PubMed Health⌕ Search

Biomedical subjects

M Moulins

Publications and source records attributed to M Moulins.

At least 19 recordsLinked to original sources
PubMed1997

Conditional dendritic oscillators in a lobster mechanoreceptor neurone.

1. Intra- and extracellular recordings were made from in vitro preparations of the lobster (Homarus gammarus) stomatogastric nervous system to study the nature and origin of pacemaker-like activity in a primary mechanoreceptor neurone, the anterior gastric receptor (AGR), whose two bilateral stretch-sensitive dendrites ramify in the tendon of powerstroke muscle GM1 of the gastric mill system. 2. Although the AGR is known to be autoactive, we report here that in 20% of our preparations, rather than autogenic tonic discharge, the receptor fired spontaneously in discrete bursts comprising three to ten action potentials and repeating at cycle frequencies of 0.5-2.5 Hz in the absence of mechanical stimulation. Intrasomatic recordings revealed that such rhythmic bursting was driven by slow oscillations in membrane potential, the frequency of which was voltage sensitive and dependent upon the level of stretch applied to the receptor terminals of the AGR. 3. Autoactive bursting of the AGR originated from an endogenous oscillatory mechanism in the sensory dendrites themselves, since (i) during both steady, repetitive firing and bursting, somatic and axonal impulses were always preceded 1:1 by dendritic action potentials, (ii) hyperpolarizing the AGR cell body to block triggering of axonal impulses revealed attenuated somatic spikes that continued to originate from the two peripheral dendrites, (iii) the timing of burst firing could be phase reset by brief electrical stimulation of either dendrite, and (iv) spontaneous bursting continued to be expressed by an AGR dendrite after physical isolation from the GM1 muscle and the stomatogastric nervous system. 4. Although a given AGR in vitro could switch spontaneously from dendritic bursting to tonic firing and vice versa, exogenous application of micromolar (or less) concentrations of the neuropeptide F1 (TNRNFLRFamide) to the dendritic membrane could rapidly and reversibly switch the receptor firing pattern from repetitive firing to the bursting mode. Exposure of the somatic and axonal membrane of the AGR to F1 was without effect, as were applications of other neuroactive substances such as serotonin, octopamine and proctolin. 5. We conclude that, as for many oscillatory neurones of the central nervous system, the intrinsic activity pattern of this peripheral sensory neurone may be dynamically conferred by extrinsic modulatory influences, presumably according to computational demands. Moreover, the ability of the AGR to behave as an endogenous burster imparts considerable integrative complexity since, in this activity mode, sensory coding not only occurs through the frequency modulation of on-going dendritic bursts but also via changes in the duration of individual bursts and their inherent spike frequencies.

Animals↗
PubMed1997

Sensory-induced plasticity of motor pattern selection in the lobster stomatogastric nervous system.

In a previous study, a bilateral sensory input pathway to the crustacean stomatogastric nervous system was reported to induce the functional switching of an identified motor neuron (VD) from one rhythm generating neural network (the pyloric circuit) to another (the cardiac sac network). In the present in vitro study on the spiny lobster, Palinurus vulgaris, we have shown that under certain conditions, repetitive trains of phasic stimulation (1 s, 40 Hz) of one of these sensory nerves elicits either an increase or a decrease in efficacy of the VD switching response. In preparations showing no previous sign either of increase or decrease in VD switching, either response can be induced by prior conditioning stimulation. The increasing effect can be induced by unpaired conditioning stimulation of the contralateral sensory nerve. Conversely, the decrease in switching efficacy is obtained by pairing stimulation of the sensory-motor pathway with that applied to its contralateral partner. Both the experimentally induced increase and decrease in VD switching are long-lasting, remaining observable for at least 20 min and in some cases up to 3 h after the original conditioning procedure. Our results suggest that this system provides a suitable 'simple' model for the analysis of experience-related plasticity of the switching of a neuron from one network to another.

Animals↗
PubMed1995

Structural and functional characterization of a muscle tendon proprioceptor in lobster.

