Phase Relationships Between Segmentally Organized Oscillators in the Leech Heartbeat Pattern Generating Network

2002 ◽  
Vol 87 (3) ◽  
pp. 1572-1585 ◽  
Author(s):  
Mark A. Masino ◽  
Ronald L. Calabrese
Keyword(s):  
Spike Activity ◽  
Motor Pattern ◽  
Initiation Site ◽  
Pattern Generator ◽  
Primary Site ◽  
Secondary Site ◽  
Cycle Period ◽  
Spike Initiation ◽  
Phase Relationships ◽  
Phase Differences

Motor pattern generating networks that produce segmentally distributed motor outflow are often portrayed as a series of coupled segmental oscillators that produce a regular progression (constant phase differences) in their rhythmic activity. The leech heartbeat central pattern generator is paced by a core timing network, which consists of two coupled segmental oscillators in segmental ganglia 3 and 4. The segmental oscillators comprise paired mutually inhibitory oscillator interneurons and the processes of intersegmental coordinating interneurons. As a first step in understanding the coordination of segmental motor outflow by this pattern generator, we describe the functional synaptic interactions, and activity and phase relationships of the heart interneurons of the timing network, in isolated nerve cord preparations. In the timing network, most (∼75%) of the coordinating interneuron action potentials were generated at a primary spike initiation site located in ganglion 4 (G4). A secondary spike initiation site in ganglion 3 (G3) became active in the absence of activity at the primary site. Generally, the secondary site was characterized by a reluctance to burst and a lower spike frequency, when compared with the primary site. Oscillator interneurons in G3 inhibited spike activity at both initiation sites, whereas oscillator interneurons in G4 inhibited spike activity only at the primary initiation site. This asymmetry in the control of spike activity in the coordinating interneurons may account for the observation that the phase of the coordinating interneurons is more tightly linked to the G3 than G4 oscillator interneurons. The cycle period of the timing network and the phase difference between the ipsilateral G3 and G4 oscillator interneurons were regular within individual preparations, but varied among preparations. This variation in phase differences observed across preparations implies that modulated intrinsic membrane and synaptic properties, rather than the pattern of synaptic connections, are instrumental in determining phase within the timing network.

Period Differences Between Segmental Oscillators Produce Intersegmental Phase Differences in the Leech Heartbeat Timing Network

2002 ◽  
Vol 87 (3) ◽  
pp. 1603-1615 ◽  
Author(s):  
Mark A. Masino ◽  
Ronald L. Calabrese
Keyword(s):  
Central Pattern Generator ◽  
Phase Relationship ◽  
Pattern Generator ◽  
The Other ◽  
Cycle Period ◽  
Pharmacological Manipulation ◽  
The Third ◽  
The Individual ◽  
Phase Relationships ◽  
Phase Differences

Considerable experimental and theoretical effort has been exerted to understand how constant intersegmental phase relationships are produced between oscillators in segmentally organized pattern generating networks. The phase relationship between the segmental oscillators in the isolated timing network of the leech heartbeat central pattern generator is quite regular within individual preparations. However, it varies considerably among different preparations. Our goal is to determine how the phase relationships in this network are established. Here we assess whether inherent period differences, as suggested by the excitability-gradient hypothesis, play a role in establishing the phase relationships between the two coupled segmental oscillators of the leech heartbeat timing network. To do this we developed methods for reversibly uncoupling the segmental oscillators (sucrose knife) and pharmacological manipulation of the individual oscillators (split bath). Differences in inherent cycle periods between the third and fourth segmental oscillators (G3 and G4) were present in most (20 of 26) preparations. These period differences correlated with the phase differences observed between the segmental oscillators in the recoupled timing network, such that the oscillator with the faster cycle period, regardless of the segment in which it was located, led in phase in proportion to its period difference with the other oscillator. The phase differences between the original (coupled) and recoupled states of individual preparations were similar. Thus application and removal of the sucrose knife did not alter the period difference between the segmental oscillators in the timing network. Pharmacological manipulation of the uncoupled oscillators to alter the period difference between the oscillators led to similar correlated phase differences in the recoupled timing network. Across all experiments the uncoupled segmental oscillator with the faster cycle period established the cycle period of the timing network when recoupled. In conclusion, our findings indicate that an excitability-gradient plays a role in establishing the phase relationship between the segmental oscillators of the leech heartbeat central pattern generator since inherent period differences present between the oscillators are correlated to the phase relationships of the coupled/recoupled timing network.

