Michael P. Nusbaum - US grants

DESCRIPTION (Adapted from applicant's abstract): Discrete neural networks within the central nervous system of both vertebrates and invertebrates are responsible for generating the patterned neural activity that mediates rhythmic behaviors, such as locomotion, respiration and the chewing and processing of food. Each network produces multiple distinct but related motor patterns as a result of modulatory inputs from other regions of the nervous system. A long-term goal of this proposal is to understand the cellular mechanisms underlying the selection and generation of the appropriate motor pattern at the behavioral appropriate time. This includes identifying the projection neurons responsible for activating, modulating and terminating neural network activity, and characterizing the effects of each projection neuron on the neural network and on other projection neurons to that network. This also includes studying the presence and functional consequences of presynaptic inputs onto the spatially and electronically distant terminals of these projection neurons. This proposal focuses on modulation of the well-characterized pyloric and gastric mill motor patterns in the crustacean stomatogastric ganglion (STG) by distinct projection neurons that innervate the STG, in the crab Cancer borealis. Electrophysiological techniques, including simultaneous intrasomatic recordings of STG network neurons and both intrasomatic and intra-axonal recordings of projection neurons, as well as dye filling and double labeling techniques will be used to address the following hypotheses: (1) Different projection neurons use different strategies to elicit distinct pyloric and gastric mill motor patterns. (2) Motor pattern selection in the STG by projection neurons includes presynaptic influences onto the STG terminals of other projection neurons. (3) There is an extensive network of electrical coupling in the STG involving the terminals of individual projection neurons. (4) Presynaptic input onto a projection neuron functionally compartmentalizes the activity of that neuron within the STG neuropil. The results of these experiments will provide a new level of understanding, previously unobtainable, about how individual projection neurons influence neural network activity, including the roles played by presynaptic inputs onto the distant terminals of these projection neurons. This will help guide conceptual understanding and experimental approaches aimed at understanding neural network modulation in the similar, but less accessible, vertebrate nervous system.

confocal scanning microscopy; biomedical equipment purchase; neurosciences;

DESCRIPTION (provided by applicant): We propose to continue a flexible interdisciplinary Graduate Training Program, now entering its 24th year, that is designed to prepare exceptional students for productive research careers in Systems and Integrative Biology (SIB). Our SlB Training Program focuses on training graduate students in the area of Systems and Integrative Neuroscience, based in the Neuroscience Graduate Group, an interdepartmental group composed of sixty-nine faculty from twenty-three departments in four Schools of the University of Pennsylvania. Graduate education in the Life Sciences at Penn is based on such independent, interdepartmental Graduate Groups. The Office of Biomedical Graduate Studies (BGS) ensures curricular development, quality control and uniform admission standards across all Graduate Groups. Direct management of this Training Program is in the hands of a six-person directorate that sets and reviews policy, and selects trainees. Faculty membership is governed by three criteria: (1) expertise in a field relevant to the Program, (2) significant contribution to training, and (3) extramural funding to support trainees. A BGS committee consisting of a representative from each Graduate Group decides admission of students to Graduate Programs. Admission to this Training Program is determined by the Executive Committee in consultation with BGS. Selected students will come primarily from the Neuroscience, Graduate Group, but they may also come from one of several other Graduate Groups. The Program will consist of two years of coursework plus at least three, varied laboratory rotations. All students will be required to take a course on the ethical conduct of scientific research. Students will also be exposed to additional training, activities including seminars, journal clubs, annual retreats, scientific meetings, practice in teaching, paper and poster presentation, and scientific publication, as well as social events to encourage interdisciplinary contacts. Successful completion of a comprehensive "Prelim" examination marks the beginning of independent research toward a dissertation. Thesis research is conducted under the supervision of a faculty advisor and is monitored by a four-member thesis committee and the Graduate Group's Academic Review Committee. The dissertation defense takes place when the thesis advisor and committee agree that the work is complete. Based on the number of potential trainees, we request support for 12 predoctoral trainees per year for the next 5 years.

IBN-9808356 Nusbaum LAY ABSTRACT The goal of this proposal is to understand, at the cellular level, how specific rhythmic motor patterns are selected from a multifunctional neuronal network. Previous work in several invertebrate and vertebrate systems has shown that the networks generating rhythmic movements are functionally flexible. That is, the same neuronal ensemble generates distinct rhythmic motor patterns when influenced by different neuromodulatory inputs. We do not fully understand how any individual motor pattern is selected for activation from such a network. Motor pattern selection, however, is likely involve the coactivation of distinct inputs from higher centers. This and related issues regarding motor pattern selection are readily addressed in the stomatogastric nervous system. This is a very well-characterized model system that contains a set of distinct but interacting networks that generate the motor patterns underlying rhythmic contractions of striated foregut muscles involved in the ingestion, chewing and processing of food. As is true for all rhythmically active networks, these networks can still operate in the completely isolated nervous system, where all experiments will be performed. The working hypothesis is that motor pattern selection from a multifunctional neuronal network results in part from different input pathways (i.e.- different sensory systems) having distinct effects on overlapping subsets of modulatory projection neurons. To examine the validity of this hypothesis, we proposed to examine whether: (1) different input pathways evoke different motor patterns from the same network; (2) these different input pathways activate different subsets of projection neurons that influence this network; (3) different co-transmitters released by an identified sensory neuron are used to influence spatially separate neuronal targets, and (4) an individual sensory pathway exhibits an activity- dependent compartmentalization of action. Combining electrophysiological, pharmacological and anatomical approaches will attain these aims. This proposed study will provide novel physiological information regarding how the nervous system selects different motor patterns from a multifunctional neuronal network. This will be a valuable model for comparable but less accessible events occurring in the numerically more complex vertebrate nervous system. It will also provide extensive technical and intellectual training for pre- and post- doctoral students interested in the functional organization of the central nervous system.

