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Departments of
1 Integrative Physiology
2 Orthopaedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
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Abstract |
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- and C-afferent-mediated excitatory postsynaptic currents (EPSCs) in more than 70% of the neurones tested at the L5 level. Both A- and C-afferent EPSCs were also recorded in more than 50% of the neurones at L4. At L3 and L6, the number of neurones receiving the C-afferent EPSCs (> 40%) was significantly greater than that of A-afferent EPSCs (< 20%). On the other hand, the A- and C-afferent-mediated inhibitory postsynaptic currents (IPSCs) elicited by L5 DRS were almost equally observed from L2 to S1. In the current-clamp mode, L5 DRS evoked A- and C-afferent-mediated EPSPs, some of which initiated action potentials (APs). Most of the A-afferent-mediated APs were limited at the L5 level, while C-afferent-mediated APs were observed at L5 and L4. As the L2 DRS-evoked APs in the L2 SG neurones were suppressed by L5 DRS, the widespread distribution of the inhibitory inputs was considered to be functional. These findings suggest that the excitatory projection of the C afferents to the SG neurones was thus spread more rostrocaudally than that of the A afferents, thereby contributing to more diffuse pain transmission. In addition, the widespread distribution of the inhibitory inputs may thus play a role as a lateral inhibitory network and thereby prevent the expansion of the excitatory inputs of noxious stimuli.
(Received 27 May 2004;
accepted after revision 2 August 2004;
first published online 5 August 2004)
Corresponding author T. Katafuchi: Department of Integrative Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan. Email: kataf{at}physiol.med.kyushu-u.ac.jp
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Introduction |
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and unmyelinated C afferents (Rexed, 1952; Kumazawa & Perl, 1978; Light & Perl, 1979; Yoshimura & Jessell, 1989). SG neurones are interneurones that have different morphological and electrophysiological properties from those of the neurones in other laminae of the spinal dorsal horn and they play an important role in the modulation of the nociceptive transmission receiving inputs from primary afferent fibres (Cervero & Iggo, 1980; Brown, 1982; Yoshimura, 1996).
Experiments using retrograde neuronal tracers such as WGA-HRP (Swett & Woolf, 1985; Molander & Grant, 1985; LaMotte et al. 1991), isolectin B4-HRP (Kitchener et al. 1993; Wang et al. 1994), and intracellular single fibre tracings (Light & Perl, 1979; Sugiura et al. 1986, 1989; Mizumura et al. 1993) have demonstrated that most of the A and C afferents terminate in the marginal layer (lamina I) and the SG, thereby extending rostrocaudally for several spinal segments. Furthermore, the nociceptive neuronal circuits of A and C afferents have been reported to change in density and segmental distribution in the SG after peripheral inflammation (Ruda et al. 2000) and nerve injury (Shortland & Fitzgerald, 1994; Doubell et al. 1997), thus suggesting that the dynamic re-organizations of the central terminal fields may play an important role in the altered responses to noxious stimuli during these insults. Although traditional neuroanatomical methods have enabled us to visualize the central termination of the noxious afferents, it is difficult to clarify the functional mapping of the noxious inputs in the spinal dorsal horn. On the other hand, electrophysiological studies have shown that SG neurones receive both excitatory (Schneider & Perl, 1988; Yoshimura & Jessell, 1989; Baba et al. 1994; Furue et al. 1999) and inhibitory inputs (Yoshimura & Nishi, 1993, 1995; Baba et al. 1994; Narikawa et al. 2000; for review see Yoshimura, 1996). In addition, the physiological and pharmacological properties of the afferent inputs to the SG have previously been demonstrated at the single neurone level in the spinal cord (Cerne et al. 1992; Yoshimura et al. 1993; Sandkühler et al. 1997; Nakatsuka et al. 2000; Ito et al. 2000; Morisset & Urban, 2001 Chen & Randic, 2003; Lu & Perl, 2003). However, it is still unclear as to how the information from the primary afferents is processed in the spinal cord over several segmental levels. In this study, we therefore sought to investigate the spinal distribution of the excitatory and inhibitory postsynaptic responses of the SG neurones, at different segmental levels, that are evoked by the stimulation of a single dorsal root. For this purpose, we used horizontal spinal cord slices in adult rats which could preserve afferent fibres extending rostrocaudally in the superficial dorsal horn. In addition, we herein report the evidence for the modification of nociceptive transmission by the inputs from other remote spinal segmental levels.