scholarly journals Maintenance of motor pattern phase relationships in the ventilatory system of the crab

1997 ◽  
Vol 200 (6) ◽  
pp. 963-974
Author(s):  
R Dicaprio ◽  
G Jordan ◽  
T Hampton
Keyword(s):  
Membrane Potential ◽  
Central Pattern Generator ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Rate Of Change ◽  
Cycle Period ◽  
Potential Oscillation ◽  
Cycle Frequency ◽  
Membrane Potential Oscillation ◽  
Phase Relationships

The central pattern generator responsible for the gill ventilation rhythm in the shore crab Carcinus maenas can produce a functional motor pattern over a large (eightfold) range of cycle frequencies. One way to continue to generate a functional motor pattern over such a large frequency range would be to maintain the relative timing (phase) of the motor pattern as cycle frequency changes. This hypothesis was tested by measuring the phase of eight events in the motor pattern from extracellular recordings at different rhythm frequencies. The motor pattern was found to maintain relatively constant phase relationships among the various motor bursts in this rhythm over a large (sevenfold) range of cycle frequencies, although two phase-maintaining subgroups could be distinguished. Underlying this phase maintenance is a corresponding change in the time delay between events in the motor pattern ranging from 470 to 1800 ms over a sevenfold (300­2100 ms) change in cycle period. Intracellular recordings from ventilatory neurons indicate that there is very little change in the membrane potential oscillation in the motor neurons with changes in cycle frequency. However, recordings from nonspiking interneurons in the ventilatory central pattern generator reveal that the rate of change of the membrane potential oscillation of these neurons varies in proportion to changes in cycle frequency. The strict biomechanical requirements for efficient pumping by the gill bailer, and the fact that work is performed in all phases of the motor pattern, may require that this motor pattern maintain phase at all rhythm frequencies.

Aminergic modulation in lobster stomatogastric ganglion. I. Effects on motor pattern and activity of neurons within the pyloric circuit

1986 ◽  
Vol 55 (5) ◽  
pp. 847-865 ◽  
Author(s):  
R. E. Flamm ◽  
R. M. Harris-Warrick
Keyword(s):  
Biogenic Amines ◽  
Spike Activity ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Stomatogastric Ganglion ◽  
Motor Patterns ◽  
Cycle Frequency ◽  
Panulirus Interruptus ◽  
Generator Circuit ◽  
Phase Relationships

We investigated the effects of dopamine, octopamine, and serotonin on the motor output of the pyloric circuit in the stomatogastric ganglion of the lobster, Panulirus interruptus. Amines were bath applied at concentrations from 10(-8) to 10(-4) M, and the responses of the six classes of pyloric neurons were monitored both intracellularly and extracellularly. Each amine modified the pyloric motor pattern in a specific way. In addition, dopamine and octopamine were each able to produce different motor patterns at different concentrations. Amine effects on pyloric neurons included initiation and enhancement or inhibition of spike activity, changes in the phase relationships of neurons, and changes in the cycle frequency of the pyloric rhythm. These results show that the motor pattern produced by this well-studied central pattern generator circuit is highly plastic and can be modulated by endogenous biogenic amines.

Gating of Afferent Input by a Central Pattern Generator

1999 ◽  
Vol 81 (2) ◽  
pp. 950-953 ◽  
Author(s):  
Ralph A. DiCaprio
Keyword(s):  
Central Pattern Generator ◽  
Sensory Input ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Afferent Input ◽  
Inhibitory Input ◽  
Cycle Period ◽  
Intracellular Recordings ◽  
Afferent Fibers ◽  
Sufficient Magnitude

Gating of afferent input by a central pattern generator. Intracellular recordings from the sole proprioceptor (the oval organ) in the crab ventilatory system show that the nonspiking afferent fibers from this organ receive a cyclic hyperpolarizing inhibition in phase with the ventilatory motor pattern. Although depolarizing and hyperpolarizing current pulses injected into a single afferent will reset the ventilatory motor pattern, the inhibitory input is of sufficient magnitude to block afferent input to the ventilatory central pattern generator (CPG) for ∼50% of the cycle period. It is proposed that this inhibitory input serves to gate sensory input to the ventilatory CPG to provide an unambiguous input to the ventilatory CPG.

