Larval lampreys (ammocoetes) exhibit a rapid vibration-evoked startle response involving a bilate... more Larval lampreys (ammocoetes) exhibit a rapid vibration-evoked startle response involving a bilateral activation of musculature along the length of the body. The resulting movement is variable, contingent on the animal's prestimulus posture: lateral curves along the trunk and tail contract more on the inner side of the curve than on the outer side. Thus, the startle response increases preexisting body curvature. Because ammocoetes are burrowing filter feeders, this startle behavior results in rapid withdrawal of the head into the burrow. A vibratory pulse to the otic capsules in a semi-intact preparation evokes simultaneous action potentials in both primary Mauthner neurons. Vibration also excites several Müller cells. Intracellular stimulation of one primary Mauthner axon (eliciting one action potential) produces bilateral trunk electromyographic potentials that are smaller than those evoked by vibration; simultaneous stimulation of both Mauthner axons (one action potential each) reproduces the vibration-evoked electromyographic amplitudes. The Mauthner cell's sensitivity to vestibular input is centrally modulated during changes in behavioral state. Mauthner action potentials are most easily elicited by vibratory or electrical stimulation of vestibular afferents while an intact animal is at rest; the same stimuli become subthreshold for Mauthner activity while the animal is swimming. A similar depression of Mauthner excitability is observed in semi-intact preparations during arousal. 'Arousal' was defined by the occurrence of tonic, descending spinal cord discharge. Mauthner cells are tonically depolarized during arousal and exhibit an increased membrane conductance; excitatory postsynaptic potentials evoked by vibratory or electrical stimulation of vestibular afferents are greatly attenuated. Modulated sensory transmission to the Mauthner cell may help to prevent inappropriate activation of the startle circuit.
The isolated lamprey spinal cord, when bathed in 2 millimolar D-glutamic acid, will generate a pa... more The isolated lamprey spinal cord, when bathed in 2 millimolar D-glutamic acid, will generate a pattern of motor neuron discharge that has generally been assumed to represent the central motor program for swimming. Motion pictures of behaving lampreys were analyzed by a computer algorithm to estimate undulatory movement parameters that could be directly compared with those generated during D-glutamate--induced undulations. The D-glutamate--induced movement parameters were significantly different from those observed during normal behaviors, including swimming, but accurately predicted the undulations produced by spinally transected adult lampreys.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1989
A low-spinal immobilized turtle displays a fictive scratch reflex in hindlimb muscle nerves in re... more A low-spinal immobilized turtle displays a fictive scratch reflex in hindlimb muscle nerves in response to mechanical stimulation of specific regions of the shell (Robertson et al., 1985). There are 3 forms of the scratch reflex: the rostral, the pocket, and the caudal; each exhibits rhythmic activation of hindlimb motor neurons. Cutaneous stimulation of the distal hindlimb elicits a fictive flexion reflex that exhibits tonic excitation of hip protractor (flexor) motor neurons and tonic inhibition of knee extensor motor neurons (Stein et al., 1982). In the present study, we describe the motor pattern blends that resulted from transient activation of either the ipsilateral or the contralateral flexion reflex pathway during ongoing scratch motor patterns. Two types of blends were observed: (1) insertions of a flexion reflex synergy into an interrupted scratch cycle and (2) deletions of parts of a scratch cycle. Associated with each type of motor pattern blend was a permanent reset of ...
Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the c... more Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the contralateral dorsolateral funiculus (cDLF) at the level of the third postcervical segment (D(3)). Fictive hindlimb motor output was recorded as electroneurograms (ENGs) from up to five peripheral nerves on the right side, including three knee extensors (KE; iliotibialis [IT]-KE, ambiens [AM]-KE, and femorotibialis [FT]-KE), a hip flexor (HF), and a hip extensor (HE). Quantitative analyses of burst amplitude, duty cycle and phase were used to demonstrate the close similarity of these cDLF-evoked fictive motor patterns with previous myographic recordings obtained from the corresponding hindlimb muscles during actual swimming. Fictive rostral scratching was elicited in the same animals by cutaneous stimulation of the shell bridge, anterior to the hindlimb. Fictive swim and rostral scratch motor patterns displayed similar phasing in hip and knee motor pools but differed in the relative ampli...
