 |
 Previous Article | Next Article 
The Journal of Neuroscience, September 15, 2000, 20(18):7074-7079
Dynorphin Promotes Abnormal Pain and Spinal Opioid
Antinociceptive Tolerance
Todd W.
Vanderah,
Luis R.
Gardell,
Shannon E.
Burgess,
Mohab
Ibrahim,
Ahmet
Dogrul,
Cheng-Min
Zhong,
En-Tan
Zhang,
T. Philip
Malan Jr,
Michael H.
Ossipov,
Josephine
Lai, and
Frank
Porreca
Departments of Pharmacology and Anesthesiology, University of
Arizona, Tucson, Arizona 85724
 |
ABSTRACT |
The nonopioid actions of spinal dynorphin may promote aspects of
abnormal pain after nerve injury. Mechanistic similarities have been
suggested between opioid tolerance and neuropathic pain. Here, the
hypothesis that spinal dynorphin might mediate effects of sustained
spinal opioids was explored. Possible abnormal pain and spinal
antinociceptive tolerance were evaluated after intrathecal administration of [D-Ala2,
N-Me-Phe4,
Gly-ol5]enkephalin (DAMGO), an opioid µ agonist. Rats infused with DAMGO, but not saline, demonstrated tactile
allodynia and thermal hyperalgesia of the hindpaws (during the DAMGO
infusion) and a decrease in antinociceptive potency and efficacy of
spinal opioids (tolerance), signs also characteristic of nerve injury.
Spinal DAMGO elicited an increase in lumbar dynorphin content and a
decrease in the µ receptor immunoreactivity in the spinal dorsal
horn, signs also seen in the postnerve-injury state. Intrathecal
administration of dynorphin A(1-17) antiserum blocked tactile
allodynia and reversed thermal hyperalgesia to above baseline levels
(i.e., antinociception). Spinal dynorphin antiserum, but not control
serum, also reestablished the antinociceptive potency and efficacy of
spinal morphine. Neither dynorphin antiserum nor control serum
administration altered baseline non-noxious or noxious thresholds or
affected the intrathecal morphine antinociceptive response in
saline-infused rats. These data suggest that spinal dynorphin promotes
abnormal pain and acts to reduce the antinociceptive efficacy of spinal
opioids (i.e., tolerance). The data also identify a possible mechanism for previously unexplained clinical observations and offer a novel approach for the development of strategies that could improve the
long-term use of opioids for pain.
Key words:
dynorphin; abnormal pain; morphine tolerance; spinal; dynorphin antiserum; µ-opioid receptors
| |
INTRODUCTION |
An important clinical observation is
that sustained spinal administration of µ-opioids produces abnormal
pain that is reminiscent of neuropathic pain (Woolf, 1981 ; Ali, 1986;
Arner et al., 1988; Yaksh and Harty, 1988; De Conno et al., 1991;
Trujillo and Akil, 1991; Devulder, 1997). Paradoxical opioid-induced
novel pain often occurs in areas isolated from the site of the original
pain complaint (De Conno et al., 1991). Additionally, decreased
analgesia after sustained spinal µ-opioids is similar to the
diminished effects of spinal µ-opioids in animal models of
neuropathy. Thus, both opioid tolerance and neuropathic conditions
share features of diminished µ-opioid analgesia with abnormal pain
(thermal hyperalgesia and tactile allodynia). These common features
have led to suggestions of common mechanisms in nerve-injury and in
spinal µ-opioid tolerance states (Mao et al., 1994, 1995a,b).
A similarity linking abnormal pain from opioids or nerve injury is the
sensitivity to NMDA antagonists. NMDA antagonists reverse thermal
hyperalgesia after nerve injury (Mao et al., 1995a,b; Wegert et al.,
1997; Bian et al., 1999). Additionally, the loss of morphine
antinociception in rats with spinal nerve injury was restored by
intrathecal MK-801, an NMDA antagonist (Ossipov et al., 1995a,b).
Similarly, tolerance and hyperalgesia produced by spinal injections
and/or infusions of morphine were prevented by MK-801 (Mao et al.,
1994) or dextromethorphan (Trujillo and Akil, 1991; Tiseo and
Inturrisi, 1993; Mao et al., 1994; Tiseo et al., 1994; Manning et al.,
1996); MK-801 did not produce antinociception alone and did not
increase morphine antinociception in nontolerant rats.
Although the blockade of nerve-injury pain by NMDA antagonists may be
caused by the blockade of afferent discharge from injured nerves, the
mechanism by which NMDA antagonists block or reverse opioid tolerance
is not understood because the source of the NMDA receptor activation
during chronic opioid exposure is uncertain. NMDA receptors may coexist
on cells expressing opioid receptors, including primary afferent fibers
(Liu et al., 1994, 1997). Primary afferent neurons do not tend to
discharge spontaneously and are probably not essential to the
development of opioid tolerance (Price, 1988), suggesting the
importance of intracellular pathways as a potential mechanism by which
NMDA antagonists might affect tolerance. Another possibility may be
that an intermediary might mechanistically link opioid tolerance and
nerve injury directly or indirectly via the NMDA receptor.
A feature of both nerve-injury pain and opioid treatment is increased
spinal dynorphin (Cho and Basbaum, 1989; Kajander et al., 1990; Draisci
et al., 1991; Dubner, 1991; Dubner and Ruda, 1992; Rattan and Tejwani,
1997). Dynorphin might be pronociceptive in chronic pain states (Bian
et al., 1999; Malan et al., 2000). Possible pronociceptive actions by
spinal dynorphin are supported because dynorphin antiserum, but not
control serum, (1) blocks nerve-injury hyperalgesia (Wegert et
al., 1997), (2) restores spinal morphine antinociception after nerve
injury (Nichols et al., 1997; Wegert et al., 1997), (3) elicits spinal
morphine antiallodynia, and (4) restores the expected synergy of
spinal/supraspinal morphine that is lost after nerve injury (Bian et
al., 1999). The effects of dynorphin A(1-17) antiserum parallel those
seen with MK-801 and suggest that dynorphin may interact, directly or
indirectly, with the NMDA receptor (Wegert et al., 1997; Bian et al.,
1999; Tang et al., 1999).
Here, the hypothesis that abnormal pain and decreased spinal opioid
antinociception seen after sustained opioid exposure might be mediated
by spinal dynorphin was tested.
| |
MATERIALS AND METHODS |
Male Sprague Dawley rats (Harlan Sprague Dawley,
Indianapolis, IN), 200-300 gm at the time of testing, were maintained
in a climate-controlled room on a 12 hr light/dark cycle (lights on at
06:00 A.M.) with food and water available ad libitum. All of
the testing was performed in accordance with the policies and recommendations of the International Association for the Study of Pain
and the National Institutes of Health guidelines for the handling and
use of laboratory animals and received approval from the Animal Care
and Use Committee of the University of Arizona. Groups of 5-10 rats
were used in all experiments.