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Methods |
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Preparation of the slice
The methods used for obtaining spinal cord slices from adult rats were similar to those previously described (Baba et al. 1994; Fig. 1). Briefly, male Sprague-Dawley rats (6–8 weeks old) were deeply anaesthetized with urethane (1.2–1.5 g kg–1, intraperitoneal). After a thoraco-lumbar laminectomy was performed at the level of Th11 to L3, a 2.0–3.0 cm length of the spinal cord with ventral and dorsal roots was excised and placed in pre-oxygenated cold (4–6°C) Krebs solution. The rats were killed by exsanguination. All of the ventral and dorsal roots, with the exception of the L5 dorsal root (length, 1–1.5 cm) on the right side, were cut and the pia-arachnoid membrane was removed. In some cases, two dorsal roots were left intact for the double root stimulation. The spinal cord was placed in a shallow groove formed in an agar block. A horizontal slice, in which the dorsal surface of the spinal cord was intact and a dorsal root was left (thickness, 500 µm), was made using a vibratome while the spinal cord was immersed in cold Krebs solution. Next the slice was mounted on a nylon mesh in a recording chamber, and perfused continuously at a flow rate of 25–40 ml min–1 with Krebs solution equilibrated with 95% O2–5% CO2 at 36 ± 1°C. The Krebs solution contained (mM): NaCl 117, KCl 3.6, CaCl2 2.5, MgCl2 1.2, NaH2PO4 1.2, NaHCO3 25 and glucose 11. The flow of the solution was induced by gravity through a polyethylene tube from the reservoir.
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Blind whole-cell voltage-clamp and current-clamp recordings were made from SG neurones, as previously described (Yoshimura & Nishi, 1993; Yang et al. 2001). The patch pipettes were filled with a solution containing (mM): Cs2SO4 110, TEACl 5, CaCl2 0.5, MgCl2 2, EGTA 5, Hepes 5 and MgATP 5 in the voltage-clamp mode; and potassium gluconate 136, KCl 5, CaCl2 0.5, MgCl2 2, EGTA 5, Hepes 5 and MgATP 5 in the current-clamp mode. The tip resistance of the patch pipette was 8–12 M
. Signals were acquired with a patch clamp amplifier (Axopatch 200B, Axon Instruments, Union City, CA, USA). The data were digitized with an analog-to-digital converter (Digidata 1321 A, Axon Instruments), stored on a personal computer using a data acquisition program (Clampex version 8.0, Axon Instruments), and analysed using a special software package (Clampfit version 4.1, Axon Instruments). In the voltage-clamp mode, the holding potentials (VH) were 70 mV and 0 mV, at which glycine- and GABA-mediated inhibitory postsynaptic currents (IPSCs), and glutamate-mediated excitatory postsynaptic currents (EPSCs) were negligible, respectively (Yoshimura & Nishi, 1993). Stimuli (duration, 100 µsec) to elicit EPSCs and IPSCs were given to the dorsal root at a frequency of 0.2 Hz via a suction electrode at intensities from 1.2 to 1.5 times the threshold required to elicit a response in the most excitable A or C afferent fibres. The A- or C-afferent-mediated responses evoked by the dorsal root stimulation (DRS) were distinguished on the basis of the conduction velocity (CV) of the afferent fibres (C, < 0.8 m s–1; A, 2–11 m s–1) and stimulus threshold (C, > 300 µA; A, 40–200 µA), as previously described (Yoshimura & Jessell, 1989; Nakatsuka et al. 1999; Ito et al. 2000). The CV was calculated from the latency of synaptic responses from a stimulus artifact and the length of dorsal root or determined by measuring the difference in the latencies of the responses evoked by two focal monopolar electrodes separately positioned on the root as shown in Fig. 1B (Park et al. 1999). The A-afferent-mediated EPSCs were considered to be monosynaptic in nature when the latency remained constant and there was no failure during repetitive stimulation at 20 Hz for 1 s. Whereas, C-afferent-mediated EPSCs were considered to be monosynaptic when failures did not occur during stimulation at 2 Hz for 10 s (Nakatsuka et al. 1999, 2000; Ito et al. 2000). On the other hand, the IPSCs were thought to be polysynaptic responses mediated by glycinergic and/or GABAergic interneurones (Yoshimura & Nishi, 1995).
