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Volume 17, Number 18, Issue of September 15, 1997 pp. 6872-6883
Copyright ©1997 Society for Neuroscience

Modulation of Force during Locomotion: Differential Action of Crustacean Cardioactive Peptide on Power-Stroke and Return- Stroke Motor Neurons

Received May 7, 1997; revised June 26, 1997; accepted June 30, 1997.

Brian Mulloney¹, Hisaaki Namba¹, Hans-Jürgen Agricola², and Wendy M. Hall¹

¹ Section of Neurobiology, Physiology, and Behavior, University of California Davis, Davis, California 95616-8755, and ² Biologisch-Pharmazeutische Fakultät, Friedrich-Schiller-Universität, D-07743 Jena, Germany

Crustacean cardioactive peptide (CCAP) elicited expression of the motor pattern that drives coordinated swimmeret beating in crayfish and modulated this pattern in a dose-dependent manner. In each ganglion that innervates swimmerets, neurons with CCAP-like immunoreactivity sent processes to the lateral neuropils, which contain branches of swimmeret motor neurons and the local pattern-generating circuits.

CCAP affected each of the four functional groups of motor neurons, power-stroke excitors (PSE), return-stroke excitors (RSE), power-stroke inhibitors (PSI), and return-stroke inhibitors (RSI), that innervate each swimmeret. When CCAP was superfused, the membrane potentials of these neurons began to oscillate periodically about their mean potentials. The mean potentials of PSE and RSI neurons depolarized, and some of these neurons began to fire during each depolarization. Both intensity and durations of PSE bursts increased significantly. The mean potentials of RSE and PSI neurons hyperpolarized, and these neurons were less likely to fire during each depolarization. When CCAP was superfused in a low Ca²⁺ saline that blocked chemical transmission, these changes in mean potential persisted, but the periodic oscillations disappeared.

These results are evidence that CCAP acts at two levels: activation of local premotor circuits and direct modulation of swimmeret motor neurons. The action on motor neurons is differential; PSEs and RSIs are excited, but RSEs and PSIs are inhibited. The consequences of this selectivity are to increase intensity of bursts of impulses that excite power-stroke muscles.

Key words: neuropeptide; pattern generation; crayfish; immunocytochemistry; modulation; neuropil

This article has been cited by other articles:

				M. S. Kirby and M. P. Nusbaum Peptide Hormone Modulation of a Neuronally Modulated Motor Circuit J Neurophysiol, December 1, 2007; 98(6): 3206 - 3220. [Abstract] [Full Text] [PDF]

				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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