Cannulation and drug administration. While under halothane
anesthesia, all of the rats were implanted with intrathecal catheters (polyethylene-10 tubing; 7.5 cm) as described previously (Yaksh and
Rudy, 1976) for drug administration at the level of the lumbar spinal
cord. Chronic spinal infusions were performed with osmotic minipumps
(Alza, Mountain View, CA). The osmotic pumps delivered saline at 1 µl/hr or [D-Ala2,
N-Me-Phe4,
Gly-ol5]enkephalin (DAMGO) at 1 nmol · µl 1 · hr1
for 7 d. The minipumps were attached to the indwelling intrathecal catheters and placed in the subcutaneous space. On day 6 all animals were tested for tactile allodynia and thermal hyperalgesia while the
infusions continued. On day 7 the minipumps were disconnected from the
infusion catheter while the animals were briefly anesthetized with
halothane and the infusion catheter was exteriorized. Morphine, control
serum, or antiserum to dynorphin A(1-17) (200 µg per injection) was
injected through the intrathecal catheter in a volume of 5 µl
followed by a 9 µl saline flush.
Nociceptive/allodynic testing. Paw withdrawal thresholds
were determined in response to probing with von Frey filaments in a
range normally not found to be noxious (i.e., 0.40, 0.70, 1.20, 2.00, 3.63, 5.50, 8.50, and 15.1 gm). Each filament was applied perpendicularly to the plantar surface of the right paw of rats kept in
suspended wire-mesh cages. The paw withdrawal threshold was determined
by sequentially increasing and decreasing the stimulus strength
("up-and-down" method) and analyzed with a Dixon nonparametric test
(Dixon, 1980; Chaplan et al., 1994). Tactile allodynia was indicated by
a significant (p  0.05; Student's
t test) reduction in the paw withdrawal threshold when
compared with that obtained before any manipulations. Tactile allodynia
was measured on day 6 of DAMGO infusion while the DAMGO infusion was maintained.
Thermal hyperalgesia was determined by focusing a radiant heat source
onto the plantar aspect of a hindpaw of the rat. After paw withdrawal,
a photodetection device interrupted both the stimulus and the
timer. A maximal cutoff of 40 sec was used to prevent tissue
damage. Paw withdrawal latencies were determined to the nearest 0.1 sec. Hyperalgesia was indicated by a significantly (p 0.05; Student's t test)
shorter paw withdrawal latency than that detected before any
manipulations (i.e., preinfusion). Thermal hyperalgesia was measured on
day 6 of DAMGO infusion while the DAMGO infusion was maintained.
Antihyperalgesia was indicated by a return of the response latencies to
preinfusion baseline values, and antinociception was indicated by a
significant (p 0.05) increase in withdrawal
latencies above the normal baseline values. In both tactile allodynia
and thermal hyperalgesia testing, animals were acclimated to their
surroundings for 30 min and tested only once.
Nociceptive testing was performed by placing the distal third of the
tail of a rat in a water bath maintained at 52°C. The latency to
withdrawal was measured to 0.1 sec, and a cutoff latency of 10 sec was
used to prevent tissue injury. The tail-flick test was used to
determine the antinociceptive A90 dose (the dose
estimated to produce 90% antinociception) of either intrathecal DAMGO
or morphine in rats before and after a 7 d DAMGO infusion.
Tolerance to the antinociceptive effect of opioids was indicated by a
significant reduction in the tail-flick latency after challenge with an
A90 dose. Data were converted to percent
antinociception to generate dose-response curves by the following
formula: (response latency  baseline latency)/(cutoff baseline latency) × 100. Animals received either intrathecal
morphine alone or morphine 10 min after intrathecal pretreatment with
either control serum or antiserum to dynorphin A(1-17) (200 µg/5
µl) and were tested 10 min later by the use of the tail-flick test
(i.e., dynorphin antiserum given 20 min before the test).
Dynorphin A immunoassay. Rats were deeply anesthetized with
ether and decapitated on day 7 of DAMGO infusion. The spinal cord was
injected with ice-cold saline and placed on an iced glass Petri dish,
and the lumbar cord was rapidly dissected. These tissue samples were
immediately frozen on dry ice and stored at 70°C. Thawed tissue was
placed in 1N acetic acid, disrupted with a Polytron homogenizer, and
incubated for 20 min at 95°C. After centrifugation at 10,000 × g for 20 min (4°C), the supernatant was lyophilized and
stored at 70°C. Protein concentrations were determined by the use
of the bicinchoninic acid method with bovine serum albumin as a
standard. Immunoassay was performed by the use of a commercial enzyme
immunoassay kit with an antibody specific for dynorphin A(1-17)
(Peninsula Laboratories, Belmont, CA). Standard curves were constructed
and the dynorphin content was determined with Graph Pad Prism (San
Diego, CA). Pairwise comparisons between treatments were detected by
Student's t test. Significance was determined at the
p < 0.05 level.
Immunohistochemistry. The naive, saline-infused, and
DAMGO-infused rats were deeply anesthetized with ketamine and perfused transcardially with 200 ml of PBS, pH 7.4, containing heparin (1500 IU/l), followed by 500 ml of cold 4% paraformaldehyde. After perfusion the spinal cords were isolated and post-fixed for 4 hr in 4%
paraformaldehyde and then cryoprotected with 30% sucrose in PBS
overnight at 4°C.
Frontal frozen sections (40 µm) were prepared from the lumbar
enlargement of the spinal cord. These sections were immunolabeled either with a guinea pig antiserum against prodynorphin or with a
rabbit antiserum against the rat µ-opioid receptor (MOR; antisera were kindly provided by Dr. Robert Elde, University of Minnesota). Briefly, the spinal cord sections were rinsed twice for 5 min each in
PBS and then preincubated with PBS containing 4% normal goat serum,
0.3% Triton X-100, and 1% bovine serum albumin for 30 min at room
temperature. The sections were then incubated with the primary
antiserum diluted in the preincubation buffer overnight at 4°C
(prodynorphin antiserum at 1:40,000 dilution; MOR antiserum at 1:20,000
dilution). The sections were washed three times for 10 min each in PBS,
followed by incubation with a biotinylated secondary antibody (goat
anti-guinea pig IgG or goat anti-rabbit IgG; Vector Laboratories,
Burlingame, CA) at 1:1000 in PBS with 0.25% bovine serum albumin and
0.1% Triton X-100 (PBS-BT) for 60 min at room temperature. Sections
were washed three times for 10 min each in PBS and stained with the
avidin-biotin complex (ABC kit; Vector Laboratories); sections
were incubated with an avidin-biotinylated horseradish peroxidase
complex diluted 1:500 in PBS-BT for 2 hr at room temperature, washed
three times for 10 min each in PBS, and developed with a solution of
diaminobenzidine and H2O2
(FAST DAB SETS; Sigma, St. Louis, MO) maintained uniformly throughout
the experiments. Sections from control and treated animals were
processed in parallel under identical experimental conditions.
