Brain Research, 507 (1990) 11-16 Elsevier
11
BRES 15110
Antinociception in the rat induced by a cold environment Patrlcm F Osgood, Darnel B Carr, Arthur Kazmms, James W Kemp, Nancy E Atchison and S K Szyfelbem Department of Anesthesta, Analgestc Pepttde Research Umt, Massachusetts General Hospttal Harvard Medtcal ~chool Shrmers Burns lnstttute, Boston, MA ( U 5 A ) (Accepted 13 June 1989)
Key words Stress-reduced analgesm Environmental cold Op~old kappa receptor
Rats placed in a cold environment (4 °C) for 2 h had a sustained increase in tad fhck latency (TFL) as well as an increase m tad pinch latency (TPch) that was often biphaslc with an early peak response at 15 mm and a later, often higher, peak at 2 h Plasma beta-endorphm levels after a modest increase at 5 mm (24%) dechned throughout the remaining time m the cold The long-acting oplold antagomst naltrexone had no effect on TFL increases but led to greater increases m TPch (P < 0 041 In morphine-tolerant rats TFL response was the same as m controls but TPch increases were greater (P < 0 04) Rats exposed to 2 h of cold for 17 or 18 consecutive days generally developed tolerance to the analgesia of cold, 1 e TFL and TPch increases were diminished, however, the response to morphine on da~, 18 was the same as m rats never exposed to cold Adrenalectomy and hypophysectomy led to significantly smaller increases in TFL (P < 0 02 and P < 0 001 respectively) The TPch response in contrast was greater m adrenalectomlzed (P < 0 001) and the same m hypophvsectomlzed rats compared to sham controls An opmld kappa receptor antagomst (Mr 1452) given prior to cold reduced both TFL and TPch response during the first hour Thus the analgesia induced by cold appeared to shift from an early possibly kappa oplold to a later non-oplmd torm The TFL effects seemed to be under hormonal influence while the TPch were not
INTRODUCTION
In t h e p r e s e n t s t u d y , t h o u g h t h e n o n - o p t o l d e l e m e n t of the analgesia of cold was confirmed, there appeared to be
Endogenous by numerous
pam-mhlbltory systems may be actwated stressors or environmental
c h a n g e s 19 l~
a n o p l o l d c o m p o n e n t as well, m e d m t e d p e r h a p s by o p t o l d kappa receptors
I n a d d t t l o n , we f o u n d t h a t t h e tall f h c k
The analgesta thus induced may be optotd or non-oplold
l a t e n c y r e s p o n s e to c o l d s e e m e d to b e u n d e r h o r m o n a l
tn n a t u r e a n d s o m e f o r m s , p a r t i c u l a r l y t h e o p t o l d , a p p e a r
i n f l u e n c e w h t l e tall p i n c h l a t e n c y w a s n o t
to depend
upon
the Integrity of the pttultary-adrenal
a x i s 2 0 36 4o
MATERIALS AND METHODS
In a prehmmary
s t u d y we f o u n d t h a t r a t s e x p o s e d t o
a c o l d e n ~ t r o n m e n t (4 °C) f o r 2 h d e v e l o p e d a n a n a l g e s m that was naloxone,
largely
i n s e n s i t i v e to t h e
httle tnfluenced
op~old a n t a g o m s t
by I n h i b i t i o n o f a l p h a 2 o r
beta-adrenergxc receptors and accompanied by an early modest increase followed by a steady declme m plasma beta-endorphm lmmunoacttvlty throughout the remamd e r o f t h e 2-h t i m e in t h e c o l d 24 In these earher studies noclceptlon was assessed by tad flick l a t e n c y , a t e s t p a r t t c u l a r l y s e n s t t t v e t o a c t i v a t i o n o f o p t o t d p a t h w a y s rich in m u r e c e p t o r s 3~ 38 ~9 A t e s t u s i n g a p r e s s u r e r a t h e r t h a n a h e a t s t t m u l u s s h o u l d b e less influenced by conditions of cold, therefore, to further explore the apparent non-optold analgesta mduced by a cold envtronment pinch latency,
we h a v e n o w in a d d i t i o n a s s e s s e d tall
a test more
r e c e p t o r a c t i v a t i o n 3Z ~
Correspondence
s e n s t t l v e to op~otd k a p p a