A morphological and electrophysiological study was made on a unique primary mechanosensory neuron, the anterior gastric receptor (AGR), previously shown to arise from power-stroke muscle gm1 of the gastric mill system in the lobster foregut. Ultrastructural analysis of horseradish peroxidase injected AGR demonstrated that its peripheral dendrites do not ramify in muscle but are confined strictly to the connective tissue/epidermal interface in the tendon of gm1. These terminals are rich in mitochondria and at their very endings are free of glial cell wrapping, suggesting that they are the site at which mechano-transduction occurs. Extracellular axonal recordings from an in vitro neuromuscular preparation consisting of the gm1 muscle still attached to the stomatogastric nervous system, revealed that AGR is activated by passive stretch of gm1. The response to ramp stimuli displays dynamic and static components, both of which increase with the amplitude of applied stretch, while the dynamic component is also velocity sensitive. AGR is also activated by muscle contraction here elicited either by application of exogenous acetylcholine, the excitatory neurotransmitter for gm1, or by electrical stimulation of the motoneurons (GM) themselves. Consistent with a receptor lying in-series with its muscle, therefore, the effective stimulus of AGR in vivo is probably an increase in tension exerted on the tendon during active muscle contraction. In neuromuscular preparations including the bilateral commissural ganglia, stretching gm1 reflexly activates GM motoneurons at low stimulus strengths but leads to an inactivation of GM motoneurons at high stimulus strengths. This is consistent with earlier findings that both responses can be elicited by direct electrical stimulation of AGR. The functional implications of AGR's anatomical relationship with muscle gm1, the receptor's response properties, and its central effects on motor output to gm1 are discussed. Comparison is also drawn between this first reported example of a true tendon receptor in invertebrates and muscle receptors of vertebrates.

Animals↗
PubMed1995

Modulation and dynamic specification of motor rythm-generating circuits in crustacea.

The operation of central pattern generators (CPGs), oscillatory neural circuits responsible for rhythmic motor behavior, is now known to depend both on the synaptic interactions between constituent neurons and their intrinsic membrane properties (oscillatory, plateauing, etc). Moreover, these synaptic and cellular properties are not invariant, but are subject to a wide range of neuromodulatory influences that, by modifying the bioelectrical character of individual neurons and/or the strength of their synapses, are able to adapt the output of a given CPG circuit to the changing needs of the animal. Despite this ability to produce different functional configurations, however, the assumption remains of a CPG as a predefined assemblage of interconnected neurons dedicated to a particular behavior and functionally distinguishable from other circuits responsible for other tasks. However, our recent studies on the stomatogastric nervous system (STNS) of crustacea have begun to question this concept of the CPG as a discrete and identifiable entity within the central nervous system. Here we review evidence showing that under neuromodulatory instruction, individual neurons can participate in different oscillatory motor circuits and hence more than one rhythmic behaviour, and even more profoundly, preexisting networks can be dismantled to specify dynamically a new circuit for an entirely different behaviour. This de novo network construction is achieved again by neuromodulatory-induced alterations in the oscillatory and synaptic properties of individual target neurons. On this basis, therefore, a functional CPG network must be seen in a more dynamic context than previously thought since it may exist only in a particular behavioural situation dictated by modulatory influences.

Animals↗
PubMed1994

Dynamic construction of a neural network from multiple pattern generators in the lobster stomatogastric nervous system.

In the stomatogastric nervous system (STNS) of the lobster Homarus gammarus, the rhythmic discharge of a pair of identified modulatory neurons (PS cells) is able to construct de novo a functional network from neurons otherwise belonging to other functional networks. The PS interneurons are electrically coupled and possess endogenous oscillatory properties that can be activated synaptically by stimulation of an identified sensory pathway. PS neurons themselves project synaptically onto the three major neural networks (esophageal, gastric mill, and pyloric) of the STNS. When a PS is rhythmically active in vitro, either spontaneously (rarely) or in response to direct stimulation, it dramatically restructures the otherwise independent activity patterns of all three target networks. This functional reconfiguration elicited by a single cell does not rely on changes in neuronal allegiance to pre-existing circuits, or on a simple merger of these different circuits. Rather, PS is responsible for the creation of an entirely new motor rhythm in that, via its widespread synaptic connections, the interneuron is able to subjugate the ongoing activity of the three STNS circuits and selectively appropriate individual elements to its own intrinsic rhythm. In addition, PS excites motor neurons that innervate dilator muscles of a valve situated between the esophagus and the stomach. The reorganization of the regional foregut motor rhythms by the interneuron is therefore coordinated to the opening of this valve, which itself carries sensory receptors that have been found to activate bursting in PS. Our data suggest that the role of PS in massively restructuring stomatogastric output is to generate a unique motor pattern appropriate for swallowing-like behavior. In a wider context, moreover, the results demonstrate that a neural network may not exist as a predefined entity within the CNS, but may be dynamically assembled according to changing behavioral circumstances.

