Excitatory synaptic currents in lumbosacral parasympathetic preganglionic neurons
evoked by stimulation of the lateral funiculus in the neonatal rat.
Miura, Akira, Masahito Kawatani, and William C. De Groat.
*Department of Pharmacology, University of Pittsburgh, School of Medicine,
Pittsburgh, PA 15261, USA.; **Department of Physiology, Akita University, School of
Medicine, Akita 010-8543, Japan.
APStracts 8:0238J, 2001.
Excitatory postsynaptic currents (EPSCs) in parasympathetic preganglionic neurons
(PGN) were examined using the whole-cell patch-clamp recording technique in L6 and
S1 spinal cord slices from neonatal rats (6-11 days old). PGN were identified by labeling
with retrograde axonal transport of a fluorescent dye (Fast Blue) injected into the
intraperitoneal space 3-7 days before the experiment. Synaptic responses were evoked in
PGN by field stimulation of the lateral funiculus (LF) in the presence of bicuculline
methiodide (10 ?M) and strychnine (1 ?M). In approximately 40% of the cells (total,
100), single-shock electrical stimulation of the LF elicited short, relatively constant
latency (3.0 ? 0.1 ms) fast EPSCs consistent with a monosynaptic pathway. The
remainder of the cells did not respond to stimulation. At low intensities of stimulation the
EPSCs often occurred in an all-or-none manner indicating that they were mediated by a
single axonal input. Most cells (n = 33) exhibited only fast EPSCs (Type 1), but some
cells (n = 8) had fast EPSCs with longer, more variable latency polysynaptic EPSCs
superimposed on a slow inward current (Type 2). Type 1 fast synaptic EPSCs were
pharmacologically dissected into two components: a transient component which was
blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5?M) a non-NMDA
glutamatergic antagonist and a slow decaying component which was blocked by 2-
amino-5-phosphonovalerate (APV, 50 ?M) a NMDA antagonist. Type 2 polysynaptic
currents were reduced by 5 ?M CNQX and completely blocked by combined application
of 5 ?M CNQX and 50 ?M APV. The fast monosynaptic component of Type 1 EPSCs
had a linear current-voltage relationship and reversed at a membrane potential of 5.0 ?
5.9 mV (n = 5); whereas the slow component exhibited a negative slope conductance at
holding potentials greater than –20 mV. The Type 1 fast synaptic EPSCs had a time to
peak of 1.4 ? 0.1 ms and exhibited a biexponential decay (time constants, 5.7 ? 0.6 and
38.8 ? 4.0 ms). In the majority of PGN (n = 11 of 15 cells) EPSCs evoked by electrical
stimulation of LF exhibited paired-pulse inhibition (range; 25-33% depression) at
interstimulus intervals ranging from 60 to 120 ms. These results indicate that PGN
receive monosynaptic and polysynaptic glutamatergic excitatory inputs from axons in the
lateral funiculus.
Received 12 December 2000; accepted in final form 30 May 2001
APS Manuscript Number J901-0.
Article publication pending Am J Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 31 July 2001