HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: 91/5/2380    most recent 01184.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Stein, P. S. G. Articles by Daniels-McQueen, S. Search for Related Content PubMed PubMed Citation Articles by Stein, P. S. G. Articles by Daniels-McQueen, S.

Report

Variations in Motor Patterns During Fictive Rostral Scratching in the Turtle: Knee-Related Deletions

Department of Biology, Washington University, St. Louis, Missouri 63130

Submitted 9 December 2003; accepted in final form 7 January 2004

	ABSTRACT

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Agonist motor neurons usually alternate between activity and quiescence during normal rhythmic behavior; antagonist motor neurons are usually active during agonist motor neuron quiescence. During an antagonist deletion, a naturally occurring motor-pattern variation, there is no antagonist activity and no quiescence between successive bursts of agonist activity. Motor neuron recordings of normal fictive rostral scratching in the turtle displayed rhythmic alternation between activity and quiescence for hip flexors, knee flexors, and knee extensors. Knee-flexor activity occurred during knee-extensor quiescence. During a hip-extensor deletion, a variation of rostral scratching, rhythmic hip-flexor bursts occurred without intervening hip-flexor quiescence. There were 3 distinct patterns of knee motor activity during the cycle before or after a hip-extensor deletion. In most cycles, there was knee flexor-extensor rhythmic alternation. In some cycles, termed knee-flexor deletions, there was no knee-flexor activity and rhythmic knee-extensor bursts occurred without intervening knee-extensor quiescence. In other cycles, termed knee-extensor deletions, there was no knee-extensor activity and rhythmic knee-flexor bursts occurred without intervening knee-flexor quiescence. The concept of a module refers to a population of motor neurons and interneurons with similar activity patterns; interneurons in a module coordinate agonist and antagonist motor neuron activities, either with excitation of agonist motor neurons and interneurons, or with inhibition of antagonist motor neurons and interneurons. Previous studies of hip-extensor deletions support the concept of a rhythmogenic hip-flexor module. The knee-related deletions described here support the concept of rhythmogenic knee-flexor and knee-extensor modules linked by reciprocal inhibition.

	INTRODUCTION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Rhythmic alternation between agonist activity and quiescence occurs during normal motor rhythms; antagonist activity usually occurs during agonist quiescence (Stein and Smith 1997). The concept of a spinal module [termed unit-burst-generator by Grillner (1981)], a set of motor neurons and interneurons with similar activity patterns, has played a key role in several hypotheses of spinal motor organization. In the classic half-center modular hypothesis for a hindlimb (Jankowska et al. 1967; Lundberg 1981), all extensors are grouped into an extensor module and all flexors are grouped into a flexor module. In other hypotheses (Grillner 1981; Jordan 1991; Stein and Daniels-McQueen 2002, 2003a), a separate module is proposed for each direction of each degree of freedom of a hindlimb (e.g., a hip-flexor module, a hip-extensor module, a knee-flexor module, a knee-extensor module, etc.). Reciprocal inhibition between agonist and antagonist modules contributes to agonist-antagonist rhythmic alternation during normal motor rhythms (Grillner 1981, 2003).

We studied fictive rostral scratching in the spinal turtle: there was rhythmic alternation between hip-flexor and hip-extensor motor activities and between knee-flexor and knee-extensor motor activities (Robertson et al. 1985; Stein and Daniels-McQueen 2003a). Rostral scratching is a mixed-synergy motor pattern; knee-extensor activity occurs during the latter portion of hip-flexor activity.

Deletions are naturally occurring variations of normal rhythms. In an antagonist deletion, antagonists are quiet and successive bursts of agonist activity occur without intervening agonist quiescence. A rhythmogenic agonist module contributes to agonist rhythms during antagonist deletions (Stein et al. 1995). We studied hip-extensor deletions during rostral scratching in the spinal turtle; hip-extensor motor neurons were quiet and successive bursts of hip-flexor motor activity occurred with no intervening hip-flexor quiescence (Robertson and Stein 1988). We characterized interneurons, termed hip-extensor interneurons, that were active during hip-extensor motor neuron activity of normal rostral scratching; hip-extensor interneurons were quiet during rostral-scratch cycles that ended with a hip-extensor deletion (Stein and Daniels-McQueen 2002). These observations support the concepts that 1) reciprocal inhibition between hip modules is not required for hip-flexor rhythmicity and 2) the hip-flexor module is rhythmogenic.

We describe here knee-related deletions that occurred during hip-extensor deletions. We discussed these in an abstract (Stein and Daniels-McQueen 2003b). Our observations provide support for the existence of rhythmogenic knee-related spinal modules.

