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Effects of dapiprazole, clonidine and yohimbine on the development of dependence and withdrawal behaviour in mice
73
Drug and Alcohol Dependence,
23 (1989173- 77 Elsevier Scientific Publisher Ireland Ltd.
Effects of dapiprazole, clonidine and yohimbine on the development of dependence and withdrawal behaviour in mice P. Valeri, B. Martinelli, Institute
of Pharmacology
G. Pimpinella
and Pharmacognosy,
University
and C. Severini
of Rome ‘La Sapiensa’, 00185 Rome Utalyl
(Received September 26th, 19881
There is evidence that central noradrenergic hyperactivity is involved in the manifestation of the major signs and symptoms of the opiate withdrawal syndrome. In order to assess whether or not the noradrenergic system is also implicated in the development of opiate dependence, we studied dapiprazole, an alpha-l selective adrenoceptor antagonist, clonidine and yohimbine using the acute dependence model in mice. When administered just before naloxone, after dependence development, all three drugs reduce abstinence signs. When injected 15 min before morphine to observe the drugs’ effects on the development of dependence, dapiprazole depresses all the symptoms registered while clonidine decreases only jumping, but increases paw and head shakes. None of these drugs affects the naloxone precipitated withdrawal syndrome when injected 1 h before morphine. It is suggested that the noradrenergic system is involved in both the manifestation of the withdrawal syndrome and in the development of opiate dependence. Diapiprazole may be a useful tool in patients and in pharmacological studies of dependence and abstinence. Key WO&XMorphine; dependence; withdrawal; dapiprazole; clonidine; yohimbine
Introduction
Opiate drugs induce in animals and man a complex chain of behavioural and biochemical events which lead to physiological and psychological dependence and the withdrawal syndrome. Many neurotransmitter and neuroregulatory systems (see Redmond and Krystal, 1984 for revew [l]) are involved in these phenomena, but the noradrenergic system seems to have a prominent role [2,3]. Sympathetic noradrenergic neurons are depressed by opiates [4] and become hyperactive during the abstinence syndrome and this hyperactivity may account for some of its manifestations [5]. Clonidine and other alpha-2 adrenoceptor agonists suppress many of the effects of opiate withdrawal in both animals and humans indicating important interactions of the opiate and adrenergic systems [2,5- lo]. Dapiprazole, a selec-
tive alpha-l adrenergic antagonist [ll], suppresses the opioid withdrawal symptoms in both animals and patients (12,131,further supporting the notion that noradrenergic hyperactivity is linked with the withdrawal syndrome. The present study was undertaken to establish whether dapiprazole and other adrenergic drugs such as clonidine and yohimbine affect not only the expression of the opiate withdrawal syndrome but also the development of opiate dependence. In mice we scored the stereotyped jumping precipitated by a narcotic antagonist as has been done in many studies [14 -181 and widely accepted as one of the most reliable indices for quantifying physical dependence in mice [19]. The acute dependence model was used in order to avoid the disadvantages of multiple injections of morphine or pellet implantation and to focus on the very early stages of physical dependence.
0376-8716/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
74
Material and Methods
Swiss Albino male CD-l mice (Charles River, Italy) weighing 20 -25 g were housed 10 - 12 per cage in a room controlled for temperature (23 f 1°C) and light (light on 08:00- 18:00 h) kept in the laboratory for 4 days prior to experiments. According to Smits [20] mice were injected i.p. with morphine (25 mg/kgl and 2 h later with naloxone (12.5 mglkgl. Drugs were administered i.p. 15 min before naloxone or 15 -60 min before morphine injection. A similar procedure was used for the control animals which received the same volume of saline instead of the drugs. Immediately after the naloxone injection the mice were palced two at a time in plexiglass cylinders (25 cm high, 20 cm diameter1 and the number of mice jumping and the number of jumps per mouse during a 10 min period were recorded. Head and paw shakes were also observed. Each mouse was tested once. Withdrawal symptoms were scored by an observer ‘blinded’ to the experimental treatment. Experiments were carried out between 09:OO14:00 h. Intracerebroventricular (i.c.v.1 administration of dapiprazole or saline was performed in intact animals as described by Laursen and Belknap [21]. Hydrochloric drugs were dissolved in saline and injected at 10 ml/kg i.p. and 5 @mouse i.c.v. All doses refer to the salt form. The results were analyzed by ANOVA followed by Dunnet t-test. Ail drug doses were based on available data [12,24,23]. Dapiprazole was kindly provided by Angelini (Rome), clonidine by Boehringer (Ingelheiml yohimbine by Sigma (St. Louis) naloxone and morphine by SIFAC (Milan). Results
The administration of naloxone (12.5 mg/kg) following a single dose of morphine (25 mg/kg) caused sustained jumping behaviour and paw and head shakes (Table Il. The mice show all the signs, although less marked, of abrupt withdrawal typical of chronically treated mice,
Effect of dapiprazole. clonidine and yohimbine Table I. injected i.p. 15 min before naloxone on acute morphine withdrawal in mice. *P < 0.05; **P < 0.02; l**P < 0.01. Mice jumping
Jumping episodes (LC-c SE.)
