1Department of Pharmacology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261; and 2Department of Physiology, School of Medicine, Akita University, Akita 010-8543, Japan
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Miura, Akira,
Masahito Kawatani, and
William C. de
Groat.
Excitatory Synaptic Currents in Lumbosacral Parasympathetic
Preganglionic Neurons Elicited From the Lateral Funiculus.
J. Neurophysiol. 86: 1587-1593, 2001.
Excitatory postsynaptic currents (EPSCs) in parasympathetic
preganglionic neurons (PGNs) were examined using the whole cell patch-clamp recording technique in L6 and
S1 spinal cord slices from neonatal rats (6-16
days old). PGNs 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 PGNs by field stimulation of the lateral
funiculus (LF) in the presence of bicuculline methiodide (10 µM) and
strychnine (1 µM). In approximately 40% of the cells (total, 100),
single-shock electrical stimulation of the LF elicited short,
relatively constant latency [3.0 ± 0.1 (SE) 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 that was blocked
by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 5 µM), a non-NMDA
glutamatergic antagonist, and a slow decaying component that was
blocked by 2-amino-5-phosphonovalerate (APV, 50 µM), a NMDA
antagonist. Type 2 polysynaptic currents were reduced by 5 µM CNQX
and completely blocked by combined application of 5 µM CNQX and 50 µM 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 PGNs (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 50 to 120 ms. These
results indicate that PGNs receive monosynaptic and polysynaptic
glutamatergic excitatory inputs from axons in the lateral funiculus.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Lumbosacral parasympathetic
preganglionic neurons (PGNs) play an important role in regulating
pelvic visceral organs including bladder, distal bowel and sex
organs (de Groat and Steers 1990; de Groat et al.
1981
, 1982
). The reflex activation of many of these neurons is
controlled in part by axons descending in the lateral funiculus from
various nuclei in the brain including the pontine micturition center,
locus coeruleus, hypothalamus, and raphe nuclei (de Groat et al.
1993
; Kuru 1965
; Morrison 1987
). Multiple neurotransmitters (glutamate, serotonin, norepinephrine, oxytocin, corticotropin releasing factor) are likely to be involved in
the bulbospinal control of the lumbosacral PGNs (de Groat et al.
1993
; Espey and Downie 1995
; Giuliano et
al. 1995
; Loewy et al. 1979
; Matsumoto et
al. 1995a
,b
; Pavcovich and Valentino 1995
; Steers and de Groat 1989
; Sutin and Jacobowitz
1988
; Suzuki et al. 1990
, 1991
; Thor et
al. 1990
; Valentino et al. 1994
;
Yoshimura et al. 1990
). For example, in the rat glutamic
acid acting on N-methyl-D-aspartate (NMDA) and
non-NMDA receptors is the major excitatory transmitter in the
bulbospinal limb of the micturition reflex (Matsumoto et al.
1995a
,b
), whereas serotonin and corticotropin releasing factor
may function as inhibitory transmitters in pathways controlling
micturition. Supraspinal inputs to the lumbosacral parasympathetic
nucleus may be mediated via direct monosynaptic connections to the PGNs
or via multisynaptic connections through interneurons in the spinal
cord (Blok and Holstege 1997
; Holstege et
al. 1986
; Yoshimura et al. 1990
).
This issue was examined in the present experiments by studying the
excitatory synaptic currents induced in parasympathetic PGNs by
electrical stimulation of axons in the lateral funiculus (LF) in the
neonatal rat spinal slice preparation. The whole cell patch-clamp
recording technique was used to record activity in PGNs identified by
retrograde axonal tracing techniques. Previous experiments in neonatal
rat pups in vivo (Kruse and de Groat 1990) and in the
brain stem-spinal cord-bladder preparation in vitro (Sugaya and
de Groat 1994a
) revealed that bulbospinal excitatory inputs to
bladder parasympathetic pathways are functional in 1- to 2-week-old
animals. The present study showed that stimulation of LF axons elicited
monosynaptic and polysynaptic glutamatergic excitatory responses in
lumbosacral PGN. A preliminary account of some of the observations has
been presented in an abstract (de Groat et al. 1998
).