	METHODS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Red-eared turtles (n = 4), Trachemys scripta elegans (formerly Pseudemys scripta elegans), weighing 500–900 g, were placed on crushed ice 1 h before surgery to induce hypothermic analgesia (Melby and Altman 1974). Each turtle was spinalized caudal to the forelimb enlargement by a complete spinal transection midway between the D2 and D3 dorsal roots (Stein and Daniels-McQueen 2003a). All procedures were approved by the Washington University Animal Studies Committee.

After surgery was completed, the turtle was allowed to warm up to room temperature and was immobilized with gallamine at a dosage of 6–8 mg/kg body weight. We obtained bipolar electroneurographic recordings (ENGs) from 4 nerves of the right hindlimb: knee-flexor, biarticular knee-extensor, monoarticular knee-extensor, and hip-flexor (Stein and Daniels-McQueen 2003a). Each nerve was cut near its muscle; each electrode pair was placed on the nerve central to the cut. Fictive rostral scratch motor patterns were elicited by mechanical stimulation of sites in the right rostral-scratch receptive field.

We determined burst start- and end-phases for quantitative analyses as described previously (Stein and Daniels-McQueen 2002, 2003a). ENGs were digitized at 2 kHz and means ("integration") of absolute values ("full-wave rectification") of 20 successive data points were calculated. Baseline ENGs were obtained in the absence of motor neuron activity. Baseline amplitude was defined as maximum minus minimum baseline value. We defined threshold for each burst of full-wave rectified integrated data as baseline amplitude plus maximum baseline value. A motor burst occurred when there were 5 successive full-wave rectified integrated values greater than threshold; motor quiescence occurred when there were 5 successive full-wave rectified integrated values less than threshold. Some analyses of data during normal rostral scratching in these 4 turtles were described previously (Figs. 1 and 2 of Stein and Daniels-McQueen 2003a). We present from these 4 turtles additional analyses of normal rostral scratching as well as new analyses during the hip-extensor deletion variation of rostral scratching.

View larger version (53K): [in this window] [in a new window]   FIG. 1. Fictive rostral scratching motor patterns in response to stimulation of a site in the right rostral scratch receptive field. Electroneurographic (ENG) recordings from the right knee-flexor nerve, the right biarticular knee-extensor nerve, the right monoarticular knee-extensor nerve, and the right hip-flexor nerve. A: normal rostral scratching. Knee-flexor activity marked with unfilled rectangles and biarticular knee-extensor quiescence marked with gray-filled rectangles. B: rostral scratching with hip-extensor deletions. Hip-extensor deletions are marked with unfilled triangles, knee-flexor deletion is marked with unfilled circle, and rhythmic knee-flexor bursts during knee-extensor quiescence are marked with unfilled diamonds.

View larger version (29K): [in this window] [in a new window]   FIG. 2. Plot of the duration of biarticular knee-extensor quiescence as a function of the duration of the knee-flexor burst. Normal cycles (n = 200) are shown with filled circles and their best-fit least-squares line is dashed. Hip-extensor deletion cycles with knee flexor-extensor rhythmic alternation (n = 34) are shown with unfilled diamonds and their best-fit least-squares line is solid. Hip-extensor deletion cycles with knee-flexor deletions (n = 13) are shown with unfilled circles.

	RESULTS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

During normal rostral scratching in the turtle, there was rhythmic alternation between knee-flexor and knee-extensor motor activity (Fig. 1A; see also Stein and Daniels-McQueen 2003a). Knee-flexor motor activity began during hip-flexor quiescence and ended in the middle of hip-flexor activity. Knee-flexor motor bursts (unfilled rectangles in Fig. 1A) occurred during knee-extensor quiescence (gray-filled rectangles in Fig. 1A). In early portions of the episode, the durations of knee-flexor activity and knee-extensor quiescence were short and, in later portions of the episode, these durations were longer. There was a significant positive correlation during normal rostral scratching between the duration of the knee-flexor burst and the duration of the corresponding biarticular knee-extensor quiescence (filled circles in Fig. 2, n = 200, r = 0.86, P < 0.0001, t-test; Zar 1999).

Hip-extensor deletion variation of rostral scratching

During rostral scratching with hip-extensor deletions (marked with unfilled triangles in Figs. 1B and 3), there were rhythmic bursts of hip-flexor activities with no intervening hip-flexor quiescence (Stein and Daniels-McQueen 2002). We observed 3 distinct patterns of knee motor activity during the cycle just before or just after each hip-extensor deletion.

