Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2012 Oct 11.
Published in final edited form as: Brain Res. 2007 Aug 19;1174:39–46. doi: 10.1016/j.brainres.2007.08.030

Time-Dependent Effect of Epidural Steroid on Pain Behavior Induced by Chronic Compression of Dorsal Root Ganglion in Rats

Xiaoping Gu 1, Shuxing Wang 2, Liling Yang 2, Backil Sung 2, Grewo Lim 2, Ji Mao 2, Qing Zeng 2, Yang Chang 2, Jianren Mao 2,*
PMCID: PMC3468942  NIHMSID: NIHMS32361  PMID: 17869229

Abstract

Although epidural steroid injection has been commonly used to treat radicular pain, its clinical efficacy remains controversial. In a rat model of radicular pain induced by chronic compression of lumbar dorsal root ganglion (CCD), we examined the effect of epidural steroid on CCD-induced pain behavior. Triamcinolone [a glucocorticoid receptor (GR) agonist] or RU38486 (a GR antagonist) was given epidurally once either on day 3 (early treatment) or day 10 (late treatment) after CCD. The results showed that 1) early treatment with triamcinolone and RU38486 alone, respectively, reduced and exacerbated mechanical allodynia and thermal hyperalgesia, 2) late treatment with triamcinolone alone failed to improve mechanical allodynia and only transiently attenuated thermal hyperalgesia, and 3) late treatment with RU38486 alone improved mechanical allodynia and thermal hyperalgesia in CCD rats. Moreover, a second dose of triamcinolone given on day 10 paradoxically exacerbated pain behavior in CCD rats that received a first dose of triamcinolone on day 3. These results indicate that the effect of epidural steroid on radicular pain may be time-dependent. Clinical implications for epidural steroid treatment are discussed in light of these preclinical findings.

Keywords: Epidural, Steroid, Glucocorticoid receptor, Dorsal root ganglia, Hyperalgesia, Allodynia, Sciatica, Radicular pain, Neuropathic pain

1. Introduction

Lumbosacral radicular pain (e.g., pain from sciatica) is a common clinical condition. The prevalence of sciatica is about 5.3% in men and 3.7% in women, representing a nearly 6 % of total disability cases (Heliovaara et al., 1987). Epidural steroid injection has been commonly used as a non-surgical treatment for radicular pain (Bogduk et al., 1994; Goebert et al., 1961). While a number of open-label clinical studies have shown the beneficial effects of epidural steroid injection (e.g., Spaccarelli et al., 1996), several prospective, randomized, controlled studies have failed to provide convincing evidence for its clinical efficacy (Armon et al., 2007; Carette et al., 1997; Arden et al., 2005; Price et al., 2005; Valat et al., 2003). To date, it remains unclear with regard to the clinical efficacy of epidural steroid injection for the treatment of radicular pain (Armon et al., 2007).

Epidural steroid injection has been used to treat radicular pain because 1) glucocorticoid has strong anti-inflammatory effects, 2) epidural steroid injection is likely to attain a high local steroid concentration over inflamed nerve roots and/or dorsal root ganglion (DRG), and 3) glucocorticoid receptors (GR) are known to mediate the anti-inflammatory effect of glucocorticoid (Bogduk et al., 1994; Manchikanti et al., 2000). However, recent experiments have shown that neuronal GR was upregulated within the spinal cord dorsal horn after peripheral nerve injury, which adversely contributed to the pathogenesis of neuropathic pain behavior in rats (Wang et al., 2004). These data suggest that endogenous and/or exogenous glucocorticoids could conceivably produce a complex effect on radicular pain conditions.

In a rat model of radicular pain induced by chronic compression of L5 lumbar dorsal root ganglion (CCD) using a surgical matrix (SURGIFLO), we examined the hypothesis that the effect of epidural glucocorticoid steroid (triamcinolone) on pain behavior would depend on the time of drug administration after CCD. Our results support the hypothesis that the effect of epidural steroid injection on CCD pain behavior is time-dependent and mediated by GR.

2. Results

2.1. CCD-induced thermal hyperalgesia and mechanical allodynia

As compared with baseline, the different score (contralateral side minus ipsilateral side) of thermal withdrawal latencies was significantly increased in the CCD group, which began on postoperative day 1 and lasted up to 35 days after CCD (Fig. 1A, P<0.05). There were no statistically significant differences in thermal withdrawal latencies of the hindpaw contralateral to CCD (P>0.05), nor were there significant changes of thermal withdrawal latencies in rats with sham operation (Fig. 1A, P >0.05).

Fig. 1.

Fig. 1

Open in a new tab

Time course of changes in paw-withdrawal latency to thermal stimulation (A) or threshold bending force to von Frey filament stimulation (B); D0, 1, 3, 5, 7, 10, 14, 21, 28, 35, and 42 indicate days of CCD. All data points represent mean ± SEM. *P<0.05, as compared with sham rats. Difference scores refer to differences in paw-withdrawal latency (PWD) or threshold bending force (VF) between the contralateral (C) and ipsilateral (I) side.

