The contralateral coordination of walking legs in the crayfish Astacus leptodactylus

The coupling mechanisms which coordinate the movement of ipsilateral walking legs in the crayfish have been described in earlier investigations. Concerning the coupling between contralateral legs it was only known that these influences are weaker than those acting between ipsilateral legs. The nature of these coupling mechanisms between contralateral legs of the crayfish are investigated here by running left and right legs on separate walking belts at different speeds. The results show that coordination is performed by a phase-dependent shift of the anterior extreme position of the influenced leg. This backward shift leads to a shortening of both the return stroke and the following power stroke. As the coupling influence is only weak, several steps might be necessary to retain normal coordination after a disturbance. This corresponds to v. Holst's relative coordination. The influences act in both directions, from left to right and vice versa. However, one side may be more or less dominant. A gradient was found in the way that anterior leg pairs show less strong coordination than posterior legs. In some cases the coupling between diagonally neighbouring legs was found to be stronger than between contralateral legs of the same segment. The interpretation of this result is still open.     

The control of walking movements in the leg of the rock lobster

1. Experiments with rock lobsters walking on a treadmill were undertaken to obtain information upon the system controlling the movement of the legs. Results show that the position of the leg is an important parameter affecting the cyclic movement of the walking leg. Stepping can be interrupted when the geometrical conditions for terminating either a return stroke or a power stroke are not fullfilled. 2. The mean value of anterior and posterior extreme positions (AEP and PEP respectively) of the walking legs do not depend on the walking speed (Fig. 1). 3. When one leg is isolated from the other walking legs by placing it on a platform the AEPs and PEPs of the other legs show a broader distribution compared to controls (Figs. 2 and 3). 4. Force measurements (Fig. 4) are in agreement with the hypothesis that the movement of the leg is controlled by a position servomechanism. 5. When one leg stands on a stationary force transducer this leg develops forces which oscillate with the step rhythm of the other legs (Fig. 5). 6. A posteriorly directed influence is found, by which the return stroke of a leg can be started when the anterior leg performs a backward directed movement. 7. Results are compared with those obtained from stick insects. The systems controlling the movement of the individual leg are similar in both, lobster and stick insect but the influences between the legs seem to be considerably different.     

A modular artificial neural net for controlling a six-legged walking system

 A system that controls the leg movement of an animal or a robot walking over irregular ground has to ensure stable support for the body and at the same time propel it forward. To do so, it has to react adaptively to unpredictable features of the environment. As part of our study of the underlying mechanisms, we present here a model for the control of the leg movement of a 6-legged walking system. The model is based on biological data obtained from the stick insect. It represents a combined treatment of realistic kinematics and biologically motivated, adaptive gait generation. The model extends a previous algorithmic model by substituting simple networks of artificial neurons for the algorithms previously used to control leg state and interleg coordination. Each system controlling an individual leg consists of three subnets. A hierarchically superior net contains two sensory and two ‘premotor’ units; it rhythmically suppresses the output of one or the other of the two subordinate nets. These are continuously active. They might be called the ‘swing module’ and the ‘stance module’ because they are responsible for controlling the swing (return stroke) and the stance (power stroke) movements, respectively. The swing module consists of three motor units and seven sensory units. It can produce appropriate return stroke movements for a broad range of initial and final positions, can cope with mechanical disturbances of the leg movement, and is able to react to an obstacle which hinders the normal performance of the swing movement. The complete model is able to walk at different speeds over irregular surfaces. The control system rapidly reestablishes a stable gait when the movement of the legs is disturbed. Received: 13 July 1994/Accepted in revised form: 15 November 1994     

Levels of cyclic GMP and cyclic AMP in regenerating forelimbs of adult newts following denervation

