Allen I. Selverston - US grants

The neural connections and mechanisms underlying rhythmic motor patterns is at present not known. In an effort to understand these mechanisms, and invertebrate model system, the lobster stomatogastric ganglion can be used to study the genesis of rhythmic motor patterns. This ganglion of only 30 cells produces two separate rhythms in isolated and completely deafferented preparation. THe neural circuitry underlying both patterns has been determined. Using a new dye-sensitized photoinactivation technique, the mechanisms for the production of the pyloric rhythm have been elucidated. This proposal is to complete an analysis of the gastric system using the same experimental technique, but in a more quantitative manner. We have formulated a tentative hypothesis for the gastric mechanism which allows us to predict the consequences of particular cell deletions. These will be experimentally tested and the hypothesis modified as required. In addition we will begin an examination of the sensory control of the stomatogastric pattern generation and the effects of the neuromodulatory substances neurodepressing hormone from the eyestalk; serotonin and octopamine, which are found in the stomatogastric system.

This program project outlines a group of studies investigating the basic mechanisms underlying neuronal signalling. A group of six core facilities and six individual projects propose a coordinated, multidisciplinary series of studies on diverse nervous sytems. The core will serve an overall administrative function as well as including centralized data management and analysis, biochemical and electron microscopic instrumentation and electronics and machine shop services. Project 1 will study the mechanisms underlying neuromodulatory control of a completely described neural circuit. Project 2 will study the regulation of mammalian neuronal nicotinic receptors. Project 3 will test the hypothesis that the membranes of radial glial cells upon which the growth cones of embryonic retinal axons travel on their way to the tectum contain factors that support neurite outgrowth. Project 4 will investigate the cellular mechanisms by which leech Retzius neurons change their identity after target contact. Project 5 will test two hypotheses about the molecular modifications of ion channels that occur during embryonic development in Xenopus and Project 6 will study the molecular mechanisms used for signal transduction in Drosophila.

This award will support collaborative research in behavioral neuroendocrinology between Dr. Allen I. Selverston, University of California at San Diego, and Dr. Dr. Allain Van Wormhoudt, Laboratory for Marine Biology, College of France, Concarnu, France. The objective of the project is to purify, sequence and synthesize a crustacean CCK-like peptide from the spiny lobster Panulirus interruptus, and to determine its physio- logical activity on the gastric mill network in the stomato- gastric ganglion. This peptide has profound modulatory effects on a simple neural circuit, the gastric mill circuit of crustaceans, and is involved in the feeding- induced activation of the gastric mill. Obtaining a sequence from this peptide will allow the investigators to study in detail the mechanisms by which a neuropeptide activates and modulates a well understood neural circuit. This project is of particular importance, since the lobster CCK-like peptide is the first peptide modulating the stomatogastric rhythms, whose patterns of release in the lobster have been shown. The stomatogastric system has been for many years one of the most important and instructive model systems available for studying both the control of rhythmic patterns and its modulation by various neurotrans- mitters. This project will take advantage of the known information to enhance our understanding of these modulatory processes. The project will benefit from the mutual expertise of the two investigators: Dr. Selverston is a leader in the field of small systems neurobiology and Dr. Von Wormhoudt is an experienced biochemist who has studied CCK in other crustacea.

This program project application aims to continue studies on the molecular and biophysical mechanisms involved in neuronal signalling by the neurobiology group of the Biology Department at UCSD. Six separate projects, using a wide variety of animal models, from leeches and fruit flies to lobsters and frogs, will be undertaken. Ion channels, their regulation and modulation represent a major focus of the work since they represent identified membrane components of fundamental importance to neuronal signalling. Second messengers and intracellular cascade systems also represent a central unifying theme. Target selection during development and target mediated neuronal differentiation represent other foci of integrative signalling. The diversity of approaches provide an integrated analysis of signalling mechanisms from the molecular level to the functioning circuit.