Male Sprague-Dawley rats weighing 260 k (S D ) 60 1 g, were obtained from Tacomc Farms Germanto',~n, N ~ and maintained on a 12-h hght/dark cycle 5 or 6 to a cage v, lth free access to food and water for at least one week before an experiment Antlnoc~ceptlon (analgesia) was assessed b~ tail flick latency (TFL), determined as the mean ol 3 trials at one-ram intervals w~th a maximum exposure (cut off) to the heat stimulus of 7 s Another measure of analgesm tad pinch latenc~ (TPch) the time to a squeak response alter placing a hardwood clothespin on the base of the tad (pressure 1 27 kg) was assessed as the mean of 5 trials at l-mm intervals w~th a cut off ot 30 s The day before the experiment rats were trained to a vocal response to the TPch, to reduce baseline vanabdlty ~" On the day of the experiment each rat was placed m a separate cage with fret. access to water and food prehmmarv measurements made, then e~ther sahne or a drug administered following by a second set ot premeasures Rats were then placed for 2 h m a room held at 4 °C and TFL and TPch repeated at 15, 30, 60 and 120 ram, upon remo,~al from the cold measurements were repeated at intervals for up to 2 h In group 1 (6 rats) a cannula was placed in the right jugular veto (under 50 mg/kg pentobarbltal anesthesia) 2 days before exposure
P F Osgood Shrmers Burns Institute Room 25~ 5l Blossom Street Boston, MA 2114 U S A
0006-8993/90/$03 50 © 1990 Elsevier Science Publishers B V (Blome&cal Dwlslon)
12 to cold Blood samples (0 5 ml) for plasma heta-endorphm rad~oimmunoassax ~2 were drawn tmmediatelv before FFL and TPch at the times mentioned abo~e (with an additional sample taken alter 5 mln m the cold) Plasma was separated at once and lrozen until assa'v (for further details see Osgood et al 2s) Red blood cells were diluted back to the original volume with 0 9r~ sodium chloride (salme) vortexed and injected intravenously attcr each sample (between the times ot FFL and TPch measurement) In group II naltrexone (5 0 mg/kg) or saline m a comparable volume was injected subcutaneousl~ (s c ) 25 mm before cold (6 rats each treatment) Group III was made tolerant to morphine b~ placement under pentobarbital anesthesia (50 mg/kg), of 2 s c pellets each containing 75 mg of morphine (8 rats) or a placebo (8 rats) pellet (NIDA Drug Supply Program trom Research Triangle lnst N C ) Folerance to morphine ~as assumed v, hen TFL ,~aluc.s returned to the pre-pellet level (2-3 days) Group IVA (6 rats) were placed m the cold room for 2 h a day for ]7 consecutive days and TFL measured on days, 1 3, 8 14 and 17 Group IVB (12 rats) were placed m the cold for 18 consecunve days TFL and TPch were measured before and after 2 h of cold on the first and last da) as well as on the same intervening days a~ m Group IVA On day 18, after a return to pie-cold levels, TFL and TPch v, ere measured for a period of 2 h after lntrapentoneal (l p ) administration of 4 0 mg/kg of morphine In group IVC, 12 rats never exposed to cold were given the same dose of morphine (i p ) Group V rats were exposed to cold approximately one week after adrenalectomy (6 rats) or sham (9 rats) operation (Taconic Farms) Prior to and durmg cold, adrenaleetom~zed rats were given saline as drinking water Group VI rats were h~pophysectomized (10 rats) or shamhvpophysectomized (10 rats) and maintained on 5°6 dextrose solutmn before cold exposure To test for the completenes~ of hvpophvsectomy following the experiment, these rats were anesthetized and jugular venous blood samples drawn for measurement of the pltmtary hormone prolactm (Hazelton Blotechnologms Co Vienna, VA) Prolactln plasma levels were 31 _+ 16 2 (S D ) ng/ml m shams and 2 6 _+ 1 3 m hypophysectomized rats (normal levels are 15-.$0 ng/ml) Group VII were given the antihistamine diphenhydramme (2S mg/kg I p )~4 (9 rats) or saline (6 rats) one h before cold In the final group (VIII A and B) rats received Mr 1452, a predominant b opioid kappa receptor antagonist (a gift from Boehrlnger-Ingelheim, KG) in a dose ot 3 0 mg/kg (s c )io Group A were given Mr 1452 (6 rats) or saline (6 rats) after 2 h m the cold Group B received Mr 1452 (7 rats) or sahne (7 rats) one min before exposure to cold The TFL and TPch responses were determined as the level at each time of measurement minus the level immediately prior to cold The sum of each measure over the 2-h period in the cold was used for stanstlcal comparisons (paired, or non-paired t-tests and analysis ot variance [ANOVA]) In addition, m some experiments the area under the rime course-percent ot maximum possible response curve ( A U C ) was determined by the trapezoid method 32