The effect of short-term denervation (0, 12, 24, and 72 hours) on the levels of cyclic 3'5'-guanosine monophosphate (cGMP) and cyclic 3'5'-adenosine monophosphate (cAMP) in adult newt (Notophthalmus viridescens) forelimbs at 15, 22, and 35 days of regeneration was investigated. Regenerate blastema and stump cyclic nucleotide levels were compared with those of the contralateral intact forelimb and hindlimb, with levels in the normally regenerating blastema, and with levels measured in the forelimbs of intact, nonoperated animals. Variations in cyclic nucleotide levels occurred according to regeneration stage and tissue type. Changes in level were noted immediately upon denervation and subsequently at other sample times in all regenerate and control series. Parallel fluctuations occurred in regenerate stump and contralateral intact forelimbs. Our results from nonamputated denervated and sham-denervated animals indicate that short-term, denervation-associated cyclic nucleotide fluctuations cannot be attributed solely to the loss of innervation.     

Leg coordination during turning on an extremely narrow substrate in a bug, Mesocerus marginatus (Heteroptera, Coreidae)

The turning movement of a bug, Mesocerus marginatus, is observed when it walks upside-down below a horizontal beam and, at the end of the beam, performs a sharp turn by 180 degrees . The turn at the end of the beam is accomplished in three to five steps, without strong temporal coordination among legs. During the stance, leg endpoints (tarsi) run through rounded trajectories, rotating to the same side in all legs. During certain phases of the turn, a leg is strongly depressed and the tarsus crosses the midline. Swing movements rotate to the same side as do leg endpoints in stance, in strong contrast to the typical swing movements found in turns or straight walk on a flat surface. Terminal location is found after the search through a trajectory that first moves away from the body and then loops back to find substrate. When a leg during stance has crossed the midline, in the following swing movement the leg may move even stronger on the contralateral side, i.e. is stronger depressed, in contrast to swing movements in normal walking, where the leg is elevated. These results suggest that the animals apply a different control strategy compared to walking and turning on a flat surface.     

Effect of axotomy on cholinergic enzyme activities in the spinal cord and sciatic nerve of the dog

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activity measured in the ventral and dorsal part of the dog spinal cord (L6-S2) and in the stumps of the sciatic nerve 5, 10, 15 and 21 days after its transection were compared with the corresponding activities in the intact contralateral nerve and in sham-operated animals. AChE was also examined histochemically. Changes in the enzyme activities in the central nerve stump were correlated with activity changes in the spinal cord. In the central nerve stump, a marked (25%) increase in AChE activity was found on the fifth day after transection, but by the 21st day it fell below control value levels; up to the 15th day it showed good correlation with AChE activity in the ventral spinal cord. Histochemically, pronounced reduction of enzymatic activity was found in the ipsilateral part of the spinal cord. On the 15th day, ChAT activity in the ventral spinal cord was also significantly decreased and the accumulation of the enzyme in the central nerve stump was negligible. On the contrary, at the last 21-day interval examined, a significant increase in ChAT activity and a nonsignificant increase in AChE activity was found in the spinal cord, but their activities in the central nerve stump were decreased. In the degenerated peripheral nerve stump ChAT activity dropped by an average of 99% and AChE activity by 48% during the first 15 days after transection but, on the 21st day, AChE activity was 22% higher than at the preceding interval.     

Central and peripheral hemodynamics during maximal leg extension exercise

The purpose of this study was to examine the central and peripheral hemodynamic adaptations to maximal leg extension exercise. Seventeen men (X = 25 years, 84 kg) performed leg extension exercise (Universal equipment) for 12 repetitions (90s) to fatigue. Each repetition consisted of a 3s lifting motion, 1s pause, and 3s lowering motion. Impedance cardiography was used to measure stroke volume (SV), cardiac output (Q), systolic time intervals, and impedance contractility indices on a beat-by-beat basis. There were significant increases in systolic, diastolic, mean arterial pressure, total peripheral resistance, and HR during exercise. The mean Q remained similar throughout the protocol. SV decreased even though indices of myocardial performance indicated an enhancement of contractility. The magnitude of Q and SV were dependent upon the phase of leg extension. SV and Q during the lifting portions of the exercise were smaller than the lowering portions. The differences in SV and Q during the concentric and eccentric phases of the exercise most likely reflect the large static forces in exercising muscle which impeded venous return and increased afterload.     

