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1 Biology, Emory University, Atlanta, GA, USA
* To whom correspondence should be addressed. E-mail: rcalabre{at}biology.emory.edu.
The rhythmic beating of the tube-like hearts in the medicinal leech is driven and coordinated by rhythmic activity in segmental heart motor neurons (Maranto and Calabrese 1984b; Thompson and Stent 1976b). The motor neurons are controlled by rhythmic inhibitory input from a network of heart interneurons that compose the heartbeat central pattern generator (Calabrese et al. 1995). In the preceding paper (Wenning et al. 2003), we described the constriction pattern of the hearts in quiescent intact animals and showed that one heart constricts in a rear-to-front wave (peristaltic coordination mode), while the other heart constricts in near unison over its length (synchronous coordination mode) and that they regularly switch coordination modes. Here we analyze intersegmental and side-to-side-coordination of the fictive motor pattern for heartbeat in denervated nerve cords. We show that the intersegmental phase relations among heart motor neurons in both coordination modes are independent of heartbeat period. This finding enables us to combine data from different experiments to form a detailed analysis of the relative phases, duty cycle, and intraburst spike frequency of the bursts of the segmental heart motor neurons. The fictive motor pattern and the constriction pattern seen in intact leeches closely match in their intersegmental and side-to-side coordination, indicating that sensory feedback is not necessary for properly phased intersegmental coordination. Moreover, the regular switches in coordination mode of the fictive motor pattern mimic those seen in intact animals indicating that these switches likely arise by a central mechanism.
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  P. S. Garcia, T. M. Wright, I. R. Cunningham, and R. L. Calabrese Using a Model to Assess the Role of the Spatiotemporal Pattern of Inhibitory Input and Intrasegmental Electrical Coupling in the Intersegmental and Side-to-Side Coordination of Motor Neurons by the Leech Heartbeat Central Pattern Generator J Neurophysiol, September 1, 2008; 100(3): 1354 - 1371. [Abstract] [Full Text] [PDF]
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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. J. Norris, A. L. Weaver, A. Wenning, P. S. Garcia, and R. L. Calabrese A Central Pattern Generator Producing Alternative Outputs: Pattern, Strength, and Dynamics of Premotor Synaptic Input to Leech Heart Motor Neurons J Neurophysiol, November 1, 2007; 98(5): 2992 - 3005. [Abstract] [Full Text] [PDF]
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 A. Wenning and E. P. Meyer Hemodynamics in the leech: blood flow in two hearts switching between two constriction patterns J. Exp. Biol., August 1, 2007; 210(15): 2627 - 2636. [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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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. Wenning, G. S. Cymbalyuk, and R. L. Calabrese Heartbeat Control in Leeches. I. Constriction Pattern and Neural Modulation of Blood Pressure in Intact Animals J Neurophysiol, January 1, 2004; 91(1): 382 - 396. [Abstract] [Full Text]
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