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The Journal of Neuroscience, July 6, 2005, 25(27):6316-6321; doi:10.1523/JNEUROSCI.0843-05.2005

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BRIEF COMMUNICATION
Periodic High-Conductance States in Spinal Neurons during Scratch-Like Network Activity in Adult Turtles

A. Alaburda,¹ R. Russo,² N. MacAulay,³ and J. Hounsgaard³

¹Department of Biochemistry and Biophysics, Faculty of Natural Sciences, Vilnius University, 03101 Vilnius, Lithuania, ²Unidad Asociada Neurofisiologia, Instituto de Investigacious Biologicas Clemente, Estable, Facultad de Ciencias, CP-11600 Montevideo, Uruguay, and ³Department of Medical Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark

Intense synaptic activity may alter the response properties of neurons in highly interconnected networks. Here we investigate whether the excitability and the intrinsic response properties of neurons in the spinal cord are affected by the increased synaptic conductance during functional network activity. Scratch episodes were induced by mechanical stimulation in the isolated carapace-spinal cord preparation from the adult turtle. Intracellular recordings revealed a dramatic increase in synaptic activity in interneurons and motoneurons during scratch activity. Superimposed slow depolarizing waves were phase-related to the rhythmic bouts of spike activity in the hip flexor nerve. The increase in synaptic conductance in interneurons and motoneurons varied with the scratch rhythm. During individual episodes, the conductance shifted smoothly with the scratch rhythm from near-resting levels to levels two to four times higher. In slice experiments, we found that even moderate increases in the conductance of motoneurons suppressed the slow afterhyperpolarization and the plateau potentials. We conclude that the excitability and the intrinsic response properties of spinal neurons are periodically quenched by high synaptic conductance during functional network activity.

Key words: spinal cord integrated preparation; modulation; membrane conductance; motoneuron; reflex; synaptic plasticity

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Received March 3, 2005; revised May 19, 2005; accepted May 22, 2005.

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