The difference score (contralateral minus ipsilateral) of withdrawal threshold to mechanical stimulation (von Frey filament) was also significantly increased in the CCD group, which began on day 1 and lasted up to 28 days after CCD (Fig. 1B, P<0.05). Similar to thermal withdrawal latencies, there were no significant postoperative changes in mechanical threshold in the sham group, nor on the contralateral hindpaw of CCD rats (Fig. 1B, P> 0.05). The results indicate that CCD produced lasting thermal hyperalgesia and mechanical allodynia, resembling a clinical situation of radicular pain.

2.2 Effect of early treatment with triamcinolone or RU38486

Epidural treatment with triamcinolone (50-200 μg but not 6.25 or 25 μg), given once on postoperative day 3, significantly reduced thermal hyperalgesia (Fig. 2A, P<0.05) and mechanical allodynia (Fig. 2B, P < 0.05) as compared with vehicle-treated CCD rats. Specifically, 1) the effect of triamcinolone on thermal hyperalgesia lasted up to at least 7 days after a single injection on postoperative day 3; 2) triamcinolone also significantly reduced mechanical allodynia but with a shorter duration (up to 3 days after a single injection); and 3) triamcinolone itself had no effect on thermal and mechanical nociceptive threshold in sham rats, nor did it change the baseline threshold in the contralateral hindpaw of CCD rats. These results indicate that triamcinolone had a therapeutic effect on pain behavior when given during the early stage of CCD.

Fig. 2.

Fig. 2

Open in a new tab

The dose-response effect of early treatment with triamcinolone (TRI) on thermal hyperalgesia (A) and mechanical allodynia (B) in CCD rats. All injections were given epidurally once on postoperative day 3. All data points represent mean ± SEM. * P<0.05, as compared with CCD+vehicle (VEH) in each group. Triamcinolone alone did not affect the behavior response in sham rats (A, B).

Moreover, epidural treatment with the GR antagonist RU38486 alone (20 μg but not 5 μg) on postoperative day 3 transiently (for 24-48 hours) worsened thermal hyperalgesia and mechanical allodynia, as compared with vehicle-treated CCD rats (Fig. 3A, B; P<0.05). RU38486 (20 μg) alone had no effect on thermal and mechanical nociceptive threshold in both hindpaws of sham rats or the contralateral hindpaw of CCD rats. This result is consistent with the effect of triamcinolone on pain behavior and suggests that endogenous glucocorticoid steroids may have a protective effect on pain behavior as well during the early stage of CCD.

Fig. 3.

Fig. 3

Open in a new tab

The dose-response effect of early treatment with RU38486 (RU) on thermal hyperalgesia (A) and mechanical allodynia (B) in CCD rats. All injections were given epidurally once on postoperative day 3. All data points represent mean ± SEM. *P<0.05, as compared with CCD+vehicle (VEH) in each group. RU38486 alone did not affect the behavioral response in sham rats (A, B).

2.3. Effect of late treatment with triamcinolone or RU38486

In contrast to a clear protective effect on pain behavior when given on postoperative day 3, epidural triamcinolone (50 –200 μg) only transiently reduced thermal hyperalgesia (Fig. 4A, P< 0.05) and failed to attenuate mechanical allodynia (Fig. 4B, P> 0.05) when given on postoperative day 10. Similarly, differing from its effect on pain behavior when given alone on postoperative day 3, epidural treatment with RU38486 alone (5 or 20 μg) on postoperative day 10 reduced thermal hyperalgesia (Fig. 5A; P<0.05) and mechanical allodynia (Fig. 5B; P < 0.05) as compared with vehicle-treated CCD rats. RU38486 (20 μg) itself had no effect on thermal or mechanical nociceptive threshold in contralateral hindpaws of CCD rats. These results indicate that glucocorticoid steroid (exogenous or endogenous) had an adverse effect on established CCD pain behavior, which differs from its protective effect on pain behavior during the early stage of CCD.

Fig. 4.

Fig. 4

Open in a new tab

The dose-response effect of late treatment with triamcinolone (TRI) on thermal hyperalgesia (A) and mechanical allodynia (B) in CCD rats. All injections were given epidurally once on postoperative day 10. All data points represent mean ± SEM. *P<0.05, as compared with CCD+vehicle (VEH) in each group. Triamcinolone alone did not affect the behavioral response in sham rats (A, B).

Fig. 5.

Fig. 5

Open in a new tab

The dose-response effect of late treatment with RU38486 (RU) on thermal hyperalgesia (A) and mechanical allodynia (B) in CCD rats. All injections were given epidurally once on postoperative day 10. All data points represent mean ± SEM. *P<0.05, as compared with CCD+vehicle (VEH) in each group. RU38486 alone did not affect the behavioral response in sham rats (A, B).