![]() |
METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Preparation
Sprague-Dawley rats, 6-16 days old, were killed by
decapitation, and the spinal cord was rapidly removed. The
L6-S1 segments of spinal cord were
embedded in 2% agar (Sigma) in a physiological salt solution (see
composition of external solution in the following text) at 8°C. The
spinal cord was sectioned into 150-µm transverse slices using a
vibrating slicer (Vibratome, Technical Products International, St.
Louis, MO). The slices were incubated at 37°C for 1 h in
oxygenated external solution and then transferred to a recording
chamber (0.5 ml) on an upright microscope equipped with fluorescent
optics (Olympus BH-2). Slices were perfused continuously with the
external solution at a rate of 1.5 ml/min. PGNs in lumbosacral spinal
cord slices were identified by retrograde axonal transport of a
fluorescent dye (Fast Blue, EMS-Polyloy, GrossUmstadt, Germany) that
was injected (5 µl of 4% solution) into the peritoneal space 3-12
days before the experiment. This procedure has been shown to
efficiently label autonomic PGNs in the spinal cord (Anderson and Edwards 1994).
Electrophysiological study
The basic procedures for recording whole cell currents from
individual neurons in slice preparations of the cord were identical to
those described by Takahashi (1990). Each slice of
lumbosacral cord was surveyed for Fast Blue-containing neurons along
the intermediolateral border of the gray matter using an upright
microscope equipped with fluorescence optics. Motoneurons in the
ventral horn were often labeled, but it was easy to distinguish between
PGNs and motoneurons by their location. After identification of a cell, it was viewed with Nomarski optics, and its surface was cleaned by a
stream of the external solution from a glass pipette that was
positioned near the cell. Whole cell currents were recorded from the
labeled neurons using an Axopatch 200A patch-clamp amplifier (Axon
Instruments, Foster City, CA). The patch pipettes were made from
borosilicate glass capillaries (1B150F-4, World Precision Instruments,
Sarasota, FL) and had resistances of 2.5-3.5 M
when filled with
pipette solution (see following text) and after the tip had been heat
polished. Synaptic responses were evoked in PGNs by electrical
stimulation with a glass micropipette filled with external solution.
The stimulating pipette was placed in the lateral funiculus 100-150
µm lateral or dorsolateral to the labeled PGNs. A voltage pulse (70 µs, 0.2 Hz) of varying intensity (1-12 V) and negative in polarity
relative to a reference electrode placed in the recording chamber was
applied to the stimulating pipette. The latency of excitatory
postsynaptic currents (EPSCs) was measured from the onset of the
stimulus artifact to the onset of the synaptic currents. The time to
peak was defined as the time between the start of the current
inflection and the peak of the EPSCs. The time constants of the rising
and decay phase of EPSCs were determined using a nonlinear simplex fit
routine based on the least-squares method. Bicuculline methiodide (10 µM) and strychnine (1 µM) were applied in the perfusion solution to
block GABAA and glycine receptor-mediated
synaptic inhibitory potentials (Araki and de Groat
1996
). The liquid-junction potentials between the pipette
solution and the perfusion fluid were corrected using the tip potential
offset control. All experiments were performed at room temperature
(20-25°C). Current and voltage recordings were filtered at 1-5 kHz,
digitized using a Digidata 1200 interface (10 kHz, Axon Instruments),
and stored on a ZIP drive disk connected to an IBM-compatible personal
computer for off-line analysis using pClamp6 software (Axon
Instruments). Numerical data are presented as mean ± SE.
Statistical analysis was performed using a two-tailed t-test
or Mann-Whitney test with a significance limit of P < 0.05.
Solutions
The standard external solution contained (in mM) 130 NaCl, 5 KCl, 2 CaCl2, 1 MgCl2, 10 N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid (HEPES), and 11 glucose. The pH was adjusted to 7.40 with NaOH.
