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Journal of Acupuncture and Meridian Studies

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J Acupunct Meridian Stud 2014;7(1):25e32

- RESEARCH ART ICLE -

Cord Dorsum Potentials Evoked byElectroacupuncture Applied to the HindLimbs of Rats

Salvador Quiroz-Gonzalez 1,2,*, Bertha Segura-Alegrıa 3,Jose Carlos Guadarrama-Olmos 2, Ismael Jimenez-Estrada 2

1Department of Acupuncture and Rehabilitation, State University of Ecatepec Valley,Ecatepec State of Mexico, Mexico2Department of Physiology, Biophysics and Neuroscience, Center for Research andAdvanced Studies, National Polytechnic Institute, Mexico City, Mexico3 Superior Studies Faculty, FES Iztacala, UNAM, Mexico

Available online 5 July 2013

Received: Feb 6, 2013Revised: Jun 3, 2013Accepted: Jun 4, 2013

KEYWORDSacupuncture point;cord dorsum potentials;electroacupuncture;spinal cord

* CLE

CopypISSNhttp

orresponding author. Departmenteona Vicario, Colonia Valle de An-mail: quiroz@fisio.cinvestav.mx

right ª 2014, International Pharm2005-2901 eISSN 2093-8152

://dx.doi.org/10.1016/j.jams.201

AbstractThe longitudinal distribution of the cord dorsum potentials (CDPs) produced by electro-acupuncture (EA) stimulation at acupuncture points (APs) located on the hind limbs ofrats was analyzed in this study. Single electrical pulses (0.05 ms, 1 Hz) applied to thebladder (BL) and the gallbladder (GB) APs produced CDPs on several spinal segmentsand were composed of the following four components: an afferent volley, two negativecomponents (N1 and N2), and one positive component (P wave). The larger evoked CDPsdiffered in their rostrocaudal distributions depending on the stimulated AP site, withthose evoked by GB32e33 (at L3) and GB36e37 (at L4) being more caudal than thosegenerated by BL58e59 (at L5) and BL37e38 (at L6). The CDPs produced by stimulatingnonacupoints (NAPs) showed similar components and rostrocaudal distributions thatwere smaller in amplitude than those evoked by stimulating APs. The CDPs producedby stimulating NAPs located on a meridian acupuncture area were similar in amplitudeand longitudinal distribution to those produced by stimulating APs. Our results suggest

of Acupuncture and Rehabilitation, State University of Ecatepec Valley, Avenida Central s/n, Esquinaahuac Seccion “A”, Codigo Postal 55210, Ecatepec Estado de Mexico, Mexico.(S. Quiroz-Gonzalez).

acopuncture Institute

3.06.013

26 S. Quiroz-Gonzalez et al.

that the specificity of EA stimulation for CDPs responses is mainly related to an activa-tion of meridian pathways associated with peripheral nerve routes rather than to arestricted point specificity of APs.

1. Introduction

Acupuncture is a therapeutic modality that emerged fromtraditional Chinese medicine. The efficacy of acupuncturetreatment has been accepted worldwide. The World HealthOrganization recommends the use of acupuncture for thetreatment of a large variety of diseases [1]. As amodern newkind of traditional acupuncture, electrical stimulation ofacupuncture points (APs), which is called electro-acupuncture (EA), is widely used in both clinical and exper-imental studies [2,3]. According to traditional acupuncture,the functional organic system is connected through anetwork of channels called meridians, where the Qi streamsto the whole body. The insertion of acupuncture needles inspecific meridian APs may neutralize imbalances of thestreaming Qi within the organism. However, recent neuro-physiological and neurochemical studies have shown thatmany of the effects of acupuncture are mediated by bothhumoral and neurochemical factors [3e5]. The AP stimula-tion has been reported to provoke the activation of Aa, Ad,and C fibers [3,6,7], and the effect of acupuncture has beenreported to correlatewell with the activity of several centraland peripheral structures in the nervous system of verte-brates [3,8,9]. The skin andmuscles contain a large variety ofsensory receptors that code a considerable variety of sensorymodalities (cold, pressure, strength, pain, etc.) [10]. Thesereceptors are innervated by afferent fibers that arrive atseveral segments of the spinal cord [11e14].

