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Dissociation of antinociceptive and motor effects of supraspinal opioid agonists in the rat
Brain Research, 563 (1991) 123-126 © 1991 Elsevier Science Publishers B.V. All rights reserved. 0006-8993/91/$03.50 ADONIS 0006899391171106
123
BRES 17110
Dissociation of antinociceptive and motor effects of supraspinal opioid agonists in the rat Linda S. Franck 1, Christine Miaskowski 1, Jane Putris and Jon D. Levine 2'3 Schools of 1Nursing, 2Medicine and 3Dentistry, University of California, San Francisco, CA 94143 (U.S.A.) (Accepted 11 June 1991)
Key words: Antinociception; Motor effect; p-Opioid; 6-Opioid;/~-Opioid agonist; di-Opioid agonist; Intracerebroventricular
This study compared the antinociceptive and motor effects produced by intracerebroventricular administration of selective/~- (DAMGO) and di- (DPDPE) opioid receptor agonists in the rat. Changes in nociceptive thresholds were measured using the Randall-Selitto paw-withdrawal test and changes in motor coordination were evaluated using the rotarod treadmill test. Both DAMGO and DPDPE produced statistically significant, dose-dependent increases in mechanical nociceptive thresholds compared to vehicle controls. However, in the motor coordination studies, neither opioid agonist produced statistically significant changes in rotarod performance scores. The dissociation of antinociceptive and motor effects at this supraspinal site differs from the strong association between antinociceptive and motor effects produced by intrathecal administration of the same opioid agonists. INTRODUCTION A n a c c u r a t e e v a l u a t i o n of the d o s e - d e p e n d e n t anti-
ICV cannulae to keep them patent. Rats that exhibited neurological deficits, following the surgical procedure, were eliminated from the study.
n o c i c e p t i v e effects p r o d u c e d by the a d m i n i s t r a t i o n of
Antinociceptive testing
o p i a t e s and o p i o i d p e p t i d e s using b e h a v i o r a l m e a s u r e s
The Randall-Setitto paw-withdrawal test ~7 was used to measure mechanical nociceptive threshold. A mechanical stimulus was applied with a Basile analgesymeter (Stoelting, Chicago, IL) which generates a linearly increasing mechanical force, applied by a dome-shaped plastic tip to the dorsal surface of the rat's hindpaw. The nociceptive threshold was defined as the force in grams at which the animal withdraws its paw. The rats were trained in the test procedure, for 3 h daily, for 5 days prior to data collection 19. On the day of the experiment, rats were first tested at 5 min intervals for 2h. Baseline paw-withdrawal thresholds were defined as the mean of the last 6 measurements prior to drug administration. The average baseline nociceptive threshold, in this group of rats, was 96.71 -+ 0.25 g (mean - S.E.M., n = 28). The effect of saline vehicle and each of the opioid agonists on nociceptive threshold were tested 15, 20, and 25 rain after ICV administration, at the time of peak effect of these agents 7. The antinociceptive effect of the drug was calculated as the average percentage change from baseline threshold of these 3 consecutive measurements. A cut-off of 500 g was used for the paw-withdrawal test and a value of 500 g assigned if an animal reached cut-off. Dose-response curves for ICV administration of the selective /~-opioid agonist, DAMGO and the selective di-opioid agonist, [D-Pen2'5]-enkephalin (DPDPE), both from Peninsula Laboratories (Belmont, CA), were determined by administering sequentially increasing doses of each drug in a volume of 1 #1, at 30 min intervals. In addition, repeated ICV injections of saline vehicle were done as controls. The number of rats, in each group, is indicated in the figure legends. Each rat was used once.
such as the p a w - w i t h d r a w a l and tail-flick tests assumes that an a n i m a l has a n o r m a l l y f u n c t i o n i n g m o t o r system. In r e c e n t e x p e r i m e n t s , h o w e v e r , we h a v e d e m o n s t r a t e d that the i n t r a t h e c a l (IT) a d m i n i s t r a t i o n , in t h e rat, of selective/~- ( D A M G O ) 8 and 6- ( D P D P E ) 13 o p i o i d agonists p r o d u c e d significant d o s e - d e p e n d e n t d e c r e a s e s in m o t o r coordination that w e r e associated with significant dose-dep e n d e n t increases in nociceptive thresholds 12. Since antinociceptive effects have also b e e n d e m o n s t r a t e d with intracerebroventricular ( I C V ) administration of selective/~- and 6-agonists 9a4"15, in this study we c o m p a r e d the antinociceptive and m o t o r effects p r o d u c e d by I C V administration of DAMGO
and D P D P E .