6O
I
~°
I
Tad t- lick Latency ( T~I ~
2"(
~ 40
~ ~o ~zo i~
~/i..---
|TodRnchLotency(TPch) , ,~A.I~
,OO q3
5o
~0
n 6
_ I~1 ~nto C0id
0
15
30
60
(:ut
'~
120
150
~ 0
*
TIME/minutes)
Fig I The time course of the effects of 2 h exposure of rats to a temperature of 4 °C on plasma beta-endorphln immunoacnvlty (iB-EP), open squares, tall flick latency (TFL), open circles, and tail pinch latency (TPch), closed circles Mean values from 6 rats _+ the standard error of the mean (S E M ) are shown
(Fig 1), B-EP had returned to pre-cold levels by 24 h, however The oplold antagonist naltrexone (group II) had no effect on the TFL response to cold but actually augmented the TPch response (P < 0 037) (Fig 2) In rats tolerant to morphine (group III) the TFL was no different than in the rats with placebo pellets (compared as the overall response or at one h) but as with naltrexone TPch rose to higher levels in the tolerant rats (P < 0 04) (Fig 3) Repeated exposure to cold (groups 1VA and B) generally led to the development of tolerance to the TFL and TPch responses but m approximately 30% of each group (2 of 6 m IVA and 4 of 12 in IVB) there was no dlmunltlOn of these effects between the first and last day of cold, i e no tolerance was apparent In group A the TFL response on day 17 was less than on day 1 (P < 0005) at 30 min but not at 1 and 2 h In Group IVB, however, tolerance to the analgesic effect of cold,
Tad- Pinch Latency (T-Pch/
Tall Fhck Latency {TFL) 7O
140
( 6 Rats eoch ) 0 SALINE
/r--1I
NALTREXaNE
•
~so
t
RESULTS
•
C~
~, 30 W h e n rats (group I) were placed m a cold environment (4 °C) there was a rise m T F L that was sustained and an increase m TPch that was often biphaslc w~th a p e a k at 15 m m followed by a second p e a k at 2 h that was generally higher than the first (e g see Ftgs 3, 4 and 5) A f t e r r e m o v a l from the cold r o o m at 2 h these measures r e t u r n e d to pre-cold levels in a p p r o x i m a t e l y 30 mm Plasma b e t a - e n d o r p h l n (B-EP) after an early (5 m m in the cold) m i n o r increase (24%) t e n d e d to dechne during cold and c o n t i n u e d to fall m the 3-h period after cold
I
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,20
L
~oo
t
H80
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i
/
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6o~
I
1 Q~ 40~
i
0 t ~ c°ld I
0
t I0
J
Cold ~ L__ I 1 _1 0 10 20 3 0 L
I
20
t
30 HOURS
o ~
Fig 2 The effect of subcutaneous (s c ) administration of 5 0 mg/kg of naltrexone 25 rain before exposure to cold (closed circles) or saline (open circles), 6 rats per treatment The ordinates are tail flick latency (left panel) and tall pinch latenc~ (right panel) m seconds, the abscissa is time in hours
13 Tad Flick Latency (TFL)
Toll Flick Latency (TFL)
Toll- Pinch Lalency (T-Pch) 5C
7"0 ~o
~4c
(8 Rols each) 0 PLACEBOPELLETS • MORPHINETOLERANT
~u 5 0
5O
"to
II
,,a
4\,'' #
~
50
I
C5
0 Sham HYPX (tO Rals)
/I i~
40 ~
3O
30~
201
20C5
i
101
i~o~
°
~o
LCold __
0 ~
0
L
I0
o
•
Cold r
~"
J
20
0
3O
40
30
20
Fig 3 The effect of cold in rats made tolerant to morphine by 2 subcutaneous (s c ) 75-rag morphine pellets (closed circles/ as compared to controls (2 s c placebo pellets open circles) Mean values from 8 rats lor e a c h treatment are depicted Axes are the same as in F~g 2