We examined interactions between the spinal networks that generate right and left rostral scratch... more We examined interactions between the spinal networks that generate right and left rostral scratch motor patterns in turtle hindlimb motoneurons before and after transecting the spinal cord within the anterior hindlimb enlargement. Our results provide evidence that reciprocal inhibition between hip circuit modules can generate hip rhythmicity during the rostral scratch reflex. "Module" refers here to the group of coactive motoneurons and interneurons that controls either flexion or extension of the hip on one side and coordinates that activity with synergist and antagonist motor pools in the same limb and in the contralateral limb. The "bilateral shared core" hypothesis states that hip flexor and extensor (HF and HE) circuit modules interact via crossed and uncrossed spinal pathways: HF modules make reciprocal inhibitory connections with contralateral HF and ipsilateral HE modules and mutual excitatory connections with contralateral HE modules. It is currently unc...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
Analyses of fictive scratching motor patterns in the spinal turtle with transverse hemisection pr... more Analyses of fictive scratching motor patterns in the spinal turtle with transverse hemisection provided support for the concept of bilateral shared spinal cord circuitry among neurons responsible for generating left- and right-side rostral, pocket, and caudal fictive scratching. Rhythmic bursts of hip flexor activity, the hip extensor deletion variation of fictive rostral scratching, were elicited by ipsilateral stimulation in the rostral scratch receptive field of a spinal turtle [transection at the segmental border between the second (D2) and third (D3) postcervical spinal segments] with a contralateral transverse hemisection one segment anterior to the hindlimb enlargement (at the D6-D7 segmental border). In addition, other sites were stimulated in this preparation: (1) contralateral sites in a rostral, pocket, or caudal scratch receptive field or (2) ipsilateral sites in a caudal scratch receptive field. A reconstructed fictive rostral scratch motor pattern of rhythmic alternati...
We examined the rhythmogenic capacity of the midbody D3-D7 spinal cord during stimulation of the ... more We examined the rhythmogenic capacity of the midbody D3-D7 spinal cord during stimulation of the rostral scratch reflex in turtles. Fictive scratching was recorded bilaterally as electroneurograms (ENGs) from prehindlimb enlargement nerves [transverse D7 (TD7) and oblique D7 (OD7)] and hip flexor nerves (HF). TD7 and OD7 innervate transverse- and oblique-abdominus muscles, respectively. D3-end preparations had intact spinal cords caudal to a D2-D3 transection site. Unilateral stimulation of the rostral receptive field in D3-end preparations evoked rhythmic bursting in the ipsilateral (ipsi) HF nerve and bilateral rhythmic discharge in the TD7 and OD7 nerves. Right HF bursts were coactive with right TD7 and left OD7 bursts and alternated with left TD7 and right OD7 bursts. D3-D7 preparations received a second spinal transection at the caudal end of segment D7, thus resulting in activation of strictly preenlargement circuitry in response to rostral scratch stimulation and preventing a...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
Cutaneous stimulation within the rostral scratch receptive field in a low spinal-immobilized turt... more Cutaneous stimulation within the rostral scratch receptive field in a low spinal-immobilized turtle elicits a fictive rostral scratch reflex characterized by robust rhythmic motor output from ipsilateral hindlimb muscle nerves and weaker, alternating motor discharge in contralateral nerves. Simultaneous bilateral stimulation elicits bilateral rostral scratch motor patterns in which activity on the right and left sides alternates. We investigated the role of glycinergic inhibition in the generation and coordination of fictive rostral scratch motor patterns. Glycine (2 or 5 mM) and strychnine (5-50 microM), a glycine antagonist, were superfused over the anterior spinal hindlimb enlargement while fictive rostral scratch motor output was recorded bilaterally from hindlimb muscle nerves in the form of electroneurograms (ENGs). Although glycine reduced rostral scratch burst frequencies, strychnine tended to increase burst frequency. Strychnine also changed the shape of hip flexor ENG burs...