The long-range goal of this work is to understand, at the cellular level, how the central nervous system selects and generates the neuronal activity patterns underlying coordinated movements. This includes understanding how the activity of distinct but behaviorally-related neuronal circuits is coordinated to generate complex behavior. This work focusses on rhythmic motor circuits, such as those underlying locomotion, respiration and the chewing of food. A well-defined model system, the stomatogastric nervous system of the crab will be used for this purpose. Previous work has documented that the same organizing principals underlie the generation of individual rhythmic motor programs in all invertebrates and vertebrates. Relatively simple model systems are more accessible than the comparable systems in the vertebrate spinal cord and brainstem. Thus, they are more useful for a cellular analysis of neuronal circuits. This proposal aims to extend previous studies by performing a cellular analysis of how the activity of behaviorally- related neuronal circuits is coordinated. The working hypotheses is that the coordination between related, rhythmically active neuronal circuits is state-dependent. The working hypothesis is that the coordination between related, rhythmically active neuronal circuits is state- dependent. This hypothesis will be tested by examining the coordination between different versions of the motor patterns produced by the gastric mill and pyloric neural circuits in the crab stomatogastric ganglion. The following four specific aims will be examined. First: inter-circuit interactions are different between distinct forms of the gastric mill and pyloric motor programs. Second: there are distinct cellular mechanisms subserving these different inter-circuit interactions. Third: the interactions, and their functional consequences, between these two circuits are modified by locally-released and circulating neuromodulators. Fourth: patterned feedback from these two circuits onto the projection neurons that influence them enables these circuits to regulate and coordinate the activity of these projection neurons. These aims will be investigated using a cellular electrophysiological approach, combined with a computer program called the Dynamic Clamp that enables the injection of an artificial synapse, in situ, into any neuron after the neuronally-elicited synaptic input is removed. The electrophysiological experiments will include four simultaneous intracellular recordings plus multiple extracellular recordings. This enables a comprehensive recording of all circuit activity, and the ability to manipulate all members of the studied circuits. Despite the fact that most complex behaviors, in all animals, result from interactions between distinct motor circuits, there are no existing physiological models of motor circuit coordination at the cellular level. Consequently, these proposed studies will provide a useful template for both experimental and computational models of motor pattern coordination in the numerically larger and technically less accessible vertebrate central nervous system.

DESCRIPTION:(provided by applicant) The long-term goal of this proposal is to determine, at the cellular level, how distinct motor patterns are elicited by different sensory and descending inputs to multifunctional neural networks that underlie behavior. Previous work in many model systems showed that one common principle underlying the neural basis of behavior is that single neural networks produce many different neural activity patterns, thereby producing distinct behaviors. The multifunctional character of such networks derives from the actions of modulatory neurotransmitters which alter the cellular and synaptic properties of the network neurons. Thus far, little is known regarding how the nervous system selects which activity pattern should be elicited by a given network. In this context, identified projection and sensory neurons will be studied to determine how this selection process is orchestrated. This will include a determination of the roles played by the (a) co-release of neurotransmitters, (b) activity-dependent regulation of transmitter release, and (c) activation of distinct sets of projection neurons. This proposal aims to take advantage of a well-defined model system, the stomatogastric nervous system of the crab, to elucidate the cellular mechanisms whereby multitransmitter modulatory neurons elicit distinct outputs from well-defined networks. Because neural networks are basic building blocks underlying all behaviors, and many of the same organizing principles pertain to network activity in all animals, this work aims to better elucidate how the nervous system generates behavior. This will facilitate a better understanding of network dysfunction that produces aberrant or loss of behavior, such as occurs after spinal cord injury or stroke. Because this research will study the modulation of network function, it will also contribute to general principles that must be understood to address aberrant behaviors occurring during altered states, for example as occurs as a result of drug addiction. This proposal aims to combine cellular neurophysiological, pharmacological and anatomical approaches to elucidate general principles about motor pattern selection from multifunctional networks. This will guide comparable studies in the more complex, mammalian nervous system.