Several experimental studies have demonstrated thatimpulses originating from the peripheral nerves during EAtreatment converge at the level of the spinal cord, wherecomplex neuronal processes are activated [3,15e17]. Inrats, non-noxious stimulation of large-diameter cutaneousfibers triggers segmental mechanisms in the correspondingspinal dermatome to reduce the perception of nociceptiveinputs [3,18].

Electrical activation of cutaneous nerves induces theactivation of conglomerates of sensory neurons located inthe dorsal horn of the spinal cord [19e21], which producescord dorsum potentials (CDPs) consisting of four clearlydefined components. The first is the afferent volley (AV),which is caused by the electrical activation of low-threshold afferent fibers [21]. This is followed by twonegative components (named N1 and N2), which aregenerated by the monosynaptic and disynaptic activationsof dorsal-horn neurons through the Ab- and Ad-afferent fi-bers in the cutaneous nerves [19e21]. Subsequently, a long-lasting positive component, named the P wave, which isascribed to the current flows generated during the primaryafferent depolarization (PAD) and presynaptic inhibition,occurs [22,23]. However, little is known about the poten-tials evoked by EA stimulation on the spinal cord dorsum.This study aims to compare the segmental longitudinaldistribution of CDPs produced by EA stimulation on APs,

nonacupoints (NAPs), and NAPs located at the acupuncturemeridian (NAPsM).

2. Materials and methods

2.1. Animals

Male Wistar rats (n Z 13) weighting 250e300 g (8e10 weeksold) obtained from the animal house of our institute wereused. All animals had free access to water and were housedunder identical environmental conditions of light and darkcycles (12:12 hours) and temperature (22e24 �C). All ex-perimentswere carriedout in accordancewith theguidelinesof the Mexican Official Norm (NOM-062-ZOO-1999) and theNational Institutes of Health Guide for the Care and Use ofLaboratory Animals (NIH Publication Number 8023, revised in1978). The study protocol had been approved by the insti-tutional bioethical committee for Care and Handling ofLaboratory Animals (Protocol 0267-05, CINVESTAV).

2.2. Surgical procedures

At the beginning of the experiment, the animal was initiallyanesthetized with an intraperitoneal injection of a mixedsolution of ketamine (100 mg/kg) and xylazine (2 mg/kg).This was supplemented every hour by additional doses ofketamine (50 mg/kg) applied in the same low abdominal re-gion to ensure that an adequate level of anesthesia, definedas the absence of withdrawal reflexes, was maintained.Subsequently, a bilateral laminectomy was performed in thelumbosacral enlargement (from the L3 to the S2 segments) ofthe spinal cord, and the rats were then secured in a stereo-taxic frame. The animal’s body temperature was monitoredusing a thermal probe located at the back muscles and con-nected to both an automatic feedback control unit and aheating blanket in order to maintain the animal’s bodytemperature at 37 �C. The skin flaps and muscle around theexposed tissues were raised and tied to a metal stereotaxicframe in order to form a pool, which was filled with warmmineral oil to prevent the tissues from drying.

2.3. EA stimulation

Pairs of stainless-steel acupuncture needles (0.25 mm indiameter and 5 mm in length) were inserted perpendicu-larity at a depth of 5 mm in the left hind limb in both NAPsand APs located on the bladder (BL) and the gallbladder(GB) meridians. In this study, we included the combinationsof FeiyangeFuyang (BL58e59), YinmeneFuxi (BL37e38),ZhongdueYangguan (GB32e33), and WaiqiueGuangming(GB36e37) APs (Table 1), and the transpositional method[24,25] for rats was used to determine the GB and the BLmeridians as well as to establish the presence of APs.

Table 1 Acupoint location and neuroanatomy [6].

Acupoint Subcutaneous nerves Deep-layer nerves Location

Feiyang (BL58) Lateral sural cutaneous nerve Tibial nerve On the posterior leg at thelower edge of the intersectionof the two heads of thegastrocnemius.