The sections were washed and mounted on glass slides, air-dried
overnight, rinsed in histological clearing solvent, and coverslipped
with DPX.
Chemicals. Morphine sulfate was purchased from Sigma.
DAMGO was purchased from Research Biochemicals (Natick, MA).
Antiserum to dynorphin A(1-17) was obtained from Peninsula
Laboratories. This rabbit antiserum was 100% cross-reactive with
dynorphin A(1-13) and dynorphin A(1-8). Control serum was serum
collected from the same species of rabbits without injection of antigen
but not from the same rabbit used to generate dynorphin antiserum. All
chemicals were dissolved in normal saline.
Data analysis. The data were converted to the percent
of maximal possible effect (% MPE) by the formula: % MPE = (WT CT)/(CO CT) × 100, where WT is the withdrawal
threshold or latency obtained experimentally, CT is the baseline
control value before drug administration, and CO is the cutoff value
(i.e., 15 gm for tactile allodynia, 40 sec for the paw-flick test, and
10 sec for the tail-flick test). Dose-response curves were generated
where possible, and the A50 value (the dose
estimated to produce 50% MPE) and 95% confidence intervals were
determined for additional statistical calculations (Tallarida and
Murray, 1987).
| |
RESULTS |
Spinal infusion of the µ-opioid agonist DAMGO over a 7 d
period elicited antinociceptive tolerance to a subsequent challenge with intrathecal DAMGO (1 µg) and cross-tolerance to challenge with
intrathecal morphine (10 µg) (Fig. 1).
The effect produced by DAMGO in the tail-flick test before the start of
the DAMGO infusion was 92 ± 4% antinociception. The same dose of
DAMGO given immediately after disconnection of the intrathecal catheter
from the infusion pump on day 7 produced a significantly reduced
antinociceptive response of 12 ± 4% antinociception in the
tail-flick test, indicating the development of tolerance to the
antinociceptive actions of DAMGO (p 0.05;
Student's t test). Similarly, intrathecal morphine given
before the intrathecal DAMGO infusion produced 91 ± 6%
antinociception in the tail-flick test, whereas the same morphine dose
given to animals receiving spinal DAMGO infusion over a 7 d period
resulted in a significantly reduced antinociceptive effect of 25 ± 6% antinociception, indicating cross-tolerance between DAMGO and
morphine (p 0.05; Student's t
test). The antinociceptive effect of intrathecal morphine was not
altered in animals receiving chronic saline via minipumps over a 7 d period; intrathecal morphine (10 µg) produced 88 ± 8.6 and
89 ± 11.4% antinociception before and after saline infusion, respectively.
View larger version (24K):
[in this window]
[in a new window]
|
Figure 1.
Left, Male Sprague Dawley rats
received an intrathecal infusion of saline or of DAMGO (1 nmol · µl1 · hr1)
for 7 d. The spinal cords were removed and assayed for dynorphin
content with an enzyme immunoassay. The rats with DAMGO infusions
showed a significant (*p 0.05; Student's
t test) increase in spinal dynorphin content when
compared with saline-infused rats. Right,
Antinociceptive tolerance on day 8 to intrathecal DAMGO (1 µg/5 µl;
n = 8; top) or cross-tolerance to
intrathecal morphine (10 µg/5 µl; n = 8;
bottom) in the 52°C water tail-flick test is
demonstrated.
|
|
The content of dynorphin was quantitated by immunoprecipitation using
an antiserum raised against dynorphin A(1-17). In animals that had
received an intrathecal infusion of DAMGO, the level of dynorphin in
the dorsal half of the lumbar spinal cord showed a significant increase
when compared with that in saline-infused animals (1700 ± 120 pg/mg of protein vs 1297 ± 95 pg/mg of protein in DAMGO-treated
and saline control animals, respectively; p 0.05 by
Student's t test). These data were based on an average of
six to eight rats. To characterize this apparent elevation of spinal
dynorphin in DAMGO-infused rats further, the distribution of its
precursor peptide prodynorphin was also examined by
immunohistochemistry using an antiserum specific for prodynorphin. The
immunoreactivity (-IR) of prodynorphin was found mainly in the
superficial laminae, laminae IV and V, and lamina X of the
dorsal horn of the lumbar spinal cord (Fig.
2). In the superficial laminae, discrete
cell bodies and numerous fibers were labeled (Fig.
2A,B), whereas in laminae V and VI (Fig.
2C,D) and lamina X (Fig. 2E,F),
prodynorphin-IR was predominantly associated with fibers. Lumbar spinal
sections from DAMGO-infused rats exhibited a reduction of
prodynorphin-IR in all the laminae stated above when compared with the
saline-infused control (Fig. 2). This reduction appeared to be
primarily caused by a loss of fiber staining in these laminae (Fig.
2B,D,F). In the superficial laminae, staining
was still clearly present in cell bodies; the density of immunolabeled
cell bodies was similar between control and DAMGO-infused rats (Fig.
2A,B).
View larger version (115K):
[in this window]
[in a new window]
|
Figure 2.
Immunohistochemical analysis of prodynorphin in
lumbar spinal sections. Rats have been infused with either saline
(control) or DAMGO for 7 d. Lumbar spinal cross sections (40 µm)
were labeled with the antiserum for prodynorphin (1:40,000) and
processed for DAB staining by the ABC method. Spinal cord halves are
represented in close juxtaposition to allow visual comparison.
Top, The left half
is obtained from the saline-infused control, and the
right half is obtained from the
DAMGO-infused rat. The micrographs were acquired via a Hamamatsu
digital-imaging system with a Nikon microscope. Bottom,
As seen under higher magnification, the superficial laminae (A,
B), discrete cell bodies, and numerous fibers were labeled,
whereas in laminae V and VI (C, D) and in
lamina X (E, F), prodynorphin-IR
was predominantly associated with fibers. Lumbar spinal sections from
DAMGO-infused (B, D,
F) rats exhibited a reduction of prodynorphin-IR
in all the laminae stated above when compared with the saline-infused
control (A, C, E). This
reduction appears to be primarily caused by a loss of fiber staining in
these laminae. In the superficial laminae, staining was still clearly
present in cell bodies; the density of immunolabeled cell bodies was
similar between control and DAMGO-infused rats.
|
|
Lumbar spinal cord sections from control and DAMGO-infused rats were
also labeled with µ-opioid receptor-specific antibodies. µ-Opioid
receptor-IR was associated predominantly with the superficial laminae
of the dorsal horn of the spinal cord (Fig.
3). When compared with tissue sections
from control rats, sections from the DAMGO-infused rats exhibited a
significant reduction in MOR-IR in the superficial laminae (Fig.
3).
View larger version (102K):
[in this window]
[in a new window]
|
Figure 3.
