Analysis of EPSCs and IPSCs carrying rhythmic, locomotor related
information in the isolated spinal cord of the neonatal rat.
Morten Raastad, Bruce R. Johnson and Ole Kiehn.
Section of Neurophysiology, Department of Physiology, University of
Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark and Section of
Neurobiology and Behavior, Cornell University, Seeley Mudd Hall, Ithaca 14853,
NY, USA.
APStracts 4:0115N, 1997.
ABSTRACT
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-HT and NMDA induced fictive
locomotion. Using a computer algorithm, we identified postsynaptic currents
(PSCs) in rhythmically active interneurons in laminae VII and X. In order to
test whether the PSCs actually participated in the transmission of the cyclic,
locomotor related signal, we constructed an analytical 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 analytical 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 analytical 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 modulation also suggests that the large range of available PSC
amplitudes seen in these neurons was not used very efficiently to code the
cyclic information.
Received 7 May 1997; accepted in final form 25 June 1997.
APS Manuscript Number J371-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 24 July 1997