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The Journal of Neurophysiology Vol. 87 No. 3 March 2002, pp. 1572-1585
Copyright ©2002 by the American Physiological Society
Biology Department, Emory University, Atlanta, Georgia 30322
Masino, Mark A. and
Ronald L. Calabrese.
Phase Relationships Between Segmentally Organized Oscillators in
the Leech Heartbeat Pattern Generating Network. J. Neurophysiol. 87: 1572-1585, 2002. Motor pattern
generating networks that produce segmentally distributed motor outflow
are often portrayed as a series of coupled segmental oscillators that
produce a regular progression (constant phase differences) in their
rhythmic activity. The leech heartbeat central pattern generator is
paced by a core timing network, which consists of two coupled segmental
oscillators in segmental ganglia 3 and 4. The segmental oscillators
comprise paired mutually inhibitory oscillator interneurons and the
processes of intersegmental coordinating interneurons. As a first step
in understanding the coordination of segmental motor outflow by this
pattern generator, we describe the functional synaptic interactions,
and activity and phase relationships of the heart interneurons of the
timing network, in isolated nerve cord preparations. In the timing
network, most (~75%) of the coordinating interneuron action
potentials were generated at a primary spike initiation site located in
ganglion 4 (G4). A secondary spike initiation site in ganglion 3 (G3)
became active in the absence of activity at the primary site.
Generally, the secondary site was characterized by a reluctance to
burst and a lower spike frequency, when compared with the primary site.
Oscillator interneurons in G3 inhibited spike activity at both
initiation sites, whereas oscillator interneurons in G4 inhibited spike
activity only at the primary initiation site. This asymmetry in the
control of spike activity in the coordinating interneurons may account
for the observation that the phase of the coordinating interneurons is
more tightly linked to the G3 than G4 oscillator interneurons. The
cycle period of the timing network and the phase difference between the
ipsilateral G3 and G4 oscillator interneurons were regular within
individual preparations, but varied among preparations. This variation
in phase differences observed across preparations implies that
modulated intrinsic membrane and synaptic properties, rather than the
pattern of synaptic connections, are instrumental in determining phase
within the timing network.
This article has been cited by other articles:
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  B. J. Norris, A. L. Weaver, A. Wenning, P. S. Garcia, and R. L. Calabrese A Central Pattern Generator Producing Alternative Outputs: Phase Relations of Leech Heart Motor Neurons With Respect to Premotor Synaptic Input J Neurophysiol, November 1, 2007; 98(5): 2983 - 2991. [Abstract] [Full Text] [PDF]
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B. Mulloney and W. M. Hall Local and Intersegmental Interactions of Coordinating Neurons and Local Circuits in the Swimmeret System J Neurophysiol, July 1, 2007; 98(1): 405 - 413. [Abstract] [Full Text] [PDF]
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A. Olypher, G. Cymbalyuk, and R. L. Calabrese Hybrid Systems Analysis of the Control of Burst Duration by Low-Voltage-Activated Calcium Current in Leech Heart Interneurons J Neurophysiol, December 1, 2006; 96(6): 2857 - 2867. [Abstract] [Full Text] [PDF]
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A.-E. Tobin and R. L. Calabrese Endogenous and Half-Center Bursting in Morphologically Inspired Models of Leech Heart Interneurons J Neurophysiol, October 1, 2006; 96(4): 2089 - 2106. [Abstract] [Full Text] [PDF]
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B. J. Norris, A. L. Weaver, L. G. Morris, A. Wenning, P. A. Garcia, and R. L. Calabrese A Central Pattern Generator Producing Alternative Outputs: Temporal Pattern of Premotor Activity J Neurophysiol, July 1, 2006; 96(1): 309 - 326. [Abstract] [Full Text] [PDF]
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A.-E. Tobin and R. L. Calabrese Myomodulin Increases Ih and Inhibits the Na/K Pump to Modulate Bursting in Leech Heart Interneurons J Neurophysiol, December 1, 2005; 94(6): 3938 - 3950. [Abstract] [Full Text] [PDF]
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S. H. Jezzini, A. A. V. Hill, P. Kuzyk, and R. L. Calabrese Detailed Model of Intersegmental Coordination in the Timing Network of the Leech Heartbeat Central Pattern Generator J Neurophysiol, February 1, 2004; 91(2): 958 - 977. [Abstract] [Full Text] [PDF]
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A. Wenning, A. A. V. Hill, and R. L. Calabrese Heartbeat Control in Leeches. II. Fictive Motor Pattern J Neurophysiol, January 1, 2004; 91(1): 397 - 409. [Abstract] [Full Text]
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A. A.V. Hill, M. A. Masino, and R. L. Calabrese Intersegmental Coordination of Rhythmic Motor Patterns J Neurophysiol, August 1, 2003; 90(2): 531 - 538. [Full Text] [PDF]
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 G. S. Cymbalyuk, Q. Gaudry, M. A. Masino, and R. L. Calabrese Bursting in Leech Heart Interneurons: Cell-Autonomous and Network-Based Mechanisms J. Neurosci., December 15, 2002; 22(24): 10580 - 10592. [Abstract] [Full Text] [PDF]
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M. A. Masino and R. L. Calabrese A Functional Asymmetry in the Leech Heartbeat Timing Network Is Revealed by Driving the Network across Various Cycle Periods J. Neurosci., June 1, 2002; 22(11): 4418 - 4427. [Abstract] [Full Text] [PDF]
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A. A. V. Hill, M. A. Masino, and R. L. Calabrese Model of Intersegmental Coordination in the Leech Heartbeat Neuronal Network J Neurophysiol, March 1, 2002; 87(3): 1586 - 1602. [Abstract] [Full Text] [PDF]
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M. A. Masino and R. L. Calabrese Period Differences Between Segmental Oscillators Produce Intersegmental Phase Differences in the Leech Heartbeat Timing Network J Neurophysiol, March 1, 2002; 87(3): 1603 - 1615. [Abstract] [Full Text] [PDF]
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