Immunohistochemical analysis of the µ-opioid
receptor in lumbar spinal sections. Rats have been infused with either
saline (control) or DAMGO for 7 d. Lumbar spinal cross sections
(40 µm) were labeled with the antiserum for rat MOR (1:20,000) and
processed for DAB staining by the ABC method. Spinal cord halves are
represented in close juxtaposition to allow visual comparison. The
left half is obtained from the
saline-infused control, and the right
half is obtained from the DAMGO-infused rat.
Substantially higher MOR immunoreactivity is observed in the
superficial laminae (I and II) of the control cord, indicating a
greater concentration of µ-opioid receptors, than in that of the
DAMGO-treated group. The micrographs were acquired via a Hamamatsu
digital-imaging system with a Nikon microscope.
|
|
The sensory threshold for a response to a non-noxious stimulus was
significantly reduced in rats receiving an intrathecal infusion of
DAMGO (1 nmol · µl1 · hr1
for 7 d). When tested on the sixth day of DAMGO infusion (i.e., while the infusion was continuing), the hindpaw response to probing with von Frey filaments decreased from a baseline of 15 ± 0.0 gm (before initiation of infusion) to 4.1 ± 0.5 gm (Fig.
4), indicating the development of tactile
allodynia during the DAMGO infusion. Animals receiving an intrathecal
infusion of saline by osmotic minipump showed no change between their
preinfusion baseline (i.e., 15 ± 0.0 gm) and the response
threshold at the sixth day of infusion (i.e., 15 ± 0.0 gm). The
intrathecal administration of an antiserum to dynorphin A(1-17) at the
termination of the intrathecal DAMGO infusion on day 7, however,
significantly reversed tactile allodynia; the paw withdrawal threshold
was 11.5 ± 2.2 gm (Fig. 4).The intrathecal administration of
control (preimmune) serum at the termination of the intrathecal DAMGO
infusion on day 7 had no effect on tactile allodynia; the von Frey
response after control serum was 4.2 ± 0.5 gm (n = 10), a value that was not significantly different from that
determined on day 6 during the DAMGO infusion. Neither control serum
nor antiserum to dynorphin A(1-17) alone had any effect on the paw
withdrawal thresholds after the intrathecal saline infusion (baseline
and postserum values were 15 ± 0.0 gm; n = 10).
View larger version (18K):
[in this window]
[in a new window]
|
Figure 4.
Male Sprague Dawley rats received intrathecal
infusions of saline or of DAMGO (1 nmol · µl1 · hr1)
for 7 d. Antinociceptive tolerance after chronic infusion of DAMGO
was accompanied by tactile allodynia, indicated by a significant
(*p 0.05; Student's t test;
n = 10) decrease in paw withdrawal thresholds to
probing with von Frey filaments on the sixth day of infusion. The acute
intrathecal injection of 200 µg of antiserum to dynorphin A(1-17) on
day 7 blocked tactile allodynia when given 20 min before testing in
DAMGO-tolerant rats (n = 10). DYN
A/S, Dynorphin antiserum.
|
|
The latencies to withdrawal of the hindpaw from a noxious thermal
stimulus were also significantly reduced in rats receiving an
intrathecal infusion of DAMGO. When tested on the sixth day of DAMGO
infusion (i.e., while the infusion was continuing), the hindpaw
response to noxious heat decreased from a preinfusion baseline of
17.3 ± 1.5 to 10.8 ± 1.2 sec (Fig.
5), indicating the development of thermal
hyperalgesia during the DAMGO infusion. Animals receiving an
intrathecal infusion of saline showed no change between their
preinfusion baseline paw withdrawal latencies (i.e., 18.9 ± 1.1 sec) and the response latencies at the sixth day of infusion
(i.e.,18.7 ± 0.9 sec). The intrathecal administration of an
antiserum to dynorphin A(1-17) at the termination of the spinal DAMGO
infusion on day 7, however, significantly reversed thermal
hyperalgesia; the paw-flick response after dynorphin antiserum was
35.6 ± 3.6 sec, which was significantly greater than the
preinfusion baseline latency (Fig. 5). This response indicates not only
a reversal of hyperalgesia but also the production of antinociception. The intrathecal administration of control serum at the termination of
the DAMGO infusion on day 7 had no effect on thermal hyperalgesia; the
mean paw withdrawal latency obtained after the intrathecal injection of
control serum was 12.7 ± 0.8 sec, which was not significantly different (p > 0.05) from the response latency
determined on day 6 during the spinal infusion of DAMGO (see above).
Neither control serum nor antiserum to dynorphin A(1-17) had any
effect on paw withdrawal latencies after the spinal infusion of saline
(i.e., preinfusion baseline values were 20 ± 0.7 sec, and
postcontrol serum or dynorphin A(1-17) antiserum values were 20.5 ± 0.7 and 19.7 ± 0.6 sec, respectively).
View larger version (18K):
[in this window]
[in a new window]
|
Figure 5.
Male Sprague Dawley rats received intrathecal
infusions of saline or of DAMGO (1 nmol · µl1 · hr1)
for 7 d. Antinociceptive tolerance was accompanied by thermal
hyperalgesia after chronic infusion of DAMGO, indicated by a
significant (*p 0.05; Student's
t test; n = 10) decrease in paw
withdrawal latencies to radiant heat applied to the plantar aspect of
the hindpaw on the sixth day of infusion. The acute intrathecal
injection of 200 µg of antiserum to dynorphin A(1-17) on day 7 reversed thermal hyperalgesia when given 20 min before testing in
DAMGO-tolerant rats ( p 0.05; Student's
t test; n = 10).
|
|
Dose-response curves for the antinociceptive effect of intrathecal
morphine in the 52°C water tail-flick test were generated in naive,
saline-infused, and DAMGO-infused rats. The A50
values (and 95% confidence limits) for intrathecal morphine were 3.1 µg (2.4-4.1 µg), 3.3 µg (2.9-3.8 µg), and >10 µg,
respectively (Fig. 6). Administration of
control serum did not alter the antinociceptive effect of a single
intrathecal morphine dose (10 µg/5 µl; n = 8) in
animals infused with intrathecal saline; this dose of morphine elicited
91.6 ± 6 and 93.5 ± 5% antinociception before and after control serum, respectively. Antiserum to dynorphin A(1-17) also did
not alter the antinociceptive effect of intrathecal morphine in animals
infused with intrathecal saline, with the A50
(and 95% confidence limits) for intrathecal morphine being 3.7 µg
(3.1-4.4 µg) after dynorphin A(1-17) antiserum. However, the
decreased morphine antinociceptive response seen in animals infused
with intrathecal DAMGO was reversed by the antiserum to dynorphin
A(1-17) (Fig. 6). After intrathecal dynorphin A(1-17) antiserum, the
A50 for intrathecal morphine in DAMGO-infused
rats was 3.6 µg (2.9-4.3 µg), a value that did not differ
significantly from that of saline-infused rats (see above). Control
serum (200 µg/5 µl, intrathecally; 20 min before the test) had no
effect on the antinociceptive effect of intrathecal morphine in animals
infused with intrathecal DAMGO. The effect of a single intrathecal dose
of morphine (10 µg) in DAMGO-infused rats before and after control
serum was 3.3 ± 2.1 and 2.8 ± 1.9% antinociception
(n = 4), respectively, indicating significant
cross-tolerance between DAMGO and morphine. Control serum had no effect
on the antinociceptive effect of intrathecal morphine in animals
infused with intrathecal saline. The effect of a single intrathecal
dose of morphine (10 µg) in saline-infused rats before and after
control serum was 88 ± 8.6 and 93.0 ± 5.3% antinociception
(n = 4), respectively.