Cycle Period of a Network Oscillator Is Independent of Membrane Potential and Spiking Activity in Individual Central Pattern Generator Neurons

2004 ◽  
Vol 92 (3) ◽  
pp. 1904-1917 ◽  
Author(s):  
Paul S. Katz ◽  
Akira Sakurai ◽  
Stefan Clemens ◽  
Deron Davis
Keyword(s):  
Nervous System ◽  
Membrane Potential ◽  
Central Pattern Generator ◽  
Temperature Sensitivity ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Membrane Potentials ◽  
Cycle Period ◽  
Wide Range ◽  
Spiking Activity

Rhythmic motor patterns are thought to arise through the cellular properties and synaptic interactions of neurons in central pattern generator (CPG) circuits. Yet, when examining the CPG underlying the rhythmic escape response of the opisthobranch mollusc, Tritonia diomedea, we found that the cycle period of the fictive swim motor pattern recorded from the isolated nervous system was not altered by changing the resting membrane potential or the level of spiking activity of any of the 3 known CPG cell types: ventral swim interneuron-B (VSI-B), the dorsal swim interneurons (DSIs), and cerebral neuron 2 (C2). Furthermore, tonic firing in one or more DSIs or C2 evoked rhythmic bursting that did not differ from the cycle period of the motor pattern evoked by nerve stimulation, regardless of the firing frequency. In contrast, the CPG produced a large range of cycle periods as a function of temperature. The temperature sensitivity of the fictive motor pattern produced by the isolated nervous system was similar to the temperature sensitivity of the swimming behavior produced by the intact animal. Thus, although the CPG is capable of producing a wide range of cycle periods under the influence of temperature, the membrane potentials and spiking activity of the identified CPG neurons do not determine the periodicity of the motor pattern. This suggests that the timing of activity in this network oscillator may be determined by a mechanism that is independent of the membrane potentials and spike rate of its constituent neurons.

Control of multiple impulse-initiation sites in a leech interneuron

1980 ◽  
Vol 44 (5) ◽  
pp. 878-896 ◽  
Author(s):  
R. L. Calabrese
Keyword(s):  
Rhythmic Activity ◽  
Initiation Site ◽  
Primary Site ◽  
Burst Duration ◽  
Secondary Site ◽  
Impulse Frequency ◽  
Burst Frequency ◽  
Burst Period ◽  
Free Running ◽  
The One

1. Several heart interneurons (HN cells) of the leech nerve cord have impulse-initiation sites in every segmental ganglion through which their single axons pass. All these initiation sites are capable of producing rhythmic impulse bursts. However, under normal conditions a dominant primary initiation site in the ganglion where the cell body is located suppresses the activity of the other secondary sites. 2. Hyperpolarization of the primary initiation site by injected current permits immediate expression of rhythmic activity by a secondary site, usually the one located in the next posterior ganglion. 3. The free-running impulse burst rhythm of the primary site is stronger than that of the secondary site, having a greater burst duration and a tendency toward a higher burst frequency. 4. Bursts of primary-site impulses intercalated into the secondary-site impulse burst rhythm have a twofold effect. First, early to midway through the secondary-site's burst cycle, they phase delay its impulse burst rhythm. Second, early in the secondary-site's burst cycle, they tend to suppress ongoing impulse bursts, and late in the secondary-site's burst cycle, they tend to suppress the next expected impulse burst. The amount of burst suppression seen early and late in the secondary-site burst cycle depends on the burst duration and intraburst impulse frequency of the intercalated burst. 5. The ability of a train of primary-site impulse bursts to completely suppress secondary-site activity depends on burst duration, intraburst impulse frequency, and burst period. 6. Primary-site impulse trains with burst parameters close to those of naturally occurring primary-site bursts completely suppress secondary-site activity. 7. These results are consistent with the notion that the primary-site impulse burst rhythm of an HN cell suppresses the activity of its secondary site because, cycle by cycle, it delays and/or suppresses the next secondary-site burst so that no secondary-site bursts are produced. Dominance of the primary site over the secondary site is ensured by virtue of the primary-site's stronger impulse burst rhythm.

