Endogenous Motor Neuron Properties Contribute to a Program-Specific Phase of Activity in the Multifunctional Feeding Central Pattern Generator of Aplysia

2007 ◽  
Vol 98 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Geidy E. Serrano ◽  
Clarissa Martínez-Rubio ◽  
Mark W. Miller
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Central Pattern Generators ◽  
Ingestive Behavior ◽  
Membrane Properties ◽  
Motor Patterns ◽  
Effector System ◽  
Bilateral Pair ◽  
Pattern Generators ◽  
Specific Phase

Multifunctional central pattern generators (CPGs) are circuits of neurons that can generate manifold actions from a single effector system. This study examined a bilateral pair of pharyngeal motor neurons, designated B67, that participate in the multifunctional feeding network of Aplysia californica. Fictive buccal motor programs (BMPs) were elicited with four distinct stimulus paradigms to assess the activity of B67 during ingestive versus egestive patterns. In both classes of programs, B67 fired during the phase of radula protraction and received a potent inhibitory postsynaptic potential (IPSP) during fictive radula retraction. When programs were ingestive, the retraction phase IPSP exhibited a depolarizing sag and was followed by a postinhibitory rebound (PIR) that could generate a postretraction phase of impulse activity. When programs were egestive, the depolarizing sag potential and PIR were both diminished or were not present. Examination of the membrane properties of B67 disclosed a cesium-sensitive depolarizing sag, a corresponding Ih-like current, and PIR in its responses to hyperpolarizing pulses. Direct IPSPs originating from the influential CPG retraction phase interneuron B64 were also found to activate the sag potential and PIR of B67. Dopamine, a modulator that can promote ingestive behavior in this system, enhanced the sag potential, Ih-like current, and PIR of B67. Finally, a pharyngeal muscle contraction followed the radula retraction phase of ingestive, but not egestive motor patterns. It is proposed that regulation of the intrinsic properties of this motor neuron can contribute to generating a program-specific phase of motor activity.

scholarly journals Localization of Motor Neurons and Central Pattern Generators for Motor Patterns Underlying Feeding Behavior in Drosophila Larvae

PLoS ONE ◽  
2015 ◽  
Vol 10 (8) ◽  
pp. e0135011 ◽  
Author(s):  
Sebastian Hückesfeld ◽  
Andreas Schoofs ◽  
Philipp Schlegel ◽  
Anton Miroschnikow ◽  
Michael J. Pankratz
Keyword(s):  
Feeding Behavior ◽  
Motor Neurons ◽  
Central Pattern Generators ◽  
Motor Patterns ◽  
Drosophila Larvae ◽  
Pattern Generators

scholarly journals A genetic manipulation of motor neuron excitability does not alter locomotor output in Drosophila larvae

2014 ◽  
Author(s):  
Erin C. McKiernan
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Motor Behavior ◽  
Genetic Manipulation ◽  
Motor Output ◽  
Membrane Properties ◽  
Neuron Excitability ◽  
Motor Neuron Excitability ◽  
The Face

Motor activity, like that producing locomotion, is generated by networks of neurons. At the last output level of these networks are the motor neurons, which send signals to the muscles, causing them to contract. Current research in motor control is focused on finding out how motor neurons contribute to shaping the timing of motor behaviors. Are motor neurons just passive relayers of the signals they receive? Or, do motor neurons shape the signals before passing them on to the muscles, thereby influencing the timing of the behavior? It is now well accepted that motor neurons have active, intrinsic membrane properties - there are ion channels in the cell membrane that allow motor neurons to respond to input in non-linear and diverse ways. However, few direct tests of the role of motor neuron intrinsic properties in shaping motor behavior have been carried out, and many questions remain about the role of specific ion channel genes in motor neuron function. In this study, two potassium channel transgenes were expressed in Drosophila larvae, causing motor neurons to fire at lower levels of current stimulation and at higher frequencies, thereby increasing excitability. Mosaic animals were created in which some identified motor neurons expressed the transgenes while others did not. Motor output underlying crawling was compared in muscles innervated by control and experimental neurons in the same animals. Counterintuitively, no effect of the transgenic manipulation on motor output was seen. Future experiments are outlined to determine how the larval nervous system produces normal motor output in the face of altered motor neuron excitability.

scholarly journals Central pattern generators in the turtle spinal cord: selection among the forms of motor behaviors

2018 ◽  
Vol 119 (2) ◽  
pp. 422-440 ◽  
Author(s):  
Paul S. G. Stein
Keyword(s):  
Spinal Cord ◽  
Motor Pattern ◽  
Central Pattern Generators ◽  
Knee Extensor ◽  
Motor Patterns ◽  
Motor Behaviors ◽  
Multiple Behaviors ◽  
Pattern Generators ◽  
Electrical Stimuli