Comparison of forces developed by the leg of the rock lobster when walking free or on a treadmill

Summary In the free walking rock lobster the forces developed by legs 4 and 5 were investigated during the power stroke. Two orthogonal force components lying in the horizontal plane were measured. Based on these results the diffent tasks of the two legs during walking are discussed. The forces developed by leg 4 were compared when the animal walked freely and on a treadmill. In these two situations the results differ qualitatively as in driven walking the forces are nearly identical in a long series of consecutive steps whereas in free walking the forces can vary greatly from step to step. However, similar mean values of force were measured with those on the treadmill being somewhat higher. This shows that, although the treadmill is driven by a motor, the animal does perform active walking movements. In the treadmill situation the forces increase as the speed of treadmill motor is decreased.Supported by DAAD and DFG (Cr 58) for H. Cruse and by ATP (80 119.112) INSERM for F. Clarac     

Coordination between the legs and tail during digging and swimming in sand crabs

Rhythmic leg movements and tailflipping are mutually exclusive behaviours in most decapod crustaceans, but sand crabs (Anomura: Hippoidea) combine leg movements with simultaneous tailflipping or uropod beating for both digging and swimming. We examined the coordination between the legs and tail (abdomen and tailfan) of Blepharipoda occidentalis, Lepidopa californica (Albuneidae), and Emerita analoga (Hippidae). When either albuneid swims, the tail cycles at a higher frequency than the legs, and the two rhythms are not coupled. When albuneids begin digging, the tail's frequency drops to that of the legs, and its rhythm becomes phase coupled to the legs. In E. analoga the legs seldom move during swimming by uropod beating. During digging the frequency of the uropods and fourth legs starts at about double that of the second and third legs, but drops to that of the second and third legs as digging progresses. The fourth legs in E. analoga are coupled with the uropods; their outward movement (= power stroke) is concurrent with the uropod return stroke. The familial differences in leg coordination and in the coordination of the legs and tail account for the smooth descent of E. analoga beneath sand compared to the stepwise descent of the albuneids. Accepted: 23 August 1996     

Enhancement of the resistance of the escape reaction to ethanol after substance P]

An ability of substance P (30 micrograms/kg intravenously) to prevent deleterious effects of ethanol (E) (0.5 g/kg intravenously) on central mechanisms of escape reaction elicited by threshold electrical stimulation of the ventromedial hypothalamus was investigated in chronic experiments upon rabbits. Substance P was found to prevent E effects on excitability of the ventromedial hypothalamus (VMH) and on facilitatory influences of the midbrain reticular formation on this emotional centre which were observed in intact animals. Inhibitory effects of the dorsal hippocampus on the VMH could not be evaluated due to its alterations in response to previous substance P administration. The authors suggest that substance P can be considered to be a possible endogenous factor to increase a tolerance of emotional behavioural reactions of an organism to alcohol.     

Motor output to the protractor and retractor coxae muscles in stick insects walking on a treadwheel

ABSTRACT. The motor output to the protractor and retractor mucles moving the coxa of the middle leg of Carausius morosus was recorded from the thoracic nerves during walking on a treadwheel. The leg movements on the wheel were generally similar to those found in free-walking animals, but tripod coordination was relatively independent of period, and the coordination of the adult animal on the wheel was most closely related to that found in free-walking first instars. The activity of a common inhibitor and four excitatory axons of the retractor and an excitatory axon of the protractor were followed for 850 steps (in six animals) to give a summary of the behaviour of the different units. The motor activity is less stereotyped than that previously reported for insects. There was strong reciprocity between the antagonists, but this was not directly correlated with the forward and backward movements of the legs. The first part of the stance phase of the leg was accompanied by a strong burst in the protractor nerve and relatively little retractor activity. This was followed by the main retractor burst which occupied the last 60% of the stance phase. The results are compared with motor output records of the locust and with earlier force-plate measurements on the stick insect. It must be concluded that the mesothoracic leg initially resists forward movement of the body by the other legs during a typical walking step.     

