Coupled motoneurones are part of the crayfish swimmeret central oscillator

Heitler, W. J.

doi:10.1038/275231a0

Cited by 84 publications

(53 citation statements)

References 6 publications

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“…Motoneuronal contributions to pattern generation also have been reported in the crab ventilatory system (Simmers and Bush, 1983) and the crayfish swimmeret system (Heitler, 1978), in which motoneurons are thought to provide a positive feedback loop to sustain and reinforce an ongoing pattern. In the sea slugs Tritonia and Apl ysia, buccal and cerebral motoneurons can themselves drive repeating rhythms (Willows, 1980;Hurwitz et al, 1994;Perrins and Weiss, 1996), but these probably occur with the mediation of so-far unidentified C PG-type interneurons.…”

Section: Discussionmentioning

confidence: 99%

“…In most other systems, however, separate sets of C PG interneurons and motoneurons are present more obviously. Although there is evidence that motoneurons can have an influence on the generation of the motor pattern in such systems, too (Heitler, 1978;Friesen, 1989), the cellular mechanisms integrating interneuronal and motoneuronal activity are not understood clearly.…”

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confidence: 99%

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Pattern-Generating Role for Motoneurons in a Rhythmically Active Neuronal Network

1998

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The role of motoneurons in central motor pattern generation was investigated in the feeding system of the pond snail Lymnaea stagnalis, an important invertebrate model of behavioral rhythm generation. The neuronal network responsible for the three-phase feeding motor program (fictive feeding) has been characterized extensively and divided into populations of central pattern generator (CPG) interneurons, modulatory interneurons, and motoneurons. A previous model of the feeding system considered that the motoneurons were passive followers of CPG interneuronal activity. Here we present new, detailed physiological evidence that motoneurons that innervate the musculature of the feeding apparatus have significant electrotonic motoneuron3interneuron connections, mainly confined to cells active in the same phase of the feeding cycle (protraction, rasp, or swallow). This suggested that the motoneurons participate in rhythm generation. This was assessed by manipulating firing activity in the motoneurons during maintained fictive feeding rhythms. Experiments showed that motoneurons contribute to the maintenance and phase setting of the feeding rhythm and provide an efficient system for phase-locking muscle activity with central neural activity. These data indicate that the distinction between motoneurons and interneurons in a complex CNS network like that involved in snail feeding is no longer justified and that both cell types are important in motor pattern generation. This is a distributed type of organization likely to be a general characteristic of CNS circuitries that produce rhythmic motor behavior.

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Pattern-Generating Role for Motoneurons in a Rhythmically Active Neuronal Network

1998

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“…Grinnell, 1970;Shupliakov et al 1990) is unlikely in Xenopu.s embryos where motorneurones lack dorsally projecting axons. The possibility that vertebrate motoneurones could be integral members of a CPG, as is the case in many invertebrate systems (crayfish swimmerets: Heitler, 1978; crab gill chamber ventilation: Simmers & Bush, 1983) clearly requires further study. This possibility has only infrequently been suggested in vertebrate systems (e.g.…”

Section: Discussionmentioning

confidence: 99%

Cholinergic and electrical synapses between synergistic spinal motoneurones in the Xenopus laevis embryo.

Perrins

Roberts

1995

The Journal of Physiology

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connections were found which crossed the cord. The fast PSPs were blocked by 10 /M mecamylamine but not by 1 mm kynurenic acid, so were mediated by nicotinic acetylcholine receptors (nAChRs). These are the first unitary excitatory postsynaptic potentials (EPSPs) mediated by nAChRs recorded intracellularly within the vertebrate central nervous system. 4. Bidirectional electrical synapses were found between five pairs of motoneurones. All these pairs were on the same side of the spinal cord and less than 70 um apart. Each neurone responded in a graded manner to either hyperpolarizing or depolarizing current injected into the other. 5. Since motoneurones are rhythmically active during swimming, both chemical and electrical synapses will add to the fast on-cycle excitation underlying spiking activity in other motoneurones. This may increase the reliability and local synchrony of synergistic motoneurone firing during locomotion.

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“…In the mollusc, Limax maximus, it has been demonstrated that exogenous ACh applied to the cerebral ganglia was able to trigger the feeding motor program, while antagonist substances blocked it (Ring et al, 1987). meret system, Heitler (1978) was unable to demonstrate plateau properties, but he did find that current injection into some motor neurons can increase the frequency of the swimmeret rhythm. By contrast, in other preparations, motor neurons are considered only as followers, without direct or indirect access to the CPG.…”

Section: And Barkermentioning

confidence: 99%

Fictive locomotion in the fourth thoracic ganglion of the crayfish, Procambarus clarkii

Chrachri

Clarac

1990

J. Neurosci.

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Bath application of muscarinic agonists induced rhythmic motor activity in an in vitro preparation of the thoracic nervous system of the crayfish, Procambarus clarkii. In 70% of the cases, the rhythm was organized into 1 of the 2 normal patterns: “backward” walking or “forward” walking. In the rest (30%), the ganglion produced either a series of bursts of impulses or no rhythm at all, just an increase in the tonic activity. When it was isolated from all ascending and descending afferents, the fourth thoracic ganglion was still able to generate rhythmic motor output during bath application of muscarinic agonists. In certain motor neurons, muscarinic agonists induced plateau potentials. Under these conditions, some of these motor neurons were able to change the period of the motor pattern, which might suggest that these motor neurons were part of the central pattern generator (CPG) for locomotion. In the presence of 5 x 10(-6)M TTX, the membrane potential of these motor neurons continued to oscillate with organized rhythmic membrane potential oscillations into 1 of the 2 patterns. Under these conditions, current injection into certain motor neurons demonstrated that they continued to affect the CPG. Two classes of walking leg interneurons have been found. First, there are those with a sustained membrane potential: injection of a steady depolarizing current into some of these interneurons induced rhythmic activity in all thoracic motor nerves, even in the absence of any pharmacological activation. Second, there are those with an oscillating membrane potential: these seemed to enable silent motor neurons to be involved in an ongoing rhythm.

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Coupled motoneurones are part of the crayfish swimmeret central oscillator

Cited by 84 publications

References 6 publications

Pattern-Generating Role for Motoneurons in a Rhythmically Active Neuronal Network

Pattern-Generating Role for Motoneurons in a Rhythmically Active Neuronal Network

Cholinergic and electrical synapses between synergistic spinal motoneurones in the Xenopus laevis embryo.

Fictive locomotion in the fourth thoracic ganglion of the crayfish, Procambarus clarkii

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