View larger version (33K): [in this window] [in a new window]   FIG. 3. Fictive rostral scratching motor pattern in response to stimulation of a site in the right rostral scratch receptive field. Hip-extensor deletion is marked with an unfilled triangle and the knee-extensor deletion is marked with an unfilled ellipse. First 6 cycles of this episode are examples of normal rostral scratching.

KNEE-FLEXOR DELETIONS. During the cycle before or after some hip-extensor deletions, we also observed knee-flexor deletions: there was no knee-flexor activity (unfilled circle in Fig. 1B). These were plotted with unfilled circles in Fig. 2 (n = 13). In 7 of these cycles, rhythmic biarticular knee-extensor activity occurred with no intervening quiescence. In the example marked with an unfilled circle in Fig. 1B, there were rhythmic biarticular and monoarticular knee-extensor activities with no intervening quiescence. Knee-extensor motor rhythms were expressed with hip-flexor motor rhythms in the absence of knee-flexor and hip-extensor motor rhythms.

KNEE-EXTENSOR DELETIONS. During the cycle before or after some hip-extensor deletions, we also observed knee-extensor deletions (n = 16): there was no knee-extensor activity (unfilled ellipse in Fig. 3). In 9 of these cycles, successive bursts of knee-flexor motor activity occurred with no intervening knee-flexor quiescence. Knee-flexor motor rhythms were expressed with hip-flexor motor rhythms and in the absence of knee-extensor and hip-extensor motor rhythms.

	DISCUSSION

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Knee flexor-extensor motor rhythmic alternation

Knee-flexor and knee-extensor motor activities rhythmically alternated during normal rostral scratching (Fig. 1A; see also Stein and Daniels-McQueen 2003a) and during some cycles of the hip-extensor deletion variation of rostral scratching (unfilled diamonds in Fig. 1B). Reciprocal inhibitory connections between interneurons in knee-flexor and knee-extensor modules have been proposed as a mechanism for ensuring knee motor-neuron alternation as well as for generating knee motor-neuron rhythmicity (Grillner 1981; Stein and Daniels-McQueen 2003a).

During hip-extensor deletions, hip-extensor motor neurons and interneurons are quiet (Robertson and Stein 1988; Stein and Daniels-McQueen 2002). Our observation of knee flexor-extensor alternation during hip-extensor deletions is consistent with the concept that knee modules can display reciprocal activity even when the entire hip-extensor module is quiet. Activation of the knee-extensor module when the hip-extensor module is quiet is consistent with hypotheses that include a knee-extensor module with interneurons different from those in a hip-extensor module (Grillner 1981; Stein and Daniels-McQueen 2003a). Our observation of knee flexor-extensor alternation during hip-extensor deletions conflicts with predictions of the classical half-center hypothesis that groups all hindlimb extensor interneurons into a single extensor half-center (Jankowska et al. 1967; Lundberg 1981).

Knee-agonist motor rhythms without intervening knee-antagonist activity

RHYTHMOGENIC KNEE-EXTENSOR MODULE. During knee-flexor deletions, successive bursts of knee-extensor motor activity occurred without intervening quiescence and without intervening knee-flexor motor activity (unfilled circle in Fig. 1B). This observation is consistent with the concept that the interneurons of the knee-extensor module can be rhythmogenic even in the absence of knee-flexor module activity.

Previously, we described the behavior of interneurons, termed OFF-units, whose end-phases were positively correlated with the start-phases of knee-extensor motor activity during normal rostral scratching (Stein and Daniels-McQueen 2003a). We proposed that these units were candidate members of the knee-flexor module. We predict that future studies of OFF-units will demonstrate their quiescence during knee-flexor deletions.

RHYTHMOGENIC KNEE-FLEXOR MODULE. During knee-extensor deletions, successive bursts of knee-flexor motor activity occurred without intervening quiescence and without intervening knee-extensor motor activity (unfilled ellipse in Fig. 3). This observation is consistent with the concept that interneurons of the knee-flexor module can be rhythmogenic even in the absence of knee-extensor module activity.

Previously, we described the behavior of interneurons, termed ON-units, whose start-phases were positively correlated with the start-phases of knee-extensor motor activity during normal rostral scratching (Stein and Daniels-McQueen 2003a). We proposed that these units were candidate members of the knee-extensor module. We predict that future studies of ON-units will demonstrate their quiescence during knee-extensor deletions.

