Stomatogastric Ganglion Module

STGfigureUnderstanding how neuronal networks enable animals, including humans, to make coordinated movements is a continuing goal of neuroscience research. The stomatogastric nervous system of decapod crustaceans and particularly the networks of the stomatogastric ganglion (STG), which control feeding functions, have significantly contributed to our present understanding of general principles underlying rhythmic motor circuit operation at the cellular level, and has shed light on the mechanisms of network homeostasis and plasticity.

Rhythmic behaviors include all motor acts that, at their core, involve a rhythmic repeating set of movements (e.g., locomotion, breathing, chewing and scratching). The circuits underlying such rhythmic behaviors, central pattern generators (CPGs), operate on the same general principles across all nervous systems. These networks can generate rhythmic output in the completely isolated nervous system, even in the absence of any rhythmic neuronal input, including feedback from sensory systems. Although the details differ in each circuit, all CPGs use the same set of cellular-level mechanisms for circuit construction. More importantly, CPG circuits are usually not dedicated to producing a single neuronal activity pattern. This flexibility results largely from the ability of many different neuromodulators to change the cellular and synaptic properties of individual circuit neurons. When the properties of circuit components are changed, the output of the circuit itself is modified.

The STG contains a set of distinct but interacting motor circuits. The value of this system has resulted from its experimental accessibility, owing to the small number of large and individually identifiable neurons and the use of several innovative techniques. Because of the many similarities between vertebrate and invertebrate systems, especially with regards to basic principles of neuronal function, invertebrate model systems such as the crustacean stomatogastric nervous system continue to provide key insight into how neural circuits operate in the numerically larger and less accessible vertebrate CNS.

The stomatogastric cycle (STG cycle) examines mechanisms of generation, regulation and plasticity of rhythmic neural activity produced by CPG networks. The STG cycle exercises highlight fundamental features of the cellular basis of motor pattern generation and the characterization of dynamical neural systems. Students obtain hands-on experience with the principle that rhythmically active networks can continue to generate rhythmic motor patterns in the isolated CNS, a defining feature of CPGs. We also focus on the fact that anatomically hard-wired circuits remain functionally flexible. All neural networks are malleable through the action of neuromodulatory inputs and intrinsic homeostatic mechanisms, which modify time and voltage-dependent properties of intrinsic membrane properties, and functional synaptic connectivity. Additionally, several key aspects of neuronal communication are studied, including properties of spike-mediated and graded synaptic transmission, short-term synaptic plasticity and the input/output properties of electrical synapses.

We build on skills developed during Cycle I, emphasizing electrophysiological analysis of neural network activity, and its underlying ionic mechanisms, in an isolated nervous system. We emphasize modern experimental tools and paradigms: intracellular recordings of multiple identified neurons; extracellular recordings of identified neurons; single-electrode discontinuous current clamp methods for current injection and recording; synaptic pharmacology defined with pharmacological agonists and antagonists; superfusion of neuromodulators and their release by identified projection neurons; study of graded transmitter release, the dynamic clamp technique for determining the functional impact of intrinsic and synaptic currents in network function, and quantitative analysis of electrophysiological recordings.

Students spend the first week building their understanding of STG networks. For example, students will learn dynamical system techniques to describe activity network parameters, such as phase analysis, resetting, entrainment and phase response curves (PRCs). The two-electrode voltage clamp technique is introduced to quantify time and voltage dependent properties of membrane channels and to clarify how ionic currents (which will be characterized mathematically using the Hodgkin-Huxley framework) contribute to neuronal and network function. These ionic currents will be manipulated using the dynamic clamp technique to understand the functional significance of mathematically defined ionic conductances. The dynamic clamp technique will also be used to examine the role of synapses in the network, by artificially adding or removing synapses in the biological network.

The second week of the STG Cycle is dedicated to independent projects that reflect contemporary research issues asking questions about mechanisms underlying neural network activity, and address specific principles of motor network function common to all animals. These projects are expected, with guidance from faculty mentors, to gather new, previously unpublished data, much as preliminary experiments would accomplish in a research lab. Almost all projects in the STG cycle address unknown conceptual questions and many projects in recent years have led to novel results.

 

STG Faculty and Teaching Assistants


blitzdDawn Blitz
Miami University

In my lab, we use the well-defined model system, the stomatogastric nervous system of the Jonah crab, Cancer borealis to determine cellular, synaptic and systems-level mechanisms used by the nervous system to select particular outputs from neural networks capable of generating many different output patterns.  We use electrophysiological approaches such as current clamp, voltage clamp and dynamic clamp recording techniques along with immunocytochemistry, single cell dye-fills, photoablation, and confocal microscopy.

Current projects include:

  • examining the role of network feedback to descending modulatory inputs, a common feature of rhythmic motor systems.
  • anatomical tracing of sensory-motor pathways to identify the stimuli that elicit particular network outputs
  • determining how the composition of networks is modulated such that neurons change their participation between networks

I was a NS&B student in 1995, TA from 1996-2001, and a faculty member from 2006-2008 and since 2012 and continue to greatly value the NS&B and MBL experience, and the opportunity to use my research model system in this immersion science educational setting.

