Probing Motoneuron Dendritic Integration During Locomotion with Targeted Ion Channel Manipulation in Drosophila

Project: Research project

Description

The generation of rhythmic motor patterns, such as breathing, walking, and flying, relies upon activity in central pattern generating (CPG) networks. CPGs are at the core of motor networks in all animals and can generate patterned motor output in the absence of sensory feedback. Motoneurons (MNs) are the relay output from the CPG networks to the muscles. Although the network plays critical roles in generating the timing of complex patterned spiking output to the muscles, MNs are not merely passive interpreters of synaptic input from pre-motor neurons of the CPG. They are equipped with intrinsic and conditional membrane properties that sculpt the final motor output. Therefore, motor output is determined not only by the synaptic interconnectivity of neurons within the CPG, but also by the intrinsic ionic currents of MNs. MN ion channels are further influenced by neuromodulatory substances which can be released during locomotor activity to shape patterned motor output. Despite a half century of studying MNs by means of intracellular recordings, imaging and computational approaches, our knowledge of how active and conditional membrane properties shape MN synaptic integration and spiking output remains fragmentary. One major problem in identifying the distinct functions of specific ion channel proteins for sculpting behaviorally adequate patterned spiking output in MNs has been that most pharmacological or genetic loss-offunction studies target all neurons of the network. The proposed project will use the genetic power of Drosophila to target specific genetic manipulations to subsets of identified MNs without affecting the rest of the network. To avoid potential developmental effects of targeted expression of transgenes, conditional knock-downs will be used to test for the functional consequences of acute loss of ion channel proteins. The investigators have developed methods for driving and analyzing neural activity underlying locomotion in Drosophila. In combination with in situ whole cell recordings, extracellular recordings and imaging, this will reveal the contribution of three ion channel types that are thought to be particularly critical for the integration of input information and the shaping of behaviorally adequate firing patterns of MNs: calcium, calcium-activated potassium, and hyperpolarizationactivated channels. The experiments will focus on two locomotor activities with distinct requirements for MN activation; larval crawling and adult flight in Drosophila. Crawling motoneurons fire rhythmical bursts, whereas adult flight motoneurons fire tonically during locomotion. We will test the specific roles of for the three channel types in synaptic integration, spike frequency regulation, burst termination and plateau potentials in functionally different motoneurons. This project will also test the role of biogenic amines that are know to affect Drosophila crawling and flight behavior for adjusting conditional membrane properties in MNs. Broader Impacts: Understanding single neuron computation is a crucial step toward understanding brain function. The proposed studies will investigate the relative contributions of three specific ion channels for the generation of behaviorally relevant patterned spiking output in MNs. This provides a powerful model to identify shared mechanisms of MN pattern generation and to test specific hypotheses concerning human movement disorders. Other neurons, including CPG interneurons and cortical neurons are equipped with similar ion channel proteins. Therefore, determining the specific functions of ion channels located on different parts of the neuron will have broad implications for our understanding of neuronal integration and rhythmic circuits within the brain. Drs. Duch and Levine are involved in multidisciplinary graduate degree programs that strive to educate students in approaches to solving complex biological problems, with an emphasis on building qu
StatusFinished
Effective start/end date8/15/107/31/13

Funding

  • NSF: Directorate for Biological Sciences (BIO): $523,766.00

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Motor Neurons
Locomotion
Ion Channels
Drosophila
Neurons
Membranes
Calcium-Activated Potassium Channels
Muscles
Sensory Feedback
Proteins
Biogenic Amines
Movement Disorders
Brain
Patch-Clamp Techniques
Interneurons
Transgenes