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Eve Marder

Publications and source records attributed to Eve Marder.

At least 19 recordsLinked to original sources
PubMed2007

Neuronal morphology and neuropil structure in the stomatogastric ganglion of the lobster, Homarus americanus.

The stomatogastric nervous system (STNS) has long been used as a model system for the study of central pattern generation, neuromodulation, and network dynamics. Anatomical studies of the crustacean stomatogastric ganglion (STG) in different species have mostly been restricted to subsets of neurons and/or general structural features. For the first time, we describe the morphology of all STG neurons belonging to the two circuits that produce the well-described pyloric and gastric rhythms in the lobster, Homarus americanus. Somata sit on the dorsal and lateral surface of the STG and send a single primary neurite into the core of the neuropil, which is mostly made up of larger lower order branches. The perimeter of the neuropil consists mostly of finer higher order branches. Immunohistochemical labeling for synaptic proteins is associated with the small diameter branches. Somata positions are not constant but show preferred locations across individuals. The number of copies is constant for all neuron types except the PY and GM neurons (PY neuron number ranges from 3 to 7, and GM neuron number ranges from 6 to 9). Branch structure is largely nondichotomous, and branches can deviate substantially from cylindrical shape. Diameter changes at branch points can be as large as 20-fold. Clearly, the morphology of a specific neuron type can be quite variable from animal to animal.

Animals↗
PubMed2007

Understanding circuit dynamics using the stomatogastric nervous system of lobsters and crabs.

Studies of the stomatogastric nervous systems of lobsters and crabs have led to numerous insights into the cellular and circuit mechanisms that generate rhythmic motor patterns. The small number of easily identifiable neurons allowed the establishment of connectivity diagrams among the neurons of the stomatogastric ganglion. We now know that (a) neuromodulatory substances reconfigure circuit dynamics by altering synaptic strength and voltage-dependent conductances and (b) individual neurons can switch among different functional circuits. Computational and experimental studies of single-neuron and network homeostatic regulation have provided insight into compensatory mechanisms that can underlie stable network performance. Many of the observations first made using the stomatogastric nervous system can be generalized to other invertebrate and vertebrate circuits.

Animals↗
PubMed2006

Neuromodulation of spike-timing precision in sensory neurons.

The neuropeptide allatostatin decreases the spike rate in response to time-varying stretches of two different crustacean mechanoreceptors, the gastropyloric receptor 2 in the crab Cancer borealis and the coxobasal chordotonal organ (CBCTO) in the crab Carcinus maenas. In each system, the decrease in firing rate is accompanied by an increase in the timing precision of spikes triggered by discrete temporal features in the stimulus. This was quantified by calculating the standard deviation or "jitter" in the times of individual identified spikes elicited in response to repeated presentations of the stimulus. Conversely, serotonin increases the firing rate but decreases the timing precision of the CBCTO response. Intracellular recordings from the afferents of this receptor demonstrate that allatostatin increases the conductance of the neurons, consistent with its inhibitory action on spike rate, whereas serotonin decreases the overall membrane conductance. We conclude that spike-timing precision of mechanoreceptor afferents in response to dynamic stimulation can be altered by neuromodulators acting directly on the afferent neurons.

Afferent Pathways↗
PubMed2006

Structure and visualization of high-dimensional conductance spaces.

Neurons, and realistic models of neurons, typically express several different types of voltage-gated conductances. These conductances are subject to continual regulation. Therefore it is essential to understand how changes in the conductances of a neuron affect its intrinsic properties, such as burst period or delay to firing after inhibition of a particular duration and magnitude. Even in model neurons, it can be difficult to visualize how the intrinsic properties vary as a function of their underlying maximal conductances. We used a technique, called clutter-based dimension reordering (CBDR), which enabled us to visualize intrinsic properties in high-dimensional conductance spaces. We applied CBDR to a family of models with eight different types of voltage- and calcium-dependent channels. CBDR yields images that reveal structure in the underlying conductance space. CBDR can also be used to visualize the results of other types of analysis. As examples, we use CBDR to visualize the results of a connected-components analysis, and to visually evaluate the results of a separating-hyperplane (i.e., linear classifier) analysis. We believe that CBDR will be a useful tool for visualizing the conductance spaces of neuronal models in many systems.

Algorithms↗
PubMed2006

Mass spectrometric characterization and physiological actions of GAHKNYLRFamide, a novel FMRFamide-like peptide from crabs of the genus Cancer.