1. The vibration-evoked startle response mediates rapid withdrawal in burrowed larval lampreys (a... more 1. The vibration-evoked startle response mediates rapid withdrawal in burrowed larval lampreys (ammocoetes). Ammocoetes withdraw in response to vibration by contracting pre-existing lateral bends in the trunk and tail, thus pulling their heads deeper into the burrow. 2. The motor effects of an ammocoete startle response are dependent on pre-existing posture. Areas of lateral body curvature contract more and exhibit larger electromyogram (EMG) amplitudes on their inner sides than on their outer sides. 3. Both of the anterior Mth and posterior Mth' (Mauthner) cells and both of the B1 and B2 (bulbar) Müller cells fired action potentials in response to vibration of the otic capsules. Both B3 and B4 Müller cells were inhibited by vibration, while M (mesencephalic) and I1 (isthmic) Müller cells were inhibited by ipsilateral vibration and excited by contralateral vibration. 4. Simultaneous action potentials in both of the anterior Mth cells were appropriate and sufficient for initiatin...
Larval lampreys (Petromyzon marinus) exhibit a combination of cranial reflexes during their vibra... more Larval lampreys (Petromyzon marinus) exhibit a combination of cranial reflexes during their vibration-evoked startle response, including strong contractions of the gill chamber, velum and oral hood. These reflexes were confirmed by applying brief vibratory stimuli to an otic capsule and recording movement and electromyograms in moving preparations and efferent cranial nerve activity in curarized preparations. Vibration elicited efferent discharge in cranial nerves V, IX and X on both sides. The responses were lost following labyrinthectomy. The larval startle response results in water from the contracting gill chamber being expelled through the mouth and temporarily reduces head width. Reduced head width may facilitate the rapid withdrawal which is observed during startle behavior in burrowed larvae [S. Currie (1985) Neurosci. Abstr. 11, 268; S. Currie and R. C. Carlsen J. exp. Biol. (in Press)]. Adult lampreys (Entosphenus tridentata) attached to the wall of an aquarium by their su...
1. A low-spinal, immobilized turtle displays a fictive scratch reflex in hindlimb motor neurons i... more 1. A low-spinal, immobilized turtle displays a fictive scratch reflex in hindlimb motor neurons in response to tactile stimulation of the shell (17, 19). Turtles exhibit three forms of the scratch reflex: rostral, pocket, and caudal. Each form is elicited by tactile stimulation of a different receptive field on the body surface. The ventral-posterior pocket (VPP) cutaneous nerve innervates the ventral-posterior portion of the pocket scratch receptive field (Fig. 1). Natural stimulation within the VPP nerve's receptive field evoked a pocket scratch reflex (Fig. 2A). Electrical stimulation of this nerve elicited robust pocket scratch reflexes (Fig. 2, B and C). 2. A single electrical pulse to the VPP nerve delivered at a voltage (greater than 5 V, 0.1 ms) that activated all the axons in the nerve was termed a "maximal" pulse. A single maximal pulse did not evoke a scratch motor response. It raised the excitability of the pocket scratch central pattern generator for sever...
1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the... more 1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the turtle by electrically stimulating the shell at sites within the rostral-scratch receptive field. To examine the cellular mechanisms for these multisecond increases in scratch excitability, we recorded from single cutaneous afferents and sensory interneurons that responded to stimulation of the shell within the rostral-scratch receptive field. A single segment of the midbody spinal cord (D4, the 4th postcervical segment) was isolated in situ by transecting the spinal cord at the segment's anterior and posterior borders. The isolated segment was left attached to its peripheral nerve that innervates part of the rostral-scratch receptive field. A microsuction electrode (4-5 microns ID) was used to record extracellularly from the descending axons of cutaneous afferents and interneurons in the spinal white matter at the posterior end of the D4 segment. 2. The turtle shell is innervated b...
