Neural Coding of Leg Proprioception in Drosophila
authors: Akira Mamiya, Pralaksha Gurung, John C. Tuthill
doi: 10.1016/j.neuron.2018.09.009
CITATION
Mamiya, A., Gurung, P., & Tuthill, J. C. (2018). Neural Coding of Leg Proprioception in Drosophila. Neuron, 100(3), 636-650.e6. https://doi.org/10.1016/j.neuron.2018.09.009
ABSTRACT
fleeting notes
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2p calcium imaging of proprioceptive sensory neurons during controlled movements of the fly tibia
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axons are organized into distinct functional projections containing topographic representations of kinematic features — does this just mean movement?
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one group = tibia position (flexion and extension)
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one group = tibia movement direction
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one group = tibia bidirectional movement and vibration frequency
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“proprioceptive stimuli from single leg joint are encoded by diverse population of sensory neurons and how proprioceptive feedback signals are used by motor circuits to coordinate body”
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Femoral chordotonal organ - FeCO
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population imaging from proprioceptive neurons labeled by iav-gal4
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chose to control leg kinematics with a magnetic bar that moved the joint angle
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calculated pairwise correlations between calcium signal in each pixel in order to cluster activity then performed kmeans clustering on the correlation matrix
- this revealed spatially separated groups of axons that encode distinct proprioceptive stim features
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to find the functional organization of FeCO axons
- first clustered trial to trial from four regions of interest
- combined responses from same region in different flies
- then grouped again using kmeans clustering
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5 basic subclasses of responses in FeCO axons
- two tonic non adapting
- 3 phasic adapting
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tonic response - increase activity when tibia extends or flexes
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phasic response - transient increase during movement phase of swing
- one responded to either direction
- 2 responded only to one direction
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different projections of proprioceptive axons have different tuning and are organized similarly across flies
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club - labels axons that run laterally through center of leg (R64C04-Gal4)
- terminate near midline. some toward brain or other segments
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claw - shaped like a claw. projections split into 3 smaller branches. X,Y,Z branches. (R73D10-Gal4)
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hook - projections run along Z branch of the claw and extend a longer arborization toward midline (R21D21-Gal4)
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claw neurons tonically increase activity in response to flexion or extension of tibia
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club neurons phasically increase activity in response to flexion or extension
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hook neurons active more during flexion
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ramp and hold stimulus to explore position dependent tuning of proprioceptor subclasses
- claw neurons responded with tonic increases during flexion or extension
- activity of extension tuned pixels increased when tibia was between 90 and 180 degrees
- flexion tuned pixels increased when tibia was less than 90 degrees
- none active during middle of range
- linear tuning of femur tibia joint angle
- club neurons respond phasically to each tibia movement regardless of direction across all joint angles
- hook neurons phasically increase activity during flexion not extension. slightly weaker when fully extended
- claw neurons responded with tonic increases during flexion or extension
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used a piezoelectric chip to vibrate magnet attached to leg at different frequencies (100-2000 hz)
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club neurons have large response to tibia vibration
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claw and hook do not respond to vibration
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spatial organization of responses in club neurons in response to frequency range
- a frequency map
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single club neurons are tuned to different frequencies
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single claw neurons are tuned to have peak responses at different femur tibia angles