Identification of SG neurones
The superficial dorsal grey matter lateral to the dorsal column was distinguishable as a relatively translucent band under Lissauer's tract in the horizontal slice under a binocular microscope (Fig. 1A). The SG neurones were identified by the depth from the dorsal surface, and from their morphological features. The neurones were recorded at a depth of 30–120 µm from the L2 to S1 levels of the spinal cord. The neurones were further confirmed by the intracellular injection of neurobiotin (0.1–0.2% in the electrode solution; Vector Laboratories, Burlingame, CA, USA) through a patch pipette. After termination of the electrophysiological recordings, the spinal cord slices were immersed overnight in 4% paraformaldehyde in 0.1 M phosphate buffer (PB, pH 7.4) at 4°C, rinsed in PB, and then sectioned sagittally into slices (500 µm thick) using a vibratome. Free-floating sections were incubated overnight at 4°C in phosphate-buffered saline (PBS) with 0.3% Triton X-100 containing streptavidin-Texas Red (diluted 1: 500; Jackson ImmunoResearch, West Grove, PA), washed several times in PBS, and mounted in glycerol-based mounting medium (Vectashield, Vector). Some slices were incubated with isolectin B4 from Bandeiraea simplicifolia conjugated directly to fluorescein isothiocyanate (IB4-FITC, 0.5 µg ml–1; Sigma, St Louis, MO, USA) in order to infer the border between lamina II and III. The sections were viewed and photographed using an LSM 510 laser scanning confocal microscope (Carl Zeiss, Oberkochen, Germany).
Drug application
Drugs dissolved in Krebs solution were applied by exchanging solutions via a three-way stopcock without altering the perfusion rate or temperature. Drugs used were 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 µM; Tocris Cookson, St Ellisville, MO, USA), strychnine (2 µM; Sigma, St Louis, MO, USA), and bicuculline (20 µM; Sigma).
Statistical analysis
All numerical data were expressed as the mean ± S.E.M. Statistical significance was determined as P < 0.05 using the 
2 test. In all cases, n refers to the number of neurones tested. The membrane potentials were not corrected for the liquid junction potential between the Krebs and patch-pipette solutions.
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Results |
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, respectively, which were almost the same as those reported previously (Furue et al. 1999; Ito et al. 2000). The neurones injected with neurobiotin (n = 90) were located in the dorsal part of the ventral boundary of IB4 labelling, which has been demonstrated to be a marker of the inner lamina II (Silverman & Kruger, 1990). They showed morphological features similar to those previously described (Woolf & Fitzgerald, 1983; Beal & Bicknell, 1985; Grudt & Perl, 2002; Fig. 2). Namely, the majority of the SG neurones extended their dendrites either rostrocaudally (Fig. 2A) or dorsoventrally (Fig. 2B) in parasagittal histological sections. As shown in Fig. 2C1 and C2, a neurone which was located deeper from the ventral boundary of IB4 labelling was judged to be a lamina III neurone. Although the axons might be identified by its thinner and relatively constant size from the soma outwards, the details of the axon trajectory and the degree of branching were not examined in the present study.
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When the intensity of the threshold stimulus was plotted against the CV (Fig. 3), the A- and C-afferent-mediated EPSCs in the L5 segmental level were classified by the stimulus threshold (C, > 300 µA; A, 40–200 µA), except for only six responses (6/106; Fig. 3
). Therefore, the intensity of the stimulus threshold as well as the CV was used to determine the A- and C-afferent-mediated responses in other segmental levels.
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- and C-afferent-mediated monosynaptic EPSCs recorded at the L5 segmental level, respectively, thus demonstrating no failure and a constant latency with repetitive stimuli at 20 Hz (upper) and no failure at 2 Hz (middle) in spite of variable latencies. The CVs of the responses were calculated as 11.0 m s–1 (upper) and 0.7 m s–1 (middle). On the other hand, the EPSC shown in the lower panel of Fig. 4B shows variable latencies, failures with repetitive stimuli at 2 Hz, and a CV of 0.6 m s–1, thus indicating the C-afferent-mediated polysynaptic EPSCs. All of the EPSCs in each segmental level were classified into either the A- or C-afferent-mediated response based on the stimulus threshold intensity and CV as described above. Figure 4C shows the representative responses of the SG neurones recorded from the L2 to S1 level by stimulation of the L5 dorsal root. The L5 DRS evoked at least two different EPSCs at the L5 level that had different latencies and thus are considered to be mediated by A (arrow head) and C fibres (arrow), respectively. These EPSCs were judged to be monosynaptic by the repetitive stimulation as described in the methods. A- and C-afferent-mediated EPSCs were still observed at the L3 to L6 level, although the amplitude became smaller as the distance away from the L5 segment increased. At the L2 and S1 levels, only one C-afferent-mediated polysynaptic EPSC, but no A-afferent-mediated EPSCs was observed.