Larval lampreys (ammocoetes) exhibit a rapid vibration-evoked startle response involving a bilate... more Larval lampreys (ammocoetes) exhibit a rapid vibration-evoked startle response involving a bilateral activation of musculature along the length of the body. The resulting movement is variable, contingent on the animal's prestimulus posture: lateral curves along the trunk and tail contract more on the inner side of the curve than on the outer side. Thus, the startle response increases preexisting body curvature. Because ammocoetes are burrowing filter feeders, this startle behavior results in rapid withdrawal of the head into the burrow. A vibratory pulse to the otic capsules in a semi-intact preparation evokes simultaneous action potentials in both primary Mauthner neurons. Vibration also excites several Müller cells. Intracellular stimulation of one primary Mauthner axon (eliciting one action potential) produces bilateral trunk electromyographic potentials that are smaller than those evoked by vibration; simultaneous stimulation of both Mauthner axons (one action potential each) reproduces the vibration-evoked electromyographic amplitudes. The Mauthner cell's sensitivity to vestibular input is centrally modulated during changes in behavioral state. Mauthner action potentials are most easily elicited by vibratory or electrical stimulation of vestibular afferents while an intact animal is at rest; the same stimuli become subthreshold for Mauthner activity while the animal is swimming. A similar depression of Mauthner excitability is observed in semi-intact preparations during arousal. 'Arousal' was defined by the occurrence of tonic, descending spinal cord discharge. Mauthner cells are tonically depolarized during arousal and exhibit an increased membrane conductance; excitatory postsynaptic potentials evoked by vibratory or electrical stimulation of vestibular afferents are greatly attenuated. Modulated sensory transmission to the Mauthner cell may help to prevent inappropriate activation of the startle circuit.
The isolated lamprey spinal cord, when bathed in 2 millimolar D-glutamic acid, will generate a pa... more The isolated lamprey spinal cord, when bathed in 2 millimolar D-glutamic acid, will generate a pattern of motor neuron discharge that has generally been assumed to represent the central motor program for swimming. Motion pictures of behaving lampreys were analyzed by a computer algorithm to estimate undulatory movement parameters that could be directly compared with those generated during D-glutamate--induced undulations. The D-glutamate--induced movement parameters were significantly different from those observed during normal behaviors, including swimming, but accurately predicted the undulations produced by spinally transected adult lampreys.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1989
A low-spinal immobilized turtle displays a fictive scratch reflex in hindlimb muscle nerves in re... more A low-spinal immobilized turtle displays a fictive scratch reflex in hindlimb muscle nerves in response to mechanical stimulation of specific regions of the shell (Robertson et al., 1985). There are 3 forms of the scratch reflex: the rostral, the pocket, and the caudal; each exhibits rhythmic activation of hindlimb motor neurons. Cutaneous stimulation of the distal hindlimb elicits a fictive flexion reflex that exhibits tonic excitation of hip protractor (flexor) motor neurons and tonic inhibition of knee extensor motor neurons (Stein et al., 1982). In the present study, we describe the motor pattern blends that resulted from transient activation of either the ipsilateral or the contralateral flexion reflex pathway during ongoing scratch motor patterns. Two types of blends were observed: (1) insertions of a flexion reflex synergy into an interrupted scratch cycle and (2) deletions of parts of a scratch cycle. Associated with each type of motor pattern blend was a permanent reset of ...
Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the c... more Fictive swimming was elicited in low-spinal immobilized turtles by electrically stimulating the contralateral dorsolateral funiculus (cDLF) at the level of the third postcervical segment (D(3)). Fictive hindlimb motor output was recorded as electroneurograms (ENGs) from up to five peripheral nerves on the right side, including three knee extensors (KE; iliotibialis [IT]-KE, ambiens [AM]-KE, and femorotibialis [FT]-KE), a hip flexor (HF), and a hip extensor (HE). Quantitative analyses of burst amplitude, duty cycle and phase were used to demonstrate the close similarity of these cDLF-evoked fictive motor patterns with previous myographic recordings obtained from the corresponding hindlimb muscles during actual swimming. Fictive rostral scratching was elicited in the same animals by cutaneous stimulation of the shell bridge, anterior to the hindlimb. Fictive swim and rostral scratch motor patterns displayed similar phasing in hip and knee motor pools but differed in the relative ampli...