DESCRIPTION (provided by applicant): The long-term goals of this project are to understand, at the cellular level, how the central nervous system selects and generates the neuronal activity patterns underlying movement. This includes determining the flexibility inherent in motor circuits and during coordination of behaviorally-related circuits, plus determining the cellular mechanisms underlying such events. This work focuses on rhythmically active motor circuits, such as those underlying walking, breathing, and chewing. A well-defined model system, the crab stomatogastric nervous system, will be used. Previous work has shown that the same general principles underlie the generation of rhythmic motor programs in all animals. This proposal aims to extend previous work by determining the mechanisms used by identified modulatory projection neurons to alter the output of two well-defined motor circuits, the gastric mill (chewing) and pyloric (filtering of chewed food) circuits. Three hypotheses will be tested: (1) Different modulatory inputs can elicit the same neuronal activity pattern via distinct cellular mechanisms; (2) The neurons and synapses responsible for rhythm generation can be altered by projection neuron-elicited modulation; (3) Circuit regulation of projection neuron activity can determine circuit output. These studies will be done using electrophysiological and pharmacological approaches to monitor and manipulate the activity of circuit and projection neurons. A computer program called the Dynamic Clamp will be used to inject realistic versions of synaptic and ionic currents into single neurons. The stomatogastric system is one of the few biological systems in which a detailed intracellular analysis of neuronal network activity is possible and in which there is a population of identified projection neurons. Thus, the proposed studies will provide a valuable template for understanding comparable events in the numerically larger and less accessible mammalian central nervous system. It will also facilitate understanding the motor dysfunctions that occur as a result of events such as spinal cord injury and stroke.

The long-term goal of this proposal is to determine, at the cellular level, how different extrinsic modulatory inputs select distinct motor patterns from multifunctional neural networks that underlie behavior. In all animals, neuromodulation enables single motor circuits to produce many different activity patterns, thereby producing distinct behaviors. The multifunctional character of such networks derives largely from the actions of modulatory transmitters which alter the cellular and synaptic properties of neurons. These substances are released by sensory, humoral and projection neurons to influence these networks. Thus far, little is known about how specific extrinsic modulatory pathwaysselect a particular motor pattern from a multifunctional network. This issue will be addressed using a well-defined model system, the isolated crabstomatogastric nervous system, in which all of the relevant neurons, synapses and membrane properties can be identified and manipulated. Specifically, (1) the distinct chewing motor pattern triggered by a newly identified extrinsic modulatory pathway will be characterized and compared with the patterns elicited by two previously studied sensory pathways. (2) This will include identifying the intervening projection neurons that mediate this action, including the underlying cellular and synaptic mechanisms. This will help establish a new cellular-level model regarding whether distinct extrinsic inputs elicit different motor outputs from the same network by activating the same, overlapping or different sets of projection neurons. (3) The state-dependent and state- independent consequences from the overlapping or sequential activation of distinct extrinsic inputs will also be determined, as will (4) the roles played by distinct co-releasedtransmitters in these processes. This proposal aims to combine cellular neurophysiological, pharmacological and anatomical approaches to elucidate general principles about motor pattern selection from multifunctional networks. This will guide comparable studies in the more complex and less accessible mammalian nervous system. Because the same organizing principles underlie network activity in all animals, this work will also facilitate a better understanding of network dysfunction that produces aberrant or loss of behavior, such as occurs as a consequence of spinal cord injury, stroke or altered modulatory states such as after drug addiction.

? DESCRIPTION (provided by applicant): Our long-term goal is to understand, at the cellular level, how specific neural activity patterns are selected from multifunctional networks in the intact animal. This project aims to address the largely unknown but prevalent aspect of neural circuit regulation resulting from the parallel influence of multiple, behaviorally-linked modulator inputs (i.e. co-modulation). A set of behaviorally-linked peptide hormones that co-modulate the gastric mill (chewing) motor circuit in the crab stomatogastric nervous system will be identified, and their separate and collective actions on this circuit will be characterized. This work will motivate future studies in the mammalian CNS, insofar as many of the same principles underlie rhythmic motor pattern generation and modulation for all rhythmic movements (e.g. walking, breathing, chewing) in all animals. Specifically, we aim to determine and characterize (1) the behavioral (feeding) state- specific influence of hormone-conveying hemolymph (crab blood) on the gastric mill circuit, and (2) the relationship between co-circulating peptide hormone actions on this circuit and their individual actions. Similar events are not yet elucidated in any defined neural circuit. Hemolymph will first be collected from unfed and recently fed crabs and applied, separately, to the isolated nervous system to determine its effect on the gastric mill (chewing) motor pattern. In parallel, the identity and concentration of the 5 peptide hormones in the hemolymph that exhibit the largest increase from the unfed to fed state will be determined by mass spectrometric methods. These 5 peptides will then be examined, singly and collectively, for their influence on the gastric mill motor pattern. The cellular mechanisms underlying any changes in the gastric mill motor pattern will be determined and compared using current-, voltage- and dynamic-clamp manipulations. This is one of the few biological systems where such a detailed analysis of an identified microcircuit is possible, and where the consequences of in vivo events can be examined in detail with the same system in vitro. These studies will be foundational for understanding comparable events in the mammalian CNS, where circuits are also co-modulated but where a comparable analysis is not yet feasible, and where such systems can become dysfunctional.