Animals↗
PubMed1994

Muscarinic modulation of a pattern-generating network: control of neuronal properties.

The aim of this article is to investigate the cellular mechanisms underlying cholinergic modulation of the pyloric network in the stomatogastric ganglion (STG) of the Cape lobster Jasus Ialandii. Bath application of the muscarinic agonists muscarine, oxotremorine, and pilocarpine on the STG activates a rhythmic pattern from a quiescent pyloric network. The mechanisms of this modulation were investigated on individual pyloric neurons isolated both from synaptic interactions within the network (by photoinactivation of most of the presynaptic neurons and pharmacological blockade of the remaining synapses) and from central inputs (by a sucrose block of the input nerve). All three muscarinic agonists activated bursting and plateau properties of all the neurons comprising the pyloric network. The activation was dose dependent, and was blocked by the muscarinic antagonists atropine, pirenzepine, and scopolamine. The oscillatory behavior triggered by the muscarinic stimulation was specific to each type of pyloric neuron. The isolated neuron AB had the shortest oscillation period and depolarizing phase. The constrictor neurons (LP, PY, IC) were the slowest oscillators, and only oscillated upon hyperpolarizing current injection. Under muscarinic modulation, the individual bursting activities of the isolated pyloric neurons were of the same type as their activities when isolated from the network but modulated by central inputs (Bal et al., 1988). The VD neuron is an exception since it was a rapid oscillator in the latter situation and became a slow oscillator when modulated by a single muscarinic agonist. To determine the relative importance of the muscarinic-dependent bursting properties of the individual pyloric neurons in the operation of the intact network, a progressive reconstruction of the synaptic circuitry was attempted. We found that under certain conditions of muscarinic modulation a new composite pacemaker could be created, composed of the electrically coupled VD, AB, and PD neurons. This can result in the generation of new pyloric patterns that were very sensitive to the membrane potential of individual network neurons. The data also confirmed that, in a rhythmic "pattern-generating network," the pacemaker role may not be definitely attributed to a given neuron but instead could be assigned to other neurons by modulation of their respective oscillatory capabilities.

Animals↗
PubMed1993

Tetrodotoxin-sensitive dendritic spiking and control of axonal firing in a lobster mechanoreceptor neurone.

1. A primary mechanosensory neurone, the anterior gastric receptor (AGR) associated with gastric mill muscle in the lobster foregut was examined in vitro with extra- and intra-cellular recording techniques to understand processes of dendritic integration and dendro-axonal communication. 2. AGR has a 'T'-shaped geometry; its two long (> 3 mm) primary dendrites project distally to spatially separate, stretch sensitive terminals and converge centrally onto a common apical neurite that leads to a bipolar soma and single axon. 3. The receptor's bilateral dendrites are independently capable of generating action potentials. These appear to be Na+ dependent since they are blocked by tetrodotoxin, but not by Co2+ or a lack of Ca2+ in the bath saline. 4. Both dendrites are autogenically active, although impulses in the dendrite with the higher intrinsic excitability may cross over and activate the trigger zone on the contralateral side. Moreover, spikes arising on either dendrite do not actively invade the soma, but are conveyed as decremented potentials to a third trigger zone on the initial axon segment. 5. Focal applications of TTX (tetrodotoxin) demonstrated the existence and allowed precise definition of a central membrane compartment of AGR that appears to lack in functional Na+ channels. This inexcitable region includes the soma, the apical neurite and the central branch point of the two dendrites. A failure to observe collision block of bilateral dendritic potentials as they traverse the neurite supported this conclusion. 6. Horseradish peroxidase injections and staining revealed two morphological features of the apical neurite that differed markedly from other regions of the cell. In addition to a relatively large diameter, the neurite's plasma membrane is heavily convoluted and coiled to form a lamellar transverse profile. This latter feature may itself contribute to membrane inexcitability while the former is consistent with an elevated space constant for electrotonic conduction. 7. It is concluded that the inhomogeneous distribution of membrane excitability in AGR enhances the integrative capability of the receptor's dendrites, permitting mechanical input at diverse loci to be encoded and processed prior to transformation into axonal discharge.