We examined interactions between the spinal networks that generate right and left rostral scratch... more We examined interactions between the spinal networks that generate right and left rostral scratch motor patterns in turtle hindlimb motoneurons before and after transecting the spinal cord within the anterior hindlimb enlargement. Our results provide evidence that reciprocal inhibition between hip circuit modules can generate hip rhythmicity during the rostral scratch reflex. "Module" refers here to the group of coactive motoneurons and interneurons that controls either flexion or extension of the hip on one side and coordinates that activity with synergist and antagonist motor pools in the same limb and in the contralateral limb. The "bilateral shared core" hypothesis states that hip flexor and extensor (HF and HE) circuit modules interact via crossed and uncrossed spinal pathways: HF modules make reciprocal inhibitory connections with contralateral HF and ipsilateral HE modules and mutual excitatory connections with contralateral HE modules. It is currently unc...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1998
Analyses of fictive scratching motor patterns in the spinal turtle with transverse hemisection pr... more Analyses of fictive scratching motor patterns in the spinal turtle with transverse hemisection provided support for the concept of bilateral shared spinal cord circuitry among neurons responsible for generating left- and right-side rostral, pocket, and caudal fictive scratching. Rhythmic bursts of hip flexor activity, the hip extensor deletion variation of fictive rostral scratching, were elicited by ipsilateral stimulation in the rostral scratch receptive field of a spinal turtle [transection at the segmental border between the second (D2) and third (D3) postcervical spinal segments] with a contralateral transverse hemisection one segment anterior to the hindlimb enlargement (at the D6-D7 segmental border). In addition, other sites were stimulated in this preparation: (1) contralateral sites in a rostral, pocket, or caudal scratch receptive field or (2) ipsilateral sites in a caudal scratch receptive field. A reconstructed fictive rostral scratch motor pattern of rhythmic alternati...
We examined the rhythmogenic capacity of the midbody D3-D7 spinal cord during stimulation of the ... more We examined the rhythmogenic capacity of the midbody D3-D7 spinal cord during stimulation of the rostral scratch reflex in turtles. Fictive scratching was recorded bilaterally as electroneurograms (ENGs) from prehindlimb enlargement nerves [transverse D7 (TD7) and oblique D7 (OD7)] and hip flexor nerves (HF). TD7 and OD7 innervate transverse- and oblique-abdominus muscles, respectively. D3-end preparations had intact spinal cords caudal to a D2-D3 transection site. Unilateral stimulation of the rostral receptive field in D3-end preparations evoked rhythmic bursting in the ipsilateral (ipsi) HF nerve and bilateral rhythmic discharge in the TD7 and OD7 nerves. Right HF bursts were coactive with right TD7 and left OD7 bursts and alternated with left TD7 and right OD7 bursts. D3-D7 preparations received a second spinal transection at the caudal end of segment D7, thus resulting in activation of strictly preenlargement circuitry in response to rostral scratch stimulation and preventing a...
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
Cutaneous stimulation within the rostral scratch receptive field in a low spinal-immobilized turt... more Cutaneous stimulation within the rostral scratch receptive field in a low spinal-immobilized turtle elicits a fictive rostral scratch reflex characterized by robust rhythmic motor output from ipsilateral hindlimb muscle nerves and weaker, alternating motor discharge in contralateral nerves. Simultaneous bilateral stimulation elicits bilateral rostral scratch motor patterns in which activity on the right and left sides alternates. We investigated the role of glycinergic inhibition in the generation and coordination of fictive rostral scratch motor patterns. Glycine (2 or 5 mM) and strychnine (5-50 microM), a glycine antagonist, were superfused over the anterior spinal hindlimb enlargement while fictive rostral scratch motor output was recorded bilaterally from hindlimb muscle nerves in the form of electroneurograms (ENGs). Although glycine reduced rostral scratch burst frequencies, strychnine tended to increase burst frequency. Strychnine also changed the shape of hip flexor ENG burs...