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Two kinds of IPSCs were observed at the VH of 0 mV, which were distinct in their duration and pharmacology. The upper trace in Fig. 5A shows a short IPSC (duration, < 50 ms), that was not abolished by bicuculline (Bic, 20 µM), but was blocked by strychnine (St, 2 µM); the bottom trace shows a long IPSC (duration, > 50 ms), that was abolished by Bic (lower), thus suggesting that they were mediated by glycine and GABAA receptors, respectively, as reported previously (Yoshimura & Nishi, 1993; Baba et al. 1998; Kohno et al. 1999). All of the A- and C-afferent-mediated IPSCs recorded from the stimulation segment (L5) and remote segment (L3) were blocked by St and/or Bic. As shown in Fig. 5B, the latencies of the IPSCs also varied depending on the CV of the primary afferents. As the IPSCs of the SG neurones are considered to be polysynaptic (Yoshimura & Nishi, 1995), the CV was calculated by stimulating the dorsal root at two points. The CVs of the upper and lower panel were 4.5 and 0.6 m s–1, respectively. In addition to this, the stimulus thresholds of these responses were 130 and 1000 µA, respectively, thus suggesting these responses to be A- and C-afferent-mediated IPSCs, respectively. All of the IPSCs were classified into either the A- or C-afferent-mediated responses. Aß-afferent-mediated IPSCs have not been detected under our recording conditions. As shown in Fig. 5C, the L5 DRS evoked the largest IPSCs at the L5 level which were considered to be mediated by A (arrow head) and C fibres (arrow). Unlike the EPSCs (Fig. 4C), these two IPSCs were often observed throughout from L2 to S1, although the amplitude also decreased as the distance away from the stimulation segment increased (L5).
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Table 1 shows the averages of the peak amplitude of the EPSCs and IPSCs at each segmental level. The largest amplitudes of EPSCs and IPSCs were recorded at the L5 level in both the A- and C-afferent-mediated responses. The averages of the amplitudes of all responses decreased as the distance away from L5 increased. There seemed to be no difference in the extent of the decrease between the A- and C-afferent-mediated responses. As shown in Fig. 6, L5 DRS produced A- and C-afferent-mediated EPSCs in more than 70% of the neurones tested at the L5 level. Although both A- and C-afferent-mediated EPSCs were still recorded in more than 50% of neurones at the L4, there was a difference in the distribution between the EPSCs evoked by A and C fibres at more distant segments. Namely at L3 and L6, the EPSCs evoked by C fibres were also recorded in about 40% of the neurones tested, whereas the response rate of the A-afferent-mediated EPSCs was less than 20%, and the difference was statistically significant at L3 and L6. Although the C-afferent-mediated EPSCs were distributed in L2 and S1, the A EPSC was not observed at the L2 and S1 levels. On the other hand, the IPSCs elicited by L5 DRS were almost equally observed throughout from L2 to S1, and there was no significant difference in the response rates of the A- and C-afferent-mediated IPSCs at any segmental level.
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In order to investigate the functional significance of the EPSCs and IPSCs, the changes in the postsynaptic membrane potentials of the SG neurones induced by L5 DRS were recorded in the current-clamp mode from L2 to S1 (n = 20 at each segmental level). The average resting membrane potential of the SG neurones was –67 ± 0.9 mV (n = 120) in this experiment. As shown in Fig. 7A, L5 DRS produced early and late onset EPSPs that were considered to be mediated by A and C fibres, respectively, and they were sometimes accompanied by action potentials (APs, arrow head and arrow). At the L4 level both EPSPs were observed, but the early EPSPs often lacked APs. At the L3 and L6 levels, the C fibre-, but not A-, mediated small EPSPs were observed. Furthermore, the L5 DRS produced late, small and long-lasting IPSPs, but not EPSPs, at the L2 and S1 levels. As summarized in Fig. 7B, the L5 DRS evoked both the A- and C-afferent-mediated APs at L5 in 40% of the SG neurones tested. The response rate of the A-afferent-mediated APs significantly decreased at L4 (5%), while that of the C-afferent-mediated APs did not (35%). At L3 and L6, only the C-afferent-mediated APs were recorded in 5% of the neurones, and no APs were evoked at all by L5 DRS at the L2 and S1 levels.
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To confirm the functional role of the widespreading inhibitory inputs elicited by the L5 DRS (Fig. 5C and 6), the effects of the L5 DRS on the L2 DRS-induced APs recorded from L2 SG neurones were examined using horizontal spinal cord slices with double dorsal roots (Fig. 8A, n = 18). As shown in Fig. 8B, the L2 DRS evoked the C-afferent-mediated AP (top panel), while the L5 DRS induced the C-afferent-mediated IPSP in the same L2 SG neurones (second panel). When the L2 DRS was performed after the L5 DRS, the AP was abolished in a reversible manner (third and bottom panels). The abolition of L2 APs by the L5 DRS was observed in five neurones (5/18, 28%), in which two were the A-, and three were the C-afferent-mediated APs. In addition, three neurones showed a prolongation of the latency of APs of the L2 DRS-induced APs following L5 DRS (two A- mediated AP and one C-afferent-mediated AP; data not shown). Thus in total, about 45% (8/18) of the L2 SG neurones were effectively suppressed by L5 DRS.
