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The Journal of Neuroscience, January 24, 2007, 27(4):919-928; doi:10.1523/JNEUROSCI.4035-06.2007

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Development/Plasticity/Repair
ERG Conductance Expression Modulates the Excitability of Ventral Horn GABAergic Interneurons That Control Rhythmic Oscillations in the Developing Mouse Spinal Cord

Francesco Furlan,¹ Giuliano Taccola,² Micaela Grandolfo,² Leonardo Guasti,³ Annarosa Arcangeli,³ Andrea Nistri,² and Laura Ballerini¹

¹Physiology and Pathology Department, Center for Neuroscience B.R.A.I.N., University of Trieste, 34127 Trieste, Italy, ²Neurobiology Sector, International School for Advanced Studies, 34014 Trieste, Italy, and SPINAL Project, Udine, ³Department of Experimental Pathology and Oncology, University of Firenze, 50134 Firenze, Italy

Correspondence should be addressed to Dr. Laura Ballerini, Physiology and Pathology Department, Center for Neuroscience B.R.A.I.N., University of Trieste, via Fleming 22, 34127, Trieste, Italy. Email: ballerin{at}psico.units.it

During antenatal development, the operation and maturation of mammalian spinal networks strongly depend on the activity of ventral horn GABAergic interneurons that mediate excitation first and inhibition later. Although the functional consequence of GABA actions may depend on maturational processes in target neurons, it is also likely that evolving changes in GABAergic transmission require fine-tuning in GABA release, probably via certain intrinsic mechanisms regulating GABAergic neuron excitability at different embryonic stages. Nevertheless, it has not been possible, to date, to identify certain ionic conductances upregulated or downregulated before birth in such cells. By using an experimental model with either mouse organotypic spinal cultures or isolated spinal cord preparations, the present study examined the role of the ERG current (I_K(ERG)), a potassium conductance expressed by developing, GABA-immunoreactive spinal neurons. In organotypic cultures, only ventral interneurons with fast adaptation and GABA immunoreactivity, and only after 1 week in culture, were transformed into high-frequency bursters by E4031, a selective inhibitor of I_K(ERG) that also prolonged and made more regular spontaneous bursts. In the isolated spinal cord in which GABA immunoreactivity and m-erg mRNA were colocalized in interneurons, ventral root rhythms evoked by NMDA plus 5-hydroxytryptamine were stabilized and synchronized by E4031. All of these effects were lost after 2 weeks in culture or before birth in coincidence with decreased m-erg expression. These data suggest that, during an early stage of spinal cord development, the excitability of GABAergic ventral interneurons important for circuit maturation depended, at least in part, on the function of I_K(ERG).

Key words: potassium channels; interneurons; spinal circuits; firing adaptation; ERG; inhibition; organotypic cultures; bursting

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Received Sept. 15, 2006; revised Dec. 14, 2006; accepted Dec. 20, 2006.

Correspondence should be addressed to Dr. Laura Ballerini, Physiology and Pathology Department, Center for Neuroscience B.R.A.I.N., University of Trieste, via Fleming 22, 34127, Trieste, Italy. Email: ballerin{at}psico.units.it

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