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Disruptive effects of naloxone on development of morphine tolerance
Pergamon Prese
Life Scieacea, Vol . 21, pp . 509-512 Printed In The U.S .A .
DISRUPTIVE EFFECTS OF NALOXONE ON DBVELOPI~NT OF MORPHINE 10LERANCE Rayannd P. Icesner and Dee 1 . Priano Departsent of Psychology University of Utah Salt Lake City, Utah 84112 (Received in final form July 6, 1977) Su~ar~! In rats the development of one-trial tolerance to the analgesic actions of mrphine is disrVpted by the postadministratian of naloxane at 5 min, 3 hrs, or 24 hrs. Naloxons injections alone 24 or 48 hrs prior to the analgesic test failed to counteract morphine induced analgesia . It is suggested that naloxane initiates long term biochemical changes that oppose those produced by morphine . Recently, it has been shown that electroconvulaive shock (ECS) or frontal cortex stimulation treatments applied after a pretreatment with morphine are capable of disrupting, on a time-dependent basis, the develop ment of tolerance to either the analgesic or locosotor excitaat action of mrphine (1,2) . In other words, these treatments are capable of disrupting the development of tolerance when applied immediately after an initial morphine experience, but became ineffective when delayed 2 or 3 hours . Similarly, Mushlin and Cochin (3) have shown that naloxone, a specific morphine antagonist (4), injected 35 min after morphine pretreatment, disrupted the development of tolerance to mrphine. Even though the latter study did not test for time-dependent effects, the similarity in results among the above mentioned studies suggests the possibility that ECS could have disrupted the development of mrphine tolerance by a direct antagonistic action similar to naloxgne . The purpose of the present study was to test whether post-morphine injections of naloxone could produce similar flee-dependent susceptibility gradients of the type previously reported for ECS or frontal cortex stimulation. Methods Fifty-nine male Long-Evens rats (weighing between 300-450 grams) were used as subjects . Morphine sulfate, naloxone hydrochloride, or isotonic saline solutions were administered intra~feritoneally as described below . The aninals were randomly assigned to seven groups . The first four groups received an initial injection of morphine (30 mg/kg) followed either 5 min (n~8), 3 hrs (n~8), or 24 hrs (n~8) later by an -injection of naloxone (.8 mg/kg) or S nin (n~14) later by an injection of saline . The initial dose of 30 mg/kg was selected because in our laboratory it represented the
509.
510
Naloxone and Morphine Tolerance
Vol . 21, No . 4, 1977
threshold dose above which there was a high incidence of gortality . The regaining three groups received an initial injection of saline folloxed either 5 gin (n~7) or 24 hrs (n~6) later by an injection of naloxone ( .8 gg/kg) or 5 gin (n~8) later by an injection of saline . Forty-eight hours later each anigal received an injection of gorphine (15 gg/kg) . The morphine test dose of 15 gg/kg was selected because at that level the greatest difference in responsiveness to shock (analgesic test) was found between saline and gorphine injected anigals . This difference xas not as pronounced at other morphine dose levels . Thirty minutes after the second injection, each animal was given a shock threshold test to detergine its sensitivity to pain . The testing apparatus consisted of a clear plexiglasa square box, 25 cm on each side, with a grid floor composed of 1/8" petal rods spaced 1 cn apart through xhich electric shocks could be delivered . The procedure was similar to that described by (5,6) . Each anigal was introduced and adapted for one minute to the sgall box. After the adaptation period, footshocks (starting with .l gA intensity) were delivered in ascending order of shock intensity until ~jugp and squeal responses xere observed for three consecutive footahocks or until a 10 gA intensity xas reached . Shocks were delivered via a constant current scrambler for 0 .5 sec; pulse repetition rate was 200 Hz and 4 cosec . pulse duration . From .1 gA to 1 .0 mA successive test shocks were increased by .1 mA and frog 1 to 10 mA by .2 gA . The intershock interval was approxigately 6 sec, but shocks were delivered only when the anigal xas Baking contact xith the grid floor with all four paxs . The behavioral responses to each shock were observed and recorded by an experimenter who was blind to prior treatment conditions . The shock intensities required to initiate flinch , ~, orj~ and squeal responses and reach the criterion of three A consecutive jump and squeal responses were used as dependent neasurea . flinch was defined as a response to shock characterized by crouching or a rapid change in posture without any concogitant govegent of the paws . A was characterized by a rapid raising of one or more paxs often owed by rapid running. A uj~ and s ueal xas characterized by the cogbination of jugging and two or gore able vocalizations . Results No significant differences were observed among the groups for the flinch and juap threshold geasures . Since the criterion geasure reflected the same pattern of results as the jump and squeal threshold measure, only the j~ and squeal threshold data are presented. The results are shown in Figure 1 and indicate that (a) naloxone injected either 5 gin, 180 min, or 24 hrs after the initial morphine injection failed to produce a reduction in jump and squeal threshold relative to the morphine-saline-morphine control groom, indicating a disruption in development of tolerance, and (b) naloxone injected 24 or 48 hrs before the pain threshold test does not It is important to note that the alter the analgesic action of morphine . level of tolerance development in the gorphine-saline-morphine group is very similar to that reported previously using the same experigental procedures (1) . A one-way analysis of variance indicated that there were
Vol .
