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1 Biology, Emory University, Atlanta, Georgia, USA
* To whom correspondence should be addressed. E-mail: rcalabre{at}biology.emory.edu.
To address the general problem of intersegmental coordination of oscillatory neuronal networks, we have studied the leech heartbeat central pattern generator. The core of this pattern generator is a timing network that consists of two segmental oscillators, each of which comprises two identified, reciprocally inhibitory oscillator interneurons. Intersegmental coordination between the segmental oscillators is mediated by synaptic interactions between the oscillator interneurons and identified coordinating interneurons. The small number of neurons (8) and the distributed structure of the timing network has made the experimental analysis of the segmental oscillators as discrete, independent units possible (Masino and Calabrese 2002a,b,c). Based on this experimental work, we have made conductance-based models to explore how intersegmental phase and cycle period are determined. We show that although a previous simple model, which ignored many details of the living system, replicated some essential features of the living system (Hill et al. 2002), the incorporation of specific cellular and network properties is necessary to capture the behavior of the system seen under different experimental conditions. For example, spike frequency adaptation in the coordinating interneurons and details of asymmetries in intersegmental connectivity are necessary for replicating driving experiments in which one segmental oscillator was injected with periodic current pulses to entrain the activity of the entire network. Nevertheless, the basic mechanisms of phase and period control demonstrated here appear to be very general and could be used by other networks that produce coordinated segmental motor outflow.
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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B. Mulloney and W. M. Hall Not by Spikes Alone: Responses of Coordinating Neurons and the Swimmeret System to Local Differences in Excitation J Neurophysiol, January 1, 2007; 97(1): 436 - 450. [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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A.-E. Tobin, S. D. Van Hooser, and R. L. Calabrese Creation and Reduction of a Morphologically Detailed Model of a Leech Heart Interneuron J Neurophysiol, October 1, 2006; 96(4): 2107 - 2120. [Abstract] [Full Text] [PDF]
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