1. The vibration-evoked startle response mediates rapid withdrawal in burrowed larval lampreys (a... more 1. The vibration-evoked startle response mediates rapid withdrawal in burrowed larval lampreys (ammocoetes). Ammocoetes withdraw in response to vibration by contracting pre-existing lateral bends in the trunk and tail, thus pulling their heads deeper into the burrow. 2. The motor effects of an ammocoete startle response are dependent on pre-existing posture. Areas of lateral body curvature contract more and exhibit larger electromyogram (EMG) amplitudes on their inner sides than on their outer sides. 3. Both of the anterior Mth and posterior Mth' (Mauthner) cells and both of the B1 and B2 (bulbar) Müller cells fired action potentials in response to vibration of the otic capsules. Both B3 and B4 Müller cells were inhibited by vibration, while M (mesencephalic) and I1 (isthmic) Müller cells were inhibited by ipsilateral vibration and excited by contralateral vibration. 4. Simultaneous action potentials in both of the anterior Mth cells were appropriate and sufficient for initiatin...
Larval lampreys (Petromyzon marinus) exhibit a combination of cranial reflexes during their vibra... more Larval lampreys (Petromyzon marinus) exhibit a combination of cranial reflexes during their vibration-evoked startle response, including strong contractions of the gill chamber, velum and oral hood. These reflexes were confirmed by applying brief vibratory stimuli to an otic capsule and recording movement and electromyograms in moving preparations and efferent cranial nerve activity in curarized preparations. Vibration elicited efferent discharge in cranial nerves V, IX and X on both sides. The responses were lost following labyrinthectomy. The larval startle response results in water from the contracting gill chamber being expelled through the mouth and temporarily reduces head width. Reduced head width may facilitate the rapid withdrawal which is observed during startle behavior in burrowed larvae [S. Currie (1985) Neurosci. Abstr. 11, 268; S. Currie and R. C. Carlsen J. exp. Biol. (in Press)]. Adult lampreys (Entosphenus tridentata) attached to the wall of an aquarium by their su...
1. A low-spinal, immobilized turtle displays a fictive scratch reflex in hindlimb motor neurons i... more 1. A low-spinal, immobilized turtle displays a fictive scratch reflex in hindlimb motor neurons in response to tactile stimulation of the shell (17, 19). Turtles exhibit three forms of the scratch reflex: rostral, pocket, and caudal. Each form is elicited by tactile stimulation of a different receptive field on the body surface. The ventral-posterior pocket (VPP) cutaneous nerve innervates the ventral-posterior portion of the pocket scratch receptive field (Fig. 1). Natural stimulation within the VPP nerve's receptive field evoked a pocket scratch reflex (Fig. 2A). Electrical stimulation of this nerve elicited robust pocket scratch reflexes (Fig. 2, B and C). 2. A single electrical pulse to the VPP nerve delivered at a voltage (greater than 5 V, 0.1 ms) that activated all the axons in the nerve was termed a "maximal" pulse. A single maximal pulse did not evoke a scratch motor response. It raised the excitability of the pocket scratch central pattern generator for sever...
1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the... more 1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the turtle by electrically stimulating the shell at sites within the rostral-scratch receptive field. To examine the cellular mechanisms for these multisecond increases in scratch excitability, we recorded from single cutaneous afferents and sensory interneurons that responded to stimulation of the shell within the rostral-scratch receptive field. A single segment of the midbody spinal cord (D4, the 4th postcervical segment) was isolated in situ by transecting the spinal cord at the segment's anterior and posterior borders. The isolated segment was left attached to its peripheral nerve that innervates part of the rostral-scratch receptive field. A microsuction electrode (4-5 microns ID) was used to record extracellularly from the descending axons of cutaneous afferents and interneurons in the spinal white matter at the posterior end of the D4 segment. 2. The turtle shell is innervated b...
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