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Discussion |
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and C inputs from a single dorsal root to the corresponding and remote segments of the spinal cord, the distribution of the excitatory and inhibitory synaptic responses, and their functional significance.
Although the A-afferent-mediated IPSCs have been extensively analysed, the C-afferent-mediated IPSPs or IPSCs in the SG neurones have been rarely observed in previous studies using transverse slice preparations of the spinal cord (Yoshimura & Nishi, 1995; Yang et al. 1999, 2001). In contrast, the present results demonstrated that L5 DRS induced the C-afferent-mediated IPSCs in 29–55% of the neurones tested from L2 to S1 in the horizontal slices. As the C-afferent-mediated IPSCs were also recorded in the rat parasagittal slice preparations (Lu & Perl, 2003), it is likely that the SG neurones receive inhibitory inputs from the C fibre-responding interneurones that are located in the rostrocaudal direction of the recorded neurones, as suggested by Lu & Perl (2003). In fact, there are characteristic neurones in the SG, called islet and central cells, that have a pronounced rostrocaudal orientation (Grudt & Perl, 2002). Both types of neurones receive monosynaptic inputs from C fibres, and contain GABA and/or glycine (Todd & McKenzie, 1989; Todd & Sullivan, 1990; Hantman et al. 2004). It is thus suggested that these cells are involved in the circuitry of the C-afferent-mediated IPSCs in the superficial dorsal horn, which are thought to be preserved in horizontal and parasagittal slice preparations, but not in transverse ones.
In contrast to the C-afferent-mediated IPSCs, the Aß-afferent-mediated responses, in which CV was faster than 14 m s–1 according to Harper & Lawson (1985), were not observed in the present study. It has been shown that the SG neurones receive glutamatergic inputs mainly from A and C-afferent fibres and most of the Aß afferents terminate in lamina III–V of the dorsal horn (Rethelyi, 1977; Light & Perl, 1979; Sugiura et al. 1989; Yoshimura & Jessell, 1989, 1990). Nevertheless, a few of the Aß-afferent-mediated responses were recorded from the most ventral part of lamina II in the transverse slices (Woolf et al. 1992; Nakatsuka et al. 1999). Therefore these findings, taken together, suggest that the Aß fibres arising from lamina III–V and terminating in lamina II might have been cut in the horizontal slices of 500 µm thickness in the present study.
As shown in Fig. 6, the L5 DRS-evoked A- and C-afferent-mediated EPSCs were distributed from the L2 to S1 segments, although the response rate decreased as the distance away from the L5 segment increased. This finding is considered to reflect the central distribution of the primary afferent fibres in the spinal cord, and the range of the distribution was compatible with findings of a previous neuroanatomical study investigating the projection fields of the rat sciatic nerve (LaMotte et al. 1991). However, the response rate of the A-afferent-mediated EPSCs was significantly smaller than that of the C-afferent-mediated EPSCs at the L3 and L6 levels and there were no A-afferent-mediated EPSCs at the L2 and S1 levels, thus indicating that the range of the A inputs was narrower than that of the C inputs in the spinal cord.
To further investigate the difference in the signal transmission by A and C fibres, the distribution of APs evoked by L5 DRS were analysed in the current-clamp mode. When the distribution of APs (Fig. 7B) is compared with that of EPSCs (Fig. 6, left), it is apparent that the A- and C-afferent-mediated APs were observed in more limited segments than EPSCs. As the IPSCs evoked by these fibres are distributed almost equally from L2 to S1 (Fig. 6, right), it is possible that EPSCs at such remote segments as L2, L3, L6 and S1 are often cancelled out by IPSCs, thereby resulting in no effective changes in the ability of the membrane potentials to induce APs. In fact, L5 DRS induced little change in the membrane potential at L3 and L6, and only a slight hyperpolarization was observed at L2 and S1 (Fig. 7A). Although there was no difference in the response rates of the EPSCs and IPSCs between L5 and L4 (Fig. 6), the A-afferent-mediated APs were recorded significantly less than the C-afferent-mediated APs at L4 (Fig. 7B). As the amplitude of the EPSCs and IPSCs decreased from L5 to L4 or L6 in a manner similar to that observed in the A- and C-afferent-mediated responses (Table 1), it is difficult to explain the decrease in the response rate of the A- and C-afferent-mediated APs at L4 in terms of changes in the amplitude of EPSCs and IPSCs. Alternatively, there is little time lag between the A-mediated EPSCs and IPSCs even in the neighbouring spinal segment, while the time lag between the C-afferent-mediated EPSCs and IPSCs is considered to be larger due to the slow CV of C fibres. This may reduce the effective timing of EPSCs and IPSCs to suppress the C-afferent-mediated APs, thereby increasing the probability of APs at L4. Nevertheless, this does not explain the small response rate of the C-afferent-mediated APs at L6 (Fig. 7B). There may be some unknown mechanisms that evoke APs at a higher but not lower segment than the corresponding segment level.
