flexor and extensor motoneurons during fictive locomotion in the cat. Exp. Brain Res. 77: 57-68, 1989. SMITH, J. L., HOY, M. G., KOSHLAND, NICKE, R. F. Intralimb coordination

G. F., PHILLIPS, D. M., AND ZERof the paw-shake response: a novel mixed synergy. J. Neurophysiol. 54: 127 1- 128 1, 1985. ZANGGER, P. The effect of 4-aminopyridine on the spinal locomotor rhythm induced by L-DOPA. Brain Res. 2 15: 2 1 l-223, 198 1. ZOMLEFER, M. R., PROVENCHER, J., BLANCHETTE, G., AND ROSSIGNOL, S. Electromyographic study of lumbar back muscles during locomotion in acute high decerebrate and in low spinal cats. Brain Res. 290: 249260, 1984.

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