The central nervous origin of the swimming motor pattern in embryos of Xenopus laevis

1982 ◽  
Vol 99 (1) ◽  
pp. 185-196 ◽  
Author(s):  
J. A. Kahn ◽  
A. Roberts
Keyword(s):  
Motor Activity ◽  
Similar Pattern ◽  
Sensory Feedback ◽  
Motor Nerve ◽  
Motor Pattern ◽  
Cycle Period ◽  
Phase Lag ◽  
Nerve Activity ◽  
Rhythmic Motor ◽  
Swimming Pattern

Rhythmic motor nerve activity was recorded in stage 37/38 Xenopus embryos paralysed with curare. The activity was similar to the swimming motor pattern in the following ways: cycle period (40–125 ms), alternation of activity on either side of a segment, rostro-caudal phase lag. Episodes of rhythmic motor activity could be evoked by stimuli that evoke swimming and inhibited by stimuli that normally inhibit swimming. On this basis we conclude that the swimming motor pattern is generated by a central nervous mechanism and is not dependent on sensory feedback. In addition to the swimming pattern, another pattern of motor activity (‘synchrony’) was sometimes recorded in curarized embryos. In this, the rhythmic bursts on either side of a segment occurred in synchrony, and the rhythm period (20–50 ms) was half that in swimming. This was probably not an artifact of curarization as there were indications of a similar pattern in uncurarized embryos. Its function remains unclear.

scholarly journals Roles of Ascending Inhibition During Two Rhythmic Motor Patterns in Xenopus Tadpoles

1998 ◽  
Vol 79 (5) ◽  
pp. 2316-2328 ◽  
Author(s):  
C. S. Green ◽  
S. R. Soffe
Keyword(s):  
Spinal Cord ◽  
Motor Pattern ◽  
Burst Duration ◽  
Major Influence ◽  
Cycle Period ◽  
Detailed Knowledge ◽  
Motor Patterns ◽  
Rhythmic Motor ◽  
Vertebrate Model ◽  
Longitudinal Pattern

Green, C. S. and S. R. Soffe. Roles of ascending inhibition during two rhythmic motor patterns in Xenopus tadpoles. J. Neurophysiol. 79: 2316–2328, 1998. We have investigated the effects of ascending inhibitory pathways on two centrally generated rhythmic motor patterns in a simple vertebrate model, the young Xenopus tadpole. Tadpoles swim when touched, but when grasped respond with slower, stronger struggling movements during which the longitudinal pattern of motor activity is reversed. Surgical spinal cord transection to remove all ascending connections originating caudal to the transection (in tadpoles immobilized in α-bungarotoxin) did not affect “fictive” swimming generated more rostrally. In contrast, cycle period and burst duration both significantly increased during fictive struggling. Increases were progressively larger with more rostral transection. Blocking caudal activity with the anesthetic MS222 (pharmacological transection) produced equivalent but reversible effects. Reducing crossed-ascending inhibition selectively, either by midsagittal spinal cord division or rostral cord hemisection (1-sided transection) mimicked the effects of transection. Like transection, both operations increased cycle period and burst duration during struggling but did not affect swimming. The changes during struggling were larger with more rostral hemisection. Reducing crossed-ascending inhibition by spinal hemisection also increased the rostrocaudal longitudinal delay during swimming, and the caudorostral delay during struggling. Weakening inhibition globally with low concentrations of the glycine antagonist strychnine (10–100 nM) did not alter swimming cycle period, burst duration, or longitudinal delay. However, strychnine at 10–60 nM decreased cycle period during struggling. It also increased burst duration in some cases, although burst duration increased as a proportion of cycle period in all cases. Strychnine reduced longitudinal delay during struggling, making rostral and caudal activity more synchronous. At 100 nM, struggling was totally disrupted. By combining our results with a detailed knowledge of tadpole spinal cord anatomy, we conclude that inhibition mediated by the crossed-ascending axons of characterized, glycinergic, commissural interneurons has a major influence on the struggling motor pattern compared with swimming. We suggest that this difference is a consequence of the larger, reversed longitudinal delay and the extended burst duration during struggling compared with swimming.