21, No . 4, 1977
Nalo~one aad Morphine Tolerance
SaI1M Smln . SouM
NorphiM AIarpMM SdIM AlorphlM IbrphIM SdIM ßmln. Smin. Smln . IBOmin . 2~M. 241r. SdIM NoloxoM NdoxoM NaloxoM NobxaM NdoxeM
FIG . 1 Effects of post-morphine injections of naloxane upon development of morphine tolerance as measured by seen shock intensity (+SE) for jump and squeal threshold . significant differences among the groups (F ~ 2 .38, df ~ 6/52, P < .OS) . Further analysis with a Duncan Multiple Range Test revealed that (a) the groups that received naloxane at either 5 min, 3 hrs, or 24 hr delay showed a significantly higher jump and squeal threshold compared to morphinesaline-morphine control group (P < .05), (b) none of the other critical comparisons reached significance . Discussion The results indicate that post-Morphine injections of naloxone adsinistered at a 5 sin, 3 hr, or 24 hr delay disrupted the development of tolerance to the analgesic actions of morphine . Since naloxone was effec tive at all three time delays, there is a possibility that naloxone disrupted the dsvelapsent of tolerance because of proactive influences upon processes directly associated with the analgesic test 24, 45, or 48 hrs later . Fbwever, the results of the present study show that following saline pretreataent a naloxane injection 24 or 48 hrs prior to the analgesic test failed to counteract morphine-induced analgesia . These results rule out a direct effect of naloxone on the analgesia test because concurrent injections of
512
Nalosione and Morphiae Tolerance
Vol . 21, No . 4, 1977
naloxone and eorphine result in aleost cospiete attenuation of the eorphineinduced analgesia (7,8) . Purthersore, injections of only naloxons lower or fail to affect pain thresholds (8,9,10) . In contrast to naloxone, ECS and frontal cortex stieulation (1) disrupted the develapeent of tolerance on a ties-dependent basis, e .g ., these treatsenta were effective at a 5 sin but ineffective at a 3 hr delay . The sechanisn of action of naloxone in disrupting tolerance is not entirely clear. One possibility is that naloxone adsinistered after a sorphine injection initiates long tore biochesical changes that oppose those produced by sorphine and thus, countsract the developsent of tolerance . For exasple, morphine initially decreases, while naloxane initially enhances, levels of dopaaine especially in the striatus (11,12,13) . Additional work is needed to specify sore clearly the exact eechanise of action of naloxone in preventing noreal developsent of eorphine tolerance. Acknowledgesents This work was supported by U .S . Public Health Service Grant MH 25706-02 . References 1. 2. 3. 4. 5. 6. 7, 8, 9, 10 . 11 . 12, 13 .
R. P . I~SNER, D . J . PRIANO, and J . R. DEWITT, Science 194 1079-1081 (1976), I . P . STOLERMAN, P . BUNi~R, C . A, JOtIIdSON, M . E . JARVIK, W . KRIVOY, and E. ZIMMERMAN, Neur harmacol . 15 309-313 (1976) . B . E . MUSHLIN and J . CO IN, Life Sci . 18 797-802 (1976) . W. R . MARTIN, Phareacol . Rev. 19 463-521 (1967) . K . A . BONNET an-~K, É . ~ETLRSON, Pharmacol ., Biochem., Behav. _3 47-55 (1975) . W . 0 . EVANS, Psychophareacol . 2 318-325 (1961) . R . MARKOWITZ, J . JACOBSON, G. BAIN, and C. KORNETSKY, J_. Phareacoi . ~. Ther . 199 385-388 (1976) . A . PET T andM. WALTER, Life Sçi. 19 1023-1032 (1976) . A . GOLDSTEIN, G . T . PRYOR, L . S . OTIS, and F . LARSEN, Life Sçi . 18 599-604 (1976) . J . J . JACOB, E. C . TREMBi11Y, snd M . COLOl~EL, Psychopharmacol . 37 217-223 (1974) . E. T. IWAMOTO, I . K . HO, and E . L . WAY, J_. Pharmacol . ~. Ther , 187 558-567 (1973) . D . H. CLOUET and M. RATHER, Science 168 854-856 (1970) . L . M. GUNNE, J, JOHNSON, and~icEHur . J . Phareacol . _ 5 338-342 (1969) .