This is a proposal for a collaboration with two outstanding Russian investigators to study the principal mechanisms of modulation and integration of neuronal networks involved in the control of feeding behavior in the mollusc Clione limacina. This preparation serves as a model system for posing general questions concerning the modulation and control of motor output and behavior by the central nervous system. The mollusc central nervous system is particularly favorable for this study because neuronal networks involved in the control of feeding behavior have been identified. The main idea is that neuronal networks are not rigidly wired formed by fixed connections between neurons, but are flexible polyfunctional structures that generate a broad range of motor outputs. The flexibility of the networks is determined by nervous and hormonal inputs that modify the properties of neurons and their connecting synapses. The properties of single neurons, synaptic connections and the feeding network will be studied by recording the responses of neurons during feeding behavior in the presence and absence of various neuromodulators found in molluscs.***//

This program project application aims to continue studies on the molecular and biophysical mechanisms involved in neuronal signalling by the neurobiology group of the Biology Department at UCSD. Six separate projects, using a wide variety of animal models, from leeches and fruit flies to lobsters and frogs, will be undertaken. Ion channels, their regulation and modulation represent a major focus of the work since they represent identified membrane components of fundamental importance to neuronal signalling. Second messengers and intracellular cascade systems also represent a central unifying theme. Target selection during development and target mediated neuronal differentiation represent other foci of integrative signalling. The diversity of approaches provide an integrated analysis of signalling mechanisms from the molecular level to the functioning circuit.

A study of the role of cellular and synaptic properties in the dynamic and flexible operation of oscillating neuronal circuits. We make use of two central pattern-generating circuits (CPGs) within the crustacean stomatogastric ganglion (STG),in a continuation of studies of this preparation begun in 1969. The stomatogastric system is the most extensively mapped neural circuit presently available. While not immediately related to health sciences, it allows us to ask basic questions about the design and function of oscillatory circuits, with implications for our understanding of motor and sensory circuits in vertebrate spinal cord and brain. 1. The role of synaptic time course in network dynamics: An assessment of the contribution of synaptic time-course to the temporal operation of the pyloric and gastric CPGs, two stomatogastric circuits that oscillate with about a 10 fold difference in frequency. 2. Modulation of cellular properties and network dynamics: An analysis of the modulation of active membrane properties in identified, single neurons and the consequent effects upon sub-circuit function. 3. Modulation of network dynamics and sensorimotor processing: A study of plasticity in sensorimotor pathways resulting from the modulation of cellular and synaptic properties in the stomatogastric motor circuits. These questions are addressed by interactive, electrophysiological, pharmacological and computer modeling techniques.

The overall object of the proposed work is to utilize Clione as a model subject for studying the neural basis of animal behavior. The specific aim is to study neural mechanisms of spatial orientation as determined by the activity of statocyst receptors. The proposal is designed to continue ongoing work on the central mechanisms responsible for changes in statocyst information processing in different behavioral contexts, one of which involves triggering a reversal in the normal response, and two of which are believed to temporarily decrease the significance of statocyst inputs during food acquisition and during passive avoidance behavior. Statocyst cells have been identified, and their activity during varying degrees of tilt has been documented with a very clever recording system. Furthermore, central neurons which receive statocyst input, and which provide output that is capable of modifying swimming activity, have been found. The missing puzzle piece is a complete identification and thorough description of tail motoneurons which produce tail bending and thus alter the direction of swimming. This represents the first goal of the project - a thorough description of tail motoneurons. Once identified, the investigators propose to describe the cellular and synaptic mechanisms of modification of swimming and tail bending activities during different behaviors. They have chosen three behavior contexts which can be easily simulated experimentally. A reversal from positive to negative geotaxis can be triggered by simply changing temperature in the recording system. The apparent inhibition of statocyst inputs during feeding behavior will be studying by simply initiating feeding activity - the circuits involved in feeding are well known to the investigators. Finally, stimuli that trigger passive avoidance behavior can be delivered in a reduced preparation, to describe behaviorally relevant changes in activity in the steering system. Overall, the investigators propose to describe behavioral plasticity in the spatial orientation system following network modulation in behaviorally relevant contexts.

