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P S Dickinson

Publications and source records attributed to P S Dickinson.

15 recordsLinked to original sources
PubMed2001

Long-term maintenance of channel distribution in a central pattern generator neuron by neuromodulatory inputs revealed by decentralization in organ culture.

Organotypic cultures of the lobster (Homarus gammarus) stomatogastric nervous system (STNS) were used to assess changes in membrane properties of neurons of the pyloric motor pattern-generating network in the long-term absence of neuromodulatory inputs to the stomatogastric ganglion (STG). Specifically, we investigated decentralization-induced changes in the distribution and density of the transient outward current, I(A), which is encoded within the STG by the shal gene and plays an important role in shaping rhythmic bursting of pyloric neurons. Using an antibody against lobster shal K(+) channels, we found shal immunoreactivity in the membranes of neuritic processes, but not somata, of STG neurons in 5 d cultured STNS with intact modulatory inputs. However, in 5 d decentralized STG, shal immunoreactivity was still seen in primary neurites but was likewise present in a subset of STG somata. Among the neurons displaying this altered shal localization was the pyloric dilator (PD) neuron, which remained rhythmically active in 5 d decentralized STG. Two-electrode voltage clamp was used to compare I(A) in synaptically isolated PD neurons in long-term decentralized STG and nondecentralized controls. Although the voltage dependence and kinetics of I(A) changed little with decentralization, the maximal conductance of I(A) in PD neurons increased by 43.4%. This increase was consistent with the decentralization-induced increase in shal protein expression, indicating an alteration in the density and distribution of functional A-channels. Our results suggest that, in addition to the short-term regulation of network function, modulatory inputs may also play a role, either directly or indirectly, in controlling channel number and distribution, thereby maintaining the biophysical character of neuronal targets on a long-term basis.

Animals↗
PubMed2001

RCPH modulation of a multi-oscillator network: effects on the pyloric network of the spiny lobster.

The neuropeptide red pigment concentrating hormone (RPCH), which we have previously shown to activate the cardiac sac motor pattern and lead to a conjoint gastric mill-cardiac sac pattern in the spiny lobster Panulirus, also activates and modulates the pyloric pattern. Like the activity of gastric mill neurons in RPCH, the pattern of activity in the pyloric neurons is considerably more complex than that seen in control saline. This reflects the influence of the cardiac sac motor pattern, and particularly the upstream inferior ventricular (IV) neurons, on many of the pyloric neurons. RPCH intensifies this interaction by increasing the strength of the synaptic connections between the IV neurons and their targets in the stomatogastric ganglion. At the same time, RPCH enhances postinhibitory rebound in the lateral pyloric (LP) neuron. Taken together, these factors largely explain the complex pyloric pattern recorded in RPCH in Panulirus.

Animals↗
PubMed2000

Different extrinsic trophic factors regulate neurite outgrowth and synapse formation between identified Lymnaea neurons.

The requirement for trophic factors in neurite outgrowth is well established, though their role in synapse formation is yet to be determined. Moreover, the issue of whether the trophic factors mediating neurite outgrowth are also responsible for synapse specification has not yet been resolved. To test whether trophic factors mediating neurite outgrowth and synapse formation between identified neurons are conserved in two molluscan species and whether these developmental processes are differentially regulated by different trophic factors, we used soma-soma and neurite-neurite synapses between identified Lymnaea neurons. We demonstrate here that the trophic factors present in Aplysia hemolymph, although sufficient to induce neurite outgrowth from Lymnaea neurons, do not promote specific synapse formation between excitatory partners. Specifically, the identified presynaptic neuron visceral dorsal 4 (VD4) and postsynaptic neuron left pedal dorsal 1 (LPeD1) were either paired in a soma-soma configuration or plated individually to allow neuritic contacts. Cells were cultured in either Lymnaea brain-conditioned medium (CM) or on poly-L-lysine dishes that were pretreated with Aplysia hemolymph (ApHM), but contained only Lymnaea defined medium (DM; does not promote neurite outgrowth). In ApHM-coated dishes containing DM, Lymnaea neurons exhibited extensive neurite outgrowth, but appropriate excitatory synapses failed to develop between the cells. Instead, inappropriate reciprocal inhibitory synapses formed between VD4 and LPeD1. Similar inappropriate inhibitory synapses were observed in Aplysia hemolymph-pretreated dishes that contained dialyzed Aplysia hemolymph. These inhibitory synapses were novel and inappropriate, because they do not exist in vivo. A receptor tyrosine kinase inhibitor (Lavendustin A) blocked neurite outgrowth induced by both Lymnaea CM and ApHM. However, it did not affect inappropriate inhibitory synapse formation between the neurons. These data demonstrate that neurite outgrowth but not inappropriate inhibitory synapse formation involves receptor tyrosine kinases. Together, our data provide direct evidence that trophic factors required for neurite outgrowth are conserved among two different molluscan species, and that neurite extension and synapse specification between excitatory partners are likely mediated by different trophic factors.