Paw and head shakes
Saline Dapiprazole
10/12
32.0 + 7.53
++
(7.5) Clonidine (0.125) (0.5) Saline Yohimhine (5)
10/12
11.6 + 5.20*
+
H/14 11/16 30138
12.6 f 3.19** 8.9 f 2.74’** 26.4 & 4.34
++ 0 ++
18139
9.9 2 2.84***
Treatment (mg/kg)
+
except for diarrhea. To confirm the validity of the model used, the effect of clonidine and yohimbine, alpha-2 adrenoceptor agonist and antagonist, respectively, on the acute withdrawal syndrome was also verified. Dapiprazole, at a dose known to be effective in the withdrawal syndrome in chronically treated mice [12], significantly attenuated all the abstinence signs considered when injected 15 min before naloxone (12.5 mglkgl. Similarly, clonidine and yohimbine reduced both jumping and paw and head shakes. The inspection of dapiprazole, clonidine, and yohimbine-treated animals revealed no motor impairment. The experiments with clonidine and dapiprazole were repeated and the same results were obtained. Table I shows the data of a typical Table II. Effect of different doses of dapiprazole, injected i.c.v. 15 min before naloxone (6.25 mglkg) on acute morphine withdrawal. *P < 0.05; **P < 0.01. Treatment (mg mouse)
Mice jumping
Jumping episodes LX + S.E.)
Saline Dapiprazoie
12/16
30.8 -+ 5.89
++
(0.5) (1) (3)
11116 7116 lo/16
23.8 f 5.63 10.8 + 5.35* 11.4 f 3.97**
+ 0 0
Paw and head shakes
75 Effect of dapiprazole, clonidine and yohimbine Table III. injected i.p. 15 min before morphine, on acute morphine withdrawal in mice. *P < 0.05; **P< 0.001. Treatment
(mg/W
Saline Dapiprazole (5) (10) Clonidine (0.125) (0.5) Yohimbine (5)
Paw and head shakes
Mice jumping
Jumping episodes (x f S.E.)
14/16
36.3 f 7.11
-I-+
14/16 14/16
22.4 f 4.69 13.3 f 3.391
++ +
10/15 2/16
14.7 + 5.31* 2.2 f 1.89+*
++ +++
10/12
32.7 + 8.31
+
experiment. The data on yohimbine are the result of three distinct experiments because of the unexpected results. To explore whether the effect of dapiprazole was centrally mediated, we injected the drug i.c.v. and obtained a notable suppression of morphine withdrawal symptoms in a doserelated fashion similar to the effect of systemic administration (Table 111.Clonidine and yohimbine were not included in this kind of experiment as their central activities, at least regarding some withdrawal signs have been studied previously [22 - 241. Both dapiprazole and clonidine, when administered 15 min before morphine to ascertain the Effect of dapiprazole. clonidine and yohimbine Table IV. injected i.p. 1 h before morphine, on acute morphine withdrawal in mice. Treatment (mglkg)
Mice jumping
Jumping episodes (x f SE.)