Fuyang (BL59) Lateral sural cutaneous nerve Tibial nerve On the posterior leg, below BL59.Yinmen (BL37) Posterior femoral cutaneous

nerveSciatic nerve Below the gluteal fold, in the

midline of the thigh, in betweenthe biceps femoris and semitendinosus.

Fuxi (BL38) Posterior femoral cutaneousnerve

Common peronealnerve

In the popliteal fossa of the posteriorknee and lateral to the center of thecrease, medial to the biceps femoristendon.

Zhongdu (GB32) Lateral femoral cutaneousnerve

Muscular branch ofthe femoral nerve

On the lateral side of the thigh, abovethe knee crease.

Yangguan (GB33) Lateral femoral cutaneousnerve

Muscular branch ofthe femoral nerve

At the depression superior to the lateralcondyle of the femur, on the lateral sideof the thigh.

Waiqiu (GB36) Superficial peroneal nerve,lateral sural cutaneous nerve

Common peronealnerve, deep peronealnerve

On the lateral side of the leg, in themidpoint of the line connecting thelateral malleolus and head of thefibula, on the anterior edge of thefibula.

Guangming (GB37) Superficial peroneal nerve,sural nerve

Deep peroneal nerve On the lateral side of the leg, on theanterior edge of the fibula below GB36.

BL Z bladder meridian; GB Z gallbladder meridian.

CDPs evoked by electroacupuncture stimulation 27

The needles were connected to an isolated-current-pulse generator (Isoflex D 4030), and the CDPs were evokedin all experiments using single square-current pulses (0.05-ms duration at 1 Hz) with various intensities. The electricalthreshold was established as the minimum stimulusstrength (usually between 0.9 and 1.3 V) necessary to causea discernible CDP response on the surface of the spinalcord. The stimulation needles for the NAPs and the NAPsMwere located at several places (see below), which areknown to be free of classical APs, on the hind limb.

2.4. CDP recording

Six chlorinated silver-ball electrodes were placed on thedorsal surface of several segments in the lumbosacral spinalcord (L3eS2) to record the CDPs (Fig. 1), and the corre-sponding reference silver electrodes were inserted into theadjacent paravertebral musculature. Each recording pair ofelectrodes was connected to an individual low-noise, high-gain differential amplifier (Grass, model P511; band-passfilters were set at 0.3e10 kHz). The resulting records weredigitized, averaged (n Z 40 at 1 Hz), and stored in a digitalcomputer using a specially designed program (built in Lab-VIEW environment). The peak amplitude of each componentin the CDPs was measured and subsequently analyzed.

2.5. Data analysis

All statistical analyses were performed using the GraphPadPrism (version 4) program. Data are expressed asmean � standard deviation. The two-way analysis of

variance test for multiple comparisons, followed by theBonferroni correction, was used to determine the differ-ences in the amplitudes of the CDPs obtained at APs, NAPs,and NAPsM. The differences were considered significant atp < 0.05 and p < 0.01

3. Results

3.1. CDPs provoked by the stimulation of APslocated in the BL meridian

Electrical pulses (3.5 � T) applied to the BL58e59 AP(Fig. 2C) evoked CDPs in different rostrocaudal segments ofthe spinal cord (Fig. 2A). Each CDP consisted of four com-ponents, namely, one initial component that correspondedto the AV, followed by two negative components (N1 andN2), and a long-lasting P wave (Figs. 1 and 2A). It isimportant to mention that the N2 component was excludedfrom this analysis because it was superposed on the fallingphase of the N1 component, making it extremely difficult tomeasure (Figs. 2 and 3A and B). These potentials were quitesimilar in shape and rostrocaudal distribution to thoseevoked by the electrical stimulation of cutaneous nerves[23]. The largest components in the CDPs that had beenevoked by BL58e59 stimulation occurred at the L5 segmentand gradually decreased in amplitude at adjacent ros-trocaudal spinal segments (Fig. 2E). Meanwhile, CDPsgenerated by electrical stimulation of NAPs (3.5 � T;Fig. 2A) showed the same number of components and a

20 ms

100

µV

AV

N1N2

P Wave

AcupunctureNeedles

Electrostimulator

Figure 1 Experimental arrangement for the recording of cord dorsum potentials (CDPs) evoked by electroacupuncture stimu-lation applied to acupoints. AVZ afferent volley; BLZ bladder; N1 Z first negative component; N2 Z second negative component;NAP Z nonacupoints; P wave Z positive component associated with PAD and presynaptic inhibition.