Life Scieacea, Vol . 21, pp . 509-512 Printed In The U.S .A .
DISRUPTIVE EFFECTS OF NALOXONE ON DBVELOPI~NT OF MORPHINE 10LERANCE Rayannd P. Icesner and Dee 1 . Priano Departsent of Psychology University of Utah Salt Lake City, Utah 84112 (Received in final form July 6, 1977) Su~ar~! In rats the development of one-trial tolerance to the analgesic actions of mrphine is disrVpted by the postadministratian of naloxane at 5 min, 3 hrs, or 24 hrs. Naloxons injections alone 24 or 48 hrs prior to the analgesic test failed to counteract morphine induced analgesia . It is suggested that naloxane initiates long term biochemical changes that oppose those produced by morphine . Recently, it has been shown that electroconvulaive shock (ECS) or frontal cortex stimulation treatments applied after a pretreatment with morphine are capable of disrupting, on a time-dependent basis, the develop ment of tolerance to either the analgesic or locosotor excitaat action of mrphine (1,2) . In other words, these treatments are capable of disrupting the development of tolerance when applied immediately after an initial morphine experience, but became ineffective when delayed 2 or 3 hours . Similarly, Mushlin and Cochin (3) have shown that naloxone, a specific morphine antagonist (4), injected 35 min after morphine pretreatment, disrupted the development of tolerance to mrphine. Even though the latter study did not test for time-dependent effects, the similarity in results among the above mentioned studies suggests the possibility that ECS could have disrupted the development of mrphine tolerance by a direct antagonistic action similar to naloxgne . The purpose of the present study was to test whether post-morphine injections of naloxone could produce similar flee-dependent susceptibility gradients of the type previously reported for ECS or frontal cortex stimulation. Methods Fifty-nine male Long-Evens rats (weighing between 300-450 grams) were used as subjects . Morphine sulfate, naloxone hydrochloride, or isotonic saline solutions were administered intra~feritoneally as described below . The aninals were randomly assigned to seven groups . The first four groups received an initial injection of morphine (30 mg/kg) followed either 5 min (n~8), 3 hrs (n~8), or 24 hrs (n~8) later by an -injection of naloxone (.8 mg/kg) or S nin (n~14) later by an injection of saline . The initial dose of 30 mg/kg was selected because in our laboratory it represented the
509.
510
Naloxone and Morphine Tolerance
Vol . 21, No . 4, 1977
threshold dose above which there was a high incidence of gortality . The regaining three groups received an initial injection of saline folloxed either 5 gin (n~7) or 24 hrs (n~6) later by an injection of naloxone ( .8 gg/kg) or 5 gin (n~8) later by an injection of saline . Forty-eight hours later each anigal received an injection of gorphine (15 gg/kg) . The morphine test dose of 15 gg/kg was selected because at that level the greatest difference in responsiveness to shock (analgesic test) was found between saline and gorphine injected anigals . This difference xas not as pronounced at other morphine dose levels . Thirty minutes after the second injection, each animal was given a shock threshold test to detergine its sensitivity to pain . The testing apparatus consisted of a clear plexiglasa square box, 25 cm on each side, with a grid floor composed of 1/8" petal rods spaced 1 cn apart through xhich electric shocks could be delivered . The procedure was similar to that described by (5,6) . Each anigal was introduced and adapted for one minute to the sgall box. After the adaptation period, footshocks (starting with .l gA intensity) were delivered in ascending order of shock intensity until ~jugp and squeal responses xere observed for three consecutive footahocks or until a 10 gA intensity xas reached . Shocks were delivered via a constant current scrambler for 0 .5 sec; pulse repetition rate was 200 Hz and 4 cosec . pulse duration . From .1 gA to 1 .0 mA successive test shocks were increased by .1 mA and frog 1 to 10 mA by .2 gA . The intershock interval was approxigately 6 sec, but shocks were delivered only when the anigal xas Baking contact xith the grid floor with all four paxs . The behavioral responses to each shock were observed and recorded by an experimenter who was blind to prior treatment conditions . The shock intensities required to initiate flinch , ~, orj~ and squeal responses and reach the criterion of three A consecutive jump and squeal responses were used as dependent neasurea . flinch was defined as a response to shock characterized by crouching or a rapid change in posture without any concogitant govegent of the paws . A was characterized by a rapid raising of one or more paxs often owed by rapid running. A uj~ and s ueal xas characterized by the cogbination of jugging and two or gore able vocalizations . Results No significant differences were observed among the groups for the flinch and juap threshold geasures . Since the criterion geasure reflected the same pattern of results as the jump and squeal threshold measure, only the j~ and squeal threshold data are presented. The results are shown in Figure 1 and indicate that (a) naloxone injected either 5 gin, 180 min, or 24 hrs after the initial morphine injection failed to produce a reduction in jump and squeal threshold relative to the morphine-saline-morphine control groom, indicating a disruption in development of tolerance, and (b) naloxone injected 24 or 48 hrs before the pain threshold test does not It is important to note that the alter the analgesic action of morphine . level of tolerance development in the gorphine-saline-morphine group is very similar to that reported previously using the same experigental procedures (1) . A one-way analysis of variance indicated that there were
Vol .