measured only at 2 h did develop A comparison of days 1, 3, 8, 14 and 18 showed no differences ( A N O V A ) nevertheless a comparison at day 1 with day 18 for TFL gave a difference of P < 0 03 and for TPch P < 0 01 On day 18, 2 h after removal from the cold, the TFL and TPch response to 4 0 mg/kg of morphine (1 p ) was entirely similar to that at a group of rats at room temperature never exposed to cold, peak increases were 2 1 +_(SD)I 56mTFLand82+_635smTPch, mthe former and 1 2 +_ 1 16 and 7 7 _+ 7 6 4 s m the latter group In adrenalectomIzed rats (group V), however the sham controls had a greater rise m ~IFL in the cold (P < 0 02) For TPch the reverse held adrenalectomized rats
Tail- Pinch Latency
Toll Fhck Latency (TFL)
I
0
110
_~ 210
[ L
310
0
Cold L
I0
j 210
310
HOURS
HOURS
(T-Pch)
80
Fig 5 The effect of hypophysectomv (HYPX, closed c~rcles) and sham hvpophysectomg (open circles) on T F L (lett) a n d T P c h (right) responses to cold Mean values from 10 rats for e a c h treamtent are presented
had higher levels than the shams (P < 0 001) (Fig 4) With hypophysectomy (group VI), the sham TFL response was also distinctly greater (P < l) 001), while the TPch response was the same in sham and hvpophysectomized rats (Fig 5) The histamine antagonist dlphenhydramine (group VII) had no influence on either the TFL or TPch effects of cold mcreases from the pre-cold TFL were 2 2 + (SD) 0 9 6 s with saline and 2 4 +_ 0 7 5 s with diphenhydramlne, for TPch, means were 2 8 +_ 2 48 and 2 7 + 3 10 s, respectively (Ftg 6) The optotd kappa antagonist Mr 1452 when administered after 2 h in the cold lowered TPch levels to an insignificant degree but when given prior to cold exposure TPch was reduced (P = 0 011) during the first h in the cold (Fig 7) When analgesia was assessed as the area under the t i m e - e t t e c t curve tar thts same interval both TFL and TPch responses were reduced by this agent (P = 0 03 and 0 02 respectively) Table I presents a summary of results
240 • ADRENALECTOMY(6 ROlS} 0 SHAMADRENALECTOMY(9 ROIS)
7O
140
•''"
?
Izo p~
6o p
11
BRES 15110
Antinociception in the rat induced by a cold environment Patrlcm F Osgood, Darnel B Carr, Arthur Kazmms, James W Kemp, Nancy E Atchison and S K Szyfelbem Department of Anesthesta, Analgestc Pepttde Research Umt, Massachusetts General Hospttal Harvard Medtcal ~chool Shrmers Burns lnstttute, Boston, MA ( U 5 A ) (Accepted 13 June 1989)
Key words Stress-reduced analgesm Environmental cold Op~old kappa receptor
Rats placed in a cold environment (4 °C) for 2 h had a sustained increase in tad fhck latency (TFL) as well as an increase m tad pinch latency (TPch) that was often biphaslc with an early peak response at 15 mm and a later, often higher, peak at 2 h Plasma beta-endorphm levels after a modest increase at 5 mm (24%) dechned throughout the remaining time m the cold The long-acting oplold antagomst naltrexone had no effect on TFL increases but led to greater increases m TPch (P < 0 041 In morphine-tolerant rats TFL response was the same as m controls but TPch increases were greater (P < 0 04) Rats exposed to 2 h of cold for 17 or 18 consecutive days generally developed tolerance to the analgesia of cold, 1 e TFL and TPch increases were diminished, however, the response to morphine on da~, 18 was the same as m rats never exposed to cold Adrenalectomy and hypophysectomy led to significantly smaller increases in TFL (P < 0 02 and P < 0 001 respectively) The TPch response in contrast was greater m adrenalectomlzed (P < 0 001) and the same m hypophvsectomlzed rats compared to sham controls An opmld kappa receptor antagomst (Mr 1452) given prior to cold reduced both TFL and TPch response during the first hour Thus the analgesia induced by cold appeared to shift from an early possibly kappa oplold to a later non-oplmd torm The TFL effects seemed to be under hormonal influence while the TPch were not
INTRODUCTION
In t h e p r e s e n t s t u d y , t h o u g h t h e n o n - o p t o l d e l e m e n t of the analgesia of cold was confirmed, there appeared to be