2.4. Effect of a second triamcinolone dose

Since early treatment with triamcinolone (100 μg) on postoperative day 3 significantly attenuated thermal hyperalgesia and mechanical allodynia, which lasted for at least 3-7 days (Fig. 2), we asked whether a second triamcinolone dose would provide further improvement of pain behavior for those rats that received the first triamcinolone dose on day 3. As discussed in Methods, day 13 after CCD was chosen to administer the second triamcinolone dose because the effect of a first triamcinolone dose had completely subsided at this time point.

The second epidural triamcinolone dose (100 μg) failed to reduce thermal hyperalgesia and mechanical allodynia and transiently exacerbated pain behavior (for 1-3 days), as compared with CCD rats treated with triamcinolone on day 3 and vehicle on day 13 (Fig. 6A,B, P<0.05). The effect of this second triamcinolone dose on pain behavior was blocked by co-administration of triamcinolone (100 μg) with RU38486 (20 μg) (Fig. 6A, B). Moreover, epidural treatment with RU38486 (20 μg) alone on postoperative day 13 significantly reduced thermal hyperalgesia and mechanical allodynia for at least one week in those CCD rats that received a first epidural triamcinolone dose (100 μg) on day 3 (Fig. 6A, B; P<0.05). These results further indicate an adverse effect of triamcinolone on pain behavior when given during a late stage of CCD.

Fig. 6.

Fig. 6

Open in a new tab

The effects of a second dose of triamcinolone or RU38486 on thermal hyperalgesia (A) and mechanical allodynia (B) in CCD rats that received a first triamcinolone dose. Rats were given the first dose of triamcinolone (100 μg) on postoperative day 3 and then given one of the following on postoperative day 13: triamcinolone 100μg (TRI+TRI); triamcinolone 100μg + RU38486 20 μg (TRI+TRI+RU]; RU38486 20μg (TRI+RU), or vehicle 20μl (TRI+VEH). All data points represent mean ± SEM. *P<0.05, as compared with the (VEH+VEH) group, + p<0.05, as compared with D0 of the corresponding group.

3. Discussion

The present data demonstrate that 1) both thermal hyperalgesia and mechanical allodynia in CCD rats were effectively reduced by early treatment with triamcinolone on day 3, 2) late treatment with triamcinolone on day 10 only transiently reduced thermal hyperalgesia and failed to improve mechanical allodynia, 3) early and late treatment with the GR antagonist RU38486, respectively, exacerbated and improved mechanical allodynia and thermal hyperalgesia, and 4) a second dose of triamcinolone given on day 13 exacerbated thermal hyperalgesia and mechanical allodynia in CCD rats that received a first triamcinolone dose on day 3. Collectively, these data indicate that the effect of epidural steroid on pain behavior is time-dependent in this rat model of radicular pain.

Triamcinolone is a synthetic glucocorticoid steroid, acting as a GR agonist with a medium potency, and has a half-life of 18-36 hours with little or no mineralocorticoid activity (Manchikanti et al., 2000). Clinically, triamcinolone is commonly used for treatment of radicular pain through the epidural route (Bogduk et al., 1994; Price et al., 2005; Manchikanti et al., 2000). In this study, triamcinolone was delivered through an epidural catheter, resembling clinical epidural steroid injection. The correct placement of each epidural catheter was confirmed before steroid injection using a lidocaine test and also by post-mortem examination of the actual catheter placement, as discussed in Methods. Only those rats with both anatomically and functionally conformed epidural catheter placement were included for the data analysis. Of note, although RU38486 has been extensively used as a GR antagonist, it does have the antiprogesterone effect (Mao et al., 1992). However, the antiprogesterone effect is unlikely to be involved in this study because only adult male rats were included. Another methodological concern is that only reflective responses (thermal hyperalgesia and mechanical allodynia) were used in the study, where in clinical radicular pain conditions spontaneous pain also is present. Indeed, animal models used in preclinical studies often show reflexive responses and there has been a lack of reliable behavioral observations that could provide valuable information on spontaneous pain (Mao, 2002). Therefore, the data interpretation should be made in the context of this methodological limitation. Of note, since the texture of a hardened SURGIFLO plaque differs from a metal rod used in another rat model (Hu and Xing, 1998; Song et al., 1999), radicular pain behaviors observed in this animal model might mimic clinical radicular pain conditions resulting from soft tissue (e.g., herniated disc) compression on the affected DRG and/or nerve root.

Steroid injections used in this study resulted in a differential effect on pain behavior when given as early (postoperative day 3) versus late (postoperative day 10) treatment. The choice of these treatment points was based on our pilot experiments and following considerations. Postoperative day 3 was selected as the time point for early treatment because 1) both thermal hyperalgesia and mechanical allodynia were clearly present at this time point but yet to be fully developed and 2) a possible confounding influence from the epidural catheter implantation on pain behavior, if any, had subsided within 24-48 hours after operation as indicated in our pilot experiments. On the other hand, day 10 was selected for late treatment with triamcinolone because pain behavior was stable on postoperative day 10 after CCD, which continued to be present for up to 4-5 postoperative weeks. In one experiment, postoperative day 13 was selected for a second triamcinolone dose because at this time point the effect of a first triamcinolone dose given on day 3 had completely subsided. In the early treatment regimen, the doses greater than 50 μg (but 6.25 or 25 μg) produced a similar therapeutic effect on thermal hyperalgesia and mechanical allodynia. In the late treatment regimen, there was a difference between 100 μg and 200 μg triamcinolone. In addition, triamcinolone at 100 μg only transiently attenuated thermal hyperalgesia in the late treatment regimen.