View larger version (18K):
[in this window]
[in a new window]
|
Figure 6.
Male Sprague Dawley rats received intrathecal
infusions of saline or of DAMGO (1 nmol · µl1 · hr1)
for 7 d. Antinociceptive dose-response functions for intrathecal
morphine were generated in the 52°C water tail-flick test 10 min
after treatment. The saline- or DAMGO-infused rats received either
intrathecal morphine alone or morphine 10 min after intrathecal
pretreatment with antiserum to dynorphin A(1-17) (i.e., dynorphin
antiserum given 20 min before the test). The following groups were
used: naive rats ( ), rats infused with saline and challenged with
morphine ( ), rats infused with saline and challenged with morphine
after pretreatment with dynorphin antiserum ( ), rats infused with
DAMGO and challenged with morphine ( ), and rats infused with DAMGO
and challenged with morphine after pretreatment with dynorphin
antiserum ( ). Five to 10 separate animals were used for each
point on the dose-response curve. i.th.,
Intrathecal.
|
|
| |
DISCUSSION |
The data from the present study, along with previous data from
nerve-injury studies, support the hypothesis of mechanistic similarities at the spinal level between states of opioid tolerance and
nerve injury. A novel concept introduced here is that spinal dynorphin
acts as a common mediator promoting these conditions. Both the spinal
infusion of an opioid µ agonist or peripheral nerve injury elicit
tactile allodynia, thermal hyperalgesia, and decreased antinociceptive
responsiveness to spinal morphine (opioid tolerance), as well as
increases in the spinal content of dynorphin. In both cases, thermal
hyperalgesia and opioid tolerance can be reversed by antiserum to
dynorphin. These data suggest that spinal dynorphin acts as an
endogenous mediator promoting opioid-induced abnormal pain as well as
opioid antinociceptive tolerance.
The finding that continuous intrathecal infusion of the µ agonist
DAMGO produces abnormal pain is consistent with multiple clinical
observations that indicate that chronic perispinal (intrathecal or
epidural) opioid administration is associated with paradoxical hyperalgesia and/or allodynia. A review of the clinical literature found that many patients who receive long-term spinal opioids developed
hyperesthesia and allodynia, especially with high doses of morphine
(Arner et al., 1988). Abnormal pain that is qualitatively different and
somatically unrelated to the original pain complaint has been reported
in several clinical studies after prolonged opioid exposure (Ali, 1986;
Stillman et al., 1987; De Conno et al., 1991; Devulder, 1997).
These clinical reports are consistent with many experimental
observations in which hyperalgesia was reported after prolonged spinal
opioid exposure in rats (Yaksh and Harty, 1988; Trujillo and Akil,
1991; Mao et al., 1994, 1995a,c). Large doses of intrathecal morphine
have been associated with paradoxical algesia and hyperesthesias, including intermittent bouts of biting and scratching at the dermatomes near the catheter tip and aggressive responses to light brushing of the
flanks (Woolf, 1981; Yaksh et al., 1986; Yaksh and Harty, 1988). These
effects of morphine were not sensitive to naloxone, nor did they
diminish with tolerance (Yaksh and Harty, 1988). In spite of these many
preclinical and clinical reports of abnormal pain elicited by opioids,
the mechanism(s) by which such pain might occur is obscure. The present
study suggests an important role for spinal dynorphin in such abnormal
pain because (1) blockade of the effects of dynorphin with
antiserum clearly blocks opioid-induced allodynia and hyperalgesia and
(2) continuous intrathecal infusion (this study) or subcutaneous
administration (Rattan and Tejwani, 1997) of the µ agonist morphine
as well as spinal nerve ligation (Cho and Basbaum, 1989; Kajander et
al., 1990; Draisci et al., 1991; Dubner, 1991; Dubner and Ruda, 1992)
results in the increase in spinal dynorphin content.
In addition to its role in abnormal pain, spinal dynorphin appears to
promote opioid tolerance. As expected, the dose effect of morphine
antinociception after a 7 d intrathecal DAMGO infusion is shifted
to the right, accompanied by a decreased maximum effect that is typical
of opioid tolerance. The efficacy of spinal morphine was restored by
the administration of antiserum to dynorphin, but not by control serum.
There are two important aspects to these findings. The first is that
the effects of the antiserum are specific because control serum has no
effect on either saline- or DAMGO-infused rats. The second is that the
antiserum to dynorphin has no effect on morphine-induced
antinociception in saline-infused rats, suggesting that dynorphin does
not play an important part in normal sensory thresholds.
These data further substantiate the parallel actions of the antiserum
to dynorphin A(1-17) and MK-801 in cases of pain and opioid tolerance,
although some reports suggest the need for multiple doses of MK-801 to
reverse established opioid tolerance (Trujillo and Akil, 1991; Lee and
Yaksh, 1995; Chaplan et al., 1997). An important feature of the present
experimental design is that allodynia and hyperalgesia were
demonstrated during the infusion of DAMGO (on day 6) and that
antiallodynic and antihyperalgesic effects of dynorphin antiserum were
measured immediately after the cessation of DAMGO infusion (on day 7),
in both cases when the peptide is still present in the spinal cord.
This procedure was designed to ensure that the observed abnormal pain
was not caused by the development of a state of opioid withdrawal.
Under these conditions, dynorphin antiserum blocks allodynia and not
only reverses hyperalgesia but is actually antinociceptive. The
antiallodynic and antinociceptive effects are probably a combined
result of blocking dynorphin activity and unmasking the agonist
activity of DAMGO. This is consistent with previous observations that
the antiallodynic, antihyperalgesic, and antinociceptive effects of
spinal morphine were all increased in the presence of antiserum to
dynorphin A(1-17) in the nerve-injured rat, suggesting a restoration
of the actions of spinal opioids after normalization of the sensitized
state of the spinal cord (Nichols et al., 1997; Wegert et al., 1997;
Bian et al., 1999).