Neuronal networks in the turtle spinal cord have considerable computational complexity even in the absence of connections with supraspinal structures. These networks contain central pattern generators (CPGs) for each of several behaviors, including three forms of scratch, two forms of swim, and one form of flexion reflex. Each behavior is activated by a specific set of cutaneous or electrical stimuli. The process of selection among behaviors within the spinal cord has multisecond memories of specific motor patterns. Some spinal cord interneurons are partially shared among several CPGs, whereas other interneurons are active during only one type of behavior. Partial sharing is a proposed mechanism that contributes to the ability of the spinal cord to generate motor pattern blends with characteristics of multiple behaviors. Variations of motor patterns, termed deletions, assist in characterization of the organization of the pattern-generating components of CPGs. Single-neuron recordings during both normal and deletion motor patterns provide support for a CPG organizational structure with unit burst generators (UBGs) whose members serve a direction of a specific degree of freedom of the hindlimb, e.g., the hip-flexor UBG, the hip-extensor UBG, the knee-flexor UBG, the knee-extensor UBG, etc. The classic half-center hypothesis that includes all the hindlimb flexors in a single flexor half-center and all the hindlimb extensors in a single extensor half-center lacks the organizational complexity to account for the motor patterns produced by turtle spinal CPGs. Thus the turtle spinal cord is a valuable model system for studies of mechanisms responsible for selection and generation of motor behaviors. NEW & NOTEWORTHY The concept of the central pattern generator (CPG) is a major tenet in motor neuroethology that has influenced the design and interpretations of experiments for over a half century. This review concentrates on the turtle spinal cord and describes studies from the 1970s to the present responsible for key developments in understanding the CPG mechanisms responsible for the selection and production of coordinated motor patterns during turtle hindlimb motor behaviors.

Segmental giant: evidence for a driver neuron interposed between command and motor neurons in the crayfish escape system

1982 ◽  
Vol 47 (5) ◽  
pp. 761-781 ◽  
Author(s):  
A. Roberts ◽  
F. B. Krasne ◽  
G. Hagiwara ◽  
J. J. Wine ◽  
A. P. Kramer
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
High Frequency ◽  
Functional Significance ◽  
Escape Behavior ◽  
Dendritic Branch ◽  
Command Neurons ◽  
Firing Threshold ◽  
Conventional Tests ◽  
Bilateral Pair

1. The giant command neurons for tailflip escape behavior in crayfish have been thought to excite the nongiant fast flexor (tailflip producing) motor neurons (FFs) via monosynaptic connections. We show here that excitation of FFs instead occurs via a bilateral pair of segmental giant neurons (SGs) interposed between the command axons and FFs in each segment. 2. Anatomically, the SGs appear to make numerous contacts with ipsilateral command axons and FFs and fewer contacts contralaterally. In contrast, the command axons have only sparse direct connections to the FFs. An SG has an axon in the ipsilateral first ganglionic root and may be a modified swimmeret motor neuron. 3. Each SG is depolarized well beyond threshold by the firing of an ipsilateral command axon and is depolarized to near threshold by the firing of a contralateral command axon. The synapses between command axons and SGs are electrical and probably rectifying. 4. Each FF is excited to a level near firing threshold by the SG ipsilateral to its axon and is excited weakly by the contralateral SG. The synapses between SGs and FFs are electrical and nonrectifying. 5. Variations in excitatory postsynaptic potentials (EPSPs) recorded in FFs during prolonged, high-frequency firing of the command axons can be accounted for by refractoriness of SG spikes, as opposed to refractoriness of dendritic branch spikes as had previously been delivered. 6. These findings illustrate the limitations of conventional tests for monosynapticity. 7. The functional significance of having driver neurons interposed between command neurons and motor neurons is discussed.

scholarly journals Feedback From Peripheral Musculature to Central Pattern Generator in the Neurogenic Heart of the Crab Callinectes sapidus: Role of Mechanosensitive Dendrites

2010 ◽  
Vol 103 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Keyla García-Crescioni ◽  
Timothy J. Fort ◽  
Estee Stern ◽  
Vladimir Brezina ◽  
Mark W. Miller
Keyword(s):  
Motor Neuron ◽  
Central Pattern Generator ◽  
Motor Neurons ◽  
Callinectes Sapidus ◽  
Motor Pattern ◽  
Pattern Generator ◽  
Neuron Spike ◽  
Effector System ◽  
Spike Bursts

