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The Journal of Neuroscience, May 31, 2006, 26(22):5920-5928; doi:10.1523/JNEUROSCI.4623-05.2006

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Cellular/Molecular
Noradrenaline Unmasks Novel Self-Reinforcing Motor Circuits within the Mammalian Spinal Cord

David W. Machacek and Shawn Hochman

Department of Physiology, Emory University, Atlanta, Georgia 30322

Correspondence should be addressed to Shawn Hochman, Department of Physiology, 615 Michael Street, Emory University, Atlanta, GA 30322. shochma{at}emory.edu

Spiking activity in motor axons represents the final central coding for muscle contraction. Recurrent collaterals in spinal cord from these same axons are known to offer a negative feedback control of motor output via a class of interposed inhibitory interneurons. Here we demonstrate that, during noradrenergic drive, a previously unknown recurrent excitatory pathway is unmasked and expressed. These excitatory projections are shown to have broad bilateral actions within and between hindlimb spinal segments and can alter ongoing pattern-generating motor behaviors. Thus, motor output strength is controlled via central positive and negative feedback loops, undoubtedly to provide a greater flexibility and dynamic range of control. That this novel function is regulated by a descending neuromodulatory transmitter indicates a conditional recruitment during certain behavioral states as part of the central noradrenergic arousal apparatus.

Key words: recurrent; excitation; motoneuron; collateral; glutamatergic; cholinergic

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Received Oct. 28, 2005; revised April 18, 2006; accepted April 19, 2006.

Correspondence should be addressed to Shawn Hochman, Department of Physiology, 615 Michael Street, Emory University, Atlanta, GA 30322. shochma{at}emory.edu

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