Action Potentials↗
PubMed1992

Humoral induction of pyloric rhythmic output in lobster stomatogastric ganglion: in vivo and in vitro studies.

In the lobster Jasus lalandii, 14 neurones of the stomatogastric ganglion (STG) are organized in a network that produces rhythmic pyloric outputs. In vitro experiments have shown that the STG neurones receive, via the stomatogastric nerve (stn), neuromodulatory inputs that influence the expression of the bursting properties of the neurones and the ability of the network to produce its rhythmic output. In contrast to these in vitro observations, in vivo transection of the stn does not abolish the pyloric rhythm. Rhythmic output can be recorded by electromyography immediately after stn transection and for up to 2 years afterwards. We have shown that, under these experimental conditions, the STG appears to be isolated from any neuronal input that might account for the maintenance of the rhythmic output. Experiments carried out in the 2 days after stn transection showed that an in vitro preparation of the isolated STG was unable to produce any rhythmic output, but blood serum added to the system could restore the pyloric output. These results suggest strongly that the pyloric network receives neural and humoral modulatory influences in parallel and that each type of influence alone is able to maintain the bursting capability of the pyloric neurones.

Animals↗
PubMed1991

A method for the determination of projection areas of GABA immunoreactive neurons in the invertebrate nervous system.

Axonal transport of metallic salts (nickel or cobalt chloride) has been widely used for the anatomical mapping of neural pathways. We show here that when nickel is introduced into GABAergic neurons it completely eliminates GABA immunolabelling. We have used this property to determine the axonal projections of GABAergic neurons in the stomatogastric system of Crustacea. For example, following nickel backfills from either cut axons or from terminals, GABA immunostaining labels only those GABA-immunoreactive neurons which had not been retrogradely labelled with nickel and hence did not project in the cut nerve or to the neuropile uptake site. By comparing such immunolabelled preparations with those not pretreated with nickel the projection patterns of all the GABA immunoreactive neurons in a given system can be revealed. This effect of nickel appears to be selective for GABA immunostaining, insofar as it does not interfere with the immunodetection of either the peptide proctolin or a FMRFamide-like peptide. This method may prove to be a useful tool for analyzing GABAergic neuronal pathways in the nervous systems of invertebrates.

Animals↗
PubMed1991

Combination of horseradish peroxidase and lucifer yellow staining for selective labeling of neurons at the electron microscopic level.

We have developed a new double labeling method for electron microscopy to characterize selectively two physiologically identified neurons on the same preparation. The stomatogastric nervous system of crustaceans was used to test the distinguishing staining characteristics of the two labels. Neurons were labeled on one side with horseradish peroxidase (HRP) and on the other side with Lucifer yellow (LY). After blue light irradiation of the tissue in the presence of diaminobendizine, the two labeled neurons could be easily observed and discriminated on the same section by the two different reaction products. This simple technique of double labeling is useful in experimental neuroanatomy for the detailed study of synaptic relationships.

Animals↗
PubMed1990

Identification of all GABA-immunoreactive neurons projecting to the lobster stomatogastric ganglion.