W e present e v i d e n c e that I C V
doses of/~- and 6-agonists, that p r o d u c e d significant antinociceptive effects, failed to p r o d u c e significant decreases in m o t o r coordination. MATERIALS AND METHODS The experiments were performed using male Sprague-Dawley rats weighing 240-300 g (Bantin and Kingman, Fremont, CA), One week prior to the experiments, under pentobarbital anesthesia (65 mg/kg), 22-gauge stainless steel cannulae were stereotactically implanted into the third ventricle and fixed in place with acrylic dental cement. Thirty-gauge stainless steel stylettes were placed in the
Motor coordination testing In a separate group of rats, the effect of the same doses of opioid agonists on motor coordination was tested using an accelerat-
Correspondence: J.D. Levine, Division of Rheumatology, U426/Box 0724, University of California, San Francisco, CA 94143-0724, U.S.A.
124
ing Rota-Rod Treadmill (Ugo Basilc, Stoelting Co., Chicago, I L ) " 2o. The rotarod was set in motion at a constant speed and the rats were placed into individual sections of the rotarod. Once all of the rats were in position, the timers were set to zero and the rotarod was switched to the accelerating mode. The rotarod accelerated from a rate of 3.7 RPMs to 37.5 RPMs over a period of 5 min. The performance score was recorded, in seconds, when thc rat, unable to stay on the rotarod, tripped a platc and stopped the timer. A m i n i m u m of 2 training sessions of 3 h duration were performed to condition the animal to the treadmill. On the day of the experiment, the rats were tested on the rotarod at 5 min intervals for 2 h. A baseline rotarod performance score was defined as thc m e a n of the last 6 m e a s u r e m e n t s prior to drug administration. The average rotarod performance score, in this group of rats, was 113.62 ± 11.5 s (mean ± S.E.M., n = 27). The cffect of the opioid agonists on rotarod performance was tested using thc same drug administration paradigm used in the antinociceptive testing. Thc effect of the drugs on rotarod performance was also calculated as a percentage change from baseline.
Statistical ana@ses Statistical analyses of the d o s e - r e s p o n s e cffccts of ICV administration of the selective opioid agonists on nociccptivc threshold and rotarod performance compared to vehiclc controls werc done using a two-factor, repeated measures analysis of variance ( A N O V A ) . In addition, in order to determine the dose-dependent effects for ~ specific opioid agonist, a one-way A N O V A was performed mm'~' m. Differences were considered statistically significant at thc f' ,z (I,05 level.
RESULTS
H-Opioid effects Fig. IA,B
illustrates the effects of i.c.v, administra-
tion of sequentially pared
increasing doses of DAMGO
to repeated
threshold
injections
and rotarod
com-
of vehicle on nociceptive
performance,
respectively.
Two-
A. PAW-WITHDRAWAL
A. PAW-WITHDRAWAL 160
140 120
• jq
t00W
z "9
6040-
i, w o z T (.3 W (..9 Z W (..) (12 W n
,/i
120-
T
100W Z W 03
200~
o
T
140-
!
80-
m 03
.<
j o
160-
l
-6--6
6--6~¢-~'-6
-205 fg
0.5 pg
50 pg
B. ROTAROD
5 ng
40.
o nl
0
b_ W
SALINE
If-- • OAMGO
(.3 w (.9
6°t
z hi 0 n~ W n
I
-.01
/T\
,,
t
60.
<~ flo
C9 Z T
0--0
80.
20.
-20
rlL
,
5 fg
,
0.5 pg
,
,
,I.
¢'e~.
50 pg
,
I
5 ng
500 ng
0 - - 0 SAUNE • • DPDPE
B. ROTAROD
-
-
60-
40-
o
20-
__!
0c
_201:
-40-
-40
5 fg
0.5 pg
LOG
50 pg
5 fg
0.5 pg
50 Pg
5 ng
500n9
5 ng
DOSE
Fig. 1. A: dose-dependence relationship for the effects of intracerebroventricular administration of sequentially increasing doses of D A M G O (n = 8) compared with vehicle controls (n = 12) on paw-withdrawal thresholds. B: dose-dependence relationship for the effects of intracerebroventricular administration of sequentially increasing doses of D A M G O (n = 8) compared with vehicle controls (n = 9) on rotarod performance scores (i.e, length of time on the rotarod). All scores are graphed as percentage change from baseline paw-withdrawal (A) or rotarod performance score (B) after drug administration. Each point in the figure represents the mean ± S.E.M. Some error bars are contained within the symbols.
