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The Journal of Neuroscience, April 16, 2008, 28(16):4192-4200; doi:10.1523/JNEUROSCI.0136-08.2008

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Behavioral/Systems/Cognitive
Dopamine Activates the Motor Pattern for Crawling in the Medicinal Leech

Joshua G. Puhl and Karen A. Mesce

Graduate Program in Neuroscience, and Departments of Entomology and Neuroscience, University of Minnesota, Saint Paul, Minnesota 55108

Correspondence should be addressed to Dr. Karen A. Mesce, Departments of Entomology and Neuroscience, University of Minnesota, 219 Hodson Hall, 1980 Folwell Avenue, Saint Paul, MN 55108, Email: mesce001{at}umn.edu

Locomotion in segmented animals is thought to be based on the coupling of "unit burst generators," but the biological nature of the unit burst generator has been revealed in only a few animal systems. We determined that dopamine (DA), a universal modulator of motor activity, is sufficient to activate fictive crawling in the medicinal leech, and can exert its actions within the smallest division of the animal's CNS, the segmental ganglion. In the entire isolated nerve cord or in the single ganglion, DA induced slow antiphasic bursting (15 s period) of motoneurons known to participate in the two-step elongation–contraction cycle underlying crawling behavior. During each cycle, the dorsal (DE-3) and ventral (VE-4) longitudinal excitor motoneurons fired 180° out of phase from the ventrolateral circular excitor motoneuron (CV), which marks the elongation phase. In many isolated whole nerve cords, DE-3 bursting progressed in an anterior to posterior direction with intersegmental phase delays appropriate for crawling. In the single ganglion, the dorsal (DI-1) and ventral (VI-2) inhibitory longitudinal motoneurons fired out of phase with each DE-3 burst, further confirming that the crawl unit burst generator exists in the single ganglion. All isolated ganglia of the CNS were competent to produce DA-induced robust fictive crawling, which typically lasted uninterrupted for 5–15 min. A quantitative analysis indicated that DA-induced crawling was not significantly different from electrically evoked or spontaneous crawling. We conclude that DA is sufficient to activate the full crawl motor program and that the kernel for crawling resides within each segmental ganglion.

Key words: locomotion; Hirudo; central pattern generator; intersegmental coordination; spinal cord; fictive behavior

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Received Jan. 11, 2008; revised March 22, 2008; accepted March 22, 2008.

Correspondence should be addressed to Dr. Karen A. Mesce, Departments of Entomology and Neuroscience, University of Minnesota, 219 Hodson Hall, 1980 Folwell Avenue, Saint Paul, MN 55108, Email: mesce001{at}umn.edu

This article has been cited by other articles:

				N. P. Lapointe, P. Rouleau, R.-V. Ung, and P. A. Guertin Specific role of dopamine D1 receptors in spinal network activation and rhythmic movement induction in vertebrates J. Physiol., April 1, 2009; 587(7): 1499 - 1511. [Abstract] [Full Text] [PDF]

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