The pipette solution contained (in mM) 140 CsCl, 10 NaCl, 15 CsOH, 5 ethylene glycol-bis (-aminoethyl ether)-N,N,
N',N'-tetraacetic acid (EGTA), and 10 HEPES, pH adjusted to 7.3 with CsOH. Bicuculline methiodide (Sigma; 10 µM), and strychnine
sulfate (Sigma; 1 µM) were always presented in the external solution
to block spontaneous inhibitory postsynaptic currents (IPSCs), and the
solution contained 5 µM 6-cyano-7-nitroquinoxaline-2, 3-dine (CNQX;
Research Biochemicals International) or 50 µM
2-amino-5-phosphonovalerate (APV; Sigma) or both to block EPSCs
(Miura et al. 2000
).
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Recordings were obtained from 100 PGNs (51 spinal slices) labeled
by retrograde axonal transport with a fluorescent dye. Among these
neurons, 41 exhibited synaptic currents in response to lateral funiculus (LF) stimulation. The mean resting membrane potential and
input resistance in these 41 cells were 54.2 ± 1.5 mV and 609.1 ± 96.3 M
, respectively. These measurements were not
significantly different from those PGNs that did not respond to LF stimulation.
Evoked EPSCs in PGNs
At a holding potential of 60 mV, bimodal or polymodal inward
synaptic currents were evoked in dye-labeled PGN by electrical stimulation of LF. The evoked synaptic currents were completely blocked
when tetrodotoxin (1 µM) was presented in the external solution
(n = 6).
The mean latency of the evoked synaptic currents was 3.0 ± 0.10 ms (n = 41, range 1.4-4.2 ms). This value is
approximately 1.5 times the mean latency (2.1 ± 0.2 ms) of the
EPSCs evoked by electrical stimulation of interneurons in the vicinity
of recorded PGN (Araki and de Groat 1996). Two types of
synaptic currents were elicited by LF stimulation (Fig.
1). The most common response (type 1, n = 33 cells) consisted of a short, relatively constant latency (range, 1.4-4.2 ms) large-amplitude (59.0 ± 7.9 pA,
n = 33) inward current (fast EPSC) followed by a
low-amplitude more prolonged current whose amplitude usually was 10%
or less than that of the initial current (Fig. 1A).
Averaging of multiple evoked responses yielded traces (Fig.
1Ab) that closely resembled individual recordings (Fig.
1Aa). In the 33 cells, the maximal EPSCs had an average
latency of 3.0 ± 0.12 ms and a time to peak of 1.4 ± 0.1 ms. A less common response (type 2, n = 8 cells)
consisted of a short, relatively constant latency (2.2-3.8 ms),
large-amplitude fast EPSC followed by large-amplitude inward current
responses that occurred at variable latency (7.2-30.9 ms; Fig.
1Ba). The average of a large number of EPSCs revealed a very
prolonged current (Fig. 1Bb).
|
The relationship between stimulus intensity and response was evaluated in detail in 11 cells. The responses occurred at threshold stimulus intensities ranging from 1 to 3 V in different PGNs. In some cells (n = 7), low stimulus intensities evoked what appeared to be all-or-none synaptic responses (Fig. 2Ab). In these cells, when the stimulus intensity was gradually increased the EPSCs suddenly appeared with frequent failures. When the stimulus intensity was increased, further the failures became infrequent. The amplitudes of individual EPSCs fluctuated but their mean value in individual cells was virtually constant (ranging from 14 to 92 pA) in a limited range of stimulus strengths (1.2 to 2.5 T, T indicates the threshold) above the threshold (Fig. 2B). In some cells (n = 4), the magnitude of the evoked synaptic currents was not all-or-none; instead it gradually increased with increasing stimulus intensities and reached a maximum (34-155 pA) at two to four times (5-10 V) the threshold voltages (Fig. 2, C and D). In three neurons exhibiting all-or-none responses, the EPSC latencies (1.7-2.6, 0.7-1.3, and 2.7-3.1 ms) and time to peak (1.0-1.3, 1.7-2.2, and 0.9-1.2 ms) had unimodal distributions in a narrow range. Data from one neuron, which is illustrated in Fig. 3, shows an average latency of 2.1 ms and time to peak of 1.1 ± 0.02 ms.