A potentially significant observation is that the effect of epidural steroid on CCD pain behavior was time-dependent, a protective effect from early treatment and an apparently adverse effect from late treatment. The protective effect of steroid demonstrated in this animal model is supported by a number of earlier studies. For example, systemic or intrathecal administration of steroid reduced regional inflammation including edema and neurogenic extravasation as well as hyperalgesia in rats with tissue injury or complete Freund’s adjuvant-induced arthritis (Abram et al., 1994; Kingery et al., 1999, 2001, Tekada et al., 2004; Zhang et al., 2004). Epidural treatment with betamethasone also improved thermal hyperalgesia in a rat model of radiculopathy (Hayashi et al., 1998). On the other hand, several recent reports have shown limited or no effect of neuraxial steroid on pain behavior. For example, epidural treatment with betamethasone in rats with spinal nerve injury only partially reduced hyperalgesia (Xie et al., 2006). Repeated intrathecal triamcinolone administration produced a mild, if any, effect during the second phase of formalin-induced pain behavior and intrathecal injection of methylprednisolone even produced transient segmental allodynia in this same animal model (Abram et al., 1994). These seemingly contradictory reports on the effect of neuraxial steroid on pain behavior may be in part due to the time of treatment in relation to the stage of a pain condition, as demonstrated in the present experiments. Of interest to note is that the time course of the triamcinolone effect on thermal hyperalgesia and mechanical allodynia differed during the early stage of CCD, suggesting a possible difference in the cellular mechanisms underlying the development of thermal hyperalgesia and mechanical allodynia.

The present study was largely observational and did not specifically examine why the steroid effect was time-dependent after CCD. However, possible mechanisms of these differential steroid effects may be speculated in light of previous studies. With regard to the protective effect of glucocorticoid steroid on pain behavior during the early stage of CCD, we think that the effect of epidural steroid is likely due to its antiinflammatory action. Several previous studies have shown that neuraxial steroid can reduce glial activation and proinflammatory cytokine expression (Takeda et al., 2004; Xie et al., 2006). Inflammatory reaction to tissue injury is reportedly present within the first few postoperative days (Brennan et al., 2005; Romero-Sandoval, Eisenach, 2007). In addition, direct exposure of an injured nerve to exogenous steroid reduced thermal hyperalgesia and mechanical allodynia in rats (Johansson and Bennett, 1997). On the other hand, the possibly adverse effect of epidural steroid on established pain behavior (late stage treatment) could be related to the interaction between GR and NMDA receptor as suggested by previous studies (Abraham et al., 2000; Diem et al., 2003; Wang et al. 2004). Future studies examining the time course of changes in inflammatory factors (e.g., cytokines and NF-kappa B) and NMDA receptor expression at various stages of CCD may help elucidate the mechanisms underlying the differential steroid effects on CCD pain behavior.

Radicular pain is a major clinical pain condition that remains difficult to treat. Although epidural steroid injection has been extensively used as a non-surgical intervention, the efficacy of this treatment varies from 18% to 90% (Manchikanti et al. 2001). In addition, although neuraxial injection of methylprednisolone has been used to treat patients with intractable postherpetic neuralgia (Kikuchi et al., 1999; Kotani et al. 2000), the clinical validity of this procedure remains controversial. It should be noted that currently controlled clinical studies have not been done to compare the time–dependent effect of repeated steroid injections on chronic pain. Therefore, the current animal data should not be readily extrapolated into clinical situations. However, these animal data may provide some insight into the debate over the effectiveness of epidural steroid injection on chronic pain management (Armon et al., 2007). Our data may also shed light on the variation regarding the clinical outcome of epidural steroid treatment for radicular pain, suggesting that the timing of steroid treatment could be considered as an important factor in clinical settings.

4. Experimental Procedures

4.1 Animal surgery and drugs

Adult male Sprague Dawley rats weighing 275–325 gm (Charles River Laboratories, Wilmington, MA) were used. The animal room was artificially lighted from 7:00 A.M. to 7:00 P.M. Rats were housed in individual cages with free access to water and food pellets. Room temperature was maintained at 24 °C. Experimental procedures were carried out in accordance with the protocol approved by our Institutional Animal Care and Use Committee. Aseptic technique was used in all surgical procedures.