Saline Dapiprazole (10) Clonidine (0.1251 to.51 Yobimbine (5)
8/10
32.3 f
6.68
++
8/10
37.2 + 13.53
++
8.10 8110
24.2 + 6.70 37.6 f 10.21
++ ++
6/10
20.1 f
+
4.65
Paw and head shakes
role of the adrenergic systems in the development of opiate dependence, were capable of decreasing jumping episodes subsequent to naloxone treatment. As shown in Table III, the jumping decrease is dose-related and statistically significant for the two clonidine doses used, whereas for dapiprazole statistical significance was reached only with the highest dose. Yohimbine administered 15 min before morphine had no effect on jumping, but reduced paw and head shakes as did dapiprazole. However, this sign was enhanced by the higher dose of clonidine. Table IV shows that neither dapiprazole, clonidine nor yohimbine, when injected 1 h before morphine, influenced the jumping behaviour in mice. Yohimbine seemed to reduce paw and head shakes. Discussion
In the present study we tried to assess whether the noradrenergic system could be involved in the development of morphine dependence. Few studies have been carried out on the effects of different transmitter systems on the development of morphine dependence [25,26]. The demonstration that dapiprazole and clonidine, injected 15 min prior to naloxone, decrease jumping behaviour and head and paw shakes further indicates the involvement of the adrenergic system in the naloxone-precipitated syndrome and is additional proof of the utility of the acute dependence model in studying the adapative changes produced by opiates. In fact, in this model dapiprazole depresses the signs of withdrawal as previously observed with chronically injected mice [12]. Since dapiprazole is a selective alpha-l adrenoceptor blocker [ll] its antiwithdrawal effect is unlikely to depend on other types of receptors as could occur with other drugs used in previous studies. It is difficult to explain the antiwithdrawal effect of yohimbine in this study, as this drug is known to counteract the effect of clonidine, including some signs of withdrawal in rats. Although our results are in agreement with
76
those described by others for body shakes in rats [27], but in contrast with other data [28], it is not clear why both an alpha-2 antagonist and alpha-2 agonist suppress withdrawal signs. The dose of yohimbine, reported to be able to act on alpha-2 adrenoceptors and counteract clonidine effects [23] could be high enough to affect also alpha-l adrenoceptors, behaving like dapiprazole in this model. Different areas in the central nervous system, where alpha adrenoceptor subtypes are not identical [29], may play important roles in the abstinence syndrome. Although other properties of yohimbine may be implicated, a better understanding of the endogenous substances or their reciprocal influences, the release of which is regulated by alpha-2 and opioid receptors, could provide a more reasonable explanation of our result obtained with yohimbine. It has been suggested that the anti-withdrawal action of clonidine is mediated by alpha-2 receptors of the locus coeruleus, thereby reducing the increased noradrenaline turnover during withdrawal [30]. However, injections of clonidine produce a marked sympathomimetic and sympatholytic effect as well as an intensification of some signs in the withdrawal syndrome [22], due to the fact that clonidine as an adrenergic agonist has only specificity for alpha-2 receptors which control the various withdrawal symptoms in different ways [27,31]. This could explain why clonidine injected 15 min before morphine decreases jumping and increases paw and head shakes. The fact that mice treated with clonidine and dapiprazole 15 min before morphine show a lower incidence of jumping suggests that the noradrenergic system plays a role also in the development of dependence. The results with dapiprazole and clonidine are in contrast to those obtained in rats since the administration of phentolamine and clonidine concomitantly with morphine did not modify any of the withdrawal signs considered [25]. Most probably the difference in inducing morphine dependence and the animal species is responsible for this fact. The observation that neither dapiprazole nor
clonidine injected 1 h before morphine seem to affect the abstinence syndrome is probably due to their short half-life and indicates that the effect of an acute block or stimulation of alphaadrenoceptors prior to morphine do not modify the devleopment of dependence [32,33]. However, further studies with drugs known to affect other systems will ascertain whether the observed effect on dependence development is specific or not. Studies are in progress with drugs interfering with the serotonin system. While dapiprazole attenuates all signs of withdrawal, clonidine exacerbates paw and head shakes, when injected 15 min before morphine. Dapiprazole in certain situations seems to reduce the overall severity of the opiate withdrawal symptoms. These data suggest the involvment of the noradrenergic system not only in the withdrawal syndrome but also in the devleopment of dependence. The pharmacological features of dapiprazole may have interesting clinical implications. References 1 2 3 4 5 6 7 8 9 10 11 12
13
D.E. Redmond and J.H. Krystal, Ann. Rev. Neurosci., 7 (1984) 443-478. D.S. Charney, et al., Life Sci., 35 (1984) 1263- 1272. D. Clovet, in: A.J. Friedhoff (Ed.), Catecholamines and Behavior, Plenum, New York, 1975, p. 103. J. Hughes, H.W. Kosteriitz and F.M. Leslie, Br. J. Pharmacol., 53 (1975) 371-381. D.E. Redmond Jr., J. Clin. Psychiatry 43 (Suppl. 6) (1982). D.R. Meyer and S.B. Sparber, Pharmacologist, 18 (1976) 236 (Abs.). R. Laverly and R.H. Roth, Brain Res., 182 (1980) 482485. M.S. Gold, D.E. Redmond Jr. and H.B. Kleber, Lancet, ii (1978) 599 - 602. D.S. Charney et al., Arch. Gen. Psychiatry, 38 (1981) 1273- 1277. J.J. Buccafusco, D.C. Marshall and R.M. Turner, Life Sci.. 35 (1984) 1401- 1408. P. Valeri, M. Palmery and B. Silvestrini, Drugs Exp. Clin. Res., 14 (1988) 53- 58. B. Siivestrini and P. Valeri, in: G. Biggio et al., (Eds.), Modulation of Central and Peripheral Transmitter Function, Fidia Research Series, Liviana Press, Springer Verlag, Berlin, 1986. E. Sternieri et al., Cob. Int. Neuro-Psychopharmacol., Vol. 2 13th Congress, Jerusalem.