|
|
Glutamatergic EPSCs and their time course
The fast component of LF stimulation-evoked type 1 synaptic
currents recorded at a holding potential of 60 mV was attenuated by
CNQX (5 µM, n = 7), a specific antagonist of non-NMDA
receptors (Fig. 4Ab). The late
component of EPSCs remaining after addition of CNQX was completely
blocked by APV (50 µM, n = 4), a specific antagonist
of NMDA receptors (Fig. 4Ac). The effects of
glutamatergic-receptor-antagonists were reversed 15-20 min after
washout (Fig. 4Ad). The fast component of LF-evoked type 2 synaptic currents recorded at a holding potential of
60 mV was
blocked by CNQX (5 µM, n = 3; Fig. 4Bb).
The late component of EPSCs remaining after addition of CNQX was
completely blocked by APV (50 µM, n = 3; Fig.
4Bc).
|
The time course of synaptic currents was measured on averaged responses
of 30 individual EPSCs from 33 cells clamped at 60 mV. The fast
rising times to peak and decay time constants of the EPSCs mediated by
non-NMDA receptors were 2.5 ± 0.2 and 5.7 ± 0.6 ms,
respectively. The decay time constant of the EPSCs mediated by NMDA
receptors was 38.8 ± 4.0 ms.
Voltage dependence of EPSCs
The current-voltage relationships of the non-NMDA and NMDA
components of evoked EPSCs were examined by measuring the peak amplitude of the EPSCs at 4-8 and 25 ms, respectively, after the stimulus. The early current at 4-8 ms was assumed to reflect mainly the non-NMDA component because the EPSCs mediated by NMDA receptors exhibited a slow time to peak and small amplitude and should make a
very small contribution to the EPSCs at this time point. On the other
hand, the non-NMDA component would make little contribution to EPSCs at
25 ms after the stimulus (Araki and de Groat 1996). Thus
the amplitude of EPSCs at this time point was assumed to reflect the
NMDA component (Araki and de Groat 1996
; Hestin
et al. 1990
; Keller et al. 1991
). The
current-voltage relationship of the non-NMDA component had a linear
conductance, whereas that of NMDA component at 25 ms after the onset of
response had a negative slope conductance at a hyperpolarized holding
potential (more negative than
20 mV) (Fig.
5). The interpolated reversal potentials of non-NMDA and NMDA currents were 5.0 ± 5.9 mV (open circle) and
3.7 ± 3.2 mV (filled circle; n = 5), respectively
(Fig. 5B).
|
Synaptic modulation using paired pulse stimulation
Paired-pulse modulation of type 1 EPSCs was examined in 15 PGN by
applying two successive stimuli to the lateral funiculus with
interstimulus intervals ranging from 50 to 120 ms at a holding potential of 60 mV. At intervals of 50, 70, 100, and 120 ms, the
responses to the second stimulus were considerably smaller (Fig.
6), the percentage of inhibition of the
peak amplitude of the second EPSCs being 67.5 ± 7.9%,
n = 4; 69.0 ± 8.6%, n = 9; 76.3 ± 7.8%, n = 6 and 63.3 ± 3.2%,
n = 11, respectively, excluding four cells of which two
showed a small facilitation (mean, 19.5%, n = 2) and
two showed no modulation. There were no significant differences in the
percentage inhibition at different stimulus intervals.
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The present experiments revealed that a large percentage (at least 40%) of parasympathetic PGNs in the lumbosacral spinal cord of the neonatal rat receive glutamatergic excitatory synaptic inputs from axons of the lateral funiculus. These excitatory inputs activate NMDA and non-NMDA glutamatergic receptors. Latencies of EPSCs revealed two distinct pathways: a pathway evoking relatively short and fixed latency EPSCs probably mediated by monosynaptic or disynaptic projections and a pathway mediating longer and more variable latency EPSCs probably representative of polysynaptic projections. The contribution of bulbospinal and propriospinal axons to these LF-evoked responses are not known but will be evaluated in future experiments.