21, No . 4, 1977
Nalo~one aad Morphine Tolerance
SaI1M Smln . SouM
NorphiM AIarpMM SdIM AlorphlM IbrphIM SdIM ßmln. Smin. Smln . IBOmin . 2~M. 241r. SdIM NoloxoM NdoxoM NaloxoM NobxaM NdoxeM
FIG . 1 Effects of post-morphine injections of naloxane upon development of morphine tolerance as measured by seen shock intensity (+SE) for jump and squeal threshold . significant differences among the groups (F ~ 2 .38, df ~ 6/52, P < .OS) . Further analysis with a Duncan Multiple Range Test revealed that (a) the groups that received naloxane at either 5 min, 3 hrs, or 24 hr delay showed a significantly higher jump and squeal threshold compared to morphinesaline-morphine control group (P < .05), (b) none of the other critical comparisons reached significance . Discussion The results indicate that post-Morphine injections of naloxone adsinistered at a 5 sin, 3 hr, or 24 hr delay disrupted the development of tolerance to the analgesic actions of morphine . Since naloxone was effec tive at all three time delays, there is a possibility that naloxone disrupted the dsvelapsent of tolerance because of proactive influences upon processes directly associated with the analgesic test 24, 45, or 48 hrs later . Fbwever, the results of the present study show that following saline pretreataent a naloxane injection 24 or 48 hrs prior to the analgesic test failed to counteract morphine-induced analgesia . These results rule out a direct effect of naloxone on the analgesia test because concurrent injections of
512
Nalosione and Morphiae Tolerance
Vol . 21, No . 4, 1977
naloxone and eorphine result in aleost cospiete attenuation of the eorphineinduced analgesia (7,8) . Purthersore, injections of only naloxons lower or fail to affect pain thresholds (8,9,10) . In contrast to naloxone, ECS and frontal cortex stieulation (1) disrupted the develapeent of tolerance on a ties-dependent basis, e .g ., these treatsenta were effective at a 5 sin but ineffective at a 3 hr delay . The sechanisn of action of naloxone in disrupting tolerance is not entirely clear. One possibility is that naloxone adsinistered after a sorphine injection initiates long tore biochesical changes that oppose those produced by sorphine and thus, countsract the developsent of tolerance . For exasple, morphine initially decreases, while naloxane initially enhances, levels of dopaaine especially in the striatus (11,12,13) . Additional work is needed to specify sore clearly the exact eechanise of action of naloxone in preventing noreal developsent of eorphine tolerance. Acknowledgesents This work was supported by U .S . Public Health Service Grant MH 25706-02 . References 1. 2. 3. 4. 5. 6. 7, 8, 9, 10 . 11 . 12, 13 .
R. P . I~SNER, D . J . PRIANO, and J . R. DEWITT, Science 194 1079-1081 (1976), I . P . STOLERMAN, P . BUNi~R, C . A, JOtIIdSON, M . E . JARVIK, W . KRIVOY, and E. ZIMMERMAN, Neur harmacol . 15 309-313 (1976) . B . E . MUSHLIN and J . CO IN, Life Sci . 18 797-802 (1976) . W. R . MARTIN, Phareacol . Rev. 19 463-521 (1967) . K . A . BONNET an-~K, É . ~ETLRSON, Pharmacol ., Biochem., Behav. _3 47-55 (1975) . W . 0 . EVANS, Psychophareacol . 2 318-325 (1961) . R . MARKOWITZ, J . JACOBSON, G. BAIN, and C. KORNETSKY, J_. Phareacoi . ~. Ther . 199 385-388 (1976) . A . PET T andM. WALTER, Life Sçi. 19 1023-1032 (1976) . A . GOLDSTEIN, G . T . PRYOR, L . S . OTIS, and F . LARSEN, Life Sçi . 18 599-604 (1976) . J . J . JACOB, E. C . TREMBi11Y, snd M . COLOl~EL, Psychopharmacol . 37 217-223 (1974) . E. T. IWAMOTO, I . K . HO, and E . L . WAY, J_. Pharmacol . ~. Ther , 187 558-567 (1973) . D . H. CLOUET and M. RATHER, Science 168 854-856 (1970) . L . M. GUNNE, J, JOHNSON, and~icEHur . J . Phareacol . _ 5 338-342 (1969) .