The stomatogastric ganglion (STG) and the cardiac ganglion (CG) of decapod crustaceans are modulated by neuroactive substances released locally and by circulating hormones released from neuroendocrine structures including the pericardial organs (POs). Using nanoscale liquid chromatography electrospray ionization quadrupole-time-of-flight tandem mass spectrometry and direct tissue matrix-assisted laser desorption/ionization Fourier transform mass spectrometry we have identified and sequenced a novel neuropeptide, GAHKNYLRFamide (previously misassigned as KHKNYLRFamide in a study that did not employ peptide derivatization), from the POs and/or the stomatogastric nervous system (STNS) of the crabs, Cancer borealis, Cancer productus and Cancer magister. In C. borealis, exogenous application of GAHKNYLRFamide increased the burst frequency and number of spikes per burst of the isolated CG and re-initiated bursting activity in non-bursting ganglia, effects also elicited by the FMRFamide-like peptides (FLPs) SDRNFLRFamide and TNRNFLRFamide. In the intact STNS (which contains the STG), exogenous application of GAHKNYLRFamide increased the frequency of the pyloric rhythm and activated the gastric mill rhythm, effects also similar to those elicited by SDRNFLRFamide and TNRNFLRFamide. FLP-like immunoreactivity in the POs and the STNS was abolished by pre-adsorption with the synthetic GAHKNYLRFamide. Different members of the FLP family exhibited differential degradation in the presence of extracellular peptidases. Taken collectively, the amino acid sequence of GAHKNYLRFamide, the blocking of FLP-like immunostaining, and its physiological effects on the CG and STNS suggest that this peptide is a novel member of the FLP superfamily.

Action Potentials↗
PubMed2006

Central pattern generating neurons simultaneously express fast and slow rhythmic activities in the stomatogastric ganglion.

Neuronal firing patterns can contain different temporal information. It has long been known that the fast pyloric and the slower gastric motor patterns in the stomatogastric ganglion of decapod crustaceans interact. However, the bidirectional influences between the pyloric rhythm and the gastric mill rhythm have not been quantified in detail from preparations that spontaneously express both patterns in vitro. We found regular and stable spontaneous gastric and pyloric activity in 71% of preparations of the isolated stomatogastric nervous system of the lobster, Homarus americanus. The gastric [cycle period: 10.96 +/- 2.67 (SD) s] and pyloric (cycle period: 1.35 +/- 0.18 s) patterns showed bidirectional interactions and coordination. Gastric neuron firing showed preferred phases within the reference frame of the pyloric cycle. The relative timing and burst parameters of the pyloric neurons systematically changed within the reference frame of the gastric cycle. The gastric rhythm showed a tendency to run at cycle periods that were integer multiples of the pyloric periods, but coupling and coordination between the two rhythms were variable. We used power spectra to quantify the gastric and pyloric contributions to the firing pattern of each individual neuron. This provided us with a way to analyze the firing pattern of each gastric and pyloric neuron type individually without reference to either gastric or pyloric phase. Possible functional consequences of these network interactions for motor output are discussed.

Action Potentials↗
PubMed2006

Variable channel expression in identified single and electrically coupled neurons in different animals.

It is often assumed that all neurons of the same cell type have identical intrinsic properties, both within an animal and between animals. We exploited the large size and small number of unambiguously identifiable neurons in the crab stomatogastric ganglion to test this assumption at the level of channel mRNA expression and membrane currents (measured in voltage-clamp experiments). In lateral pyloric (LP) neurons, we saw strong correlations between measured current and the abundance of Shal and BK-KCa mRNAs (encoding the Shal-family voltage-gated potassium channel and large-conductance calcium-activated potassium channel, respectively). We also saw two- to fourfold interanimal variability for three potassium currents and their mRNA expression. Measurements of channel expression in the two electrically coupled pyloric dilator (PD) neurons showed significant interanimal variability, but copy numbers for IH (encoding the hyperpolarization-activated, inward-current channel) and Shal mRNA in the two PD neurons from the same crab were similar, suggesting that the regulation of some currents may be shared in electrically coupled neurons.

Action Potentials↗
PubMed2006

Variability, compensation and homeostasis in neuron and network function.

Neurons in most animals live a very long time relative to the half-lives of all of the proteins that govern excitability and synaptic transmission. Consequently, homeostatic mechanisms are necessary to ensure stable neuronal and network function over an animal's lifetime. To understand how these homeostatic mechanisms might function, it is crucial to understand how tightly regulated synaptic and intrinsic properties must be for adequate network performance, and the extent to which compensatory mechanisms allow for multiple solutions to the production of similar behaviour. Here, we use examples from theoretical and experimental studies of invertebrates and vertebrates to explore several issues relevant to understanding the precision of tuning of synaptic and intrinsic currents for the operation of functional neuronal circuits.

Action Potentials↗
PubMed2006

Dynamic clamp analyses of cardiac, endocrine, and neural function.

The dynamic clamp introduces artificial conductances into cells to simulate electrical coupling, votage-dependent, leak, and synaptic conductances. This review describes how the dynamic clamp has been used to address various questions in the cardiac, endocrine, and nervous systems.

Animals↗
PubMed2005

Red pigment concentrating hormone strongly enhances the strength of the feedback to the pyloric rhythm oscillator but has little effect on pyloric rhythm period.