77
14 15 16 17 18 19 20 21 22 23 24
S. Ramaswamy and J.S. Bapna, Neuropharmacology, 26(1987)111-113. M.R. Dzoljic et al., Arch. Int. Pharmacodyn., 283 (1986) 222-228. P.C. Contreras and A.E. Takemori, J. Pharmacol. Exp. Ther., 229 (1984) 21- 26. D.G. Lange et al., J. Pharmacol. Exp. Ther., 224 (1984) 13-20. O.L. Cheney and A. Goldstein, Nature, 232 (1971) 477 478. E.L. Way, H.H. Loh and F. Shen, J. Pharmacol. Exp. Ther., 167 (1969) l-8. S.E. Smits, Res. Comm. Chem., Pathol. Pharmacol., 10 (1975) 651- 661. S.E. Laursen and J.K. Belknap, J. Pharmacol. Methods, 16 (1985) 355-357. L.F. Tseng, H.H. Loh and E.T. Wei, Eur. J. Pharmacol., 30 (1975) 93 -99. M.R. Godlberg and D. Robertson, Pharmacol. Rev., 35 (1983) 143- 180. P.S. Distefano and O.L. Brown, J. Pharmacol. Exp. Ther., 233 (1985) 339 - 344.
25 26 27 28 29 30
31 32 33
L. Cervo et al., Psychopharmacology, 74 (1981) 271274. R. Samanin, L. Cervo and C. Rochat, J. Pharm. Pharmacol., 32 (1980) 150. J.W. Van der Laan, Naunym-Schmildeberg’s, Arch. Pharmacol., 329 (1985) 293- 298. L.P. Dwoskin, B.T. Neal and S.B. Sparber, Eur. J. Pharmacol., 90 (1983) 269 - 273. J. Marwaha and G.K. Aghajanian, J. Pharmacol. Exp. Ther., 222 (1982) 287 - 293. M.S. Gold et al., in: H. La1 and S. Fieldin, (Eds.), Psychopharmacology of Clonidine, Liss, New York, 1981, pp. 285-298. I. Zebrowska-Lupina et al., Naunyn-Schmildeberg’s Arch. Pharmacol., 297 (1977) 227-231. P. Valeri, M. Palmery and B. Catanese, Pharmacol. Res. Comm., 17 (1985) 417. B. Jarrott and S. Spector, J. Pharmacol. Exp. Ther.. 207 (1978) 195 - 202.
Drug and Alcohol Dependence,
23 (1989173- 77 Elsevier Scientific Publisher Ireland Ltd.
Effects of dapiprazole, clonidine and yohimbine on the development of dependence and withdrawal behaviour in mice P. Valeri, B. Martinelli, Institute
of Pharmacology
G. Pimpinella
and Pharmacognosy,
University
and C. Severini
of Rome ‘La Sapiensa’, 00185 Rome Utalyl
(Received September 26th, 19881
There is evidence that central noradrenergic hyperactivity is involved in the manifestation of the major signs and symptoms of the opiate withdrawal syndrome. In order to assess whether or not the noradrenergic system is also implicated in the development of opiate dependence, we studied dapiprazole, an alpha-l selective adrenoceptor antagonist, clonidine and yohimbine using the acute dependence model in mice. When administered just before naloxone, after dependence development, all three drugs reduce abstinence signs. When injected 15 min before morphine to observe the drugs’ effects on the development of dependence, dapiprazole depresses all the symptoms registered while clonidine decreases only jumping, but increases paw and head shakes. None of these drugs affects the naloxone precipitated withdrawal syndrome when injected 1 h before morphine. It is suggested that the noradrenergic system is involved in both the manifestation of the withdrawal syndrome and in the development of opiate dependence. Diapiprazole may be a useful tool in patients and in pharmacological studies of dependence and abstinence. Key WO&XMorphine; dependence; withdrawal; dapiprazole; clonidine; yohimbine
Introduction
Opiate drugs induce in animals and man a complex chain of behavioural and biochemical events which lead to physiological and psychological dependence and the withdrawal syndrome. Many neurotransmitter and neuroregulatory systems (see Redmond and Krystal, 1984 for revew [l]) are involved in these phenomena, but the noradrenergic system seems to have a prominent role [2,3]. Sympathetic noradrenergic neurons are depressed by opiates [4] and become hyperactive during the abstinence syndrome and this hyperactivity may account for some of its manifestations [5]. Clonidine and other alpha-2 adrenoceptor agonists suppress many of the effects of opiate withdrawal in both animals and humans indicating important interactions of the opiate and adrenergic systems [2,5- lo]. Dapiprazole, a selec-
tive alpha-l adrenergic antagonist [ll], suppresses the opioid withdrawal symptoms in both animals and patients (12,131,further supporting the notion that noradrenergic hyperactivity is linked with the withdrawal syndrome. The present study was undertaken to establish whether dapiprazole and other adrenergic drugs such as clonidine and yohimbine affect not only the expression of the opiate withdrawal syndrome but also the development of opiate dependence. In mice we scored the stereotyped jumping precipitated by a narcotic antagonist as has been done in many studies [14 -181 and widely accepted as one of the most reliable indices for quantifying physical dependence in mice [19]. The acute dependence model was used in order to avoid the disadvantages of multiple injections of morphine or pellet implantation and to focus on the very early stages of physical dependence.