Animals↗
PubMed1997

Neurotransmitter interactions in the stomatogastric system of the spiny lobster: one peptide alters the response of a central pattern generator to a second peptide.

Two of the peptides found in the stomatogastric nervous system of the spiny lobster, Panulirus interruptus, interacted to modulate the activity of the cardiac sac motor pattern. In the isolated stomatogastric ganglion, red-pigment-concentrating hormone (RPCH), but not proctolin, activated the bursting activity in the inferior ventricular (IV) neurons that drives the cardiac sac pattern. The cardiac sac pattern normally ceased within 15 min after the end of RPCH superfusion. However, when proctolin was applied within a few minutes of that time, it was likewise able to induce cardiac sac activity. Similarly, proctolin applied together with subthreshold RPCH induced cardiac sac bursting. The amplitude of the excitatory postsynaptic potentials from the IV neurons to the cardiac sac dilator neuron CD2 (1 of the 2 major motor neurons in the cardiac sac system) was potentiated in the presence of both proctolin and RPCH. The potentiation in RPCH was much greater than in proctolin alone. However, the potentiation in proctolin after RPCH was equivalent to that recorded in RPCH alone. Although we do not yet understand the mechanisms for these interactions of the two modulators, this study provides an example of one factor that can determine the "state" of the system that is critical in determining the effect of a modulator that is "state dependent," and it provides evidence for yet another level of flexibility in the motor output of this system.

Animals↗
PubMed1995

Interactions among neural networks for behavior.

In recent years, as our understanding of the pattern-generating networks responsible for a variety of behaviors has increased, the interactions of multiple neural networks have been examined in a number of systems. These studies have shown that functionally related pattern generators can interact extensively, and that the extent to which two or more of these networks interact is not fixed, but can be altered by neuromodulators. Furthermore, a number of studies have begun to elucidate the mechanisms responsible for those interactions. In the crustacean stomatogastric system, for example, neurons can switch between different pattern generators, and whole networks can fuse into single patterns. In addition, several networks can be dismantled, and their components used to generate a new network. The mechanisms responsible for these changes are the same as those involved in other circuit re-configurations, namely alterations of both intrinsic membrane properties of component neurons and alterations in the strength of synapses within the networks.

Animals↗
PubMed1993

The neuropeptide red pigment concentrating hormone affects rhythmic pattern generation at multiple sites.

1. The cardiac sac network, which controls the rhythmic contractions of the cardiac sac in the foregut of crustaceans, is distributed throughout the stomatogastric nervous system, including the oesophageal ganglion (OG), the commissural ganglia (CGs), and the stomatogastric ganglion (STG). A red pigment-concentrating hormone (RPCH)-like peptide is likewise widely distributed. 2. The effects that bath application of the neuropeptide RPCH to the different ganglia has on the cardiac sac pattern were studied. 3. RPCH applied to the STG, the OG, or the CGs elicited bursting activity in all the known components of the cardiac sac pattern, including the two motor neurons, cardiac sac dilators 1 and 2 (CD1 and CD2), and the inferior ventricular nerve (ivn) fibers. 4. A cardiac sac pattern was also elicited when RPCH was applied to either the STG, the OG, or the CGs after synapses in that ganglion had been blocked by low Ca2+ saline containing 20 mM Co2+. 5. These data suggest that the ivn fibers are sensitive to RPCH and respond to it by generating bursting activity at or near their terminals in all four ganglia. 6. Application of RPCH to either the STG or the OG also caused an increase in the amplitude of the postsynaptic potential (PSP) from the ivn fibers to both CD1 and CD2. The increase was largest in the ganglion to which the RPCH was applied. 7. Repeated stimulation of the ivn, mimicking the bursts that occur during cardiac sac activity, also caused an increase in PSP amplitude, and so facilitation resulting from activation of ivn bursting could account for a portion of the increased amplitude seen in RPCH.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Neuropeptide fusion of two motor-pattern generator circuits.

