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The Journal of Neuroscience, November 28, 2007, 27(48):13192-13204; doi:10.1523/JNEUROSCI.1279-07.2007

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Cellular/Molecular
Dopaminergic Modulation of Spinal Neuronal Excitability

Pengcheng Han, Stan T. Nakanishi, Michelle A. Tran, and Patrick J. Whelan

Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada T2N 4N1

Correspondence should be addressed to Patrick J.Whelan, Department of Physiology and Biophysics, HSC 2119, University of Calgary, Calgary, Alberta, Canada T2N 4N1. Email: whelan{at}ucalgary.ca

It is well recognized that dopamine (DA) can modulate spinal networks and reflexes. DA fibers and receptors are present in the spinal cord, and evidence for DA release within the spinal cord has been published. A critical gap is the lack of data regarding dopaminergic modulation of intrinsic and synaptic properties of motoneurons and ventral interneurons in the mammalian spinal cord. In this paper, we address this issue by examining the cellular mechanisms underlying the excitatory effect of DA on motor systems. We examine the effects of DA on two classes of cells important for motor control, motoneurons and Hb9 interneurons, located in lamina VIII. We show that DA can boost excitability in spinal motoneurons by decreasing the first spike latency and the afterhyperpolarization. Collectively, this leads to an increase in the frequency–current slope likely attributable to modulation of I_A and SK_Ca (small-conductance calcium-activated K⁺ channel) currents. We also demonstrate that DA increases glutamatergic transmission onto motoneurons. Our data also suggest that DA stabilizes the rhythmic output of conditionally bursting interneurons. Collectively, these data indicate that DA has widespread actions on intrinsic and synaptic properties of ventral spinal neurons.

Key words: monoamines; spinal cord; central pattern generators; motoneurons; neuromodulators; mouse

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Received Nov. 23, 2006; revised Oct. 15, 2007; accepted Oct. 17, 2007.

Correspondence should be addressed to Patrick J.Whelan, Department of Physiology and Biophysics, HSC 2119, University of Calgary, Calgary, Alberta, Canada T2N 4N1. Email: whelan{at}ucalgary.ca

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