LOG DOSE
Fig. 2. A: dose-dependence relationship for the effects of intracercbroventricular administration of sequentially increasing doses of D P D P E (n = 8) compared with vehicle controls (n = 12) on pawwithdrawal thresholds. B: dose-dependence relationships for the effects of intracerebroventricular administration of sequentially increasing doses of D P D P E (n = 10) compared with vehicle controls (n = 9) on rotarod performance scores (i.e. length of time on the rotarod). All scores are graphed as percentage change from baseline paw-withdrawal (A) or rotarod performance score (B) after drug administration. Each point in the figure represents the mean -+ S.E.M. Some error bars are contained within the symbols.
125 way A N O V A revealed significant main effects of group for antinociception (F1,18 = 215.90, P < 0.001) but not for rotarod performance (F1,15 = 1.14, P > 0.05). The results for antinociception indicate that the increases in nociceptive thresholds are statistically significantly different from vehicle controls. In contrast, ICV administration of D A M G O had no effect on rotarod performance, compared to vehicle controls. One-way A N O V A demonstrated that sequentially increasing doses of ICV D A M G O produced statistically significant, dose-dependent increases in nociceptive thresholds (F8,56 --- 24.42, P < 0.001) but failed to produce dose-dependent changes in rotarod performance scores (F8,56 = 0.43, P > 0.05). 6-Opioid effects
Fig. 2A,B illustrates the effects of i.c.v, administration of sequentially increasing doses of D P D P E compared to repeated injections of vehicle on nociceptive threshold and rotarod performance, respectively. Twoway A N O V A revealed significant main effects of group for antinociception (F~,~8 = 78.72, P < 0.001) but not for rotarod performance (Fl,17 = 0.10, P > 0.05). One-way A N O V A demonstrated that sequentially increasing doses of i.c.v. D P D P E produced statistically significant, dose-dependent increases in nociceptive thresholds (F9,63 = 21.16, P < 0.001) but failed to produce dose-dependent changes in rotarod performance scores (F9,81 = 1.43, P > 0.05). DISCUSSION The results of this study demonstrate that the i.c.v. administration of D A M G O and DPDPE, over a dose range that produced significant antinociceptive effects, failed to produce significant changes in motor coordination, in the rat. This contrasts with our spinal data 12 demonstrating that, at doses which produced comparable antinociceptive effects, i.t. administration of the same opioid agonists produced marked deleterious effects on toREFERENCES 1 Atweh, S.E and Kuhar, M.J., Autoradiographic localization of opiate receptors in rat brain. I. Spinal cord and lower medulla, Brain Research, 124 (1977) 53-67. 2 Cohen, J. and Cohen, P., Applied Multiple Regression~Correlation Analysis for the Behavioral Sciences, Lawrence Erlbaum, Hillsdale, NJ, 1983, pp. 301-350. 3 Dray, A. and Metsch, R., Opioid receptor subtypes involved in the central inhibition of urinary bladder motility, Eur. J. Pharmacol., 104 (1984) 47-53. 4 Dray, A. and Nunan, L., Opioid inhibition of reflex urinary bladder contraction: dissociation of supraspinal and spinal mechanisms, Brain Research, 337 (1985) 142-145. 5 Dray, A., Nunan, L. and Wire, W., Central 6-opioid receptor
tarod performance. The supraspinal data are compatible with the work of Jensen and Yaksh 9 who also failed to demonstrate behavioral side-effects (except at the highest doses tested) with microinjection of morphine, sufentanyl, DADL, and DSTLE (D-Ser2-Thr6-1eucine enkephalin) into the periaqueductal gray and medial/paramedial medullary reticular formation. The mechanism regulating the concurrent increases in antinociceptive effects with associated decreases in motor coordination produced by i.t. administration of opioid agonists is unknown. These concurrent effects may be due to activation of 2 functionally distinct groups of opioid receptors (i.e. one mediating antinociception and the other motor effects). This hypothesis is supported by data demonstrating opioid receptors in both the dorsal and the ventral horns of the spinal cord 1. Alternatively, spinal circuitry may differ from that located at the supraspinal site in that activation of a single group of opioid receptors results ultimately in both antinociceptive and motor effects. The findings of an association between motor and antinociceptive effects produced by opioids administered at the spinal but not at the supraspinal site contrasts with what has been demonstrated with other opioid-induced side-effects. For example, the effect of opioids on gastrointestinal transit time is mediated through supraspinal p-opioid receptors 7'15 as well as through spinal H- and 6-opioid receptors 16. In addition, studies of the effects of selective opioid agonists on urinary bladder activity have demonstrated that H- and 6-, but not r-opioid receptors are involved in modulation of bladder motility through activation of supraspinal as well as spinal sites 3-5. Further studies are needed to determine whether receptor-specific opioid agonists, administered at different anatomical sites, might be useful in selectively reducing opioid-induced side-effects.