The most likely mechanism for the acute effects of dynorphin antiserum
is by sequestering dynorphin after its release from spinal
interneurons, suggesting that abnormal pain and opioid tolerance may be
caused by direct or indirect actions of dynorphin. This possibility is
supported by the observation that spinal dynorphin content was elevated
after DAMGO infusion, suggesting that spinal opioid administration can
regulate the expression of spinal dynorphin, probably as a result of
opioid receptor occupation. The involvement of opioid receptors in
regulating dynorphin expression seems likely because subcutaneous
implantation of morphine pellets or spinal delivery of opioid  agonists such as [D-Ala2,
Glu4]deltorphin also increases levels of
spinal dynorphin (L. R. Gardell, E. J. Bilsky, and F. Porreca, unpublished observations). However, the increase in dynorphin
content was concomitant with an apparent reduction in the level of its
precursor, prodynorphin, when compared with spinal cord tissues from
saline-infused rats. These findings suggest that spinal opioid infusion
may enhance the processing and subsequent release of dynorphin while
having modest effects on prodynorphin synthesis.
In addition to the changes in the content of dynorphin, the data show
that spinal opioid infusion elicits a clear downregulation of µ receptors in the spinal dorsal horn. Because receptor downregulation is
one of the mechanisms for opioid tolerance in a variety of in
vitro systems, a reduction in µ receptor density would be
consistent with a diminished response to a subsequent challenge of
morphine after DAMGO infusion. However, because dynorphin antiserum can effectively restore morphine efficacy, these data also indicate that
the loss of receptors is not sufficient for the manifestation of opioid
tolerance and that homologous receptor desensitization and
downregulation are not likely to be the primary mediators of opioid
tolerance in vivo.
Although the mechanism(s) by which dynorphin promotes abnormal pain is
not entirely clear, it seems reasonable to speculate that decreased µ receptor expression on primary afferent fibers might promote abnormal
pain via an increase in the release of excitatory neurotransmitters
because of possibly diminished endogenous opioid tone. In this regard,
µ-opioid receptor knock-out mice were shown to be hyperalgesic by the
use of a warm-water tail-flick and hot-plate test (Sora et al., 1997)
and further demonstrated tactile allodynia by the use of von Frey
filaments (T. W. Vanderah and F. Porreca, unpublished
observations). Furthermore, peripheral nerve injury also
results in a decrease in µ-opioid receptor expression, supporting
the possibility of diminished opioid tone as a factor in abnormal pain
(Porreca et al., 1998). The overexpression of spinal dynorphin is also
likely to have consequences on the release of excitatory
neurotransmitters. Recent observations have shown that dynorphin
A(1-17) can increase the release of capsaicin-stimulated substance P (Arcaya et al., 1999) and that the des-Tyr fragments of
dynorphin can increase capsaicin-stimulated calcitonin gene-related peptide release (Claude et al., 1999) (Vanderah and Porreca,
unpublished observations). These observations indicate a common
mechanism in both the nerve-injury and opioid-tolerant states by which
the nonopioid actions of this peptide might act to promote a state of
"spinal sensitization."
Elevated spinal dynorphin may represent an endogenous mechanism that
promotes opioid tolerance and spinal opioid-associated pain as well as
the consequences of nerve injury. Such observations suggest the
possibility of therapeutic interventions such as the development of a
specific dynorphin antibody for clinical use or approaches that can
block the actions of, or facilitate the degradation of, spinal
dynorphin. These possibilities may be of considerable significance
because NMDA antagonists, which produce actions similar to those of the
antiserum to dynorphin, may ultimately be limited in their clinical
utility because of their significant side-effect profile. Inhibiting
the pathological actions resulting from overexpression of an endogenous
substance, such as dynorphin, may prove to provide attainable clinical
benefit for opioid tolerance and pain without the side effects
associated with the blockade of NMDA receptors.
| |
FOOTNOTES |
Received March 29, 2000; revised June 30, 2000; accepted June 30, 2000.
Correspondence should be addressed to Dr. Frank Porreca, Department of
Pharmacology, College of Medicine, University of Arizona Health
Sciences Center, Tucson, AZ 85724. E-mail: frankp{at}u.arizona.edu.
| |
REFERENCES |
-
Ali NM
(1986)
Hyperalgesic response in a patient receiving high concentrations of spinal morphine.
Anesthesiology
65:449[Web of Science][Medline].
-
Arcaya JL,
Cano G,
Gomez G,
Maixner W,
Suarez-Roca H
(1999)
Dynorphin A increases substance P release from trigeminal primary afferent C-fibers.
Eur J Pharmacol
366:27-34[Medline].
-
Arner S,
Rawal N,
Gustafsson LL
(1988)
Clinical experience of long-term treatment with epidural and intrathecal opioids
 a nationwide survey.
Acta Anaesthesiol Scand
32:253-259[Web of Science][Medline]. -
Bian D,
Ossipov MH,
Ibrahim M,
Raffa RB,
Tallarida RJ,
Malan Jr TP,
Lai J,
Porreca F
(1999)
Loss of antiallodynic and antinociceptive spinal/supraspinal morphine synergy in nerve-injured rats: restoration by MK-801 or dynorphin antiserum.
Brain Res
831:55-63[Web of Science][Medline].
-
Chaplan SR,
Bach FW,
Pogrel JW,
Chung JM,
Yaksh TL
(1994)
Quantitative assessment of tactile allodynia in the rat paw.
J Neurosci Methods
53:55-63[Web of Science][Medline].
-
Chaplan SR,
Malmberg AB,
Yaksh TL
(1997)
Efficacy of spinal NMDA receptor antagonism in formalin hyperalgesia and nerve injury evoked allodynia in the rat.
J Pharmacol Exp Ther
280:829-838[Abstract/Free Full Text].
-
Cho HJ,
Basbaum AI
(1989)
Ultrastructural analysis of dynorphin B-immunoreactive cells and terminals in the superficial dorsal horn of the deafferented spinal cord of the rat.
J Comp Neurol
281:193-205[Web of Science][Medline].
-
Claude P,
Gracia N,
Wagner L,
Hargreaves KM
(1999)
Effect of dynorphin on ICGRP release from capsaicin-sensitive fibers.
In: Ninth World Congress on Pain, p 262 Vienna: IASP Press.
-
De Conno F,
Caraceni A,
Martini C,
Spoldi E,
Salvetti M,
Ventafridda V
(1991)
Hyperalgesia and myoclonus with intrathecal infusion of high-dose morphine.
Pain
47:337-339[Web of Science][Medline].
-
Devulder J
(1997)
Hyperalgesia induced by high-dose intrathecal sufentanil in neuropathic pain.
J Neurosurg Anesthesiol
9:146-148[Web of Science][Medline].
-
Dixon WJ
(1980)
Efficient analysis of experimental observations.
Annu Rev Pharmacol Toxicol
20:441-462[Web of Science][Medline].
-
Draisci G,
Kajander KC,
Dubner R,
Bennett GJ,
Iadarola MJ
(1991)
Up-regulation of opioid gene expression in spinal cord evoked by experimental nerve injuries and inflammation.