The surgical procedure to produce CCD was performed under pentobarbital anesthesia (50 mg/kg, intraperitoneally) according to the previously published method (Hu and Xing, 1998; Song et al., 1999) with some modification. In previous studies, tiny metal rods were inserted into intervertebral foramen to induce nerve root and DRG compression (Hu and Xing, 1998; Song et al., 1999). Although this method produces post-surgical pain behavior in rats, the experimental condition appears less likely to reflect clinical radicular pain condition resulting from disc herniation with compression on an exiting nerve root and/or DRG. In this study, a surgical matrix (SURGIFLO) (John & Johnson, Somerville, NJ) was used to induce a focal compression on one side of L5 nerve root and DRG. This surgical matrix is a viscous liquid that hardens once in contact with tissues, resulting in progressive compression on the affected nerve root and DRG.

To inject SURGIFLO, paraspinal muscles were separated from the left mammillary process and transverse process and the left L5 intervertebral foreman was exposed. A stainless 22G steel needle, with a blunt angle to avoid tissue penetration, was gently inserted at approximately 4 mm into the L5 intervertebral foreman without touching the existing nerve root and DRG. The needle was inserted with a 30–40° angle towards the dorsal middle line and 10° to 15° below the vertebral horizon. Sixty μl of SURGIFLO was slowly injected (within 1-2 minutes) into the intervertebral foreman. After the injection, the muscle and skin layers were closed with 6.0 nylon sutures. Sham operation was performed using the same surgical procedure without the injection of SURGIFLO.

Each rat was also implanted with an epidural catheter under the same surgical condition. A PE-10 (Clay Adams, Parsippany, NJ) was inserted according to a previously described method (Kim et al., 1998). Briefly, a 1-2 cm midline skin incision was made at the most prominent thoracic posterior spinous process (between T12 and T13). Using a pair of microscissor, a small hole was made in the middle of ligament flavum and a PE-10 tube was gently advanced about 2-3 cm caudally in the epidural space with the catheter tip being placed approximately at the level of exiting L4 and L5 nerve roots. The proximal end of the epidural catheter was tunneled subcutaneously to the posterior cervical area and secured with sutures for later epidural injection. Incisions were closed with 6.0 nylon sutures or wound clips.

To determine the correct placement of an epidural catheter, negative aspiration of spinal fluid was confirmed following each catheter implantation and 2% lidocaine (0.15 ml) was injected through the catheter after the rat gained complete recovery from pentobarbital anesthesia. When given epidurally, this lidocaine dose produced transient paralysis in hindpaws but not forepaws. If the catheter were placed intrathecally, sudden respiratory arrest (high spinal anesthesia) and/or paralysis in all four paws would be observed with this dose of lidocaine. We observed a small percentage (about 5%) of such cases, which were excluded from the study. During the experimental period, those rats showing neurological deficits and/or behavioral abnormalities (e.g., poor eating) were excluded. Upon completion of each experiment, the final position of an epidural catheter placement (outside the dura) was verified through autopsy.

Triamcinolone and RU38486 (Mifepristone) were purchased from Bristol-Myers Squibb (Princeton, NJ) and Sigma (St. Louis, MO), respectively. Triamcinolone and RU38486 were dissolved in 10% DMSO diluted in normal saline (vehicle). Each drug was injected epidurally in a 20 μl volume followed by a 20 μl saline flush. Experiments were conducted with the experimenter blinded to treatment conditions.

4.2. Behavioral testing and statistical analysis

Animals were habituated to the test environment for three consecutive days (60 min per day) before baseline testing. Withdrawal threshold to thermal and mechanical stimulation was examined for both ipsilateral and contralateral hindpaws. For the measurement of mechanical threshold, each rat was placed into a plastic cage with a wire mesh bottom. Mechanical threshold was measured using a set of von Frey filaments as described previously (Bennett and Xie, 1988; Mao et al., 1993). A single filament was applied perpendicularly to the plantar surface of a rat’s hindpaw for five times with an interstimulation interval of 5 seconds. A positive response was defined as at least one clear withdrawal response out of five applications. The threshold force was determined using an up and down approach with different filament sizes (Xie et al., 2001).

Thermal hyperalgesia to radiant heat was determined according to a previously described method (Hargreaves et al., 1988) using a 390 Analgesia Meter (IITC Inc., CA). Briefly, a rat was placed into a Plexiglas cubicle on a transparent glass surface. The light source from a projection bulb was directed at the plantar surface of each hindpaw. The withdrawal latency was defined as the time from the onset of radiant heat to hindpaw withdrawal. The radiant heat source was adjusted to result in baseline latencies of around 12 s and a cut-off time of 20 s. Two trials with an intertrial interval of 3 min were made for each hindpaw and scores from both trials were averaged to yield mean withdrawal latencies.