Endogenous by numerous
pam-mhlbltory systems may be actwated stressors or environmental
c h a n g e s 19 l~
a n o p l o l d c o m p o n e n t as well, m e d m t e d p e r h a p s by o p t o l d kappa receptors
I n a d d t t l o n , we f o u n d t h a t t h e tall f h c k
The analgesta thus induced may be optotd or non-oplold
l a t e n c y r e s p o n s e to c o l d s e e m e d to b e u n d e r h o r m o n a l
tn n a t u r e a n d s o m e f o r m s , p a r t i c u l a r l y t h e o p t o l d , a p p e a r
i n f l u e n c e w h t l e tall p i n c h l a t e n c y w a s n o t
to depend
upon
the Integrity of the pttultary-adrenal
a x i s 2 0 36 4o
MATERIALS AND METHODS
In a prehmmary
s t u d y we f o u n d t h a t r a t s e x p o s e d t o
a c o l d e n ~ t r o n m e n t (4 °C) f o r 2 h d e v e l o p e d a n a n a l g e s m that was naloxone,
largely
i n s e n s i t i v e to t h e
httle tnfluenced
op~old a n t a g o m s t
by I n h i b i t i o n o f a l p h a 2 o r
beta-adrenergxc receptors and accompanied by an early modest increase followed by a steady declme m plasma beta-endorphm lmmunoacttvlty throughout the remamd e r o f t h e 2-h t i m e in t h e c o l d 24 In these earher studies noclceptlon was assessed by tad flick l a t e n c y , a t e s t p a r t t c u l a r l y s e n s t t t v e t o a c t i v a t i o n o f o p t o t d p a t h w a y s rich in m u r e c e p t o r s 3~ 38 ~9 A t e s t u s i n g a p r e s s u r e r a t h e r t h a n a h e a t s t t m u l u s s h o u l d b e less influenced by conditions of cold, therefore, to further explore the apparent non-optold analgesta mduced by a cold envtronment pinch latency,
we h a v e n o w in a d d i t i o n a s s e s s e d tall
a test more
r e c e p t o r a c t i v a t i o n 3Z ~
Correspondence
s e n s t t l v e to op~otd k a p p a
Male Sprague-Dawley rats weighing 260 k (S D ) 60 1 g, were obtained from Tacomc Farms Germanto',~n, N ~ and maintained on a 12-h hght/dark cycle 5 or 6 to a cage v, lth free access to food and water for at least one week before an experiment Antlnoc~ceptlon (analgesia) was assessed b~ tail flick latency (TFL), determined as the mean ol 3 trials at one-ram intervals w~th a maximum exposure (cut off) to the heat stimulus of 7 s Another measure of analgesm tad pinch latenc~ (TPch) the time to a squeak response alter placing a hardwood clothespin on the base of the tad (pressure 1 27 kg) was assessed as the mean of 5 trials at l-mm intervals w~th a cut off ot 30 s The day before the experiment rats were trained to a vocal response to the TPch, to reduce baseline vanabdlty ~" On the day of the experiment each rat was placed m a separate cage with fret. access to water and food prehmmarv measurements made, then e~ther sahne or a drug administered following by a second set ot premeasures Rats were then placed for 2 h m a room held at 4 °C and TFL and TPch repeated at 15, 30, 60 and 120 ram, upon remo,~al from the cold measurements were repeated at intervals for up to 2 h In group 1 (6 rats) a cannula was placed in the right jugular veto (under 50 mg/kg pentobarbltal anesthesia) 2 days before exposure
P F Osgood Shrmers Burns Institute Room 25~ 5l Blossom Street Boston, MA 2114 U S A
0006-8993/90/$03 50 © 1990 Elsevier Science Publishers B V (Blome&cal Dwlslon)
12 to cold Blood samples (0 5 ml) for plasma heta-endorphm rad~oimmunoassax ~2 were drawn tmmediatelv before FFL and TPch at the times mentioned abo~e (with an additional sample taken alter 5 mln m the cold) Plasma was separated at once and lrozen until assa'v (for further details see Osgood et al 2s) Red blood cells were diluted back to the original volume with 0 9r~ sodium chloride (salme) vortexed and injected intravenously attcr each sample (between the times ot FFL and TPch measurement) In group II naltrexone (5 0 mg/kg) or saline m a comparable volume was injected subcutaneousl~ (s c ) 25 mm before cold (6 rats each treatment) Group III was