Acknowledgements. This work was supported by NIH Grant DE08973 and grants from the American Nurses' and Rita Allen Foundations. C. Miaskowski is the 1990 Sterling Drug Scholar.
interactions and the inhibition of reflex urinary bladder contractions in the rat, Br. J. Pharmacol., 85 (1985) 717-726. 6 Dunham, N.W. and Miya, T.S., A note on a simple apparatus for detecting neurological deficit in rats and mice, J. Am. Pharmaceut. Assoc., 46 (1957) 208-209. 7 Galligan, J.J., Mosberg, H.I., Hurst, R., Hruby, R., Hruby, V.J. and Burks, T.E, Cerebral delta opioid receptors mediate analgesia but not the intestinal motility of intracerebroventricularly administered opioids, J. PharmacoL Exp. Ther., 229 (1984) 641-648. 8 Handa, B.K., Lane, A.C., Lord, J.A.H., Morgan, B.A., Rance, M.J. and Smith, C.EC., Analogues of fl-LPI-I61_64possessing selective agonist activity at/t-opiate receptors, Eur. J. Pharmacol., 70 (1981) 531-540. 9 Jensen, T.S. and Yaksh III, T.L., Comparison of the antinoci-
126
10
11
12
13
14
ceptive action of/~- and 6-opioid receptor ligands in the periaqueductal gray matter, medial and paramedial ventral medulla in the rat studied by microinjection technique, Brain Research, 372 (1986) 301-312. Marascuilo, L.A. and Serlin, R.C., Statistical Methods for the Social and Behavioral Sciences, W.H. Freeman, New York, 1988, pp. 448-454. Melton, J.S. and Tsokos, J.O., Statistical Methods in Biological and Health Sciences, McGraw-Hill, New York, 1983, pp. 271331. Miaskowski, C., Sutters, K.A., Taiwo, Y.O. and Levine, J.D., Comparison of the antinociceptive and motor effects of intrathecal opioid agonists in the rat, Brain Research, in press. Mosberg, H.I., Hurst, R., Hruby, V.J., Gee, K., Yamamura, H.I., Galligan, J.J. and Burks, T.E, Bis-penicillamine enkephalins possess highly improved specificity toward delta opioid receptors, Proc. Natl. Acad. Sci. U.S.A., 80 (1983) 5871-5874. Porreca, F., Heyman, J.S., Mosberg, H.I., Omnaas, J.R. and Vaught, J.L., Role of #- and 6-receptors in the supraspinal and spinal analgesic effects of [D-Pen z, D-Pen 5] enkephalin in the mouse, J. Pharmacol. Exp. Ther., 241 (1987) 393-400.
15 Porreca, E, Mosberg, H.I., Hurst, R., Hruby, V.J. and Burks, T., Roles of kt-, 6- and ~c-opioid receptors in spinal and supraspinal mediation of gastrointestinal transit effects and hot-plate analgesia in the mouse, J. Pharmacol. Exp. Ther., 230 (1984) 341-348. 16 Porreca, E and Burks, T.E, The spinal cord as a site of opioid effects on gastrointestinal transit in the mouse, J. Pharmacol. Exp. Ther., 227 (1983) 22-27. 17 Randall, L.O. and Selitto, J.J., A method for measurement of analgesic activity on inflamed tissue, Arch. Int. Pharmacodyn., 111 (1957) 409-419. 18 Sokal, R.R. and Rohlf, F.J., Introduction to Biostatistics, W.H. Freeman, New York, 1987, pp. 185-210. 19 Taiwo, Y.O., Coderre, T.J. and Levine, J.D., The contribution of training to sensitivity in the nociceptive paw-withdrawal test, Brain Research, 487 (1989) 148-151. 20 Watzman, N., Barry III, H., Kinnard Jr. W.J. and Buckley, J.P., Influence of certain parameters on the performance of mice on the rotarod, Arch. Int. Pharmacodyn., 169 (1967) 362374.