Animals make many different movements as circumstances dictate. These movements often involve the coordination of several neural networks, the output of which can be changed by modulatory substances. Here we report that the neuropeptide red pigment concentrating hormone modulates the interactions between two rhythmic pattern-generating networks in the lobster stomatogastric nervous system. Red pigment concentrating hormone markedly enhances the amplitude of synaptic interactions between elements of two pattern-generating networks--the cardiac sac and the gastric mill. Consequently, two networks operating under some circumstances virtually independently can be fused into one functional unit operating differently from either of the two original networks. These results show how a neuropeptide can alter the functional configuration of a neural network so that widely disparate outputs can be produced by the same neurons.

Animals↗
PubMed1989

Peptidergic modulation of a multioscillator system in the lobster. I. Activation of the cardiac sac motor pattern by the neuropeptides proctolin and red pigment-concentrating hormone.

1. The cardiac sac motor pattern consists of slow and irregular impulse bursts in the motor neurons [cardiac sac dilator 1 and 2 (CD1 and CD2)] that innervate the dilator muscles of the cardiac sac region of the crustacean foregut. 2. The effects of the peptides, proctolin and red pigment-concentrating hormone (RPCH), on the cardiac sac motor patterns produced by in vitro preparations of the combined stomatogastric nervous system [the stomatogastric ganglion (STG), the paired commissural ganglia (CGs), and the oesophageal ganglion (OG)] were studied. 3. Bath applications of either RPCH or proctolin activated the cardiac sac motor pattern when this motor pattern was not already active and increased the frequency of the cardiac sac motor pattern in slowly active preparations. 4. The somata of CD1 and CD2 are located in the esophageal and stomatogastric ganglia, respectively. Both neurons project to all four of the ganglia of the stomatogastric nervous system. RPCH elicited cardiac sac motor patterns when applied to any region of the stomatogastric nervous system, suggesting a distributed pattern generating network with multiple sites of modulation. 5. The anterior median (AM) neuron innervates the constrictor muscles of the cardiac sac. The AM usually functions as a part of the gastric mill pattern generator. However, when the cardiac sac is activated by RPCH applied to the stomatogastric ganglion, the AM neuron becomes active in antiphase with the cardiac sac dilator bursts. This converts the cardiac sac motor pattern from a one-phase rhythm to a two-phase rhythm. 6. These data show that a neuropeptide can cause a neuronal element to switch from being solely a component of one neuronal circuit to functioning in a second one as well. This example shows that peptidergic "reconfiguration" of neuronal networks can produce substantial changes in the behavior of associated neurons.

Action Potentials↗
PubMed1988

The pneumostome rhythm in slugs: a response to dehydration controlled by hemolymph osmolality and peptide hormones.

1. One response of the terrestrial slug, Limax maximus to dehydration is the initiation and modulation of the pneumostome rhythm. When a slug has lost 15-20% of its initial body weight by evaporation, the frequency of pheumostome closures, which is less than 0.5 closures/min in fully hydrated slugs, begins to increase. 2. The frequency increases with further dehydration, but the average duration of each closure remains constant. Thus, the proportion of time during which the pneumostome is closed increases. Simultaneously, the area of the pneumostome opening decreases. 3. This behavior appears to be controlled in part by both the osmolality of the slug's hemolymph and by a peptide closely related to arginine vasotocin (AVT) and arginine vasopressin (AVP). Injecting intact slugs with mannitol, which increases the osmolality of the hemolymph, or with AVT or AVP, can initiate the pneumostome rhythm. 4. Mannitol injections, however, do not provoke the decrease in the area of the pneumostome opening which is induced by natural dehydration or by AVT or AVP injection. This suggests that at least two systems may be involved in the overall control of the pneumostome.

Animals↗
PubMed1988

Control by an identified modulatory neuron of the sequential expression of plateau properties of, and synaptic inputs to, a neuron in a central pattern generator.

Recordings from the lateral gastric (LG) neuron, which forms part of the gastric mill central pattern generator in the red lobster, Palinurus vulgaris, indicate that regenerative membrane properties (plateau properties) and synaptic inputs interact sequentially rather than simultaneously to determine its discharge pattern. LG thus presents a composite discharge, consisting of 2 separate segments of firing and one silent period. The first firing segment depends on regenerative membrane properties; this is the endogenous component, or segment, of LG's discharge. The second firing segment is the result of extrinsic synaptic input, forming the synaptic component of LG's discharge. The relative importance of these 2 components can vary, and thus LG's discharge ranges from one in which LG fires only as a result of its endogenous component to one in which its endogenous component is entirely absent and only the synaptic component underlies action potentials. Activity in an identified modulatory neuron suppresses the endogenous segment and enhances the synaptic segment of LG's discharge. This long-lasting effect in turn changes phase relationships within the gastric mill network and provides mechanisms for producing flexibility in the gastric pattern generator and for ensuring that a specific motor output is generated by a flexible neural network.