This proposal is in response to RFA: NS-99-0001 entitled Specialized Neuroscience Research Programs (SNRP) at Minority Institutions. The University of Puerto Rico is virtually a one hundred percent Minority Instituted distributed among eleven campuses throughout the Commonwealth of Puerto Rico. Our intention in applying for this SNRP programs is that it will play a major role in the strengthening of Neuroscience research and teaching on the island by supporting three promising young Puerto Rican Neuroscientists who are at the beginning of their careers. All three will collaborate with experienced, well-funded neuroscientists at major research universities in the United States. Luis Santana from the Institute of Neurobiology will collaborate with Mark Nelson from the University of Vermont, Sandra Pena of the Biology Department on the Rio Piedras Campus will collaborate with Alcino Silva of UCLA and Jorge Miranda from the Physiology Department of the Medical School will collaborate with Scoot Whittemore from the University of Louisville. We anticipate these three scientists will play a major role in forming the nucleus of a competitive neuroscience community in Puerto Rico that will include undergraduate, graduate and postgraduate students as well as more advanced researchers who will live and work on the island. The program will be directed by Dr. Allen Selverston, the Director of the Institute of Neurobiology who has directed large Program Project Grants previously. We view this program as a rare opportunity to "jump start" mainstream Neuroscience research at the University or Puerto Rico and a chance to demonstrate the excitement of contemporary brain research to students and general population alike.

This proposal is in response to RFA: NS-99-0001 entitled Specialized Neuroscience Research Programs (SNRP) at Minority Institutions. The University of Puerto Rico is virtually a one hundred percent Minority Instituted distributed among eleven campuses throughout the Commonwealth of Puerto Rico. Our intention in applying for this SNRP programs is that it will play a major role in the strengthening of Neuroscience research and teaching on the island by supporting three promising young Puerto Rican Neuroscientists who are at the beginning of their careers. All three will collaborate with experienced, well-funded neuroscientists at major research universities in the United States. Luis Santana from the Institute of Neurobiology will collaborate with Mark Nelson from the University of Vermont, Sandra Pena of the Biology Department on the Rio Piedras Campus will collaborate with Alcino Silva of UCLA and Jorge Miranda from the Physiology Department of the Medical School will collaborate with Scoot Whittemore from the University of Louisville. We anticipate these three scientists will play a major role in forming the nucleus of a competitive neuroscience community in Puerto Rico that will include undergraduate, graduate and postgraduate students as well as more advanced researchers who will live and work on the island. The program will be directed by Dr. Allen Selverston, the Director of the Institute of Neurobiology who has directed large Program Project Grants previously. We view this program as a rare opportunity to "jump start" mainstream Neuroscience research at the University or Puerto Rico and a chance to demonstrate the excitement of contemporary brain research to students and general population alike.

DESCRIPTION:(from applicant's abstract) How can oscillatory neural circuits generate spatio-temporal activity patterns that are robust in the presence of noise yet flexible enough to provide specific, reproducible, adaptive responses to inputs? This problem is central to sensory processing as well as motor coordination. Our approach to this question involves a well-established and productive, interdisciplinary team from Biology, Physics and Nonlinear Dynamics. It combines nonlinear dynamical analysis, computational and electronic modeling, and neurophysiological studies of a tractable, oscillatory motor circuit from the crustacean stomatogastric system. Specifically, we ask: How do particular membrane properties, synaptic strengths and kinetics, and circuit architectures contribute to the production of multiple, stable and controllable patterns? How do these characteristics, and their modulation, affect dynamical responses to noise and control signals?