The L5 DRS-evoked IPSCs, which are considered to be mediated by the polysynaptic pathway through the inhibitory interneurones (Yoshimura & Nishi, 1995), are almost equally distributed from L2 to S1 (Fig. 6, right). The shape of the distribution is quite different from that of EPSCs, which has a peak of the response rate at L5 (Fig. 6, left). The wide distribution of the IPSCs in the SG without a decrease in the response rate at the remote segments suggests that the inhibitory synaptic connection is stronger than the excitatory one. Furthermore, although only a small number of C-afferent-mediated EPSCs or no A-afferent-mediated EPSCs were observed at L2 and S1, a substantial number of IPSCs could be recorded at these segments. Therefore, it is possible that most of the L5-DRS-evoked IPSCs at L2 and S1 are transmitted by long axons of inhibitory interneurones, probably including the islet and central cells (Grudt & Perl, 2002; Hantman et al. 2004), which are located at more proximal segments than L2 and S1.
The functional significance of the widespread inhibitory inputs to the SG was confirmed by a double stimulation experiment (Fig. 8). In this experiment, the L2 DRS-evoked AP in an L2 SG neurone was suppressed by the L5 DRS which was performed just before L2 DRS. As L5 DRS only induced an IPSP in the same L2 SG neurone, it is evident that the excitatory inputs induced by L5 DRS not only evokes APs at L5, but also attenuates the excitatory inputs to remote segments. It is well known that the stimulation of the receptive field produces a strong excitation of the cortex neurone, but the neurone is inhibited by the stimulation of the adjacent receptive field through inhibitory interneurones. This feedforward inhibition is called ‘lateral inhibition’, and is thus considered to contribute to tactile discrimination by sharpening the central focus of the original stimulus (Mountcastle, 1980; Gardner & Kandel, 2000). The inhibitory network revealed in the present study may also play a role in preventing the expansion of the excitatory inputs evoked by noxious stimuli in the SG, thereby acting as a ‘lateral inhibition’ system.
In conclusion, the present findings suggest (1) that the C-afferent-mediated excitatory projection field in the SG spreads more rostrocaudally than the A-afferent-mediated one, (2) that both of the A- and C-afferent-mediated inhibitory projection fields spread more rostrocaudally than the excitatory projection fields, and (3) that a lateral inhibitory network exists which may play a role in inhibiting the rostrocaudal broad excitation of the SG neurones evoked by noxious stimuli.
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References |
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-afferent glutamatergic transmission in substantia gelatinosa neurons of adult rat spinal cord slices. Pain 86, 273–282.[CrossRef][Medline]
Baba H, Kohno T, Okamoto M, Goldstein PA, Shimoji K & Yoshimura M (1998). Muscarinic facilitation of GABA release in substantia gelatinosa of the rat spinal dorsal horn. J Physiol 508, 83–93.
Baba H, Yoshimura M, Nishi S & Shimoji K (1994). Synaptic responses of substantia gelatinosa neurones to dorsal column stimulation in rat spinal cord in vitro. J Physiol 478, 87–99.
Beal J & Bicknell HR Jr (1985). Development and maturation of neurons in the substantia gelatinosa (SG) of the rat spinal cord. In Development, Organization, and Processing in Somatosensory Pathways, ed. Rowe M & Willis W D Jr, pp. 23–30. Wiley-Liss, New York.
Brown AG (1982). The dorsal horn of the spinal cord. Q J Exp Physiol 67, 193–212.[Medline]
Cerne R, Jiang M & Randic M (1992). Cyclic adenosine 3'5'-monophosphate potentiates excitatory amino acid and synaptic responses of rat spinal dorsal horn neurons. Brain Res 596, 111–123.[CrossRef][Medline]
Cervero F & Iggo A (1980). The substantia gelatinosa of the spinal cord: a critical review. Brain 103, 717–772.
Cheng G & Randic M (2003). Involvement of intracellular calcium and protein phosphatases in long-term depression of A-fiber-mediated primary afferent neurotransmission. Brain Res Dev Brain Res 144, 73–82.[CrossRef][Medline]
Doubell TP, Mannion RJ & Woolf CJ (1997). Intact sciatic myelinated primary afferent terminals collaterally sprout in the adult rat dorsal horn following section of a neighbouring peripheral nerve. J Comp Neurol 380, 95–104.[CrossRef][Medline]
Furue H, Narikawa K, Kumamoto E & Yoshimura M (1999). Responsiveness of rat substantia gelatinosa neurones to mechanical but not thermal stimuli revealed by in vivo patch-clamp recording. J Physiol 521, 529–535.