A modular broad-tuning hypothesis

The Berkowitz-Stein hypothesis (Berkowitz 2001a,b, 2002; Berkowitz and Stein 1994a,b) describes mechanisms that assist in the production of both mixed-synergy and conventional-synergy motor patterns. The hypothesis emphasizes the specific outputs of broadly tuned interneurons. We focus here on the mixed-synergy motor pattern of turtle rostral scratching; monoarticular knee-extensor motor activity occurs mainly during the latter portion of hip-flexor motor activity. In the Berkowitz-Stein hypothesis, rostral-tuned interneurons synapse on hip-related interneurons and a mixed-synergy set of motor neurons: for example, excitatory rostral-tuned interneurons excite both hip-flexor and knee-extensor motor neurons. The Berkowitz-Stein hypothesis did not include knee-flexor motor neurons.

Our work (Stein and Daniels-McQueen 2002, 2003a; this report) provides support for hip-flexor, hip-extensor, knee-flexor, and knee-extensor modules. We propose a modified hypothesis for turtle rostral scratching, termed the modular broad-tuning hypothesis, that includes the connections proposed in the Berkowitz-Stein hypothesis and describes additional synapses on knee-related interneurons and knee-flexor motor neurons. We suggest that rostral-tuned interneurons synapse on both motor neurons and interneurons in specific modules: 1) excitatory rostral-tuned interneurons in the hip-flexor module excite neurons in hip-flexor and knee-extensor modules; 2) inhibitory rostral-tuned interneurons in the hip-extensor module inhibit neurons in hip-flexor and knee-extensor modules; 3) excitatory rostral-tuned interneurons in the hip-extensor module excite neurons in hip-extensor and knee-flexor modules; and 4) inhibitory rostral-tuned interneurons in the hip-flexor module inhibit neurons in the hip-extensor and knee-flexor modules. Future experiments that examine other forms of scratching may support additions to the modular broad-tuning hypothesis appropriate for these other forms.

	ACKNOWLEDGMENTS

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
We thank Dr. Gavin Perry for software development and Drs. Ari Berkowitz and Gammon Earhart for editorial comments.

GRANTS

This work was supported by National Institute of Neurological Disorders and Stroke Grant NS-30786 to P.S.G. Stein.

	FOOTNOTES

 
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement " in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Address for reprint requests and other correspondence: P.S.G. Stein, Department of Biology, Washington University, St. Louis, MO 63130 (E-mail: stein{at}biology.wustl.edu).

	REFERENCES

TOP ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION ACKNOWLEDGMENTS REFERENCES

 
Berkowitz A. Broadly tuned spinal neurons for each form of fictive scratching in spinal turtles. J Neurophysiol 86: 1017-1025, 2001a.[Abstract/Free Full Text]

Berkowitz A. Rhythmicity of spinal neurons activated during each form of fictive scratching in spinal turtles. J Neurophysiol 86: 1026-1036, 2001b.[Abstract/Free Full Text]

Berkowitz A. Both shared and specialized spinal circuitry for scratching and swimming in turtles. J Comp Physiol 188: 225-234, 2002.

Berkowitz A and Stein PSG. Activity of descending propriospinal axons in the turtle hindlimb enlargement during two forms of fictive scratching: broad tuning to regions of the body surface. J Neurosci 14: 5089-5104, 1994a.[Abstract]

Berkowitz A and Stein PSG. Activity of descending propriospinal axons in the turtle hindlimb enlargement during two forms of fictive scratching: phase analyses. J Neurosci 14: 5105-5119, 1994b.[Abstract]

Grillner S. Control of locomotion in bipeds, tetrapods, and fish. In: Handbook of Physiology. The Nervous System. Motor Control. Bethesda, MD: Am. Physiol. Soc., 1981, sect. 1, vol. II, p. 1179-1236.

Grillner S. The motor infrastructure: from ion channels to neuronal networks. Nat Rev Neurosci 4: 573-586, 2003.[Web of Science][Medline]

Jankowska E, Jukes MGM, Lund S, and Lundberg A. The effect of DOPA on the spinal cord. 5. Reciprocal organization of pathways transmitting excitatory action to alpha motoneurones of flexors and extensors. Acta Physiol Scand 70: 369-388, 1967.[Web of Science][Medline]

Jordan LM. Brainstem and spinal cord mechanisms for the initiation of locomotion. In: Neurobiological Basis of Human Locomotion, edited by Shimamura M, Grillner S, and Edgerton VR. Tokyo: Japan Scientific Societies Press, 1991, p. 3-20.

Lundberg A. Half-centres revisited. Adv Physiol Sci 1: 155-167, 1981.

Melby ECJ and Altman NH. Handbook of Laboratory Animal Science, vol. 1. Cleveland, OH: CRC Press, 1974.