The neurogenic heart of decapod crustaceans is a very simple, self-contained, model central pattern generator (CPG)-effector system. The CPG, the nine-neuron cardiac ganglion (CG), is embedded in the myocardium itself; it generates bursts of spikes that are transmitted by the CG's five motor neurons to the periphery of the system, the myocardium, to produce its contractions. Considerable evidence suggests that a CPG-peripheral loop is completed by a return feedback pathway through which the contractions modify, in turn, the CG motor pattern. One likely pathway is provided by dendrites, presumably mechanosensitive, that the CG neurons project into the adjacent myocardial muscle. Here we have tested the role of this pathway in the heart of the blue crab, Callinectes sapidus . We performed “de-efferentation” experiments in which we cut the motor neuron axons to the myocardium and “de-afferentation” experiments in which we cut or ligated the dendrites. In the isolated CG, these manipulations had no effect on the CG motor pattern. When the CG remained embedded in the myocardium, however, these manipulations, interrupting either the efferent or afferent limb of the CPG-peripheral loop, decreased contraction amplitude, increased the frequency of the CG motor neuron spike bursts, and decreased the number of spikes per burst and burst duration. Finally, passive stretches of the myocardium likewise modulated the spike bursts, an effect that disappeared when the dendrites were cut. We conclude that feedback through the dendrites indeed operates in this system and suggest that it completes a loop through which the system self-regulates its activity.

scholarly journals A descending pathway facilitates undulatory wave propagation in Caenorhabditis elegans through gap junctions

2017 ◽  
Author(s):  
Tianqi Xu ◽  
Jing Huo ◽  
Shuai Shao ◽  
Michelle Po ◽  
Taizo Kawano ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Gap Junctions ◽  
Motor Neuron ◽  
Motor Neurons ◽  
Central Pattern Generators ◽  
The Body ◽  
C Elegans ◽  
Bending Waves ◽  
Forward Locomotion ◽  
Type Motor

Descending signals from the brain play critical roles in controlling and modulating locomotion kinematics. In the Caenorhabditis elegans nervous system, descending AVB premotor interneurons exclusively form gap junctions with B-type motor neurons that drive forward locomotion. We combined genetic analysis, optogenetic manipulation, and computational modeling to elucidate the function of AVB-B gap junctions during forward locomotion. First, we found that some B-type motor neurons generated intrinsic rhythmic activity, constituting distributed central pattern generators. Second, AVB premotor interneurons drove bifurcation of B-type motor neuron dynamics, triggering their transition from stationary to oscillatory activity. Third, proprioceptive couplings between neighboring B-type motor neurons entrained the frequency of body oscillators, forcing coherent propagation of bending waves. Despite substantial anatomical differences between the worm motor circuit and those in higher model organisms, we uncovered converging principles that govern coordinated locomotion.Significance StatementA deep understanding of the neural basis of motor behavior must integrate neuromuscular dynamics, mechanosensory feedback, as well as global command signals, to predict behavioral dynamics. Here, we report on an integrative approach to defining the circuit logic underlying coordinated locomotion in C. elegans. Our combined experimental and computational analysis revealed that (1) motor neurons in C. elegans could function as intrinsic oscillators; (2) Descending inputs and proprioceptive couplings work synergistically to facilitate the sequential activation of motor neuron activities, allowing bending waves to propagate efficiently along the body. Our work thus represents a key step towards an integrative view of animal locomotion.

scholarly journals Zebrafish Motor Neuron Subtypes Differ Electrically Prior to Axonal Outgrowth

2009 ◽  
Vol 102 (4) ◽  
pp. 2477-2484 ◽  
Author(s):  
Rosa L. Moreno ◽  
Angeles B. Ribera
Keyword(s):  
Spinal Cord ◽  
Transcription Factor ◽  
Motor Neuron ◽  
Motor Neurons ◽  
Expression Patterns ◽  
Membrane Properties ◽  
Spinal Cord Segment ◽  
Factor Expression ◽  
Voltage Dependent ◽  
Transcription Factor Expression

Different muscle targets and transcription factor expression patterns reveal the presence of motor neuron subtypes. However, it is not known whether these subtypes also differ with respect to electrical membrane properties. To address this question, we studied primary motor neurons (PMNs) in the spinal cord of zebrafish embryos. PMN genesis occurs during gastrulation and gives rise to a heterogeneous set of motor neurons that differ with respect to transcription factor expression, muscle targets, and soma location within each spinal cord segment. The unique subtype-specific soma locations and axonal trajectories of two PMNs—MiP (middle) and CaP (caudal)—allowed their identification in situ as early as 17 h postfertilization (hpf), prior to axon genesis. Between 17 and 48 hpf, CaPs and MiPs displayed subtype-specific electrical membrane properties. Voltage-dependent inward and outward currents differed significantly between MiPs and CaPs. Moreover, by 48 hpf, CaPs and MiPs displayed subtype-specific firing behaviors. Our results demonstrate that motor neurons that differ with respect to muscle targets and transcription factor expression acquire subtype-specific electrical membrane properties. Moreover, the differences are evident prior to axon genesis and persist to the latest stage studied, 2 days postfertilization.