Gardner EP & Kandel ER (2000). Touch. In Principles of Neural Science, 4th edn, ed. Kandel ER, Schwartz JH & Jessell TM, pp. 451–471. McGraw-Hill, New York.
Grudt TJ & Perl ER (2002). Correlations between neuronal morphology and electrophysiological features in the rodent superficial dorsal horn. J Physiol 540, 189–207.
Hantman AW, van del Pol AN & Perl ER (2004). Morphological and physiological features of a set of spinal substantia gelatinosa neurons defined by green fluorescent protein expression. J Neurosci 24, 836–842.
Harper AA & Lawson SN (1985). Conduction velocity is related to morphological cell type in rat dorsal root ganglion neurones. J Physiol 359, 31–46.
Ito A, Kumamoto E, Takeda M, Shibata K, Sagai H & Yoshimura M (2000). Mechanisms for ovariectomy-induced hyperalgesia and its relief by calcitonin: participation of 5-HT1A-like receptor on C-afferent terminals in substantia gelatinosa of the rat spinal cord. J Neurosci 20, 6302–6308.
Kitchener PD, Wilson P & Snow PJ (1993). Selective labelling of primary sensory afferent terminals in lamina II of the dorsal horn by injection of Bandeiraea simplicifolia isolectin B4 into peripheral nerves. Neuroscience 54, 545–551.[CrossRef][Medline]
Kohno T, Kumamoto E, Higashi H, Shimoji K & Yoshimura M (1999). Actions of opioids on excitatory and inhibitory transmission in substantia gelatinosa of adult rat spinal cord. J Physiol 518, 803–813.
Kumazawa T & Perl ER (1978). Excitation of marginal and substantia gelatinosa neurons in the primate spinal cord: indications of their place in dorsal horn functional organization. J Comp Neurol 177, 417–434.[CrossRef][Medline]
LaMotte CC, Kapadia SE & Shapiro CM (1991). Central projections of the sciatic, saphenous, median, and ulnar nerves of the rat demonstrated by transganglionic transport of choleragenoid- HRP (B-HRP) and wheat germ agglutinin-HRP (WGA-HRP). J Comp Neurol 311, 546–562.[CrossRef][Medline]
Light AR & Perl ER (1979). Spinal termination of functionally identified primary afferent neurons with slowly conducting myelinated fibers. J Comp Neurol 186, 133–150.[CrossRef][Medline]
Lu Y & Perl ER (2003). A specific inhibitory pathway between substantia gelatinosa neurons receiving direct C-fiber input. J Neurosci 23, 8752–8758.
Mizumura K, Sugiura Y & Kumazawa T (1993). Spinal termination patterns of canine identified A- and C spermatic polymodal receptors traced by intracellular labeling with Phaseolus vulgaris-leucoagglutinin. J Comp Neurol 335, 460–468.[CrossRef][Medline]
Molander C & Grant G (1985). Cutaneous projections from the rat hindlimb foot to the substantia gelatinosa of the spinal cord studied by transganglionic transport of WGA-HRP conjugate. J Comp Neurol 237, 476–484.[CrossRef][Medline]
Morisset V & Urban L (2001). Cannabinoid-induced presynaptic inhibition of glutamatergic EPSCs in substantia gelatinosa neurons of the rat spinal cord. J Neurophysiol 86, 40–48.
Mountcastle VB (1980). Neural mechanism in somesthesia. In Medical Physiology, 14th edn, ed. Mountcastle VB, pp. 348–390. The C. V. Mosby Company, St Louis.
Nakatsuka T, Ataka T, Kumamoto E, Tamaki T & Yoshimura M (2000). Alteration in synaptic inputs through C-afferent fibers to substantia gelatinosa neurons of the rat spinal dorsal horn during postnatal development. Neuroscience 99, 549–556.[CrossRef][Medline]
Nakatsuka T, Park JS, Kumamoto E, Tamaki T & Yoshimura M (1999). Plastic changes in sensory inputs to rat substantia gelatinosa neurons following peripheral inflammation. Pain 82, 39–47.[CrossRef][Medline]
Narikawa K, Furue H, Kumamoto E & Yoshimura M (2000). In vivo patch-clamp analysis of IPSCs evoked in rat substantia gelatinosa neurons by cutaneous mechanical stimulation. J Neurophysiol 84, 2171–2174.
Park JS, Nakatsuka T, Nagata K, Higashi H & Yoshimura M (1999). Reorganization of the primary afferent termination in the rat spinal dorsal horn during post-natal development. Brain Res Dev Brain Res 113, 29–36.[Medline]
Rethelyi M (1977). Preterminal and terminal axon arborizations in the substantia gelatinosa of cat's spinal cord. J Comp Neurol 172, 511–521.[CrossRef][Medline]
Rexed B (1952). The cytoarchitectonic organization of the spinal cord in the cat. J Comp Neurol 96, 415–495.[CrossRef]
Ruda MA, Ling QD, Hohmann AG, Peng YB & Tachibana T (2000). Altered nociceptive neuronal circuits after neonatal peripheral inflammation. Science 289, 628–631.