The stomatogastric ganglion of lobsters (Homarus or Jasus) contains a large number of gamma-aminobutyric acid-immunoreactive processes originating from ten fibres in the single input nerve, the stomatogastric nerve. The cell bodies and axonal pathways of these ten fibres have been identified using gamma-aminobutyric acid immunohistochemistry in combination with Lucifer Yellow staining (double labelling) and nickel chloride backfilling (selective gamma-aminobutyric acid immunoinhibition). It is shown that eight gamma-aminobutyric acid-immunoreactive neurons project to the stomatogastric ganglion: gamma-aminobutyric acid neurons 1 and 2, found posterior to the oesophageal ganglion, entering the stomatogastric nerve via the oesophageal nerve as well as sending an axonal branch into each superior oesophageal nerve; gamma-aminobutyric acid neurons 3 and 4, found anterior to the oesophageal ganglion, each sending an axonal branch into each inferior oesophageal nerve to reach the stomatogastric nerve via the commissural ganglion and the superior oesophageal nerve; and gamma-aminobutyric acid neurons 5 and 6, found in each commissural ganglion, projecting into the stomatogastric nerve via the inferior oesophageal nerve, the oesophageal ganglion and the oesophageal nerve. These gamma-aminobutyric acid-immunoreactive neurons were also characterized by electrophysiological methods coupled with Lucifer Yellow labelling, and their picrotoxin-sensitive effects on several stomatogastric ganglion neurons were demonstrated. The present results provide a firm basis for further studies concerning the physiological significance of one class of neurochemically-defined input neurons to stomatogastric ganglion networks.

Animals↗
PubMed1990

Sensory input induces long-lasting changes in the output of the lobster pyloric network.

1. A long-lasting restructuring of the pyloric neural network of the lobster stomatogastric nervous system (STS) by a multisynaptic sensory afferent is described. This restructuring can be obtained either by mechanical stimulation of the pyloric region of the stomach or by brief high-frequency electrical stimulation of a nerve that innervates this region, the lateral posterolateral nerve (lpln). Electron microscopy shows that this nerve contains several thousand very small fibers (approximately 0.3 microns diam), the activation of some subset of which is responsible for the effects of lpln stimulation. 2. These stimulation paradigms result in both short-duration changes in pyloric activity and modulatory effects long outlasting the stimulus end. The long-lasting changes include the cessation of rhythmic ventricular dilator (VD) and lateral pyloric (LP) neuron activity, and thus result in a reduced pyloric pattern in which only the pyloric dilator (PD), inferior cardiac (IC), anterior burster (AB), and pyloric (PY) neurons are active. 3. Tonic low-frequency lpln stimulation, alternatively, results in the VD neuron rhythmically firing long spike bursts with a cycle frequency much slower than that of the pyloric network while an otherwise complete pyloric pattern continues. In this new bursting pattern the VD neuron fires exclusively with another STS neural network, the cardiac sac (CS) network, and thus functionally "switches" from the pyloric to the CS network. This switch of the VD neuron from the pyloric to the CS network also occurs when the CS network is spontaneously active. 4. Our results thus demonstrate that sensory input can provoke a long-lasting modification of the functional configuration of a rhythmic neural network. They further extend the concept of flexibility in nervous systems by showing that individual neurons can belong to more than one neural network, "switching" from one to another in response to sensory input or spontaneous central nervous activity.

Animals↗
PubMed1990

Cellular and synaptic mechanisms responsible for a long-lasting restructuring of the lobster pyloric network.

1. In the lobster Palinurus vulgaris a sensory input in the lateral posterolateral nerve (lpln) of the stomatogastric nervous system (STS) is able to turn on the cardiac sac (CS) network and to induce dramatic long-lasting alterations in the output of the pyloric network. This long-lasting alteration of pyloric network output consists primarily of changes in the activity of the two neurons that innervate the muscles of the cardiopyloric valve of the stomach, with the dilator neuron (the ventricular dilator, VD) transferring from the pyloric network to the CS network and the constrictor neuron (the inferior cardiac, IC) shifting to fire earlier in the pyloric pattern. 2. The inferior ventricular (IV) neurons of the CS network make complex multiaction synaptic connections onto several pyloric neurons in a related species, Panulirus interruptus. We show that many of the short-term alterations in pyloric activity observed during CS network bursts in Palinurus are due to similar IV neuron synaptic connections. However, the long-lasting effects of lpln stimulation on pyloric output are not due to this synaptic input, because 1) direct activation of the IV neurons does not induce long-lasting changes in pyloric activity and 2) pharmacologic disconnection of this synaptic input does not abolish lpln stimulation's long-lasting effects. Lpln stimulation therefore activates two different neuronal inputs to the pyloric network. 3. The transfer of the VD neuron from the pyloric to the CS network is the result of the concerted actions of these two inputs. Lpln stimulation turns on the CS network, and the IV neurons of the CS network excite the VD neuron and ensure it fires with the CS network. The second neuronal input (that not involving known CS network neurons) abolishes in a long-lasting fashion the VD neuron regenerative (plateau) properties, and thus suppresses the ability of the VD neuron to participate in the pyloric rhythmic pattern between CS network bursts. 4. Experimental manipulation of VD neuron activity can both mimic and reverse the effects of lpln stimulation on the IC neuron. The changes in IC neuron activity are therefore not due to direct lpln-activated synaptic input onto the IC neuron, but instead are indirect "network" effects arising from the changes in VD neuron activity.