In some PGNs, LF stimulation evoked what appeared to be all-or-none
EPSCs. These responses, which varied in mean amplitudes from 14 to 92 pA (average, 59.0 ± 7.9 pA), presumably represent "unitary
EPSCs" evoked by a single LF axon. However, it is also possible that
near all-or-none behavior might reflect activation of two axons with
very similar electrical thresholds. The fairly large latency
fluctuations (e.g., 1.7-2.6 ms) observed with some unitary responses
would be consistent with this possibility. Unitary glutamatergic EPSCs
evoked by stimulation of single interneurons in the region of the
sacral parasympathetic nucleus ranged from 36 to 88 pA (Araki
and de Groat 1996).
LF-inputs were mediated exclusively by glutamatergic receptors because
combined administration of a non-NMDA (CNQX) and a NMDA (APV)
antagonist completely blocked evoked EPSCs. This situation is very
similar to the non-NMDA- and NMDA-mediated interneuronal excitatory
inputs to PGNs. The absence of nonglutamatergic synaptic currents
following LF stimulation is unexpected because the sacral parasympathetic nucleus receives bulbospinal inputs from various types
of neurons including those containing norepinephrine, serotonin (5-HT),
oxytocin, and corticotropin releasing factor (CRF). Norepinephrine and
oxytocin mediate excitatory effects, whereas 5-HT and CRF produce
inhibitory responses (Pavcovich and Valentino 1995;
Suzuki et al. 1990
, 1991
; Thor et al.
1990
). The failure to detect nonglutamatergic excitatory or
inhibitory synaptic currents in the present experiments suggests that
other pathways (e.g., monoaminergic and peptidergic) do not project
directly to the PGN.
The LF-induced non-NMDA- and NMDA-mediated synaptic currents were
similar to those evoked by interneurons located near the PGNs
(Araki 1994; Araki and de Groat 1996
).
These two types of currents could be distinguished by differences in
time course, voltage dependence, and specific receptor antagonists. The
mean time to peak of non-NMDA receptor-mediated fast EPSCs is close to
that reported for unitary EPSCs evoked in PGNs by stimulation of dorsal
or medial interneurons (Araki and de Groat 1996
) and is
comparable with that described in rat sympathetic preganglionic neurons
(Krupp and Feltz 1995
). The mean of the fast decay time constant of averaged EPSCs, representing the non-NMDA response, was
comparable with the value for fast EPSCs evoked in rat sympathetic preganglionic neurons by stimulation of intraspinal axons (Krupp and Feltz 1995
) but was longer than the value for the EPSCs
evoked in PGNs by stimulation of interneurons (Araki and de
Groat 1996
). The mean of the slower decay time constant of
averaged EPSCs, representing the NMDA receptor-mediated response, was
shorter than that reported for the EPSCs evoked in preganglionic
neurons by stimulation of axons or interneurons (Araki and de
Groat 1996
; Krupp and Feltz 1995
). However, the
current-voltage relationships for LF stimulation-induced glutamatergic
EPSCs corresponded to that of other synapses (Jonas et al.
1993
) including interneuronal-PGN synapses in the neonatal
spinal cord (Araki and de Groat 1996
).
One prominent difference between LF and interneuronal inputs to PGN was
obvious using paired-pulse stimulation. During electrical stimulation
of interneurons in spinal cord slices (Araki and de Groat
1996), paired-pulse facilitation was very prominent (mean, 75%
increase in EPSC amplitude) in the dorsal interneuronal pathway and
somewhat less prominent (mean 25% increase) in the medial interneuronal pathway. In the present study, paired-pulse inhibition of
EPSCs rather than facilitation was obtained during electrical stimulation of lateral funiculus in a large percentage (75%) of PGN.
This difference might be related to several factors. First bulbospinal
excitatory pathways might be immature in the neonatal rat; therefore
synaptic facilitatory mechanisms might be nonfunctional. This is
certainly possible in the descending limb of the micturition reflex
pathway, which does not become active until the third postnatal week
(Araki and de Groat 1997
). Development of temporal
facilitation in the bulbospinal pathway might be one mechanism which
contributes to the emergence of the supraspinal micturition reflex in
older rat pups.