28 S. Quiroz-Gonzalez et al.

similar rostrocaudal distribution, but they had smalleramplitudes (Fig. 2A and E).

By contrast, the different components of the CDPsgenerated at all segments by stimulation of NAPs werelocated at areas adjacent to the APs; however, inside thesame acupuncture meridian (NAPsM) they showed no sta-tistical differences in amplitude (p > 0.05) compared withCDPs evoked by the stimulation of APs (Fig. 2E). The elec-trical pulses (3.5 � T) applied to BL37e38 (Fig. 2D) pro-duced the largest components in the CDPs at the L6segment (Fig. 2B and F), and the components were signifi-cantly larger than those evoked by NAP stimulation(p < 0.05). No statistical differences were found betweenthe amplitudes of the different CDP components producedby stimulation of NAPsM located at the BL meridian andthose produced by stimulation of BL APs (p > 0.05; Fig. 2F).

3.2. CDPs provoked by stimulation of APs located inthe GB meridian

Electrical stimuli pulses applied to the GB32e33 AP(3.5 � T; Fig. 3C) produced CDPs containing the samenumber of components as the CDPs caused by BL AP stim-ulation (Fig. 3A). The largest components in the CDPsoccurred at the L3 segment and gradually decreased inamplitude at the adjacent rostrocaudal spinal segments(Fig. 3E). These potentials showed no statistical differencesin amplitude compared with those evoked by NAPsM stim-ulation (p > 0.05; Fig. 3A and E). Meanwhile, the compo-nents in the CDPs produced by NAP stimulation had verysmall amplitudes compared with those produced by stimu-lations at GB32e33 and NAPsM (Fig. 3E). By contrast,stimulation of GB37e36 and NAPsM (Fig. 3D) produced thelargest components in the CDPs at the L4 segment (Fig. 3B),

while stimulation of NAPs evoked larger CDPs at the L5segment, but they had smaller amplitude than those pro-voked by GB37e36 and NAPsM stimulation (Fig. 3F).

4. Discussion

The data obtained in this study showed that EA stimulationof hind-limb APs in rats causes CDPs at several lumbosacralspinal segments. The larger evoked CDPs differed in theirrostrocaudal distribution depending on the site of thestimulated hind-limb AP, with those evoked by stimulationat GB32e33 (at L3) and GB36e37 (at L4) being more caudalthan those generated by stimulation at BL58e59 (at L5) andBL37e38 (at L6), and gradually decreased in amplitude atthe adjacent rostrocaudal spinal segments. The N1 and N2

components in the CDPs generated by the electrical stim-ulation of cutaneous nerves are well established to beproduced by the monosynaptic and the disynaptic activa-tions of dorsal-horn neurons located in laminae III to VI andII through Ab- and Ad-afferent fibers [19e21], and the Pwave is ascribed to the current flows generated by thepresynaptic depolarization of afferent fibers [22].

