Mark A. Masino, BS, BA, MA, PhD - US grants

DESCRIPTION (provided by applicant): The broad objective of this proposal is to examine how spinal circuits are functionally and structurally organized to generate different motor behaviors. Although there is some good information about how spinal circuits generate particular motor behaviors, such as swimming in lampreys or frog embryos, much less is known about how multiple different behaviors are produced using the available circuitry in spinal cord. The major goals for this proposal are to determine the contribution of different classes of spinal interneurons in different motor behaviors, to examine the synaptic connectivity of interneurons active in these different behaviors, and to examine the patterns of activity within a pool of spinal interneurons not only within a single behavior, but also between different behaviors. Larval zebrafish will be the model system used for this study. The translucent nature of this preparation combined with functional imaging techniques and recent advances in genetic methods permits the means to monitor identified neurons in vivo during various behaviors and thus to correlate neuronal activity to behavior. In brief, this study will examine how spinal circuits are organized to generate swimming and struggling behaviors in zebrafish as a model for how spinal circuits use the available circuitry to produce different motor behaviors

DESCRIPTION (provided by applicant): The focus of this proposal is to examine the functional and structural organization of a vertebrate spinal network responsible for generating coordinated locomotor activity. To construct a more thorough understanding of network organization it is important to address fundamental issues including the identification of key neuronal components and the characterization of their cellular and synaptic connectivity properties, which help to generate or support the motor output. This study is designed to test specific hypotheses in an attempt to progress our understanding of the organization of the spinal network that produces swimming in larval zebrafish. The specific aims are: 1) To characterize the morphological and neurotransmitter properties of the interneuronal populations marked by Hb9 in the larval zebrafish spinal cord, 2) To test the hypothesis that an identified Hb9 spinal interneuron population or populations participate in driving the locomotor rhythm, and 3) To test the hypothesis that intrinsic membrane properties contribute to the generation of locomotor activity. A combination of neurogenetic, optical imaging and conventional electrophysiological techniques will be used to determine the functional roles specific, identified spinal interneurons play in generating the locomotor drive underlying swimming behavior in zebrafish. Ultimately, the approach outlined in this project will provide a fundamental understanding of the organization of the neural network that generates vertebrate locomotion, which can be used to inform clinical and procedural strategies to treat individuals with spinal cord injuries. PUBLIC HEALTH RELEVANCE: In vertebrates, the neural network that drives locomotion is composed of a set of interconnected interneurons located in the spinal cord. Our goal is to gain a fundamental understanding of how the vertebrate spinal networks are organized to generate a coordinated pattern of motor activity, which will provide elemental information central to the development of novel concepts and potential clinical management of spinal cord injuries.

Project Summary Abstract The focus of this proposal is to characterize DAergic modulation of coarse and fine locomotor control using a multi-level integrative approach, from behavior to receptor signaling, that employs a powerful array of approaches. To gain a fundamental understanding of the cellular, network and modulatory properties that underlie the development of vertebrate locomotor activity it is critical to examine the neural mechanisms that drive the activity. This proposal is designed to address three main points: 1) Determine the neural mechanisms underlying a developmental switch in locomotor activity from an immature to a mature pattern by a combination of pharmacological, optogenetic and calcium imaging experiments, 2) Characterize the role of descending dopaminergic drive in fine motor behaviors, such as orienting and advancing maneuvers during hunting, by high-speed kinematic analysis of larvae with targeted inactivation (laser photoablation and/or optogenetic) of dopaminergic neurons in the ventral diencephalon, and 3) Identify spinal neurons modulated by the descending dopaminergic drive by correlating the expression of dopamine receptor mRNA transcripts with identified classes of putative locomotor-related spinal neurons. The broad intellectual scope of this proposal and the use of diverse experimental techniques, from simple behavioral measurements to the optical control of neuronal activity, permit the inclusion of students across various levels of sophistication, including high school (restricted to summer months), undergraduate and graduate students, and postdoctoral associates. The lab currently has one graduate student, one post-doctoral associate (5+ years of experience), a senior research associate (over 20+ years of experience), and several undergraduates. Understanding the cellular, network and modulatory properties that underlie the development of locomotor activity will likely aid in developing therapeutic interventions for DAergic-related diseases of the motor system, such as Restless Leg Syndrome, Periodic Leg Movement Disorder and Parkinson's Disease.