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

2004 ◽  
Vol 91 (5) ◽  
pp. 2380-2384 ◽  
Author(s):  
Paul S. G. Stein ◽  
Susan Daniels-McQueen
Keyword(s):  
Motor Neuron ◽  
Motor Neurons ◽  
Activity Patterns ◽  
Motor Pattern ◽  
Knee Extensor ◽  
Reciprocal Inhibition ◽  
Knee Extensors ◽  
Motor Patterns ◽  
Knee Flexor ◽  
Hip Flexor

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.

scholarly journals Bringing up the rear: new premotor interneurons add regional complexity to a segmentally distributed motor pattern

2011 ◽  
Vol 106 (5) ◽  
pp. 2201-2215 ◽  
Author(s):  
Angela Wenning ◽  
Brian J. Norris ◽  
Anca Doloc-Mihu ◽  
Ronald L. Calabrese
Keyword(s):  
Phase Difference ◽  
Motor Neurons ◽  
Regional Difference ◽  
Motor Pattern ◽  
Central Pattern Generators ◽  
The Other ◽  
The Core ◽  
Asymmetric Pattern ◽  
Pattern Generators ◽  
Two Sides

Central pattern generators (CPGs) pace and pattern many rhythmic activities. We have uncovered a new module in the heartbeat CPG of leeches that creates a regional difference in this segmentally distributed motor pattern. The core CPG consists of seven identified pairs and one unidentified pair of heart interneurons of which 5 pairs are premotor and inhibit 16 pairs of heart motor neurons. The heartbeat CPG produces a side-to-side asymmetric pattern of activity of the premotor heart interneurons corresponding to an asymmetric fictive motor pattern and an asymmetric constriction pattern of the hearts with regular switches between the two sides. The premotor pattern progresses from rear to front on one side and nearly synchronously on the other; the motor pattern shows corresponding intersegmental coordination, but only from segment 15 forward. In the rearmost segments the fictive motor pattern and the constriction pattern progress from front to rear on both sides and converge in phase. Modeling studies suggested that the known inhibitory inputs to the rearmost heart motor neurons were insufficient to account for this activity. We therefore reexamined the constriction pattern of intact leeches. We also identified electrophysiologically two additional pairs of heart interneurons in the rear. These new heart interneurons make inhibitory connections with the rear heart motor neurons, are coordinated with the core heartbeat CPG, and are dye-coupled to their contralateral homologs. Their strong inhibitory connections with the rearmost heart motor neurons and the small side-to-side phase difference of their bursting contribute to the different motor and beating pattern observed in the animal's rear.

scholarly journals Excitatory Motor Neurons are Local Central Pattern Generators in an Anatomically Compressed Motor Circuit for Reverse Locomotion

2017 ◽  
Author(s):  
Shangbang Gao ◽  
Sihui Asuka Guan ◽  
Anthony D. Fouad ◽  
Jun Meng ◽  
Taizo Kawano ◽  
...  
Keyword(s):  
Motor Neurons ◽  
Calcium Imaging ◽  
Central Pattern Generators ◽  
Oscillatory Activity ◽  
Intrinsic Activity ◽  
C Elegans ◽  
Class A ◽  
Cell Ablation ◽  
Pattern Generators

AbstractCentral pattern generators are cell‐ or network-driven oscillators that underlie motor rhythmicity. The existence and identity of C. elegans CPGs remain unknown. Through cell ablation, electrophysiology, and calcium imaging, we identified oscillators for reverse locomotion. We show that the cholinergic and excitatory class A motor neurons exhibit intrinsic and oscillatory activity, and such an activity can drive reverse locomotion without premotor interneurons. Regulation of their oscillatory activity, either through effecting an endogenous constituent of oscillation, the P/Q/N high voltage-activated calcium channel UNC-2, or, via dual regulation – inhibition and activation ‐ by the descending premotor interneurons AVA, determines the propensity, velocity, and sustention of reverse locomotion. Thus, the reversal motor executors themselves serve as oscillators; regulation of their intrinsic activity controls the reversal motor state. These findings exemplify anatomic and functional compression: motor executors integrate the role of rhythm generation in a locomotor network that is constrained by small cell numbers.

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