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Electro-acupuncture induced NGF, BDNF and NT-3 expression
in spared L6 dorsal root ganglion in cats subjected
to removal of adjacent ganglia
Juan Chen a,b, Jian-Guo Qi a,c, Wei Zhang a,c, Xue Zhou a,c, Qing-Shu Meng b,Wei-Min Zhang b, Xu-Yang Wang b, Ting-Hua Wang a,b,c,*
a Institute of Neurological Disease, West China Hospital, Sichuan University, Chengdu 610041, Chinab Institute of Neuroscience, Kunming Medical College, Kunming 650031, China
c Department of Histology, Embryology and Neurobiology, College of Preclinical and Forensic Medicine, Sichuan University, Chengdu 610041, China
Received 25 September 2006; accepted 9 August 2007
Available online 15 August 2007
www.elsevier.com/locate/neures
Neuroscience Research 59 (2007) 399–405
Abstract
This study evaluated the effect of electro-acupuncture (EA) on the NGF, BDNF and NT-3 expression in spared L6 dorsal root ganglion (DRG) in
cats subjected to bilateral removal of L1-L5 and L7-S2 DRG, using immunostaining, in situ hybridization and RT-PCR. The positive products of
NGF, NT-3 protein and mRNA in the small and large neurons of spared L6 DRG in EA side increased greatly more than that of control side, while
the increased BDNF was only noted in small and medium-sized neurons. RT-PCR demonstrated that the mRNA level for three factors was not
influenced by EA in intact DRG, when a significant increase was seen in the spared L6 DRG of EA side. As it has been well known that DRG
neurons project to the spinal cord wherein morphological plasticity has been present after DRG removal, the present results might have some
bearing to the observed phenomenon.
# 2007 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.
Keywords: NGF; BDNF; NT-3; Dorsal root ganglion; EA; Spinal cord plasticity
1. Introduction
Neuroplasticity in the central nervous system (CNS) was
firstly demonstrated by Liu and Chambers (1958) who
proposed that after surgically removing a series of dorsal root
ganglia (DRG), axonal sprouting from the central processes of
the spared ganglion occurred in Lamina II. This pioneering
work prompted numerous researchers to look into the
mechanism on the axonal regeneration and synaptic reorga-
nization of neurons following traumatic lesions in the
mammalian spinal cord (Leong and Lund, 1973; Guth, 1974;
Steward, 1989; He, 1994; Mendell et al., 2001; Siddall and
Loeser, 2001; Wolpaw and Tennissen, 2001).
* Corresponding author at: Institute of Neurological Disease, West China
Hospital, Sichuan University, Chengdu 610041, China. Tel.: +86 871 5329245;
fax: +86 871 5342766.
E-mail address: [email protected] (T.-H. Wang).
0168-0102/$ – see front matter # 2007 Elsevier Ireland Ltd and the Japan Neuro
doi:10.1016/j.neures.2007.08.006
Arising from some recent related work is the significant
finding that failure of neurons to spontaneously regenerate after
injury in the adult CNS might be attributed to the nonpermissive
nature of the CNS environment (Aubert et al., 1995), like the
lack of growth-promoting molecules (Varon and Conner, 1994)
and the presence of inhibitory molecules (Fitch and Silver,
1997). Moreover, providing a growth supportive environment
by the administration of neurotrophic factors (NTFs) (Lindsay
et al., 1994) has been partially successful in inducing axonal
regeneration within the adult mammalian CNS.
Though a good number of studies have investigated the roles
of neurotrophic factors in preventing neuronal death or
promoting anatomical reorganization after spinal cord injury
(Huang and Reichardt, 2001; Kim et al., 2001; Liu et al., 2002),
the involvement of endogenous neurotrophic factors in the
dynamic modulation of local circuitry remains to be elucidated.
Acupuncture, an ancient craft originating in China more
than 3000 years ago, has been shown to promote functional
recovery in spinal cord injury (Li et al., 1985; He, 1994).
science Society. All rights reserved.