123
BRES 17110
Dissociation of antinociceptive and motor effects of supraspinal opioid agonists in the rat Linda S. Franck 1, Christine Miaskowski 1, Jane Putris and Jon D. Levine 2'3 Schools of 1Nursing, 2Medicine and 3Dentistry, University of California, San Francisco, CA 94143 (U.S.A.) (Accepted 11 June 1991)
Key words: Antinociception; Motor effect; p-Opioid; 6-Opioid;/~-Opioid agonist; di-Opioid agonist; Intracerebroventricular
This study compared the antinociceptive and motor effects produced by intracerebroventricular administration of selective/~- (DAMGO) and di- (DPDPE) opioid receptor agonists in the rat. Changes in nociceptive thresholds were measured using the Randall-Selitto paw-withdrawal test and changes in motor coordination were evaluated using the rotarod treadmill test. Both DAMGO and DPDPE produced statistically significant, dose-dependent increases in mechanical nociceptive thresholds compared to vehicle controls. However, in the motor coordination studies, neither opioid agonist produced statistically significant changes in rotarod performance scores. The dissociation of antinociceptive and motor effects at this supraspinal site differs from the strong association between antinociceptive and motor effects produced by intrathecal administration of the same opioid agonists. INTRODUCTION A n a c c u r a t e e v a l u a t i o n of the d o s e - d e p e n d e n t anti-
ICV cannulae to keep them patent. Rats that exhibited neurological deficits, following the surgical procedure, were eliminated from the study.
n o c i c e p t i v e effects p r o d u c e d by the a d m i n i s t r a t i o n of
Antinociceptive testing
o p i a t e s and o p i o i d p e p t i d e s using b e h a v i o r a l m e a s u r e s
The Randall-Setitto paw-withdrawal test ~7 was used to measure mechanical nociceptive threshold. A mechanical stimulus was applied with a Basile analgesymeter (Stoelting, Chicago, IL) which generates a linearly increasing mechanical force, applied by a dome-shaped plastic tip to the dorsal surface of the rat's hindpaw. The nociceptive threshold was defined as the force in grams at which the animal withdraws its paw. The rats were trained in the test procedure, for 3 h daily, for 5 days prior to data collection 19. On the day of the experiment, rats were first tested at 5 min intervals for 2h. Baseline paw-withdrawal thresholds were defined as the mean of the last 6 measurements prior to drug administration. The average baseline nociceptive threshold, in this group of rats, was 96.71 -+ 0.25 g (mean - S.E.M., n = 28). The effect of saline vehicle and each of the opioid agonists on nociceptive threshold were tested 15, 20, and 25 rain after ICV administration, at the time of peak effect of these agents 7. The antinociceptive effect of the drug was calculated as the average percentage change from baseline threshold of these 3 consecutive measurements. A cut-off of 500 g was used for the paw-withdrawal test and a value of 500 g assigned if an animal reached cut-off. Dose-response curves for ICV administration of the selective /~-opioid agonist, DAMGO and the selective di-opioid agonist, [D-Pen2'5]-enkephalin (DPDPE), both from Peninsula Laboratories (Belmont, CA), were determined by administering sequentially increasing doses of each drug in a volume of 1 #1, at 30 min intervals. In addition, repeated ICV injections of saline vehicle were done as controls. The number of rats, in each group, is indicated in the figure legends. Each rat was used once.