made tolerant to morphine b~ placement under pentobarbital anesthesia (50 mg/kg), of 2 s c pellets each containing 75 mg of morphine (8 rats) or a placebo (8 rats) pellet (NIDA Drug Supply Program trom Research Triangle lnst N C ) Folerance to morphine ~as assumed v, hen TFL ,~aluc.s returned to the pre-pellet level (2-3 days) Group IVA (6 rats) were placed m the cold room for 2 h a day for ]7 consecutive days and TFL measured on days, 1 3, 8 14 and 17 Group IVB (12 rats) were placed m the cold for 18 consecunve days TFL and TPch were measured before and after 2 h of cold on the first and last da) as well as on the same intervening days a~ m Group IVA On day 18, after a return to pie-cold levels, TFL and TPch v, ere measured for a period of 2 h after lntrapentoneal (l p ) administration of 4 0 mg/kg of morphine In group IVC, 12 rats never exposed to cold were given the same dose of morphine (i p ) Group V rats were exposed to cold approximately one week after adrenalectomy (6 rats) or sham (9 rats) operation (Taconic Farms) Prior to and durmg cold, adrenaleetom~zed rats were given saline as drinking water Group VI rats were h~pophysectomized (10 rats) or shamhvpophysectomized (10 rats) and maintained on 5°6 dextrose solutmn before cold exposure To test for the completenes~ of hvpophvsectomy following the experiment, these rats were anesthetized and jugular venous blood samples drawn for measurement of the pltmtary hormone prolactm (Hazelton Blotechnologms Co Vienna, VA) Prolactln plasma levels were 31 _+ 16 2 (S D ) ng/ml m shams and 2 6 _+ 1 3 m hypophysectomized rats (normal levels are 15-.$0 ng/ml) Group VII were given the antihistamine diphenhydramme (2S mg/kg I p )~4 (9 rats) or saline (6 rats) one h before cold In the final group (VIII A and B) rats received Mr 1452, a predominant b opioid kappa receptor antagonist (a gift from Boehrlnger-Ingelheim, KG) in a dose ot 3 0 mg/kg (s c )io Group A were given Mr 1452 (6 rats) or saline (6 rats) after 2 h m the cold Group B received Mr 1452 (7 rats) or sahne (7 rats) one min before exposure to cold The TFL and TPch responses were determined as the level at each time of measurement minus the level immediately prior to cold The sum of each measure over the 2-h period in the cold was used for stanstlcal comparisons (paired, or non-paired t-tests and analysis ot variance [ANOVA]) In addition, m some experiments the area under the rime course-percent ot maximum possible response curve ( A U C ) was determined by the trapezoid method 32
6O
I
~°
I
Tad t- lick Latency ( T~I ~
2"(
~ 40
~ ~o ~zo i~
~/i..---
|TodRnchLotency(TPch) , ,~A.I~
,OO q3
5o
~0
n 6
_ I~1 ~nto C0id
0
15
30
60
(:ut
'~
120
150
~ 0
*
TIME/minutes)
Fig I The time course of the effects of 2 h exposure of rats to a temperature of 4 °C on plasma beta-endorphln immunoacnvlty (iB-EP), open squares, tall flick latency (TFL), open circles, and tail pinch latency (TPch), closed circles Mean values from 6 rats _+ the standard error of the mean (S E M ) are shown
(Fig 1), B-EP had returned to pre-cold levels by 24 h, however The oplold antagonist naltrexone (group II) had no effect on the TFL response to cold but actually augmented the TPch response (P < 0 037) (Fig 2) In rats tolerant to morphine (group III) the TFL was no different than in the rats with placebo pellets (compared as the overall response or at one h) but as with naltrexone TPch rose to higher levels in the tolerant rats (P < 0 04) (Fig 3) Repeated exposure to cold (groups 1VA and B) generally led to the development of tolerance to the TFL and TPch responses but m approximately 30% of each group (2 of 6 m IVA and 4 of 12 in IVB) there was no dlmunltlOn of these effects between the first and last day of cold, i e no tolerance was apparent In group A the TFL response on day 17 was less than on day 1 (P < 0005) at 30 min but not at 1 and 2 h In Group IVB, however, tolerance to the analgesic effect of cold,
Tad- Pinch Latency (T-Pch/