In this study, during EA stimulation, CDPs with AV, N1, N2,and P-wave components with rostrocaudal distributionssimilar to those provoked by cutaneous nerve stimulationwere evoked [20,23]. This could suggest that acupuncturestimulation activates spinal neurons located in Rexedlaminae II to VI of the dorsal horn and presynaptic depo-larization of afferent fibers in several lumbosacral spinalsegments, where cutaneous and AP inputs may haveconverged. Anatomical studies have reported that GB andthe BL meridians are innervated by cutaneous and muscularnerves [6]. The BL58e59 AP receives innervations from thelateral sural cutaneous nerve and in a deep layer of the

BL58–59

Spinal

Segments

A

C

BL58–59 NAPs NAPsM BL37–38 NAPs NAPsM

B

D

N1 component

L3 L4 L5 L6 S1 S2

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L3 L4 L5 L6 S1 S2

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**

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L3 L4 L5 L6 S1 S2

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*

*

*

*

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** *

*

µ V

F

L3 L4 L5 L6 S1 S2

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BL37–38

NAPs

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**

*

µ V

35 ms

200

µV

Figure 2 Cord dorsum potentials (CDPs) provoked in different spinal segments by stimulation of acupoints on bladder (BL)meridians. (A) Average CDPs produced by stimulations of BL58e59, nonacupoints (NAPs), and NAPs on meridians (NAPsM). (B)Average CDPs produced by stimulations of BL37e38, NAPs, and NAPsM. (C and D) Schematic representation of the hind-limbacupoints stimulated. (E and F) Graphs illustrating the average amplitude values of the afferent volley, N1 component, and Pwave (mV) in CDPs produced by BL58e59 and BL37e38 stimulation, respectively. Asterisks indicate significant statistical differencesbetween CDP responses produced by stimulations of APs and NAPs ()p < 0.05 and ))p < 0.01). N1 Z first negative component;P wave Z positive component associated with PAD and presynaptic inhibition.

CDPs evoked by electroacupuncture stimulation 29

tibial nerve (Table 1). The BL37e38 APs are innervated bythe posterior femoral cutaneous nerve, the sciatic nerve,and the common peroneal nerve, and GB32e33 APs areinnervated by both the lateral femoral cutaneous nerve andthe muscular branch of the femoral nerve (Table 1). TheGB36e37 APs receive sensory innervation from severalnerves, such as the superficial peroneal, lateral suralcutaneous, common peroneal, and deep peroneal nerves.Stimulating the branches of the nerve innervating the hind-limb stomach meridian (deep peroneal and superficialperoneal nerves) provoked train discharges in motor

neurons [26]. If the depth of needle insertion in the hindlimb and the broad innervations of APs (Table 1) areconsidered, it thus seems reasonable to expect that duringEA stimulation, several cutaneous and/or muscle inputs willbe activated and that the different rostrocaudal distribu-tion of the CDPs produced by GB and BL APs will be asso-ciated with the broad innervations of the APs and theirprojections to the spinal-cord segments. Because the CDPswere recorded on the surface of the spinal cord, it is notpossible to disclose the probable effect evoked by APs onmotor responses [27,28].

Spinal Segments

A

NAPs NAPsM

Afferent Volley

L2 L3 L4 L5 L6 S1

0

20

40

60

80

100

*

* **

*

µ

N1

component

L2 L3 L4 L5 L6 S1

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NAPs NAPsM

B

P Wave

L2 L3 L4 L5 L6 S1

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GB32–33

NAPs

NAPsM

**

* *

µ V

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*

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CD

E

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0

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NAPs

NAPsM

**

*

µ V

200

µV

35 ms

GB32–33

Figure 3 Cord dorsum potentials (CDPs) provoked in different spinal segments by the stimulation of gallbladder meridian acu-points. (A) Average CDPs produced by stimulation of GB32e33, nonacupoints (NAPs), and nonacupoints on meridians (NAPsM). (B)Average CDPs produced by stimulation of GB36e37, NAPs, and NAPsM. (C and D) Schematic representation of acupoint localizationused by the CDP responses produced. (E and F) Graphs illustrating the average amplitude values (mV) of the afferent volley, the N1component, and the P wave in the CDPs produced by stimulations at GB32e33 and GB36e37, respectively. Asterisks indicatesignificant statistical differences between the CDP responses produced by stimulations at APs and NAPs ()p < 0.05 and))p < 0.01). GBZ gallbladder; N1 Z first negative component; P waveZ positive component associated with PAD and presynapticinhibition.