Experiments on the central pattern generator for swimming in amphibian embryos

1982 ◽  
Vol 296 (1081) ◽  
pp. 229-243 ◽  
Keyword(s):  
Spinal Cord ◽  
Central Nervous System ◽  
Nervous System ◽  
Pattern Generator ◽  
Pattern Generation ◽  
Motor Output ◽  
Cycle Period ◽  
Sensory Stimuli ◽  
Swimming Pattern ◽  
Left And Right

The central nervous system of paralysed Xenopus laevis embryos can generate a motor output pattern suitable for swimming locomotion. By recording motor root activity in paralysed embryos with transected nervous systems we have shown that: (a) the spinal cord is capable of swimming pattern generation; (b) swimming pattern generator capability in the hindbrain and spinal cord is distributed; (c) caudal hindbrain is necessary for sustained swimming output after discrete stimulation. By recording similarly from embryos whose central nervous system was divided longitudinally into left and right sides, we have shown that: (a) each side can generate rhythmic motor output with cycle periods like those in swimming; (b) during this activity cycle period increases within an episode, and there is the usual rostrocaudal delay found in swimming; (c) this activity is influenced by sensory stimuli in the same way as swimming activity; ( d) normal phase coupling of the left and right sides can be established by the ventral commissure in the spinal cord. We conclude that interactions between the antagonistic (left and right) motor systems are not necessary for swimming rhythm generation and present a model for swimming pattern generation where autonomous rhythm generators on each side of the nervous system drive the motoneurons. Alternation is achieved by reciprocal inhibition, and activity is initiated and maintained by tonic excitation from the hindbrain.

Nonspiking local interneuron in the motor pattern generator for the crayfish swimmeret

1985 ◽  
Vol 54 (1) ◽  
pp. 28-39 ◽  
Author(s):  
D. H. Paul ◽  
B. Mulloney
Keyword(s):  
Nervous System ◽  
Membrane Potential ◽  
Motor Neuron ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Local Interneuron ◽  
Postsynaptic Potentials ◽  
Essential Component ◽  
Local Interneurons

We describe a type of nonspiking premotor local interneuron (interneuron IA) in the abdominal nervous system of Pacifasticus leniusculus. All of its branches are restricted to one side of the midline. These interneurons are identifiable and occur as bilateral pairs, one neuron on each side of abdominal ganglia 3, 4, and 5. The membrane potential of interneuron IA oscillated in phase with the swimmeret rhythm, a motor pattern generated in each of these ganglia, because the neuron received postsynaptic potentials in phase with the rhythm. Sustained hyperpolarization of an individual interneuron IA initiated generation of the swimmeret rhythm in all the ganglia of a quiescent nervous system. Sustained depolarization stopped the swimmeret rhythm in all the active ganglia of a nervous system that was generating the rhythm. Currents injected into one interneuron reset the rhythm. Comparisons of the shapes of the IA interneurons in different ganglia showed that they are similar to each other and distinct from other local interneurons in these ganglia. Interneuron IA has a large integrative segment and relatively few branches that are largely restricted to the lateral neuropil, to which all other kinds of swimmeret neurons also project. We conclude that this interneuron occurs only once in each hemiganglion in abdominal segments 3, 4, and 5, and that it is identifiable. Furthermore, this interneuron is an essential component of the circuit in each hemiganglion that generates the swimmeret rhythm. The interneuron was dye coupled to a particular identifiable motor neuron and not to any other neurons. The motor neuron was not dye-coupled to any other local interneurons. The ability of this motor neuron to reset the rhythm is attributed to its being electrically coupled to interneuron IA in its ganglion.

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