Fig. 1. Drawing showing xuewei is where EA was applied.
J. Chen et al. / Neuroscience Research 59 (2007) 399–405400
Electro-acupuncture (EA) is similar to the traditional acu-
puncture but where in EA, electrical stimuli are delivered
instead of manual twist stimuli in the traditional acupuncture. It
has been known that EA can increase the number of axonal
terminal derived from spared DRG, indicating the effect of EA
in meliorating synaptic reconstruction. Previous researches had
demonstrated a correlation between the increase of some
neurotrophic factors like nerve growth factor (NGF), brain
derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3)
and neurotrophin 4/5 (NT-4/5) and the development, survival
and maintenance of neuronal function in both the peripheral
and the central nervous system (Isackson, 1995; McAllister
et al., 1999; Sendtner et al., 2000; Huang and Reichardt, 2001),
in addition endogenous neurotrophic factors may be involved in
neurite-outgrowth enhancement induced by dorsal root gang-
lionectomy (Xue et al., 1994). Moreover, our recent studies also
determined some other neurochemicals expression in DRG
after EA (Wang et al., 2005a,b, 2006). This experiment was
therefore undertaken to observe the possible effects of EA in the
expression of NGF, BDNF and NT-3 and their respective
mRNA in the spared DRG neurons of cats after adjacent DRG
removal. It is hoped that the results derived from immunohis-
tochemistry, in situ hybridization and RT-PCR can provide
some evidences for EA promoting the spinal cord plasticity,
involved in the NGF, BDNF and NT-3 expressions.
2. Materials and methods
2.1. Animals
Twenty adult male cats, weighing 3–3.5 kg for each animal, were used in this
study. The animals were provided by the Laboratory Animal Center of Kunming
Medical College. Every effort was taken to reduce the number of animals and
suffering during the experiments. Group I, consisting of 15 cats were used for
immunohistochemistry, in situ hybridization and RT-PCR for each five, respec-
tively. Animals Group II (n = 5) was also used to detect the mRNA expression
changes in the normal cats after EA by RT-PCR. The animals were maintained
under conditions of controlled light, temperature, food and water.
2.2. Surgical procedures
All experimental procedures were performed under anesthesia achieved
with intraperitoneal injection of 3.5% sodium pentobarbital (1.3 ml/kg body
weight). The DRG of cats in Group I associated with the first through the fifth
lumbar (L1-L5) and the seventh lumbar through the second sacral (L7-S2)
spinal nerves were first bilaterally removed, sparing the L6 DRG, then followed
immediately with EA on the left side at acupuncture points. Group II were used
as normal cats, and performed by EA as group I.
2.3. EA
On the day after surgery, all the cats were subjected immediately to
unilateral electrical stimulation at acupuncture points (Fig. 1) (xuewei)
zusanli-xuanzhong, and futu-sanyinjiao, both of which are known to lie in
L6 dermatome (Xue et al., 1994). Zusanli (ST36) is located 1.5 cm below the
front of the fibula head; xuanzhong (GB39), 1.5 cm above the front of the lateral
malleolus; futu (ST32), 2–3 cm above the lower end of the patella; and
sanyinjiao (SP6), 1.5 cm above the posterior end of the medial malleolus.
The pairs of acupoints were stimulated alternately at the frequency of 98 HZ for
30 min every day. During acupuncture, the electrodes were changed every
15 min. EA is similar to traditional acupuncture except that electrical stimuli are
delivered instead of manual stimuli in the traditional method.
2.4. Immunohistochemistry
The cats were perfused under anesthesia on day 7 after EA. Their L6 DRG on
both sides were removed and immersed in a 4% paraformaldehyde solution for
12 h, then placed in a 20% sucrosed phosphate buffered solution (PBS) over night.
Serial longitudinal sections of the frozen DRG were sectioned into 20 mm slices.