such as the p a w - w i t h d r a w a l and tail-flick tests assumes that an a n i m a l has a n o r m a l l y f u n c t i o n i n g m o t o r system. In r e c e n t e x p e r i m e n t s , h o w e v e r , we h a v e d e m o n s t r a t e d that the i n t r a t h e c a l (IT) a d m i n i s t r a t i o n , in t h e rat, of selective/~- ( D A M G O ) 8 and 6- ( D P D P E ) 13 o p i o i d agonists p r o d u c e d significant d o s e - d e p e n d e n t d e c r e a s e s in m o t o r coordination that w e r e associated with significant dose-dep e n d e n t increases in nociceptive thresholds 12. Since antinociceptive effects have also b e e n d e m o n s t r a t e d with intracerebroventricular ( I C V ) administration of selective/~- and 6-agonists 9a4"15, in this study we c o m p a r e d the antinociceptive and m o t o r effects p r o d u c e d by I C V administration of DAMGO
and D P D P E .
W e present e v i d e n c e that I C V
doses of/~- and 6-agonists, that p r o d u c e d significant antinociceptive effects, failed to p r o d u c e significant decreases in m o t o r coordination. MATERIALS AND METHODS The experiments were performed using male Sprague-Dawley rats weighing 240-300 g (Bantin and Kingman, Fremont, CA), One week prior to the experiments, under pentobarbital anesthesia (65 mg/kg), 22-gauge stainless steel cannulae were stereotactically implanted into the third ventricle and fixed in place with acrylic dental cement. Thirty-gauge stainless steel stylettes were placed in the
Motor coordination testing In a separate group of rats, the effect of the same doses of opioid agonists on motor coordination was tested using an accelerat-
Correspondence: J.D. Levine, Division of Rheumatology, U426/Box 0724, University of California, San Francisco, CA 94143-0724, U.S.A.
124
ing Rota-Rod Treadmill (Ugo Basilc, Stoelting Co., Chicago, I L ) " 2o. The rotarod was set in motion at a constant speed and the rats were placed into individual sections of the rotarod. Once all of the rats were in position, the timers were set to zero and the rotarod was switched to the accelerating mode. The rotarod accelerated from a rate of 3.7 RPMs to 37.5 RPMs over a period of 5 min. The performance score was recorded, in seconds, when thc rat, unable to stay on the rotarod, tripped a platc and stopped the timer. A m i n i m u m of 2 training sessions of 3 h duration were performed to condition the animal to the treadmill. On the day of the experiment, the rats were tested on the rotarod at 5 min intervals for 2 h. A baseline rotarod performance score was defined as thc m e a n of the last 6 m e a s u r e m e n t s prior to drug administration. The average rotarod performance score, in this group of rats, was 113.62 ± 11.5 s (mean ± S.E.M., n = 27). The cffect of the opioid agonists on rotarod performance was tested using thc same drug administration paradigm used in the antinociceptive testing. Thc effect of the drugs on rotarod performance was also calculated as a percentage change from baseline.
Statistical ana@ses Statistical analyses of the d o s e - r e s p o n s e cffccts of ICV administration of the selective opioid agonists on nociccptivc threshold and rotarod performance compared to vehiclc controls werc done using a two-factor, repeated measures analysis of variance ( A N O V A ) . In addition, in order to determine the dose-dependent effects for ~ specific opioid agonist, a one-way A N O V A was performed mm'~' m. Differences were considered statistically significant at thc f' ,z (I,05 level.
RESULTS
H-Opioid effects Fig. IA,B
illustrates the effects of i.c.v, administra-
tion of sequentially pared
increasing doses of DAMGO
to repeated
threshold
injections
and rotarod
com-
of vehicle on nociceptive
performance,
respectively.
Two-
A. PAW-WITHDRAWAL
A. PAW-WITHDRAWAL 160
140 120
• jq
t00W
z "9
6040-
i, w o z T (.3 W (..9 Z W (..) (12 W n
,/i
120-
T
100W Z W 03
200~
o
T
140-
!
80-
m 03
.<
j o
160-
l
-6--6
6--6~¢-~'-6
-205 fg
0.5 pg
50 pg
B. ROTAROD
5 ng
40.
o nl
0
b_ W
SALINE
If-- • OAMGO
(.3 w (.9
6°t
z hi 0 n~ W n
I
-.01
/T\
,,
t
60.
<~ flo
C9 Z T
0--0
80.
20.
-20
rlL
,
5 fg
,
0.5 pg
,
,
,I.
¢'e~.