Effects of neck and circumoesophageal connective lesions on posture and locomotion in the cockroach

Few studies in arthropods have documented to what extent local control centers in the thorax can support locomotion in absence of inputs from head ganglia. Posture, walking, and leg motor activity was examined in cockroaches with lesions of neck or circumoesophageal connectives. Early in recovery, cockroaches with neck lesions had hyper-extended postures and did not walk. After recovery, posture was less hyper-extended and animals initiated slow leg movements for multiple cycles. Neck lesioned individuals showed an increase in walking after injection of either octopamine or pilocarpine. The phase of leg movement between segments was reduced in neck lesioned cockroaches from that seen in intact animals, while phases in the same segment remained constant. Neither octopamine nor pilocarpine initiated changes in coordination between segments in neck lesioned individuals. Animals with lesions of the circumoesophageal connectives had postures similar to intact individuals but walked in a tripod gait for extended periods of time. Changes in activity of slow tibial extensor and coxal depressor motor neurons and concomitant changes in leg joint angles were present after the lesions. This suggests that thoracic circuits are sufficient to produce leg movements but coordinated walking with normal motor patterns requires descending input from head ganglia.Electronic Supplementary Material Supplementary material is available for this article at     

Differential control of temporal and spatial aspects of cockroach leg coordination

Ensembles of neuronal networks and sensory pathways participate in controlling the kinematic and dynamic parameters of animal movement necessary to achieve motor coordination. Determining the relative contribution of proprioceptive feedback is essential for understanding how animals sustain stable, coordinated locomotion in complex natural environments. Here, we focus on the role of chordotonal organs (COs), proprioceptors found in insect legs, in the spatial and temporal regulation of walking. We compare gait parameters of intact cockroaches (Periplaneta americana) and sensory-impaired ones, injected with pymetrozine, a chemical previously shown to abolish CO function in locusts. We verify that afferent CO activity in pymetrozine-treated cockroaches is inhibited, and analyze the effect of this sensory deprivation on inter-leg coordination. We find significant changes in tarsi placement and leg path trajectories after pymetrozine treatment. Leg touchdown accuracy, measured from relative tarsi positions of adjacent legs, is reduced in treated animals. Interestingly, despite poorer spatial coordination in both stance and swing, temporal properties of the gait remain largely the same as in the intact preparations, apart from changes in ipsilateral phase differences between front and middle legs. These findings provide insights into the role of COs in insect gait control and establish pymetrozine as a useful tool for further studies of insect locomotion.     

Functional recovery following manipulation of muscles and sense organs in the stick insect leg

We studied functional recovery of leg posture and walking behaviour in the femur-tibia joint control system of stick insects. Leg extensions in resting animals and during walking are produced by different parts of a single extensor muscle. (a) Ablation of the muscle part responsible for fast movements prevented leg extension during the swing phase. Resting posture remained unaffected. Within a few post-operative days, extension movements recovered, provided that sensory feedback was available. Extension movements were now driven by the muscle part which in intact animals controls the resting posture only. (b) Selective ablation of this (slow) muscle part affected the resting posture, while walking was unaffected. The resting posture partly recovered during subsequent days. To test the range of functional recovery and underlying mechanisms, we additionally transected muscle motor innervation, or we inverted or ablated sensory feedback. We found that recovery was based on both muscular and neuronal mechanisms. The latter required appropriate sensory feedback for the process of recovery, but not for the maintenance of the recovered state. Our results thus indicate the existence of a sensory template that guides recovery. Recovery was limited to a behavioural range that occurs naturally in intact animals, though in different behavioural contexts.     

Basic processes of locomotor coordination in the rock lobster

Rock lobsters are able to perform long and stereotyped stepping sequences above a motor driven treadmill. Forward walking samples are estimated by mean of statistical methods to draw out the basic rules involved in the locomotor behaviour (Fig. 1).