For an unbiased and accurate representation of the data, 5 sections were taken
randomly, representing all the samples in one animal. The selected sections were
processed for immunohistochemical demonstration of NGF, BDNF and NT-3,
using specific NGF (rabbit anti-human 1:100), BDNF (rabbit anti-human 1:500)
and NT-3 (rabbit anti-human 1:1500) antibodies using ABC (Avidin-Biotin
Complex) method. Then the sections were stained by DAB (3,30-diaminobenzi-
dine). All antibodies, bought from Chemicon, have been identified by the
Western-Blot method in our lab and shown to possess specificity for their own
antigens. In addition, control experiments in which PBS was substituted for the
primary antibody were performed to ascertain specificity of antibody staining.
2.5. In situ hybridization
The use of double-stranded cDNA as molecular probes for in situ hybri-
dization to chromosomal preparations has been effective for localizing the
position of particular genes like those of NGF, BDNF and NT-3. Slide-mounted
DRG sections were warmed to room temperature (25 8C), postfixed in 4%
paraformaldehyde (pH 7.4) for 5 min at 4 8C, rinsed in PBS, and treated with
0.25% acetic anhydride (in 0.1 M triethanoLaminae, pH 8.0) for 10 min at room
temperature. After rinsing 2� in standard saline citrate (SSC) for 10 min and
dehydration through a graded series of alcohols, the sections were delipidated in
chloroform for 5 min at room temperature and subsequently re-hydrated to 95%
ethanol in descending concentrations of alcohols and then air-dried. They were
next washed in Tris (trihydroxymethyl aminomethane) at pH 9.4 and
NaCl:MgCl2 (20:1) for 2 min, then color-developed in Tris, pH 9.4 and
NaCl:MgCl2 (20:1) in the presence of nitroblue tetrazolium (NBT) and 5-
bromo-4-chloro-2-indolyl phosphate (BCIP) for 5 h. The sections were finally
rinsed several times and mounted on glass slides with Aqua Poly/Mount
(Polysciences; Warrington, PA).
Controls for in situ hybridization: Preincubation with RNAase was used to
assess the nonspecific binding of the probes to the section. Moreover, to
demonstrate the validity of the probes of three neurotrophic factors, the cRNA
probes were substituted with double distilled water without RNAase or the
unmarked probes. No positive reaction was observed in both control experiments.
2.6. Cell number counting
The distributions of the immunopositive neurons for NGF, BDNF, NT-3 and
their respective mRNA in different sized DRG neurons on the acupunctured and
non-acupunctured side were observed and photographed in an Olympus light
microscope at 40�. In order to calculate the average number of immunoreactive
cells, photographs of DRG were scanned and projected on the screen of a
computer. Then the areas of the DRG and the number of positive neurons were
respectively measured using several manufactured square grids (0.8 cm per
square grid). Therefore the average number in the area designated as 100 grids
was acquired so as to compare the number of positive neurons in equal areas in
different sections. The average numbers of labeled neurons were recorded in
Tables 1–3.
Table 1
Average numbers of NGF and its mRNA positive neurons in the left L6 DRG
Average number NGF-IR positive neurons NGF mRNA positive neurons
Non-EA
side
EA side Non-EA
side
EA side
Large neurons 4.1 � 1.2 6.4 � 1.7* 3.3 � 1.7 5.2 � 2.3*
Medium-sized
neurons
13.2 � 2.7 11.2 � 3.9** 11.2 � 3.3 10.4 � 4.7**
Small neurons 10.4 � 3.9 15.5 � 3.4* 9.1 � 3.6 14.7 � 4.9*
* P < 0.05, compared with non-electro-acupunctured side.** P > 0.05, compared with non-electro-acupunctured side.
J. Chen et al. / Neuroscience Research 59 (2007) 399–405 401
2.7. RT-PCR
RNA preparation: Animals were allowed to survive for 7 days after EA.
Total RNA was isolated from the L6 DRG on the both sides in each cat using
TRIzol Reagent (Invitrogen, USA) according to the manufacturer’s instructions.
The RNA concentration of each sample was determined from the absorbance at
260 nm.