The neuropeptide, red pigment concentrating hormone (RPCH), strengthened the inhibitory synapse from the lateral pyloric (LP) neuron to the pyloric dilator (PD) neurons in the pyloric network of the stomatogastric ganglion (STG) of the lobster, Homarus americanus. RPCH produced several-fold increases in the amplitude of both action potential-mediated and non-impulse-mediated transmission that persisted for as long as the peptide remained present. Because the LP to PD synapse is the only feedback to the pacemaker kernel of the pyloric network, which consists of the electrically coupled two PD neurons and the anterior burster (AB) neuron, it might have been expected that strengthening the LP to PD synapse would increase the period of the pyloric rhythm. However, the period of the pyloric rhythm increased only transiently in RPCH, and a transient increase in cycle period was observed even when the LP neuron was hyperpolarized. Phase response curves were measured using the dynamic clamp to create artificial inhibitory inputs of variable strength and duration to the PD neurons. Synaptic conductance values seen in normal saline were ineffective at changing the pyloric period throughout the pyloric cycle. Conductances similar to those seen in 10(-6) M RPCH also did not evoke phase resets at phases when the LP neuron is typically active. Thus the dramatic effects of RPCH on synaptic strength have little role in modulation of the period of the pyloric rhythm under normal operating conditions but may help to stabilize the rhythm when the cycle period is too slow or too fast.

Action Potentials↗
PubMed2005

Invertebrate central pattern generation moves along.

Central pattern generators (CPGs) are circuits that generate organized and repetitive motor patterns, such as those underlying feeding, locomotion and respiration. We summarize recent work on invertebrate CPGs which has provided new insights into how rhythmic motor patterns are produced and how they are controlled by higher-order command and modulatory interneurons.

Animals↗
PubMed2005

Computational model of electrically coupled, intrinsically distinct pacemaker neurons.

Electrical coupling between neurons with similar properties is often studied. Nonetheless, the role of electrical coupling between neurons with widely different intrinsic properties also occurs, but is less well understood. Inspired by the pacemaker group of the crustacean pyloric network, we developed a multicompartment, conductance-based model of a small network of intrinsically distinct, electrically coupled neurons. In the pyloric network, a small intrinsically bursting neuron, through gap junctions, drives 2 larger, tonically spiking neurons to reliably burst in-phase with it. Each model neuron has 2 compartments, one responsible for spike generation and the other for producing a slow, large-amplitude oscillation. We illustrate how these compartments interact and determine the dynamics of the model neurons. Our model captures the dynamic oscillation range measured from the isolated and coupled biological neurons. At the network level, we explore the range of coupling strengths for which synchronous bursting oscillations are possible. The spatial segregation of ionic currents significantly enhances the ability of the 2 neurons to burst synchronously, and the oscillation range of the model pacemaker network depends not only on the strength of the electrical synapse but also on the identity of the neuron receiving inputs. We also compare the activity of the electrically coupled, distinct neurons with that of a network of coupled identical bursting neurons. For small to moderate coupling strengths, the network of identical elements, when receiving asymmetrical inputs, can have a smaller dynamic range of oscillation than that of its constituent neurons in isolation.

Animals↗
PubMed2005

Animal-to-animal variability in motor pattern production in adults and during growth.

Which features of network output are well preserved during growth of the nervous system and across different preparations of the same size? To address this issue, we characterized the pyloric rhythms generated by the stomatogastric nervous systems of 99 adult and 12 juvenile lobsters (Homarus americanus). Anatomical studies of single pyloric network neurons and of the whole stomatogastric ganglion (STG) showed that the STG and its neurons grow considerably from juvenile to adult. Despite these changes in size, intracellularly recorded membrane potential waveforms of pyloric network neurons and the phase relationships in the pyloric rhythm were very similar between juvenile and adult preparations. Across adult preparations, the cycle period and number of spikes per burst were not tightly maintained, but the mean phase relationships were independent of the period of the rhythm and relatively tightly maintained across preparations. We interpret this as evidence for homeostatic regulation of network activity.

Animals↗
PubMed2005

Constant amplitude of postsynaptic responses for single presynaptic action potentials but not bursting input during growth of an identified neuromuscular junction in the lobster, Homarus americanus.

As lobsters grow from early juveniles to adults their body size increases more than 20-fold, raising the question of how function is maintained during these ongoing changes in size. To address this question we studied the pyloric 1 (p1) muscle of the stomach of the lobster, Homarus americanus. The p1 muscle receives multiterminal innervation from one motor neuron, the lateral pyloric neuron of the stomatogastric ganglion. Staining with antibodies raised against synaptotagmin showed that as the muscle fibers increased in length, the spacing between the terminal innervation increased proportionally, so the number of synaptic contact regions/muscle fiber did not change. Muscle fibers were electrically coupled in both juveniles and adults. The amplitude of single intracellularly recorded excitatory junctional potentials evoked by motor nerve stimulation was the same in both juveniles and adults. Nonetheless, the peak depolarizations reached in response to ongoing pyloric rhythm activity or in response to high-frequency trains of stimuli similar to those produced during the pyloric rhythm were approximately twofold larger in juveniles than in adults. This suggests that homeostatic regulation of synaptic connections may operate at the level of the amplitude of the single synaptic potential rather than on the summed depolarization evoked during strong rhythmic activity.

Action Potentials↗