This goal of this project is to uncover the fundamental aspects of the biophysics associated with synchronization in small groups of neurons. The question will be addressed both in the biological laboratory as well as using numerical and electronic simulations of the neurons seen in the lab. The research will add to the understanding of how biological nervous systems can process information from the environment and pass it on in a coherent way to decision making centers. The work, while in small nervous systems of invertebrates, will directly bear on how more complex systems can organize to produce interesting functional behaviors. During the course of the project, graduate students and postdoctoral researchers from Physics and Biology will work side-by-side and will learn about the biological sciences as well as the physical processes underlying the biological activity.

DESCRIPTION:(provided by applicant) This proposal uses the marine mollusc Clione limacina as a model with which to study a common behavior; orientation to the gravitational field. Clione orients itself in the water column, in the heads-up position by means of wing and tail movements. These movements respond to signals from the statocyst organ to maintain a vertical position. The statocyst organ contains a small stone, the statolith, that rests on sensory hair cells and is moved around on these cells by changes in the animal's position in the gravitational field. After a disturbance which changes body position, signals from the statocysts are integrated in the cerebral ganglion which generates the correct spatio-temporal pattern of impulses to the wing and tail motor neurons thus reducing the statocyst signal to its previous condition. Although a seemingly straight forward negative feedback loop appears to be the basic mechanism involved, the behavior actually requires a complex coordination between three functional elements; equilibrium receptors, CNS interneurons and the wing and tail motor neurons. In addition to the equilibrium response, the animal can engage in another related behavior known as hunting. During hunting, the normal equilibrium response disappears and the animal engages in what appears to be random circular sweeps of its environment. We hypothesize that the basically unstable vertical orientation mechanism requires coordination between the CPGs for both wing movements and tail movements and the hunting mechanism involves the activation of efferent connections between the cerebral ganglion and the lattice of receptor cells in the statocyst. To prove this hypothesis we will use a combination of behavioral, electrophysiological and modeling studies. We also hypothesize that specific feedback among cerebral ganglia and statocyst receptors together with inhibitory interconnections among receptor neurons is able to stimulate a complex hunting search behavior that resembles the chaotic motion of a pendulum in three dimensional space. The behavioral analysis will quantify the phase relationships between wing and tail movements during stable and perturbed behaviors. The electrophysiology is necessary to describe the cellular responses to statocyst output and the computational analysis will employ three different models to determine which best captures the salient features of the equilibrium and hunting responses most accurately and to provide a theoretical basis for the production of the two different behaviors.

DESCRIPTION (provided by applicant): A central goal of Neuroscience is to understand the laws and mechanisms by which complex coherent activity of the nervous system can emerge from the cooperative activities of many relatively simple dynamical elements i.e., neurons and synapses. Because the arrangement of neurons and synapses in different microcircuits (MCs) vary, any general principles common to all of them will require a general theoretical framework. Dynamical System Theory (DST) is such a framework. DST gives a geometrical view of a behavior's structural elements, such as attractors, basins, and separatrices and also addresses the question of what activity is common across the spectrum of neural systems. By using small invertebrate MCs, which are central pattern generators (CPGs), virtually all synaptic connections and cellular properties can be determined. With these preparations, principles may be found which can help determine the dynamical properties of vertebrate MCs where present techniques do not allow the detailed mapping of cell to cell circuitry. To measure the dynamical properties of the MCs, particularly in relation to the competing demands of robustness and flexibility, we will change the intrinsic properties of constituent neurons, synapses and MC architecture using electronic neurons, synapses, an improved dynamic clamp technique and hybrid circuits. We will work with CPGs of lobster, crab and Clione as well as with model MCs. The proposed research provides the opportunity of obtaining fundamental dynamical principles which govern the operation of neural circuits in a wide range of nervous systems. The formulation of the dynamical principles that govern the activity of small neural circuits is important not only for the understanding of robustness, sensitivity, flexibility, and synchronization mechanisms but, even more importantly, gives us the ability to build artificial systems based on such general principles without a detailed knowledge of the biological circuits. Such artificial systems would be extremely important clinically in the design of prosthetic devices.