RT-PCR: One microgram of total RNAwas reverse-transcribed to cDNA in a
12 ml reaction volume with anchored oligo dT primer using RevertAidTM First
Stand cDNA Synthesis Kit (Fermentas, Lithuania). Three microliter of the RT
product was then used as template for PCR using 2�PCR Master Mix (Fermentas,
Lithuania). RT and PCR were performed according to the manufacturer’s pro-
tocols on PCR Express thermal cyclers (BioRad, USA). Primers were designed
using Primer Premier 5.0 software and synthesized commercially (TaKaRa,
Dalian, China). The primers used for amplification, together with their specific
optimum cycling conditions, were as follows: NGF: sense 50-GTG GCA GGG
CAG ACC CGC AAC AT-30, antisense 50-AGC ACCACC CGC CTC CAA GTC
CA-30, annealing temperature (TA) 65 8C; 30 cycles, yielding a 144 bp products;
BDNF: sense 50-TGA CAT CCT TGG CTG ACA CTT T-30, antisense 50-ACT
GGG AGT TCC AAT GCC TTT T-30, annealing temperature (TA) 55 8C; 30
cycles, yielding a 456 bp products. NT-3: sense, 50-CTC ATG GAG GAT TAC
GTG GGA-30, antisense, 50-GCC TGG CTT CTT TAC ATC TCG-30, annealing
temperature (TA) 56.5 8C; 30 cycles, yielding a 244 bp products. The primers for
b-actin used for internal contral were 50-GCTACA GTT TCA CCA CCA CCG-30
(sense), 50-ATG CCA CAG GAC TCC ATA CCC-30 (antisense), annealing
temperature (TA) 58 8C, 30 cycles, yielding a 232 bp products.
Table 2
Average numbers of BDNF and its mRNA positive neurons in the left L6 DRG
Average number BDNF-IR positive neurons
Non-EA side EA sid
Large neurons 0.98 � 0.35 1.13 �Medium-sized neurons 12.86 � 0.66 14.40 �Small neurons 34.18 � 0.98 41.30 �
* P < 0.05, compared with non-electro-acupunctured side.** P > 0.05, compared with non-electro-acupunctured side.
*** P < 0.01, compared with non-electro-acupunctured side.
Table 3
Average numbers of NT-3 and its mRNA positive neurons in the left L6 DRG
Average number NT3-IR positive neurons
Non-EA side EA sid
Large neuron 19.68 � 0.31 23.48 �Medium-sized neurons 12.14 � 1.14 12.52 �Small neuron 28.62 � 0.78 32.02 �
* P < 0.05, compared with non-electro-acupunctured side.** P > 0.05, compared with non-electro-acupunctured side.
*** P < 0.01, compared with non-electro-acupunctured side.
The amplification parameters for PCR were an initial 5 min denaturation
step followed by cycles consisting of denaturation at 94 8C for 50 s, annealing at
the specified optimum temperature for 50 s, and extension at 72 8C for 50 s. The
specified optimum total number of cycles was followed by a 10 min extension at
72 8C. 10 ml PCR products were electrophoresed through an ethidium bromide
estained 1% agarose gel, and the band intensity was analyzed using quantitative
scanning densitometry. The ratio of NGF, BDNF and NT-3 to b-actin served as
the levels of mRNA expressions.
2.8. Statistical analysis
Student’s t-tests were also applied bilaterally for comparison. A P value is
considered significant if it is less than 0.05. The 95% confidence interval (CI)
was given when P is less than 0.05. All analyses were performed using the SPSS
software.
3. Results
3.1. Immunoreactive expression of NGF, BDNF and NT-3
and their respective mRNA in L6 DRG neurons
The diameters of the immunopositive neurons in L6 DRG
were measured with a line drawn through the nucleus. The
method of measurement and classification followed the scheme
of a previous report, which showed the L6 DRG neurons of adult
cat consist of small (<42 mm), medium-sized (42–57 mm) and
large (>57 mm) neurons (Wang et al., 2000). In this experiment,
the immunoreactive products of NGF, BDNF, NT-3 appeared as a
brownish deposit in the cytoplasm of the stained DRG neurons,
and those of the genes, as a blue deposit in the cytoplasm.