- The spatial and temporal parameters defined in a single propulsive leg are either invariable in respect to the imposed speed, as the mean step length (L), the return stroke duration (Tr) and the pause times (T's, T'r), or speed dependent as the power stroke duration (Ts) and the whole period (Figs. 2 and 3).

- The interleg phase coupling is strong and stable in the ipsilateral rear pairs (4–5), these legs acting most of the time in absolute coordination (1:1) or in harmonic ratio (2:1). In the contralateral pairs (R4-L4, R5-L5) the legs roughly operate in antiphase, but the relationship appears much weaker and variable, with frequent episodes of relative coordination (Fig. 4).

- The time intervals between the ground contact of any leg and the swing initiation in the nearest ones appear somewhat constant and could be closely related to the mechanism of stepping synchronization. The “5 on - 4 off” delay, very stable and always positive, suggests that the rear legs could exert a predominant influence upon the rhythmical movements of the next anterior ipsilateral appendages (Fig. 5).

- To test the contralateral relationships, the treadmill belts can be decoupled in order to impose different walking speeds on each side. Such a conflicting stimulus reveals that:

1. The relative hierarchy always observed between the ipsilateral legs can be artificially created between the two sides (Fig. 6).
2. The driving influence of a given leg is closely linked to the intensity of EMG's discharges in its power stroke muscles.
3. The contralateral appendages are able to walk in absolute coordination despite a large speed difference between the two sides (up to 4 cm/s). Under such a constraint, the walking legs alter its invariable parameters (L and Tr) to reach a common step period and steadily maintain the alternating pattern (Figs. 6 and 7).

     

Mesenchymal stem cell therapy of brain ischemic stroke in rats

Mesenchymal stem cell (MSCs)-based therapy is a promising attempt to improve the recovery after stroke. Our experiments were carried out on inbred Wistar-Kyoto rats. MSCs were isolated, expanded in culture, and labeled with vital fluorescent dye PKH-26. Animals were subjected to middle cerebral artery occlusion (MCAO). After three days, MCAO 5 × 10⁶ isolated MSCs were injected into the tail vein of the experimental rats. The control animal group received PBS injections (negative control). Therapy results were evaluated by the following parameters: behavioral and neurological testing, the inured brain areas, damaged brain structures, neuron state, and vessel quantity in the region close to with necrosis zone. It was shown that control animals (PBS injection) did not return to their initial behavioral and neurological state within 6 weeks, while the experimental animals (MSCs injection), within 2–3 weeks after MCAO, had parameters like intact rats. The size of the damaged region in the control group was larger than in the experimental group by a factor of approximately 1.3. The damage in MSC-treated rats was limited to the neocortex; caudate nucleus, capsula externa and piriform cortex remained uninjured. The small vessel quantity in the “border” regions was twice as high as compared to the control group and approximately equal to the number of vessels in an intact brain. For the first time, we demonstrated that the vessel quantity in the neocortex and caudate nucleus of the contralateral hemisphere after MSC transplantation was twice as high as in control rats. It is concluded that the MSC transplantation exerts a beneficial influence upon the brain tissue reparation after stroke.     

A quantitative model of walking incorporating central and peripheral influences

Using the experimental results of Cruse and Saxler (1980a, b) and other authors (Graham, 1972; Pearson, 1972; Bässler, 1977, 1979) a quantitative model is developed in order to describe the behaviour of the systems controlling the leg movements of a walking insect. The whole model consists of six subsystems each of which controls the movement of an individual leg. The single subsystem (Fig. 1) consists of a central part which can assume two modes (protraction, retraction) the transition between which can be controlled by sensory influence. The central part produces the reference input for a feedback loop which controls the leg position. The reference input is however also determined by influences from other subsystems. Four different types of such connections are assumed to exist between the subsystems. Two of these produce alternating (t1, t3), two others in phase coupling (t2, t4) between the subsystems to be connected. These connections can transfer information originating from the central part as well as from the periphery of other subsystems. The model is capable of describing either quantitatively or qualitatively the experimental results of Cruse and Saxler (1980a, b) (see Figs. 3 and 4). In addition it is capable of describing the results of other authors, e.g. the temporal leg coordination of the free walking animal (Graham, 1972).Supported by DFG (Cr 58/1)     