Brain Res
560:186-192[Web of Science][Medline].
-
Dubner R
(1991)
Neuronal plasticity and pain following peripheral tissue inflammation or nerve injury.
In: Proceedings of the VIth World Congress on Pain (Bond MR,
Charlton JE,
Woolf CJ,
eds), pp 263-276. Amsterdam: Elsevier
-
Dubner R,
Ruda MA
(1992)
Activity-dependent neuronal plasticity following tissue injury and inflammation.
Trends Neurosci
15:96-103[Web of Science][Medline].
-
Kajander KC,
Sahara Y,
Iadarola MJ,
Bennett GJ
(1990)
Dynorphin increases in the dorsal spinal cord in rats with a painful peripheral neuropathy.
Peptides
11:719-728[Web of Science][Medline].
-
Lee YW,
Yaksh TL
(1995)
Analysis of drug interaction between intrathecal clonidine and MK-801 in peripheral neuropathic pain rat model.
Anesthesiology
82:741-748[Web of Science][Medline].
-
Liu H,
Wang H,
Sheng M,
Jan LY,
Jan YN,
Basbaum AI
(1994)
Evidence for presynaptic N-methyl-D-aspartate autoreceptors in the spinal cord dorsal horn.
Proc Natl Acad Sci USA
91:8383-8387[Abstract/Free Full Text].
-
Liu H,
Mantyh PW,
Basbaum AI
(1997)
NMDA-receptor regulation of substance P release from primary afferent nociceptors.
Nature
386:721-724[Medline].
-
Malan TP,
Ossipov MH,
Gardell LR,
Ibrahim M,
Bian D,
Lai J,
Porreca F
(2000)
Extraterritorial neuropathic pain correlates with multisegmental elevation of spinal dynorphin in nerve-injured rats.
Pain
86:185-194[Web of Science][Medline].
-
Manning BH,
Mao J,
Frenk H,
Price DD,
Mayer DJ
(1996)
Continuous co-administration of dextromethorphan or MK-801 with morphine: attenuation of morphine dependence and naloxone-reversible attenuation of morphine tolerance.
Pain
67:79-88[Web of Science][Medline].
-
Mao J,
Price DD,
Mayer DJ
(1994)
Thermal hyperalgesia in association with the development of morphine tolerance in rats: roles of excitatory amino acid receptors and protein kinase C.
J Neurosci
14:2301-2312[Abstract].
-
Mao J,
Price DD,
Mayer DJ
(1995a)
Experimental mononeuropathy reduces the antinociceptive effects of morphine: implications for common intracellular mechanisms involved in morphine tolerance and neuropathic pain.
Pain
61:353-364[Web of Science][Medline].
-
Mao J,
Price DD,
Mayer DJ
(1995b)
Mechanisms of hyperalgesia and morphine tolerance: a current view of their possible interactions.
Pain
62:259-274[Web of Science][Medline].
-
Mao J,
Price DD,
Phillips LL,
Lu J,
Mayer DJ
(1995c)
Increases in protein kinase C gamma immunoreactivity in the spinal cord of rats associated with tolerance to the analgesic effects of morphine.
Brain Res
677:257-267[Web of Science][Medline].
-
Nichols ML,
Lopez Y,
Ossipov MH,
Bian D,
Porreca F
(1997)
Enhancement of the antiallodynic and antinociceptive efficacy of spinal morphine by antisera to dynorphin A(1-13) or MK-801 in a nerve-ligation model of peripheral neuropathy.
Pain
69:317-322[Web of Science][Medline].
-
Ossipov MH,
Lopez Y,
Nichols ML,
Bian D,
Porreca F
(1995a)
Inhibition by spinal morphine of the tail-flick response is attenuated in rats with nerve ligation injury.
Neurosci Lett
199:83-86[Web of Science][Medline].
-
Ossipov MH,
Lopez Y,
Nichols ML,
Bian D,
Porreca F
(1995b)
The loss of antinociceptive efficacy of spinal morphine in rats with nerve ligation injury is prevented by reducing spinal afferent drive.
Neurosci Lett
199:87-90[Web of Science][Medline].
-
Porreca F,
Tang QB,
Bian D,
Riedl M,
Elde R,
Lai J
(1998)
Spinal opioid mu receptor expression in lumbar spinal cord of rats following nerve injury.
Brain Res
795:197-203[Web of Science][Medline].
-
Price DD
(1988)
In: Psychological and neural mechanisms of pain. New York: Raven.
-
Rattan AK,
Tejwani GA
(1997)
Effect of chronic treatment with morphine, midazolam and both together on dynorphin(1-13) levels in the rat.
Brain Res
754:239-244[Web of Science][Medline].
-
Sora I,
Takahashi N,
Funada M,
Ujike H,
Revay RS,
Donovan DM,
Miner LL,
Uhl GR
(1997)
Opiate receptor knockout mice define µ receptor roles in endogenous nociceptive responses and morphine-induced analgesia.
Proc Natl Acad Sci USA
94:1544-1549[Abstract/Free Full Text].
-
Stillman MJ,
Moulin DE,
Foley KM
(1987)
Paradoxical pain following high-dose spinal morphine.
Pain
4:85.
-
Tallarida RJ,
Murray RB
(1987)
In: Manual of pharmacologic calculations with computer programs, Second edition, 297 pp. New York: Springer.
-
Tang Q,
Gandhoke R,
Burritt A,
Hruby VJ,
Porreca F,
Lai J
(1999)
High-affinity interaction of (des-tyrosyl)dynorphin A(2-17) with NMDA receptors.
J Pharmacol Exp Ther
291:760-765[Abstract/Free Full Text].
-
Tiseo PJ,
Inturrisi CE
(1993)
Attenuation and reversal of morphine tolerance by the competitive N-methyl-D-aspartate receptor antagonist, LY274614.
J Pharmacol Exp Ther
264:1090-1096[Abstract/Free Full Text].
-
Tiseo PJ,
Cheng J,
Pasternak GW,
Inturrisi CE
(1994)
Modulation of morphine tolerance by the competitive N-methyl-D-aspartate receptor antagonist LY274614: assessment of opioid receptor changes.
J Pharmacol Exp Ther
268:195-201[Abstract/Free Full Text].
-
Trujillo KA,
Akil H
(1991)
Inhibition of morphine tolerance and dependence by the NMDA receptor antagonist MK-801.
Science
251:85-87[Abstract/Free Full Text].
-
Wegert S,
Ossipov MH,
Nichols ML,
Bian D,
Vanderah TW,
Malan Jr TP,
Porreca F
(1997)
Differential activities of intrathecal MK-801 or morphine to alter responses to thermal and mechanical stimuli in normal or nerve-injured rats.
Pain
71:57-64[Web of Science][Medline].
-
Woolf CJ
(1981)
Intrathecal high dose morphine produces hyperalgesia in the rat.
Brain Res
209:491-495[Web of Science][Medline].