3.1.1. Immunoreactive expression of protein and mRNA for
NGF in L6 DRG
The numbers of NGF immunopositive small and large
neurons both protein and mRNA in the spared DRG on the
acupunctured side (Fig. 2B and D) increased more than those on
BDNF mRNA positive neurons
e Non-EA side EA side
0.57** 5.01 � 1.06 4.50 � 0.90**
0.55* 14.46 � 0.75 19.23 � 0.75*
1.49*** 17.08 � 1.01 20.36 � 1.34***
NT3 mRNA positive neurons
e Non-EA side EA side
1.85* 12.82 � 1.26 17.38 � 1.54*
1.37** 6.12 � 0.58 6.18 � 0.68**
1.59*** 26.78 � 1.02 31.16 � 1.25***
Fig. 2. Expression of NGF (left column), BDNF (middle column) and NT-3 (right column) (A, B, E, F, I, J, Hematoxylin counterstained in A and B) immunoreactivity
in the spared L6 DRG and their respective mRNA (C, D, G, H, K, L) in spared DRG. Symbol I was denoted non-electro-acupunctured side and symbol II was denoted
electro-acupunctured side. Magnification: 40� (A, B, C, D); 200� (E, F, I, J); 400� (G, H, K, L). Positive neurons were indicated by symbol (!).
J. Chen et al. / Neuroscience Research 59 (2007) 399–405402
the non-acupunctured side (Fig. 2A and C) (P < 0.05), while
there was no significant difference (P > 0.05) in medium-sized
neurons (Table 1).
3.1.2. Immunopositive expression of protein and mRNA for
BDNF in L6 DRG
The numbers of BDNF immunopositive small and medium-
sized neurons both protein and mRNA in the spared DRG on the
acupunctured side (Fig. 2F and H) increased more than those on
the non-acupunctured side (Fig. 2E and G) (P < 0.05), when
there was no significant difference (P > 0.05) in large neurons
(Table 2).
3.1.3. Immunopositive expression of protein and mRNA for
NT-3 in L6 DRG
The numbers of NT-3 immunopositive small and large
neurons both protein and mRNA in the spared DRG on the
acupunctured side (Fig. 2J and L) increased more than those on
the non-acupunctured side (Fig. 2I and K) (P < 0.05).
However, there was no significant difference (P > 0.05) in
the numbers of NT-3 protein and NT-3 mRNA immunopositive
medium-sized neurons in the spared DRG (Table 3).
3.2. Quantitative changes in mRNA level for NGF, BDNF
and NT-3
The reverse transcription-polymerase chain reaction (RT-
PCR) was performed to detect the mRNA expression patterns in
both cells and small quantities of tissue. Under rational PCR
conditions, at least one specifically amplified band in each
sample clearly identified NGF, BDNF and NT-3 (Fig. 3).
In the L6 DRG, NGF, BDNF and NT-3 mRNAwere detected
in two groups, and EA did not influence three growth factor
expressions between acupunctured side and non-acupunctured
side in intact cats. However, following partial deafferentation
combined with acupuncture at two pairs of points that are
located within the innervating area of L6 spinal nerve on the
one side for 7 days, all expressions of mRNA for NGF, BDNF
and NT-3 on the acupunctured-side was significantly up-
regulated (Table 4).
Fig. 3. Quantitative changes in mRNA level for NGF, BDNF and NT-3 in the L6
DRG of non-electro-acupunctured side (line 1 and 3) and electro-acupunctured
side (line 2 and 4) in two Groups rats. RT-PCR products using primers for b-
actin were used as control.