Data from behavioral tests were analyzed by first generating difference scores between two hindpaws (contralateral minus ipsilateral), so that a higher difference score represents a higher degree of thermal hyperalgesia or mechanical allodynia. This method of analysis was used to provide a straightforward data presentation because there were no significant changes in withdrawal thresholds on contralateral hindpaws after CCD as shown in the Results section. Difference scores were analyzed by two-way ANOVA repeated across testing time points to detect overall differences among treatment groups. Whenever applicable, the data were also examined by using repeated measure two-way ANOVA across treatment groups to examine overall differences among testing time points. When significant main effects were observed, post hoc Newman–Keuls tests were performed to determine sources of differences. Differences were considered to be statistically significant at the level of p<0.05.

4.3 Experimental design

Experiment1: time course of pain behavior after CCD

In this first experiment, thermal hyperalgesia and mechanical allodynia were examined over a six-week period for both ipsilateral and contralateral hindpaws in both CCD and sham rats (n= 6–10/group). The data from this experiment was used to determine different treatment time points (early versus late) for the triamcinolone or RU38486 regimens as described below in Experiments 2, 3, 4.

Experiment 2: Effect of early treatment with triamcinolone or RU38486 on pain behavior

To examine the effect of a GR agonist (triamcinolone) or antagonist (RU38486) on CCD pain behavior, triamcinolone or RU38486 was given epidurally once on day 3 (early treatment) of CCD. This time point represented the early development of pain behavior after CCD as shown in Experiment 1. Eleven groups of rats (n= 6–8/group) were used, including (1) CCD+vehicle, (2-6) CCD+triamcinolone (6.25, 25, 50, 100, 200 μg), (7-8) CCD+RU38486 (5, 20 μg), (9) sham+vehicle, (10) sham+triamcinolone (200 μg), and (11) sham+RU38486 (20 μg). The dose range for triamcinolone or RU38486 was referenced from our previous work (e.g., Wang et al., 2004). Behavioral tests were made on day 0 (baseline), 1, 3, 4, 5, 7, 10, 14, and 21 after CCD.

Experiment 3: Effect of late treatment with triamcinolone or RU38486 on pain behavior

In this experiment, seven groups of rats (n= 6–8/group) were used, including (1) CCD+vehicle, (2-4) CCD+triamcinolone (50, 100, 200 μg), (5, 6) CCD+ RU38486 (5, 20 μg), and (7) sham+vehicle. The dose range for triamcinolone or RU38486 was based on the outcome of Experiment 2. The effect of triamcinolone or RU38486 in sham rats was examined in Experiment 2 and not repeated in this experiment. The treatment was given epidurally once on postoperative day 10 (late treatment) because pain behavior was peaked and stable at this time point as determined in Experiment 1. Behavioral tests were made on day 0, 1, 7, 10, 11, 12, 14, 17 and 21 after CCD.

Experiment 4: Effect of a second triamcinolone dose on pain behavior

In clinical settings, repeated epidural steroid injections are often used to treat persistent radicular pain. To examine the effect of a second triamcinolone dose on pain behavior in CCD rats that already received a first dose of triamcinolone, four groups of CCD rats (n=6–8 group) was used, including (1) 100 μg triamcinolone (dose 1 on day 3)+100 μg triamcinolone (dose 2 on day 13), (2) 100 μg triamcinolone (dose 1 on day 3)+100 μg triamcinolone (dose 2 on day 13)+20 μg RU38486 (on day 13), (3) 100 μg triamcinolone (on day 3)+vehicle (on day 13), (4) 100 μg triamcinolone (on day 3)+20 μg RU38486 (on day 13). The data from this experiment was also compared with that from Experiments 2 & 3 for additional controls. Day 13 was selected for the second triamcinolone dose because the data from Experiment 2 indicated that pain behavior had returned to the pretreatment level on day 12 after a first triamcinolone dose given on day 3. Behavioral tests were made on day 0, 12, 13, 14, 15, 17, and 21 after CCD.

Acknowledgments

This work was supported in part by US PHS grants NS42661, NS45681, and DE18538.