 

beenhakkerMark Beenhakker
University of Virginia

The Beenhakker lab aims to understand how the brain generates complex electrical signals, and how these signals are used to process information. A major extension of this aim is to understand why electrical activity in the brain becomes uncontrollable during certain diseases such as epilepsy. We use electrophysiological, anatomical and computational approaches to resolve these questions.

We primarily focus on cellular and circuit-level questions in the thalamus, a structure that is generally believed to function as a relay station between the outside world and the cortex. However, the thalamus also plays a critical role in generating rhythmic network activity that likely facilitates the consolidation of memories during sleep. Furthermore, seizures associated with some forms of childhood/juvenile epilepsy are thought to be driven by thalamic circuits. Thus, the thalamus is engaged in several different processes, both normal and pathological. Designing experiments to resolve the mechanisms that underlie these processes forms the core of our research program.

Current projects in the lab focus on:

  • Excessive excitability of thalamic neurons associated with chloride channel dysfunction.
  • Network-level activity patterns observed in the thalamus during sleep and epilepsy.
  • Regulation of metabotropic signaling carried out by thalamic neurons.

 

 

anna_nsb-photoAnna Schneider
NJIT/Rutgers University

I want to understand how neuropeptides and their interactions provide stability and flexibility to neural networks. In the Nadim / Bucher Lab, we use the stomatogastric nervous system to tackle these questions. Its identified pyloric network produces a stereotypic triphasic pattern with low variability across animals. However, the underlying ion channel currents and mRNA levels vary largely. One key component to reduce variability from the component to the network level could be the convergence of neuropeptides on the same target. To test this hypothesis, I compare variation of several rhythm and component parameters in the presence or absence of neuropeptides. With these results, we want to discover general rules of neuropeptide interaction.

 

Savanna-Rae Fahoum
Miami University

I want to understand the mechanisms underlying neuronal switches, such that a neuron can change its participation from one network to another, or even participate in multiple networks at once. In the Blitz lab, I use the stomatogastric nervous system to study a neuron that can switch its participation from the pyloric rhythm to dual participation in both pyloric and gastric mill rhythms, simultaneously. I am interested in determining whether this switching behavior is a result of changes to the intrinsic properties of the switching neuron, or if it is dependent on the synaptic properties between the switching neuron and others within the circuit. I am also interested in electrical coupling and how neuromodulators can alter the strength of coupling between neurons for the generation of various rhythmic behaviors.

 

 

Daniel Powell
Brandeis University

I am interested in how single cell states within a circuit influence the network(s) they participate in. I am working in Eve Marder’s lab in collaboration with Michael Nusbaum (U. Penn) using the gastric (chewing) sub-network within stomatogastric nervous system of the crab C. borealis. The beauty of this system is that it provides a tractable circuit that generates a fictive but behaviorally relevant output post dissection, and the entire output can be monitored extracellularly.  I want to understand how motor systems generating seemingly identical fictive motor patterns (within animal) can be doing so via distinctly different network states and if modulatory perturbations (hormonal and sensory) drive these motor patterns to diverge or are they truly degenerate states? Using a combination of classical electrophysiology techniques, pharmacology, and dynamic clamp, I can dissect exactly how a modulatory conductance specifically affects a single neuron with an intact circuit in real time.

liz_croninLiz Cronin
NJIT

I’m interested in understanding how neuromodulators shape activity patterns and exploring the idea of network output flexibility under single and co-modulatory conditions.  In the Bucher and Nadim labs, we use the pyloric network of the stomatogastric nervous system, a prominent and exceptionally well described small circuit for exploring questions about neuromodulation.  It has been previously shown, qualitatively, that the pyloric network generates modulator specific network outputs.  Quantification of the effects that neuromodulators have on a network output, though, have largely relied on traditional bar plots and basic statistics.  These approaches can tell you where individual differences are but are not well suited to address whether one inherently multi-dimensional network output is different from another and numerically how different they are.  By utilizing alternative approaches which are more suited to these types of data, I’m interested in asking how different one modulated output pattern is from another, how different are co-modulated network outputs from each other and how different are co-modulated outputs relative to their constituent modulators.

adrian_otopalikAdriane Otopalik
Brandeis University

I’m interested in understanding how circuit dynamics, motor patterns, and complex behaviors arise from the diverse and dynamic biophysical properties of single neurons. As a grad student in Eve Marder’s lab, I studied the biophysical mechanisms that enable the STG to generate stereotyped activity patterns, despite remarkable inter-animal variability in neuronal morphologies. As a postdoctoral fellow in Vanessa Ruta’s lab, I am investigating how descending neurons, projecting from the central brain to motor centers, integrate visual information and representations of arousal to shape real-time action selection during courtship in male drosophilids. By expanding this line of study into additional species, I hope to understand how interspecies variation in visuomotor circuits gives rise to striking behavioral diversity across the evolutionary tree. I was a student in NS&B in 2013, a Grass Fellow in 2017, and I’m thrilled to help out with the STG module for the first time this year!