Table 4
Comparison of quantitative changes in mRNA level for NGF, BDNF and NT-3
mRNA expressions Group I Group II
Non-EA side EA side Non-EA side EA side
NGF 0.54 � 0.17 0.63 � 0.16* 0.89 � 0.22** 1.37 � 0.13***
BDNF 0.66 � 0.13 0.69 � 0.11* 0.97 � 0.14** 1.44 � 0.16***
NT-3 0.84 � 0.12 0.91 � 0.17* 0.93 � 0.18* 1.57 � 0.22***
* P > 0.05, compared with non-electro-acupunctured side in Group I.** P < 0.05, compared with non-electro-acupunctured side in Group I.
*** P < 0.05, compared with non-electro-acupunctured side in Group II.
J. Chen et al. / Neuroscience Research 59 (2007) 399–405 403
4. Discussion
Previous study showed that acupuncture treatment could
obviously control the descending of spinal cord blood flow
(SCBF) in rats injured spinal cord. This suggested that
acupuncture could effectly control the descending of SCBF in
the early stage of spinal injured, improved the microcircula-
tion of spinal, abated and delayed the occurrence of
secondary lesion, promoted the recovery of function of
nerve (Wu et al., 1995). EA therapy is usually done by the
insertion of thin metal needles to the acupoints, and this is
followed by electrical stimulated action. It has been reported
that more anti-neurofilament (NF) positive labelings have
been found in the EA treatment group than seen in the control
group on the seventh day after the injury. The results
suggested that EA could be useful to the injured spinal cord
repair (Jin and Tao, 1997). In addition, functional improve-
ment was also found in rats which had been treated with
acupuncture 15 min after injury relative to those that received
no acupuncture treatment. This was accompanied by
minimization of post-traumatic cord shrinkage in acupunc-
ture-treated animals. Results point to a usefulness of
acupuncture as adjunct treatment during early stages after
spinal cord injury (Politis and Korchinski, 1990).
The neuron locating in the dorsal root ganglia consists of the
nerve cell body and the axon, a long protrusion extending into
the periphery. The length of the axon may be 10,000 to 15,000
times the diameter of the cell body. Previous study in our lab
(Wang et al., 2005a,b) had detected the average neurite length
of the normal or intact group was shorter than that of the spared
DRG group, and the spared DRG group’s was shorter than the
EA group’s at the seventh day in vitro (data are not shown). This
indicated that DRG had plasticity and EA probably promoted
the plasticity.
The neurons of DRG, with their axons projecting to the
spinal cord, provide a good approach to study the phenomenon
on the collateral sprouting deprived from sensory neurons in
spinal cord. In this study, the immunoreactive products both
protein and mRNA for NGF increased in small and large
neurons in the spared L6 ganglion after EA, this demonstrates
NGF expression has been upregulated following EA. NGF, as a
phenotype growth factor, shows not only a positive effect on the
survival of neurons, but also promotes the differentiation of
neurons as well as regulates their connection patterns (Jiang and
Smith, 1993; Orike et al., 2001). Zhang observed that NGF
increase in the spinal cord is relevant to spinal cord self-
recovery in the rat (Zhang et al., 1995). As the central processes
of small and large neurons project mainly to spinal Lamina II
and nucleus dorsalis (ND), we postulate that the increased NGF
expression in small and large neurons may be available for the
NGF transportation from DRG to ND or spinal lamina II. It
might also provide suitable conditions for some morphological
changes such as axonal sprouting and neurite-outgrowth of
DRG neurons expressing endogenous NGF.
BDNF protein is widely distributed in the CNS, beginning
early in development and extending throughout the organism’s
life span. Previous study reported that BDNF expressed in a
subpopulation of small and medium-sized neurons in the L6
DRG of normal cats. This study showed that the number of
small and medium-sized neurons for BDNF protein and mRNA
in spared DRG increased than seen in the non-acupunctured
side. The increase could clearly be attributed to the EA
procedure. BDNF can directly induce pluripotential neural
crest cells to differentiate along the sensory neuron lineage in
cultured chick neural crest cells (Sieber-Blum, 1991; Sieber-
Blum et al., 1993). Some studies also reported that endogenous
BDNF is required for peripheral nerve regeneration and
J. Chen et al. / Neuroscience Research 59 (2007) 399–405404
remyelination after injury (Zhang et al., 2000). Other results
clearly showed that BDNF, synthesized and secreted from the
DRG, is involved in the sympathetic sprouting in the DRG
following peripheral nerve injury as well (Deng et al., 2000).