Animals↗
PubMed1990

Suppressive control of the crustacean pyloric network by a pair of identified interneurons. I. Modulation of the motor pattern.

A pair of identified neuromodulatory neurons, the pyloric suppressor (PS) neurons, can individually and strongly modify the activity of the pyloric network in the stomatogastric nervous system of the lobster Homarus gammarus. The PS neurons are identified by the location of their somata in the inferior ventricular nerve, their axonal projections, and their effects on pyloric network activity in vitro. Discharge of a PS neuron evokes large EPSPs in the pyloric dilator (PD) neurons and a long-lasting cessation of rhythmic activity in the neurons that control movements of the pyloric filter: PD, lateral pyloric (LP), and pyloric (PY). This cessation of rhythmic activity can outlast by several 10s of seconds a brief discharge of PS lasting only a few seconds. The different neurons of the pyloric filter do not exhibit the same sensitivity to the suppressive effects of PS, with the LP neuron being the most sensitive. Tonic discharge in PS induces graded alterations in the pyloric pattern, depending on its firing frequency. At low (less than 5 Hz) discharge frequencies, PS provokes changes in phase relationships and duration of bursting in pyloric neurons. A slight increase in PS frequency suppresses the rhythmic activity of some pyloric neurons, resulting in a switch from a triphasic to a biphasic pattern. At higher (greater than 10 Hz) PS firing frequencies, rhythmic activity in all the pyloric neurons, including the pacemakers (PD, anterior burster), is abolished, except in cells (ventricular dilator, inferior cardiac) controlling the pyloric valve. We conclude that a central pattern generator is not only subject to activating modulatory control, but may also be the target of suppressive inputs that are themselves able to provoke functional reconfigurations of the network.

Animals↗
PubMed1990

Suppressive control of the crustacean pyloric network by a pair of identified interneurons. II. Modulation of neuronal properties.

In the lobster Homarus, the 2 identified PS neurons have a strong suppressive modulatory effect on the activity of the pyloric network in the STG (Cazalets et al., 1990). In the present paper, we consider the effects of PS on individual pyloric neurons isolated from their partners in the network by cell photoinactivation and synaptic blockade. Three types of PS action are described: (1) a transient, EPSP-mediated depolarization of the PD, VD, and AB neurons; (2) a long-lasting hyperpolarization concomitant with a loss of oscillatory properties in the PD and LP neurons; (3) a long-lasting depolarization without modification of oscillatory properties in the PY and IC neurons. The various effects of PS on isolated pyloric cells were consistent with the overall effects of PS on the intact pyloric network.

Animals↗
PubMed1989

Switching of a neuron from one network to another by sensory-induced changes in membrane properties.

A neuron that is an integral member of the pyloric neural network of the lobster stomatogastric nervous system leaves this network and instead fires exclusively with another stomatogastric nervous system network, the cardiac sac network, whenever the cardiac sac network is active. This switch is associated with the neuron losing, in a long-lasting fashion, regenerative oscillatory membrane properties that underlie its participation in the pyloric network. Functional membership of neurons in central networks is thus not fixed, and long-lasting neuromodulatory influences, controlled at least in part by sensory inputs, can switch neurons from one network to another.

Action Potentials↗