The Journal of Neurophysiology Vol. 78 No. 4 October 1997, pp. 1851-1859
Copyright ©1997 The American Physiological Society

Analysis of EPSCs and IPSCs Carrying Rhythmic, Locomotor-Related Information in the Isolated Spinal Cord of the Neonatal Rat

Morten Raastad¹, Bruce R. Johnson², and Ole Kiehn¹

¹ Section of Neurophysiology, Department of Physiology, University of Copenhagen, 2200 Copenhagen N, Denmark; and ² Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853

Raastad, Morten, Bruce R. Johnson, and Ole Kiehn. Analysis of EPSCs and IPSCs carrying rhythmic, locomotor-related information in the isolated spinal cord of the neonatal rat. J. Neurophysiol. 78: 1851-1859, 1997. To understand better the synaptic language used by neurons in active networks, we have analyzed postsynaptic currents (PSCs) received by interneurons in the isolated spinal cord from neonatal rats during 5-hydroxytryptamine- and N-methyl-D-aspartate-induced fictive locomotion. Using a computer algorithm, we identified PSCs in rhythmically active interneurons in laminae VII and X. To test whether the PSCs actually participated in the transmission of the cyclic, locomotor-related signal, we constructed an analytic current trace based on only the identified events. Each identified PSC was fitted by a mathematical function, and the shape of this function was added to a baseline with time delays given by the time positions of the identified PSCs. By averaging the resulting analytic current trace over several cycles, we showed that the identified PSCs built a cyclic signal locked to the rhythmic activity recorded from the ventral roots. Furthermore, subtraction of the analytic from the original current trace reduced the amplitude of the cyclic signal received by these cells. Thus the identified PSCs contributed to the cyclic information, allowing us to analyze how they built the compound cyclic signal. Most often there was an inverse relationship between the contribution from excitatory and inhibitory PSCs during the cyclic modulation, indicating that there was a reciprocal regulation of the presynaptic inhibitory and excitatory cells. Comparing the most inhibitory and most excitatory halves of the locomotor related cycle, there was a considerably larger modulation of the frequency of PSCs than of their amplitude. The small and sometimes insignificant modulation of PSC amplitude suggests that facilitation and depression had little importance for the information transfer. The modest amplitude modification also suggests that the large range of available PSC amplitudes seen in these neurons was not used very efficiently to code the cyclic information.

This article has been cited by other articles:

				L. Ziskind-Conhaim, L. Wu, and E. P. Wiesner Persistent Sodium Current Contributes to Induced Voltage Oscillations in Locomotor-Related Hb9 Interneurons in the Mouse Spinal Cord J Neurophysiol, October 1, 2008; 100(4): 2254 - 2264. [Abstract] [Full Text] [PDF]

				C. A. Hinckley, R. Hartley, L. Wu, A. Todd, and L. Ziskind-Conhaim Locomotor-Like Rhythms in a Genetically Distinct Cluster of Interneurons in the Mammalian Spinal Cord J Neurophysiol, March 1, 2005; 93(3): 1439 - 1449. [Abstract] [Full Text] [PDF]

				P. J Whelan Developmental aspects of spinal locomotor function: insights from using the in vitro mouse spinal cord preparation J. Physiol., December 15, 2003; 553(3): 695 - 706. [Abstract] [Full Text] [PDF]

				S. J. B. Butt, R. M. Harris-Warrick, and O. Kiehn Firing Properties of Identified Interneuron Populations in the Mammalian Hindlimb Central Pattern Generator J. Neurosci., November 15, 2002; 22(22): 9961 - 9971. [Abstract] [Full Text] [PDF]

				M.-C. Perreault Motoneurons Have Different Membrane Resistance during Fictive Scratching and Weight Support J. Neurosci., September 15, 2002; 22(18): 8259 - 8265. [Abstract] [Full Text] [PDF]

				R. Demir, B.-X. Gao, M. B. Jackson, and L. Ziskind-Conhaim Interactions Between Multiple Rhythm Generators Produce Complex Patterns of Oscillation in the Developing Rat Spinal Cord J Neurophysiol, February 1, 2002; 87(2): 1094 - 1105. [Abstract] [Full Text] [PDF]

				U. Beierholm, C. D. Nielsen, J. Ryge, P. Alstrom, and O. Kiehn Characterization of Reliability of Spike Timing in Spinal Interneurons During Oscillating Inputs J Neurophysiol, October 1, 2001; 86(4): 1858 - 1868. [Abstract] [Full Text] [PDF]

				M. Raastad and O. Kiehn Spike Coding During Locomotor Network Activity in Ventrally Located Neurons in the Isolated Spinal Cord From Neonatal Rat J Neurophysiol, May 1, 2000; 83(5): 2825 - 2834. [Abstract] [Full Text] [PDF]

				L. Ballerini, M. Galante, M. Grandolfo, and A. Nistri Generation of rhythmic patterns of activity by ventral interneurones in rat organotypic spinal slice culture J. Physiol., June 1, 1999; 517(2): 459 - 475. [Abstract] [Full Text] [PDF]

				M. Raastad, M. Enriquez-Denton, and O. Kiehn Synaptic signaling in an active central network only moderately changes passive membrane properties PNAS, August 18, 1998; 95(17): 10251 - 10256. [Abstract] [Full Text] [PDF]