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

References

  1. Abraham I, Harkany T, Horvath KM, Veenema AH, Penke B, Nyakas C, Luiten PG. Chronic corticosterone administration dose-dependently modulates Abeta(1-42)- and NMDA-induced neurodegeneration in rat magnocellular nucleus basalis. J Neuroendocrinol. 2000;12:486–494. doi: 10.1046/j.1365-2826.2000.00475.x. [DOI] [PubMed] [Google Scholar]
  2. Abram SE, Marsala M, Yaksh TL. Analgesic and neurotoxic effects of intrathecal corticosteroids in rats. Anesthesiology. 1994;81:1198–1205. doi: 10.1097/00000542-199411000-00013. [DOI] [PubMed] [Google Scholar]
  3. Arden NK, Price C, Reading I, Stubbing J, Hazelgrove J, Dunne C, Michel M, Rogers P, Cooper C. A multicentre randomized controlled trial of epidural corticosteroid injections for sciatica: the WEST study. Rheumatology (Oxford) 2005;44:1399–1406. doi: 10.1093/rheumatology/kei028. [DOI] [PubMed] [Google Scholar]
  4. Armon C, Argoff CE, Samuels J, Backonja MM. Assessment: use of epidural steroid injections to treat radicular lumbosacral pain: report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology. 2007;68:723–729. doi: 10.1212/01.wnl.0000256734.34238.e7. [DOI] [PubMed] [Google Scholar]
  5. Brennan TJ, Zahn PK, Pogatzki-Zahn EM. Mechanisms of incisional pain, Anesthesiol. Clin North America. 2005;23:1–20. doi: 10.1016/j.atc.2004.11.009. [DOI] [PubMed] [Google Scholar]
  6. Bennett GJ, Xie YK. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain. 1988;33:87–107. doi: 10.1016/0304-3959(88)90209-6. [DOI] [PubMed] [Google Scholar]
  7. Bogduk N, Christophidis N, Cherry D. Report of Working Party on Epidural Use of Steroids in the Management of Back Pain. National Health and Medical Research Council Commonwealth of Australia; Canberra: 1994. Epidural Use of Steroids in the Management of Back Pain; pp. 1–76. [Google Scholar]
  8. Carette S, Leclaire R, Marcoux S, Morin F, Blaise GA, St Pierre A, Truchon R, Parent F, Levesque J, Bergeron V, Montminy P, Blanchette C. Epidural corticosteroid injections for sciatica due to herniated nucleus pulposus. N Engl J Med. 1997;336:1634–1640. doi: 10.1056/NEJM199706053362303. [DOI] [PubMed] [Google Scholar]
  9. Diem R, Hobom M, Maier K, Weissert R, Storch MK, Meyer R, Bahr M. Methylprednisolone increases neuronal apoptosis during autoimmune CNS inflammation by inhibition of an endogenous neuroprotective pathway. J Neurosci. 2003;23:6993–7000. doi: 10.1523/JNEUROSCI.23-18-06993.2003. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Goebert HW, Jr, Jallo SJ, Gardner WJ, Wasmuth CE. Painful radiculopathy treated with epidural injections of procaine and hydrocortisone acetate: results in 113 patients. Anesth Analg. 1961;40:130–134. [PubMed] [Google Scholar]
  11. Hargreaves K, Dubner R, Brown F, Flores C, Joris J. A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia. Pain. 1988;32:77–88. doi: 10.1016/0304-3959(88)90026-7. [DOI] [PubMed] [Google Scholar]
  12. Heliovaara M, Impivaara O, Sievers K, Melkas T, Knekt P, Korpi J, Aromaa A. Lumbar disc syndrome in Finland. J Epidemiol Community Health. 1987;41:251–258. doi: 10.1136/jech.41.3.251. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Hu SJ, Xing JL. An experimental model for chronic compression of dorsal root ganglion produced by intervertebral foramen stenosis in the rat. Pain. 1998;77:15–23. doi: 10.1016/S0304-3959(98)00067-0. [DOI] [PubMed] [Google Scholar]
  14. Johansson A, Bennett GJ. Effect of local methylprednisolone on pain in a nerve injury model. A pilot study. Reg Anesth. 1997;22:59–65. doi: 10.1016/s1098-7339(06)80057-x. [DOI] [PubMed] [Google Scholar]
  15. Kikuchi A, Kotani N, Sato T, Takamura K, Sakai I, Matsuki A. Comparative therapeutic evaluation of intrathecal versus epidural methylprednisolone for long-term analgesia in patients with intractable postherpetic neuralgia. Reg Anesth Pain Med. 1999;24:287–293. doi: 10.1016/s1098-7339(99)90101-3. [DOI] [PubMed] [Google Scholar]
  16. Kim YC, Lim YJ, Lee SC. Spreading pattern of epidurally administered contrast medium in rabbits. Acta Anaesthesiol Scand. 1998;42:1092–1095. doi: 10.1111/j.1399-6576.1998.tb05382.x. [DOI] [PubMed] [Google Scholar]
  17. Kingery WS, Guo T, Agashe GS, Davies MF, Clark JD, Maze M. Glucocorticoid inhibition of neuropathic limb edema and cutaneous neurogenic extravasation. Brain Res. 2001;913:140–148. doi: 10.1016/s0006-8993(01)02763-9. [DOI] [PubMed] [Google Scholar]
