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Convergent Mechanosensory Input Structures the Firing Phase of a Steering Motor Neuron in the Blowfly, Calliphora

Fayyazuddin, Amir and Dickinson, Michael H. (1999) Convergent Mechanosensory Input Structures the Firing Phase of a Steering Motor Neuron in the Blowfly, Calliphora. Journal of Neurophysiology, 82 (4). pp. 1916-1926. ISSN 0022-3077. doi:10.1152/jn.1999.82.4.1916.

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The first basalar muscle (B1) is 1 of 17 small steering muscles in flies that control changes in wing stroke kinematics during flight. The B1 is often tonically active, firing a single phase-locked action potential in each and every wingbeat cycle. Changes in activation phase alter the biomechanical properties of B1, which in turn cause aerodynamically relevant changes in wing motion. The phase-locked firing of the B1 motor neuron (MNB1), is thought to arise from an interaction of wingbeat-synchronous inputs from the wings and from specialized equilibrium organs called halteres that beat antiphase to the wings and function to detect angular rotation of the body during flight. We investigated how the wing and haltere inputs interact to determine the firing phase of MNB1. Our results indicate that both wing and haltere afferents make strong monosynaptic connections with MNB1, consisting of fast electrical and slow Ca^(2+)-sensitive components. Although both the wing and haltere-evoked excitatory postsynaptic potentials (EPSPs) display the two components, their relative contribution is different for the two inputs. Whereas the haltere-evoked EPSP is dominated by the fast electrical component, the wing-evoked EPSP is dominated by a large chemically mediated component and displays an additional prolonged Ca^(2+)-dependent component that is absent in the haltere-evoked EPSP. Both inputs display an activity-dependent fatigue affecting both electrical and Ca^(2+)-sensitive components, from which the haltere synapse recovers more rapidly. The net result of these synaptic differences is that the two pathways differ significantly in their relative ability to evoke action potentials in MNB1. Although the haltere pathway displays greater temporal precision, the wing pathway is stronger, judged by its ability to entrain MNB1 within a background of haltere stimulation. We propose a model by which these physiological differences play a functional role in tuning the firing phase of MNB1 during flight. The wing input may serve primarily to set the background firing phase of MNB1, whereas the haltere input serves to transiently advance the firing phase during equilibrium reflexes.

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Dickinson, Michael H.0000-0002-8587-9936
Additional Information:© 1999 The American Physiological Society. Received 14 April 1999; accepted in final form 21 June 1999. This work was supported by National Institute of General Medical Sciences Training Grant T32-GM-07839 to A. Fayyazuddin and National Science Foundation Grant IBN-9723424 to M. H. Dickinson. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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NIH Predoctoral FellowshipT32 GM-07839
Issue or Number:4
Record Number:CaltechAUTHORS:20181116-153956584
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Official Citation:Convergent Mechanosensory Input Structures the Firing Phase of a Steering Motor Neuron in the Blowfly, Calliphora Amir Fayyazuddin and Michael H. Dickinson Journal of Neurophysiology 1999 82:4, 1916-1926
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90990
Deposited By: George Porter
Deposited On:17 Nov 2018 00:07
Last Modified:16 Nov 2021 03:37

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