Robertson GA, Mortin LI, Keifer J, and Stein PSG. Three forms of the scratch reflex in the spinal turtle: central generation of motor patterns. J Neurophysiol 53: 1517-1534, 1985.[Abstract/Free Full Text]

Robertson GA and Stein PSG. Synaptic control of hindlimb motoneurones during three forms of the fictive scratch reflex in the turtle. J Physiol 404: 101-128, 1988.[Abstract/Free Full Text]

Stein PSG and Daniels-McQueen S. Modular organization of turtle spinal interneurons during normal and deletion fictive rostral scratching. J Neurosci 22: 6800-6809, 2002.[Abstract/Free Full Text]

Stein PSG and Daniels-McQueen S. Timing of knee-related spinal neurons during fictive rostral scratching in the turtle. J Neurophysiol 90: 3585-3593, 2003a.[Abstract/Free Full Text]

Stein PSG and Daniels-McQueen S. Knee-flexor motor activity during fictive rostral scratching in the turtle. In: 2003 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, Program no. 188.5, 2003b.

Stein PSG and Smith JL. Neural and biomechanical control strategies for different forms of vertebrate hindlimb motor tasks. In: Neurons, Networks, and Motor Behavior, edited by Stein PSG, Grillner S, Selverston AI, and Stuart DG. Cambridge, MA: MIT Press, 1997, p. 61-73.

Stein PSG, Victor JC, Field EC, and Currie SN. Bilateral control of hindlimb scratching in the spinal turtle: contralateral spinal circuitry contributes to the normal ipsilateral motor pattern of fictive rostral scratching. J Neurosci 15: 4343-4355, 1995.[Abstract]

Zar JH. Biostatistical Analysis. Upper Saddle River, NJ: Prentice Hall, 1999.

This article has been cited by other articles:

				C. F. Honeycutt, J. S. Gottschall, and T. R. Nichols Electromyographic Responses From the Hindlimb Muscles of the Decerebrate Cat to Horizontal Support Surface Perturbations J Neurophysiol, June 1, 2009; 101(6): 2751 - 2761. [Abstract] [Full Text] [PDF]

				N. S. Bradley, Y. U. Ryu, and J. Lin Fast Locomotor Burst Generation in Late Stage Embryonic Motility J Neurophysiol, April 1, 2008; 99(4): 1733 - 1742. [Abstract] [Full Text] [PDF]

				K. E. Musselman and J. F. Yang Loading the Limb During Rhythmic Leg Movements Lengthens the Duration of Both Flexion and Extension in Human Infants J Neurophysiol, February 1, 2007; 97(2): 1247 - 1257. [Abstract] [Full Text] [PDF]

				M. G. Sirota, G. A. Pavlova, and I. N. Beloozerova Activity of the Motor Cortex During Scratching J Neurophysiol, February 1, 2006; 95(2): 753 - 765. [Abstract] [Full Text] [PDF]

				H. Ye, D. W. Morton, and H. J. Chiel Neuromechanics of Coordination during Swallowing in Aplysia californica J. Neurosci., February 1, 2006; 26(5): 1470 - 1485. [Abstract] [Full Text] [PDF]

				A. W. Jackson, D. F. Horinek, M. R. Boyd, and A. D. McClellan Disruption of Left-Right Reciprocal Coupling in the Spinal Cord of Larval Lamprey Abolishes Brain-Initiated Locomotor Activity J Neurophysiol, September 1, 2005; 94(3): 2031 - 2044. [Abstract] [Full Text] [PDF]

				P. Saltiel, K. Wyler-Duda, A. d'Avella, R. J. Ajemian, and E. Bizzi Localization and Connectivity in Spinal Interneuronal Networks: The Adduction-Caudal Extension-Flexion Rhythm in the Frog J Neurophysiol, September 1, 2005; 94(3): 2120 - 2138. [Abstract] [Full Text] [PDF]

				M. Lafreniere-Roula and D. A. McCrea Deletions of Rhythmic Motoneuron Activity During Fictive Locomotion and Scratch Provide Clues to the Organization of the Mammalian Central Pattern Generator J Neurophysiol, August 1, 2005; 94(2): 1120 - 1132. [Abstract] [Full Text] [PDF]

				J. F. Yang, E. V. Lamont, and M. Y. C. Pang Split-Belt Treadmill Stepping in Infants Suggests Autonomous Pattern Generators for the Left and Right Leg in Humans J. Neurosci., July 20, 2005; 25(29): 6869 - 6876. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: 91/5/2380    most recent 01184.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (10) Citing Articles via Google Scholar Google Scholar Articles by Stein, P. S. G. Articles by Daniels-McQueen, S. Search for Related Content PubMed PubMed Citation Articles by Stein, P. S. G. Articles by Daniels-McQueen, S.