50 pg
,
I
5 ng
500 ng
0 - - 0 SAUNE • • DPDPE
B. ROTAROD
-
-
60-
40-
o
20-
__!
0c
_201:
-40-
-40
5 fg
0.5 pg
LOG
50 pg
5 fg
0.5 pg
50 Pg
5 ng
500n9
5 ng
DOSE
Fig. 1. A: dose-dependence relationship for the effects of intracerebroventricular administration of sequentially increasing doses of D A M G O (n = 8) compared with vehicle controls (n = 12) on paw-withdrawal thresholds. B: dose-dependence relationship for the effects of intracerebroventricular administration of sequentially increasing doses of D A M G O (n = 8) compared with vehicle controls (n = 9) on rotarod performance scores (i.e, length of time on the rotarod). All scores are graphed as percentage change from baseline paw-withdrawal (A) or rotarod performance score (B) after drug administration. Each point in the figure represents the mean ± S.E.M. Some error bars are contained within the symbols.
LOG DOSE
Fig. 2. A: dose-dependence relationship for the effects of intracercbroventricular administration of sequentially increasing doses of D P D P E (n = 8) compared with vehicle controls (n = 12) on pawwithdrawal thresholds. B: dose-dependence relationships for the effects of intracerebroventricular administration of sequentially increasing doses of D P D P E (n = 10) compared with vehicle controls (n = 9) on rotarod performance scores (i.e. length of time on the rotarod). All scores are graphed as percentage change from baseline paw-withdrawal (A) or rotarod performance score (B) after drug administration. Each point in the figure represents the mean -+ S.E.M. Some error bars are contained within the symbols.
125 way A N O V A revealed significant main effects of group for antinociception (F1,18 = 215.90, P < 0.001) but not for rotarod performance (F1,15 = 1.14, P > 0.05). The results for antinociception indicate that the increases in nociceptive thresholds are statistically significantly different from vehicle controls. In contrast, ICV administration of D A M G O had no effect on rotarod performance, compared to vehicle controls. One-way A N O V A demonstrated that sequentially increasing doses of ICV D A M G O produced statistically significant, dose-dependent increases in nociceptive thresholds (F8,56 --- 24.42, P < 0.001) but failed to produce dose-dependent changes in rotarod performance scores (F8,56 = 0.43, P > 0.05). 6-Opioid effects
Fig. 2A,B illustrates the effects of i.c.v, administration of sequentially increasing doses of D P D P E compared to repeated injections of vehicle on nociceptive threshold and rotarod performance, respectively. Twoway A N O V A revealed significant main effects of group for antinociception (F~,~8 = 78.72, P < 0.001) but not for rotarod performance (Fl,17 = 0.10, P > 0.05). One-way A N O V A demonstrated that sequentially increasing doses of i.c.v. D P D P E produced statistically significant, dose-dependent increases in nociceptive thresholds (F9,63 = 21.16, P < 0.001) but failed to produce dose-dependent changes in rotarod performance scores (F9,81 = 1.43, P > 0.05). DISCUSSION The results of this study demonstrate that the i.c.v. administration of D A M G O and DPDPE, over a dose range that produced significant antinociceptive effects, failed to produce significant changes in motor coordination, in the rat. This contrasts with our spinal data 12 demonstrating that, at doses which produced comparable antinociceptive effects, i.t. administration of the same opioid agonists produced marked deleterious effects on toREFERENCES 1 Atweh, S.E and Kuhar, M.J., Autoradiographic localization of opiate receptors in rat brain. I. Spinal cord and lower medulla, Brain Research, 124 (1977) 53-67. 2 Cohen, J. and Cohen, P., Applied Multiple Regression~Correlation Analysis for the Behavioral Sciences, Lawrence Erlbaum, Hillsdale, NJ, 1983, pp. 301-350. 3 Dray, A. and Metsch, R., Opioid receptor subtypes involved in the central inhibition of urinary bladder motility, Eur. J. Pharmacol., 104 (1984) 47-53. 4 Dray, A. and Nunan, L., Opioid inhibition of reflex urinary bladder contraction: dissociation of supraspinal and spinal mechanisms, Brain Research, 337 (1985) 142-145. 5 Dray, A., Nunan, L. and Wire, W., Central 6-opioid receptor
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Acknowledgements. This work was supported by NIH Grant DE08973 and grants from the American Nurses' and Rita Allen Foundations. C. Miaskowski is the 1990 Sterling Drug Scholar.
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