The up-regulation of BDNF protein and mRNA in small and
medium-sized DRG neurons might be also useful to furnish
more BDNF to lamina II, based on the axon projection in spinal
Lamina II derived from small and medium sized neuron. BDNF
can be transported from DRG to lamina II (Zhou and Rush,
1996), indicating a possible role for BDNF in synaptic
plasticity (Wolpaw and Tennissen, 2001). In this study, we
postulate that EA promoting the spinal cord plasticity may be
linked to the up-regulation of BDNF and its transportation.
NT-3 and their mRNA in DRG were present mainly in some
small and large DRG neurons in normal cats. After adjacent
DRG removal, immunoreactive numbers for NT-3 in the spared
DRG significantly increased on the EA side, suggesting that EA
might be responsible for the up-regulation of endogenous NT-3
in small and large DRG neurons. As it is well known that small
DRG neurons project mainly to spinal lamina II whereas large
ones mainly to the nucleus dorsalis (ND), as well as nucleus
gracilis and nucleus cuneatus and NT-3 could be transported in
an anterograde direction, it is expected that more NT-3 would
be transported to these regions when there is more of it in the
DRG neurons. The earliest requirement for NT-3 has been
reported in cultured chick neural crest cells, where NT-3
functions as a mitogenic factor (Kalcheim et al., 1992; Pinco
et al., 1993). The increased amount of NT-3 derived from the
spared DRG might contribute towards sprouting within the
spinal cord as NT-3 injected into the spinal cord increases the
regenerative sprouting of the transected corticospinal tract in
adult rats (Schnell et al., 1994). NT-3-enhanced axonal
regeneration could also exert a beneficial effect on the motor
target organ (Sterne et al., 1997). These reports showed that NT-
3 might play a role in neural plasticity. The present results
indicated that the endogenous NT-3 derived from the spared
DRG might be related to the spinal cord plasticity after EA.
Interestingly, mRNA expressions for NGF, BDNF and NT-3
were not present apparently change on the two sides of L6 DRG
in normal cats, while statistically significant accumulation on
the acupunctured-side in Group I. This suggests that EA
exerting the treatment effect may be only linked to the injury
condition in our observation. In animal experiments, low-
magnitude extraneural compression was noted to decrease
intraneural microvascular flow, impair axonal transport, and
alter nerve structure and function (Rydevik et al., 1981). At
pressures rise to higher grade, all intraneural blood flow ceased.
Moreover, high-magnitude extraneural compression inhibited
retrograde axonal transport (Dahlin and McLean, 1986). That’s
to say, cell nutrition and the intraneurnal communication
system are compromised at elevated extraneural pressures. The
cat has seven lumbar vertebrae as compared with five in
humans. The spinal lumbar enlargement in humans is located at
T11-L1 and in cats at L4-L6. In the present study, the DRG of
cats in Group I associated with L1-L5 and L7-S2 spinal nerves
were first bilaterally removed, then followed immediately with
electrical-acupuncture on the left side at acupuncture points,
which are known to lie in L6 dermatome. More expressions for
NGF, BDNF and NT-3 mRNAwere found in the EA side than in
the control side with a significant difference on the seventh day
after the injury, indicating the expressions of the three
neurotrophic factors inducing by EA have been triggered.
Although it is well-established that EA could promote
morphological and functional plasticity in the spinal cord, the
mechanism is not fully understood. The present study proposed
that EA could induce an up-regulation of NGF, BDNF and NT-3
in the L6 DRG, after removal of the adjacent DRG and this
could be the factors for the axonal sprouting of L6 DRG
neurons.
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