  18. Kingery WS, Castellote JM, Maze M. Methylprednisolone prevents the development of autotomy and neuropathic edema in rats, but has no effect on nociceptive thresholds. Pain. 1999;80:555–566. doi: 10.1016/S0304-3959(98)00251-6. [DOI] [PubMed] [Google Scholar]
  19. Kotani N, Kushikata T, Hashimoto H, Kimura F, Muraoka M, Yodono M, Asai M, Matsuki A. Intrathecal methylprednisolone for intractable postherpetic neuralgia. N Engl J Med. 2000;343:1514–1519. doi: 10.1056/NEJM200011233432102. [DOI] [PubMed] [Google Scholar]
  20. Manchikanti L. Transforaminal lumbar epidural steroid injections. Pain Physician. 2000;3:374–398. [PubMed] [Google Scholar]
  21. Manchikanti L, Singh V, Kloth D, Slipman CW, Jasper JF, Trescot AM, Varley KG, Atluri SL, Giron C, Curran MJ, Rivera J, Baha AG, Bakhit CE, Reuter MW. Interventional techniques in the management of chronic pain: part 2.0. Pain Physician. 2001;4:24–98. [PubMed] [Google Scholar]
  22. Mao J. Translational pain research: bridging the gap between basic and clinical research. Pain. 2002;97:183–187. doi: 10.1016/S0304-3959(02)00109-4. [DOI] [PubMed] [Google Scholar]
  23. Mao J, Regelson W, Kalimi M. Molecular mechanism of RU 486 action: a review. Mol Cell Biochem. 1992;109:1–8. doi: 10.1007/BF00230867. [DOI] [PubMed] [Google Scholar]
  24. Mao J, Mayer DJ, Hayes RL, Price DD. Spatial patterns of increased spinal cord membrane-bound protein kinase C and their relation to increases in 14C-2-deoxyglucose metabolic activity in rats with painful peripheral mononeuropathy. J Neurophysiol. 1993;70:470–481. doi: 10.1152/jn.1993.70.2.470. [DOI] [PubMed] [Google Scholar]
  25. Price C, Arden N, Coglan L, Rogers P. Cost-effectiveness and safety of epidural steroids in the management of sciatica. Health Technol Assess. 2005;9:1–58. iii. doi: 10.3310/hta9330. [DOI] [PubMed] [Google Scholar]
  26. Romero-Sandoval A, Eisenach JC. Spinal cannabinoid receptor type 2 activation reduces hypersensitivity and spinal cord glial activation after paw incision. Anesthesiology. 2007;106:787–794. doi: 10.1097/01.anes.0000264765.33673.6c. [DOI] [PubMed] [Google Scholar]
  27. Spaccarelli KC. Lumbar and caudal epidural corticosteroid injections. Mayo Clin Proc. 1996;71:169–178. doi: 10.4065/71.2.169. [DOI] [PubMed] [Google Scholar]
  28. Song XJ, Hu SJ, Greenquist KW, Zhang JM, LaMotte RH. Mechanical and thermal hyperalgesia and ectopic neuronal discharge after chronic compression of dorsal root ganglia. J Neurophysiol. 1999;82:3347–3358. doi: 10.1152/jn.1999.82.6.3347. [DOI] [PubMed] [Google Scholar]
  29. Takahashi T, Kimoto T, Tanabe N, Hattori TA, Yasumatsu N, Kawato S. Corticosterone acutely prolonged N-methyl-d-aspartate receptor-mediated Ca2+ elevation in cultured rat hippocampal neurons. J Neurochem. 2002;83:1441–1451. doi: 10.1046/j.1471-4159.2002.01251.x. [DOI] [PubMed] [Google Scholar]
  30. Takeda K, Sawamura S, Sekiyama H, Tamai H, Hanaoka K. Effect of methylprednisolone on neuropathic pain and spinal glial activation in rats. Anesthesiology. 2004;100:1249–1257. doi: 10.1097/00000542-200405000-00029. [DOI] [PubMed] [Google Scholar]
  31. Valat JP, Giraudeau B, Rozenberg S, Goupille P, Bourgeois P, Micheau-Beaugendre V, Soubrier M, Richard S, Thomas E. Epidural corticosteroid injections for sciatica: a randomised, double blind, controlled clinical trial. Ann Rheum Dis. 2003;62:639–643. doi: 10.1136/ard.62.7.639. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Wang S, Lim G, Zeng Q, Sung B, Ai Y, Guo G, Yang L, Mao J. Expression of central glucocorticoid receptors after peripheral nerve injury contributes to neuropathic pain behaviors in rats. J Neurosci. 2004;24:8595–8605. doi: 10.1523/JNEUROSCI.3058-04.2004. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Xie J, Park SK, Chung K, Chung JM. The effect of lumbar sympathectomy in the spinal nerve ligation model of neuropathic pain. J Pain. 2001;2:70–278. doi: 10.1054/jpai.2001.24559. [DOI] [PubMed] [Google Scholar]
  34. Xie W, Liu X, Xuan H, Luo S, Zhao X, Zhou Z, Xu J. Effect of betamethasone on neuropathic pain and cerebral expression of NF-kappaB and cytokines. Neurosci Lett. 2006;393:255–259. doi: 10.1016/j.neulet.2005.09.077. [DOI] [PubMed] [Google Scholar]
  35. Zhang RX, Lao L, Qiao JT, Malsnee K, Ruda MA. Endogenous and exogenous glucocorticoid suppresses up-regulation of preprodynorphin mRNA and hyperalgesia in rats with peripheral inflammation. Neurosci Lett. 2004;359:85–88. doi: 10.1016/j.neulet.2004.02.014. [DOI] [PubMed] [Google Scholar]

RESOURCES