Action Potentials↗
PubMed1983

Control of a central pattern generator by an identified modulatory interneurone in crustacea. I. Modulation of the pyloric motor output.

In the lobsters Fasus lalandii and Palinurus vulgaris, the rhythmical activity of the pyloric pattern generator of the stomatogastric nervous system is strongly modified by the firing of a single identified interneurone, whose activity we have recorded from the cell body, in vitro. The cell body of this interneurone, the anterior pyloric modulator (APM), is located in the oesophageal ganglion and sends two axons to the stomatogastric ganglion via the inferior oesophageal nerves, the commissural ganglia, the superior oesophageal nerves and the stomatogastric nerve. Firing of neurone APM modifies the activity of all the neurones of the pyloric network, including pacemaker and follower neurones. Its effects are both quantitative (increase in the frequency of the rhythm and in the frequency of spikes within cell bursts) and qualitative (modifications in relative efficacies of the synaptic relationships within the pyloric network, which in turn lead to changes in the phase relationships between the discharges of the neurones). The effects on pyloric activity induced by firing of neurone APM are established slowly (one or two seconds) and are of long duration (ten times the duration of APM's discharge). These modifications most probably involve muscarinic cholinergic receptors. APM's influences on the activity of pyloric neurones appear to be characteristic of a neuromodulatory process and are such that they may be of behavioural significance in the intact animal.

Animals↗
PubMed1983

Control of a central pattern generator by an identified modulatory interneurone in crustacea. II. Induction and modification of plateau properties in pyloric neurones.

In the isolated stomatogastric nervous system of the lobster Fasus lalandii, the strong modifications of the pyloric motor pattern induced by firing of the single anterior pyloric modulator neurone (APM) are due primarily to modulation by APM activity of the regenerative membrane properties which are responsible for the 'burstiness' of all the pyloric neurones and particularly of the non-pacemaker neurones (constrictor motoneurones). This modulation has been studied under experimental conditions where the main extrinsic influences usually received by the pyloric constrictor neurones (intra-network synaptic interactions, activity of pacemaker neurones, and phasic central inputs from two premotor centres) are minimal. Under these conditions a brief discharge of neurone APM induces long plateaus of firing in all of the pyloric neurones. The non-pacemaker neurones of the pyloric network are not simply passive follower neurones, but can produce regenerative depolarizations (plateau potentials) during which the neurones fire spikes. The ability of the pyloric constrictor neurones to produce plateau potentials (plateau properties) contributes greatly to the generation of the rhythmical pyloric motor pattern. When these neurones spontaneously express their plateau properties, firing of neurone APM amplifies these properties. When most of the central inputs usually received by the pyloric constrictor neurones are experimentally suppressed, these neurones can no longer produce plateau potentials. In such conditions, firing of the single modulatory neurone APM can reinduce plateau properties of the pyloric constrictor neurones. In addition, firing in APM neurone slows down the active repolarization phase which terminates the plateau potentials of pyloric constrictor neurones. This effect is long-lasting and voltage-dependent. Modulation by APM of the plateau properties of the pyloric neurones also changes the sensitivity of these neurones to synaptic inputs. This effect can explain the strong modifications that an APM discharge exerts on a current pyloric motor pattern. Moreover, it might render the motoneurones of the pyloric pattern generator more sensitive to inputs from a command oscillator, and contribute to switching on the pyloric motor pattern.

Animals↗
PubMed1981

Modulatory effects of a single neurons on the activity of the pyloric pattern generator in Crustacea.

The firing of a single neuron (named anterior pyloric modulator: APM) of the esophageal ganglion considerably modifies the pyloric rhythm of the rock lobster. These modifications, characterized by a long delay to onset and a long duration, include increased frequency and amplitude of oscillations of the motor neurons, changes in the efficacy of certain synapses within the network, and voltage-dependent modifications of membrane properties of some motor neurons. APM thus seems to be a true modulatory neuron. The APM-provoked changes resemble changes seen in the whole animal, making this a suitable system for an analysis of modulation on several levels.

Animals↗