30 S. Quiroz-Gonzalez et al.

4.1. CDPs produced by APs and NAPs

According to the Traditional Chinese Medicine theory, thetherapeutic effects of AP stimulation work through 12principal meridians that represent channels through whichQi flows. Abnormal flow of Qi in a meridian is related todisease, and its natural flow can be restored by stimulationof the appropriate APs [1,29]. An acupuncturist should firstexamine the patient’s symptoms to determine which me-ridians are involved according to syndrome differentiationand subsequently choose a set of APs along the meridians to

stimulate to evoke the greatest clinical response [29].However, because several studies have shown thatacupuncture stimulation of nonmeridian, as well as me-ridian, sites provokes effects similar to those produced bystimulation at APs, the question of the physiological iden-tity of the AP and the placebo effects has been raised[30,31].

Maioli et al [32] showed that both classical APs and NAPswere similarly effective in modulating upper-limb motor-evoked potentials elicited by transcranial magneticstimulation of the primary motor cortex. Functional

CDPs evoked by electroacupuncture stimulation 31

neuroimaging studies have demonstrated a remarkableoverlap between the brain areas activated by needling atAPs and NAPs [33,34]. Until now, the precise nature of theAPs has remained unknown. However, many studies havesuggested that the distribution of APs is related to periph-eral nerve routes. Consequently, acupuncture is thought toinvolve the stimulation of specific peripheral nerves [3,6].By combining single-fiber recordings with Evans blueextravasation, Li et al [7] found that the receptive fields(RFs) of both A and C fibers were concentrated either atsites of APs or on the route of meridian channels, indicatingthat the distribution of RFs was closely, but not exclusively,associated with APs.

This study found that CDPs produced by NAPs (but NAPslocated near APs) showed components and rostrocaudaldistributions that were smaller in amplitude than thoseevoked by AP stimulation, but stimulation of NAPsM evokedCDPs with amplitudes and longitudinal distributions similarto those produced by AP stimulation. Thus, the specificityof EA stimulation for CDP responses is suggested to bemainly related to activation of meridian pathways associ-ated with peripheral nerve routes, rather than to arestricted point specificity of APs.

4.2. Functional implications

Although this study does not address a possible relationshipbetween the spinal segments activated during EA stimula-tion and the therapeutic effect of acupuncture, severalpieces of experimental evidence support a possible rela-tionship between the pain site, organic innervations, andAPs, and such a relationship would be important for thetreatment of several diseases. The most effective depres-sion of nociceptive responses occurred when APs wereselected in the skin regions in which the source of pain waslocated [35]. Similar results were found when EA at theST36 hind-limb site decreased the expression of c-fos in thesuperficial dorsal horn of the spinal cord in rats [36].

In a clinical situation, different APs in humans areselected according to the required therapy. For the treat-ment of pain located in the upper body, such as the head,neck and arm, APs in the arm are usually used whereas APsin lower body areas are used to relieve pain such as sciaticaand abdominal pain [3], which is consistent with the prin-ciple of spinal segmental innervations suggested by Satoand Schmidt [37]. Acupuncture signals entering the poste-rior horn of the spinal cord were also observed to influencethe neurons of the anterior and the lateral horns to initiatesoma-to-soma, somatovisceral, and/or soma-muscular re-flexes [3,6]. Although this study found that EA APs elicitedsensory spinal responses that strongly depended on thestimulated needling point stimulated, further studiesshould be undertaken to establish whether the larger CDPsevoked by EA are associated with a therapeutic organiceffect and/or reflex responses.

5. Conclusion

The results obtained in this study showed that EA stimula-tion of hind-limb APs and NAPs in rats caused CDPs atseveral lumbosacral spinal segments and that the larger

evoked CDPs differed in their rostrocaudal distributionsdepending on the site of the stimulated hind-limb AP. TheCDPs produced by stimulation at NAPs showed componentsand a rostrocaudal distribution that were smaller inamplitude than those evoked by stimulation at APs, butstimulation of an NAPsM evoked CDPs with amplitudes and alongitudinal distribution that were similar to those of CDPsevoked by stimulation at APs. Thus, we suggest that thespecificity of EA stimulation for CDP responses is mainlyrelated to activation of meridian pathways associated withperipheral nerve routes rather than to a restricted pointspecificity of APs.