Thoracic leg motoneurons in the isolated CNS of adult Manduca produce patterned activity in response to pilocarpine,which is distinct from that produced in larvae

In the hawkmoth, Manduca sexta, thoracic leg motoneurons survive the degeneration of the larval leg muscles to innervate new muscles of the adult legs. The same motoneurons, therefore, participate in the very different modes of terrestrial locomotion that are used by larvae (crawling) and adults (walking). Consequently, changes in locomotor behavior may reflect changes in both the CNS and periphery. The present study was undertaken to determine whether motor patterns produced by the isolated CNS of adult Manduca, in the absence of sensory feedback, would resemble adult specific patterns of coordination. Pilocarpine, which evokes a fictive crawling motor pattern from the isolated larval CNS, also evoked robust patterned activity from leg motoneurons in the isolated adult CNS. As in the larva, levator and depressor motoneurons innervating the same leg were active in antiphase. Unlike fictive crawling, however, bursts of activity in levator or depressor motoneurons of one leg alternated with bursts in the homologous motoneurons innervating the opposite leg of the same segment and the leg on the same side in the adjacent segment. The most common mode of intersegmental activity generated by the isolated adult CNS resembled an alternating tripod gait, which is displayed, albeit infrequently, during walking in intact adult Manduca. A detailed analysis revealed specific differences between the patterned motor activity that is evoked from the isolated adult CNS and activity patterns observed during walking in intact animals, perhaps indicating an important role for sensory feedback. Nevertheless, the basic similarity to adult walking and clear distinctions from the larval fictive crawling pattern suggest that changes within the CNS contribute to alterations in locomotor activity during metamorphosis. Electronic Publication     

Microfluidic chips for in vivo imaging of cellular responses to neural injury in Drosophila larvae

With powerful genetics and a translucent cuticle, the Drosophila larva is an ideal model system for live imaging studies of neuronal cell biology and function. Here, we present an easy-to-use approach for high resolution live imaging in Drosophila using microfluidic chips. Two different designs allow for non-invasive and chemical-free immobilization of 3(rd) instar larvae over short (up to 1 hour) and long (up to 10 hours) time periods. We utilized these 'larva chips' to characterize several sub-cellular responses to axotomy which occur over a range of time scales in intact, unanaesthetized animals. These include waves of calcium which are induced within seconds of axotomy, and the intracellular transport of vesicles whose rate and flux within axons changes dramatically within 3 hours of axotomy. Axonal transport halts throughout the entire distal stump, but increases in the proximal stump. These responses precede the degeneration of the distal stump and regenerative sprouting of the proximal stump, which is initiated after a 7 hour period of dormancy and is associated with a dramatic increase in F-actin dynamics. In addition to allowing for the study of axonal regeneration in vivo, the larva chips can be utilized for a wide variety of in vivo imaging applications in Drosophila.     

Running on an incline.

Seven male subjects ran at 3.0 m/s on a motorized treadmill including a force platform under the tread. The subjects ran at each of five treadmill inclinations: +0.17, +0.077, 0, -0.077, and -0.17 radians. The position of the subjects' legs were read from ciné films (100 frames/s). Results of the film and force plate analysis generally corroborated the "hanging triangle" hypothesis, which postulates that the angle between the leg and the vertical upon foot strike does not change as the treadmill is tipped up or down. A mathematical model of running, in which the leg is represented as a nonlinear spring, made satisfactory predictions of the way many parameters of running change with the treadmill angle, including the length of the leg at touchdown and liftoff and the peak leg force in the middle of a step. The peak leg force reaches a maximum at a treadmill angle near -0.12 radians, close to the downhill angle where other authors have found a minimum in the rate of oxygen consumption.