Tall Fhck Latency {TFL) 7O
140
( 6 Rats eoch ) 0 SALINE
/r--1I
NALTREXaNE
•
~so
t
RESULTS
•
C~
~, 30 W h e n rats (group I) were placed m a cold environment (4 °C) there was a rise m T F L that was sustained and an increase m TPch that was often biphaslc w~th a p e a k at 15 m m followed by a second p e a k at 2 h that was generally higher than the first (e g see Ftgs 3, 4 and 5) A f t e r r e m o v a l from the cold r o o m at 2 h these measures r e t u r n e d to pre-cold levels in a p p r o x i m a t e l y 30 mm Plasma b e t a - e n d o r p h l n (B-EP) after an early (5 m m in the cold) m i n o r increase (24%) t e n d e d to dechne during cold and c o n t i n u e d to fall m the 3-h period after cold
I
\
~°
I
]
I/
,20
L
~oo
t
H80
I
i
/
L
6o~
I
1 Q~ 40~
i
0 t ~ c°ld I
0
t I0
J
Cold ~ L__ I 1 _1 0 10 20 3 0 L
I
20
t
30 HOURS
o ~
Fig 2 The effect of subcutaneous (s c ) administration of 5 0 mg/kg of naltrexone 25 rain before exposure to cold (closed circles) or saline (open circles), 6 rats per treatment The ordinates are tail flick latency (left panel) and tall pinch latenc~ (right panel) m seconds, the abscissa is time in hours
13 Tad Flick Latency (TFL)
Toll Flick Latency (TFL)
Toll- Pinch Lalency (T-Pch) 5C
7"0 ~o
~4c
(8 Rols each) 0 PLACEBOPELLETS • MORPHINETOLERANT
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0 Sham HYPX (tO Rals)
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Cold r
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40
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Fig 3 The effect of cold in rats made tolerant to morphine by 2 subcutaneous (s c ) 75-rag morphine pellets (closed circles/ as compared to controls (2 s c placebo pellets open circles) Mean values from 8 rats lor e a c h treatment are depicted Axes are the same as in F~g 2
measured only at 2 h did develop A comparison of days 1, 3, 8, 14 and 18 showed no differences ( A N O V A ) nevertheless a comparison at day 1 with day 18 for TFL gave a difference of P < 0 03 and for TPch P < 0 01 On day 18, 2 h after removal from the cold, the TFL and TPch response to 4 0 mg/kg of morphine (1 p ) was entirely similar to that at a group of rats at room temperature never exposed to cold, peak increases were 2 1 +_(SD)I 56mTFLand82+_635smTPch, mthe former and 1 2 +_ 1 16 and 7 7 _+ 7 6 4 s m the latter group In adrenalectomIzed rats (group V), however the sham controls had a greater rise m ~IFL in the cold (P < 0 02) For TPch the reverse held adrenalectomized rats
Tail- Pinch Latency
Toll Fhck Latency (TFL)
I
0
110
_~ 210
[ L
310
0
Cold L
I0
j 210
310
HOURS
HOURS
(T-Pch)
80
Fig 5 The effect of hypophysectomv (HYPX, closed c~rcles) and sham hvpophysectomg (open circles) on T F L (lett) a n d T P c h (right) responses to cold Mean values from 10 rats for e a c h treamtent are presented
had higher levels than the shams (P < 0 001) (Fig 4) With hypophysectomy (group VI), the sham TFL response was also distinctly greater (P < l) 001), while the TPch response was the same in sham and hvpophysectomized rats (Fig 5) The histamine antagonist dlphenhydramine (group VII) had no influence on either the TFL or TPch effects of cold mcreases from the pre-cold TFL were 2 2 + (SD) 0 9 6 s with saline and 2 4 +_ 0 7 5 s with diphenhydramlne, for TPch, means were 2 8 +_ 2 48 and 2 7 + 3 10 s, respectively (Ftg 6) The optotd kappa antagonist Mr 1452 when administered after 2 h in the cold lowered TPch levels to an insignificant degree but when given prior to cold exposure TPch was reduced (P = 0 011) during the first h in the cold (Fig 7) When analgesia was assessed as the area under the t i m e - e t t e c t curve tar thts same interval both TFL and TPch responses were reduced by this agent (P = 0 03 and 0 02 respectively) Table I presents a summary of results
240 • ADRENALECTOMY(6 ROlS} 0 SHAMADRENALECTOMY(9 ROIS)
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140
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