A second factor that could contribute to difference between LF and
interneuronal paired pulse stimulation is the presence of multiple
transmitter systems in the LF. Simultaneous activation of monoaminergic
(norepinephrine and 5-HT) or peptidergic axons along with LF
glutamatergic axons could produce homosynaptic or heterosynaptic
modulation of glutamatergic transmission and thereby elicit paired
pulse inhibition. CRF is thought to be an inhibitory co-transmitter in
the descending glutamatergic excitatory pathways from pontine
micturition center to the lumbosacral parasympathetic nucleus
(de Groat et al. 1993; Pavcovich and Valentino
1995
; Sawchenko et al. 1993
; Suzuki et
al. 1990
, 1991
). Serotonergic mechanisms are also likely to be
inhibitory in the micturition reflex pathways (de Groat
1978
; Steers and de Groat 1989
; Testa et
al. 1999
) but facilitatory or inhibitory in penile erectile
pathways (Giuliano et al. 1995
; Steers and de
Groat 1989
) depending on the type of serotonergic receptor
activated (Moreland et al. 2000
). The present study
revealed that presumed LF monosynaptic inputs have a longer latency (3 ms) than interneuronal monosynaptic inputs (2.1 ms) (Araki and
de Groat 1996
). This difference might be due to slower conduction velocity of LF axons or a difference in conduction distance.
It might also reflect immaturity of bulbospinal pathways in comparison
to interneuronal pathways (see following text).
In the present study, about 60% of PGNs did not respond to electrical
stimulation of lateral funiculus. This result might reflect several
factors. First, certain populations of PGNs might not receive direct
bulbospinal inputs. For example, although the descending pathway from
pontine micturition center to PGNs is wired up in the first postnatal
week, it does not become functional in controlling the urinary bladder
until the second to third postnatal week (Kruse and de Groat
1990; Sugaya and de Groat 1994b
). In neonates,
micturition and defecation are mediated by a segmental parasympathetic
reflex pathway, which is activated by the mother licking perineum of
the pup (Beach 1966
; de Groat et al.
1975
). Starting 3 weeks after birth, this segmental
somato-parasympathetic reflex is gradually replaced by a
spino-bulbo-spinal micturition reflex pathway, which is essential for
voiding in adult animals (Araki and de Groat 1997
). Thus
many LF inputs to bladder PGNs may be "silent" in the early
postnatal period. PGNs involved in other functions might receive
excitatory bulbospinal inputs even later in developments (e.g., during
sexual maturation), and others such as colorectal PGNs, which are
regulated by spinal reflex mechanisms (de Groat et al.
1981
) might not receive direct excitatory inputs from
bulbospinal or propriospinal axons. Another factor contributing to the
low percentage of PGNs responding to LF stimulation is that collaterals
of rostrocaudal axons in the funiculus might project medially into the
PGNs on an angle rather than perpendicularly to the long axis of the
cord. Thus many of the medially projecting axons in the 150-µm slice
might be transected before entering the PGN. The use of thicker slices
could solve this technical problem.
In conclusion, the present experiments provided evidence that PGN in the lumbosacral parasympathetic nucleus of the neonatal rat receive glutamatergic monosynaptic and polysynaptic excitatory inputs from axons in the lateral funiculus. These inputs are mediated by NMDA and non-NMDA receptors similar to glutamatergic inputs from local interneurons. However, in contrast to interneuronal synapses, LF synapses exhibited paired- pulse inhibition instead of facilitation. This difference might reflect the relative immaturity of bulbospinal autonomic pathways in 1- to 2-week-old rats.
![]() |
ACKNOWLEDGMENTS |
---|
We thank Dr. Shigeo Kobayashi, Dr. Konomi Koyano of Kyoto University, and Dr. Isao Araki of Utano National Hospital for advice on the slice patch techniques.
This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant DK-51402.
![]() |
FOOTNOTES |
---|
Address for reprint requests: A. Miura, Dept. of Physiology, School of Medicine, Akita University, Akita 010-8543, Japan (E-mail: makira{at}med.akita-u.ac.jp).
Received 12 December 2000; accepted in final form 30 May 2001.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|