Disclosure statement

The author affirms there are no conflicts of interest and theauthor has no financial interest related to the material ofthis manuscript.

Acknowledgments

This work was partially supported by fellowships granted toI.J.-E. and B.S.-A. from the Sistema Nacional de Inves-tigadores and to S.Q.-G. by Universidad Estatal del Valle deEcatepec, Estado de Mexico.

References

1. Andersson S, Lundeberg T. Acupuncturedfrom empiricism toscience: functional background to acupuncture effects in painand disease. Med Hypotheses. 1995;45:271e281.

2. Vickers AJ, Cronin AM, Maschino AC, Lewith G, MacPherson H,Foster NE, et al. Acupuncture for chronic pain: individual pa-tient data meta-analysis. Arch Intern Med. 2012;172:1444e1453.

3. Zhao ZQ. Neural mechanism underlying acupuncture analgesia.Prog Neurobiol. 2008;85:355e375.

4. Han JS. Acupuncture: neuropeptide release produced byelectrical stimulation of different frequencies. Trends Neuro-sci. 2003;26:17e22.

5. Han JS. Acupuncture and endorphins. Neurosci Lett. 2004;361:258e261.

6. Zhou F, Huang D, Xia Y. Neuroanatomic basis of acupuncturepoints. In: Xia Y, Cao XD, Wu GC, Cheng JS, eds. AcupunctureTherapy for Neurological Diseases: A Neurobiological View.Berlin, Heidelberg: Springer-Verlag; 2010:32e80.

7. Li AH, Zhang JM, Xie YK. Human acupuncture points mapped inrats are associated with excitable muscle/skin-nerve com-plexes with enriched nerve endings. Brain Res. 2004;1012:154e159.

8. Pomeranz B, Cheng R, Law P. Acupuncture reduces electro-physiological and behavioral responses to noxious stimuli: pi-tuitary is implicated. Exp Neurol. 1977;54:172e178.

9. Pomeranz B, Chiu D. Naloxone blockade of acupuncture anal-gesia: endorphin implicated. Life Sci. 1976;19:1757e1762.

10. Willis WD, Coggeshall RE. Sensory Mechanisms of the SpinalCord. 2nd ed. New York: Plenum Press; 1991.

11. Takahashi Y, Nakajima Y, Sakamoto T. Dermatome mapping inthe rat hindlimb by electrical stimulation of the spinal nerves.Neurosci Lett. 1994;168:85e88.

12. Takahashi Y, Nakajima Y. Dermatomes in the rat limbs asdetermined by antidromic stimulation of sensory C-fibers inspinal nerves. Pain. 1996;67:197e202.

32 S. Quiroz-Gonzalez et al.

13. Slimp JC, Rubner DE, Snowden ML, Stolov WC. Dermatomalsomatosensory evoked potentials: cervical, thoracic, andlumbosacral levels. Electroencephalogr Clin Neurophysiol.1992;84:55e70.

14. Liguori R, Krarup C, Trojaborg W. Determination of the segmentalsensory and motor innervation of the lumbosacral spinal nerves.An electrophysiological study. Brain. 1992;115:915e934.

15. Li C, Zhu L, Li W, Ji C. Relationship between the presynapticdepolarization effect of acupuncture and g-aminobutyric acid,opioid peptide and substance P. Zhen Ci Yan Jiu. 1993;18:178e182. [Article in Chinese, English abstract].

16. Fung SJ, Chan SH. Primary afferent depolarization evoked byelectroacupuncture in the lumbar cord of the cat. Exp Neurol.1976;52:168e176.

17. Wu CP, Zhao ZQ, Cheng Y, Shao DH, Yang ZQ. Membrane po-tential changes of dorsal horn neurons elicited by electro-acupuncture. Acupunct Anaesth. 1978;1:33e34.