-
Yaksh TL,
Harty GJ
(1988)
Pharmacology of the allodynia in rats evoked by high dose intrathecal morphine.
J Pharmacol Exp Ther
244:501-507[Abstract/Free Full Text].
-
Yaksh TL,
Rudy TA
(1976)
Chronic catheterization of the spinal subarachnoid space.
Physiol Behav
17:1031-1036[Medline].
-
Yaksh TL,
Harty GJ,
Onofrio BM
(1986)
High dose of spinal morphine produces a nonopiate receptor-mediated hyperesthesia: clinical and theoretic implications.
Anesthesiology
64:590-597[Web of Science][Medline].
Copyright © 2000 Society for Neuroscience 0270-6474/00/20187074-06$05.00/0
This article has been cited by other articles:
|
|
|
|
 
J. Sandkuhler
Models and Mechanisms of Hyperalgesia and Allodynia
Physiol Rev,
April 1, 2009;
89(2):
707 - 758.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Chen, C. Geis, and C. Sommer
Activation of TRPV1 Contributes to Morphine Tolerance: Involvement of the Mitogen-Activated Protein Kinase Signaling Pathway
J. Neurosci.,
May 28, 2008;
28(22):
5836 - 5845.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. H. Ossipov, I. Bazov, L. R. Gardell, J. Kowal, T. Yakovleva, I. Usynin, T. J. Ekstrom, F. Porreca, and G. Bakalkin
Control of Chronic Pain by the Ubiquitin Proteasome System in the Spinal Cord
J. Neurosci.,
August 1, 2007;
27(31):
8226 - 8237.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Xu, M. R. Bruchas, D. L. Ippolito, L. Gendron, and C. Chavkin
Sciatic Nerve Ligation-Induced Proliferation of Spinal Cord Astrocytes Is Mediated by {kappa} Opioid Activation of p38 Mitogen-Activated Protein Kinase
J. Neurosci.,
March 7, 2007;
27(10):
2570 - 2581.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Streltzer and L. Johansen
Prescription Drug Dependence and Evolving Beliefs About Chronic Pain Management
Am J Psychiatry,
April 1, 2006;
163(4):
594 - 598.
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Dogrul, E. J. Bilsky, M. H. Ossipov, J. Lai, and F. Porreca
Spinal L-Type Calcium Channel Blockade Abolishes Opioid-Induced Sensory Hypersensitivity and Antinociceptive Tolerance
Anesth. Analg.,
December 1, 2005;
101(6):
1730 - 1735.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. C. Van Elstraete, P. Sitbon, F. Trabold, J.-X. Mazoit, and D. Benhamou
A Single Dose of Intrathecal Morphine in Rats Induces Long-Lasting Hyperalgesia: The Protective Effect of Prior Administration of Ketamine
Anesth. Analg.,
December 1, 2005;
101(6):
1750 - 1756.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Y. Xie, D. S. Herman, C.-O. Stiller, L. R. Gardell, M. H. Ossipov, J. Lai, F. Porreca, and T. W. Vanderah
Cholecystokinin in the Rostral Ventromedial Medulla Mediates Opioid-Induced Hyperalgesia and Antinociceptive Tolerance
J. Neurosci.,
January 12, 2005;
25(2):
409 - 416.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Xu, M. Petraschka, J. P. McLaughlin, R. E. Westenbroek, M. G. Caron, R. J. Lefkowitz, T. A. Czyzyk, J. E. Pintar, G. W. Terman, and C. Chavkin
Neuropathic Pain Activates the Endogenous {kappa} Opioid System in Mouse Spinal Cord and Induces Opioid Receptor Tolerance
J. Neurosci.,
May 12, 2004;
24(19):
4576 - 4584.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Celver, M. Xu, W. Jin, J. Lowe, and C. Chavkin
Distinct Domains of the {micro}-Opioid Receptor Control Uncoupling and Internalization
Mol. Pharmacol.,
March 1, 2004;
65(3):
528 - 537.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. A. Hermos, M. J. Klein, N. Gajraj, J. C. Ballantyne, and J. Mao
Opioid Therapy for Chronic Pain
N. Engl. J. Med.,
February 19, 2004;
350(8):
840 - 842.
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. Koetzner, X.-Y. Hua, J. Lai, F. Porreca, and T. Yaksh
Nonopioid Actions of Intrathecal Dynorphin Evoke Spinal Excitatory Amino Acid and Prostaglandin E2 Release Mediated by Cyclooxygenase-1 and -2
J. Neurosci.,
February 11, 2004;
24(6):
1451 - 1458.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Xu, Y. Gu, G.-Y. Xu, P. Wu, G.-W. Li, and L.-Y. M. Huang
Adeno-associated viral transfer of opioid receptor gene to primary sensory neurons: A strategy to increase opioid antinociception
PNAS,
May 13, 2003;
100(10):
6204 - 6209.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. H. Szeto, Y. Soong, D. Wu, X. Qian, and G.-M. Zhao
Endogenous Opioid Peptides Contribute to Antinociceptive Potency of Intrathecal [Dmt1]DALDA
J. Pharmacol. Exp. Ther.,
May 1, 2003;
305(2):
696 - 702.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Raghavendra, M. D. Rutkowski, and J. A. DeLeo
The Role of Spinal Neuroimmune Activation in Morphine Tolerance/Hyperalgesia in Neuropathic and Sham-Operated Rats
J. Neurosci.,
November 15, 2002;
22(22):
9980 - 9989.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Mao, B. Sung, R.-R. Ji, and G. Lim
Chronic Morphine Induces Downregulation of Spinal Glutamate Transporters: Implications in Morphine Tolerance and Abnormal Pain Sensitivity
J. Neurosci.,
September 15, 2002;
22(18):
8312 - 8323.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Mao, B. Sung, R.-R. Ji, and G. Lim
Neuronal Apoptosis Associated with Morphine Tolerance: Evidence for an Opioid-Induced Neurotoxic Mechanism
J. Neurosci.,
September 1, 2002;
22(17):
7650 - 7661.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. R. Gardell, R. Wang, S. E. Burgess, M. H. Ossipov, T. W. Vanderah, T. P. Malan Jr, J. Lai, and F. Porreca
Sustained Morphine Exposure Induces a Spinal Dynorphin-Dependent Enhancement of Excitatory Transmitter Release from Primary Afferent Fibers
J. Neurosci.,
August 1, 2002;
22(15):
6747 - 6755.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. S. Gupta, A. B. Kelson, W. E. Polgar, L. Toll, M. Szucs, and A. R. Gintzler
Ovarian Sex Steroid-Dependent Plasticity of Nociceptin/Orphanin FQ and Opioid Modulation of Spinal Dynorphin Release
J. Pharmacol. Exp. Ther.,
September 1, 2001;
298(3):
1213 - 1220.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
TOP
ABSTRACT
INTRODUCTION