Sandkühler J, Chen JG, Cheng G & Randic M (1997). Low-frequency stimulation of afferent A-fibers induces long-term depression at primary afferent synapses with substantia gelatinosa neurons in the rat. J Neurosci 17, 6483–6491.
Schneider SP & Perl ER (1988). Comparison of primary afferent and glutamate excitation of neurons in the mammalian spinal dorsal horn. J Neurosci 8, 2062–2073.[Abstract]
Shortland P & Fitzgerald M (1994). Neonatal sciatic nerve section results in a rearrangement of the central terminals of saphenous and axotomized sciatic nerve afferents in the dorsal horn of the spinal cord of the adult rat. Eur J Neurosci 6, 75–86.[CrossRef][Medline]
Silverman JD & Kruger L (1990). Selective neuronal glycoconjugate expression in sensory and autonomic ganglia: relation of lectin reactivity to peptide and enzyme markers. J Neurocytol 19, 789–801.[CrossRef][Medline]
Sugiura Y, Lee CL & Perl ER (1986). Central projections of identified, unmyelinated (C) afferent fibers innervating mammalian skin. Science 234, 358–361.
Sugiura Y, Terui N & Hosoya Y (1989). Difference in distribution of central terminals between visceral and somatic unmyelinated (C) primary afferent fibers. J Neurophysiol 62, 834–840.
Swett JE & Woolf CJ (1985). The somatotopic organization of primary afferent terminals in the superficial laminae of the dorsal horn of the rat spinal cord. J Comp Neurol 231, 66–77.[CrossRef][Medline]
Todd AJ & Mckenzie J (1989). GABA-immunoreactive neurons in the dorsal horn of the rat spinal cord. Neuroscience 31, 799–806.[CrossRef][Medline]
Todd AJ & Sullivan AC (1990). Light microscope study of the coexistence of GABA-like and glycine-like immunoreactivities in the spinal cord of the rat. J Comp Neurol 296, 496–505.[CrossRef][Medline]
Wang H, Rivero-Melian C, Robertson B & Grant G (1994). Transganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons. Neuroscience 62, 539–551.[CrossRef][Medline]
Woolf CJ & Fitzgerald M (1983). The properties of neurones recorded in the superficial dorsal horn of the rat spinal cord. J Comp Neurol 221, 313–328.[CrossRef][Medline]
Woolf CJ, Shortland P & Coggeshall RE (1992). Peripheral nerve injury triggers central sprouting of myelinated afferents. Nature 355, 75–78.[CrossRef][Medline]
Yang K, Kumamoto E, Furue H, Li YQ & Yoshimura M (1999). Action of capsaicin on dorsal root-evoked synaptic transmission to substantia gelatinosa neurons in adult rat spinal cord slices. Brain Res 830, 268–273.[CrossRef][Medline]
Yang K, Li Y, Kumamoto E, Furue H & Yoshimura M (2001). Voltage-clamp recordings of postsynaptic currents in substantia gelatinosa neurons in vitro and its applications to assess synaptic transmission. Brain Res Brain Res Protoc 7, 235–240.[CrossRef][Medline]
Yoshimura M (1996). Slow synaptic transmission in the spinal dorsal horn. Prog Brain Res 113, 443–462.[Medline]
Yoshimura M & Jessell TM (1989). Primary afferent-evoked synaptic responses and slow potential generation in rat substantia gelatinosa neurons in vitro. J Neurophysiol 62, 96–108.
Yoshimura M & Jessell TM (1990). Amino acid-mediated EPSPs at primary afferent synapses with substantia gelatinosa neurones in the rat spinal cord. J Physiol 430, 315–335.
Yoshimura M & Nishi S (1993). Blind patch-clamp recordings from substantia gelatinosa neurons in adult rat spinal cord slices: pharmacological properties of synaptic currents. Neuroscience 53, 519–526.[CrossRef][Medline]
Yoshimura M & Nishi S (1995). Primary afferent-evoked glycine- and GABA-mediated IPSPs in substantia gelatinosa neurones in the rat spinal cord in vitro. J Physiol 482, 29–38.[Medline]
Yoshimura M, Shimizu T, Yajiri Y, Inokuchi H & Nishi S (1993). Primary afferent-evoked slow EPSPs and responses to substance P of dorsal horn neurons in the adult rat spinal cord slices. Regul Pept 46, 407–409.[CrossRef][Medline]
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