18. Zhu B, Xu WD, Rong PJ, Ben H, Gao XY. A C-fiber reflex inhi-bition induced by electroacupuncture with different intensitiesapplied at homotopic and heterotopic acupoints in rats selec-tively destructive effects on myelinated and unmyelinatedafferent fibers. Brain Res. 2004;1011:228e237.

19. Bernhard CG. The spinal cord potentials in leads form the corddorsum in relation to a peripheral source of afferent stimula-tion. Acta Physiol Scand. 1953;29:1e29.

20. Willis WD, Weir MA, Skinner RD, Bryan RN. Differential distri-bution of spinal cord field potentials. Exp Brain Res. 1973;17:169e176.

21. Coombs JS, Curtis DR, Landgren S. Spinal cord potentialsgenerated by impulses in muscle and cutaneous afferent fibres.J Neurophysiol. 1956;19:452e467.

22. Rudomin P, Schmidt RF. Presynaptic inhibition in the verte-brate spinal cord revisited. Exp Brain Res. 1999;129:1e37.

23. Gonzalez SQ, Alegrıa BS, Olmos JC, Jimenez-Estrada I. Effectof chronic undernourishment on the cord dorsum potentialsand the primary afferent depolarization evoked by cutaneousnerves in the rat spinal cord. Brain Res Bull. 2011;85:68e74.

24. Yin CS, Jeong HS, Park HJ, Baik Y, Yoon MH, Choi CB, et al. Aproposed transpositional acupoint system in a mouse and ratmodel. Res Vet Sci. 2008;84:159e165.

25. Koh HK. Transpositional acupoints of the rat. J Korean Acu-punct Mox Soc. 1999;16:115e122.

26. Xie Y, Li H, Xiao W. Neurobiological mechanisms of the me-ridian and the propagation of needle feeling along the merid-ian pathway. Sci China C Life Sci. 1996;39:99e112.

27. Katz B, Miledi R. A study of spontaneous miniature potentials inspinal motoneurones. J Physiol. 1963;168:389e422.

28. Eccles JC, Magni F, Willis WD. Depolarization of central ter-minals of Group I afferent fibres from muscle. J Physiol. 1962;160:62e93.

29. Xiaoding C. History of acupuncture research in China. In: Xia Y,Cao XD, Wu GC, Cheng JS, eds. Acupuncture Therapy forNeurological Diseases: A Neurobiological View. Berlin,Heidelberg: Springer-Verlag; 2010:1e31.

30. Schneider A, Enck P, Streitberger K, Weiland C, Bagheri S,Witte S, et al. Acupuncture treatment in irritable bowel syn-drome. Gut. 2006;55:649e654.

31. Ernst E. Acupuncturedcritical analysis. J Intern Med. 2006;259:125e137.

32. Maioli C, Falciati L, Marangon M, Perini S, Losio A. Short-and long-term modulation of upper limb motor-evokedpotentials induced by acupuncture. Eur J Neurosci. 2006;23:1931e1938.

33. Yoo SS, Teh EK, Blinder RA, Jolesz FA. Modulation of cerebellaractivities by acupuncture stimulation: evidence from fMRIstudy. Neuroimage. 2004;22:932e940.

34. Wu MT, Sheen JM, Chuang KH, Yang P, Chin SL, Tsai CY, et al.Neuronal specificity of acupuncture response: a fMRI studywith electroacupuncture. Neuroimage. 2002;16:1028e1037.

35. Chen-ping W, Chih-chi C, Jen-yu W. Inhibitory effect producedby stimulation of afferent nerves on responses of cat dorso-lateral fasciculus fibres to nocuous stimulus. Sci Sin. 1974;27:688e697.

36. Dai Y, Kondo E, Fukuoka T, Tokunaga A, Miki K, Noguchi K. Theeffect of electroacupuncture on pain behaviors and noxiousstimulus-evoked Fos expression in a rat model of neuropathicpain. J Pain. 2001;2:151e159.

37. Sato A, Schmidt RF. Spinal and supraspinal components of thereflex discharges into lumbar and thoracic white rami.J Physiol. 1971;212:839e850.