0376-8716/89/$03.50 0 1989 Elsevier Scientific Publishers Ireland Ltd. Printed and Published in Ireland
74
Material and Methods
Swiss Albino male CD-l mice (Charles River, Italy) weighing 20 -25 g were housed 10 - 12 per cage in a room controlled for temperature (23 f 1°C) and light (light on 08:00- 18:00 h) kept in the laboratory for 4 days prior to experiments. According to Smits [20] mice were injected i.p. with morphine (25 mg/kgl and 2 h later with naloxone (12.5 mglkgl. Drugs were administered i.p. 15 min before naloxone or 15 -60 min before morphine injection. A similar procedure was used for the control animals which received the same volume of saline instead of the drugs. Immediately after the naloxone injection the mice were palced two at a time in plexiglass cylinders (25 cm high, 20 cm diameter1 and the number of mice jumping and the number of jumps per mouse during a 10 min period were recorded. Head and paw shakes were also observed. Each mouse was tested once. Withdrawal symptoms were scored by an observer ‘blinded’ to the experimental treatment. Experiments were carried out between 09:OO14:00 h. Intracerebroventricular (i.c.v.1 administration of dapiprazole or saline was performed in intact animals as described by Laursen and Belknap [21]. Hydrochloric drugs were dissolved in saline and injected at 10 ml/kg i.p. and 5 @mouse i.c.v. All doses refer to the salt form. The results were analyzed by ANOVA followed by Dunnet t-test. Ail drug doses were based on available data [12,24,23]. Dapiprazole was kindly provided by Angelini (Rome), clonidine by Boehringer (Ingelheiml yohimbine by Sigma (St. Louis) naloxone and morphine by SIFAC (Milan). Results
The administration of naloxone (12.5 mg/kg) following a single dose of morphine (25 mg/kg) caused sustained jumping behaviour and paw and head shakes (Table Il. The mice show all the signs, although less marked, of abrupt withdrawal typical of chronically treated mice,
Effect of dapiprazole. clonidine and yohimbine Table I. injected i.p. 15 min before naloxone on acute morphine withdrawal in mice. *P < 0.05; **P < 0.02; l**P < 0.01. Mice jumping
Jumping episodes (LC-c SE.)
Paw and head shakes
Saline Dapiprazole
10/12
32.0 + 7.53
++
(7.5) Clonidine (0.125) (0.5) Saline Yohimhine (5)
10/12
11.6 + 5.20*
+
H/14 11/16 30138
12.6 f 3.19** 8.9 f 2.74’** 26.4 & 4.34
++ 0 ++
18139
9.9 2 2.84***
Treatment (mg/kg)
+
except for diarrhea. To confirm the validity of the model used, the effect of clonidine and yohimbine, alpha-2 adrenoceptor agonist and antagonist, respectively, on the acute withdrawal syndrome was also verified. Dapiprazole, at a dose known to be effective in the withdrawal syndrome in chronically treated mice [12], significantly attenuated all the abstinence signs considered when injected 15 min before naloxone (12.5 mglkgl. Similarly, clonidine and yohimbine reduced both jumping and paw and head shakes. The inspection of dapiprazole, clonidine, and yohimbine-treated animals revealed no motor impairment. The experiments with clonidine and dapiprazole were repeated and the same results were obtained. Table I shows the data of a typical Table II. Effect of different doses of dapiprazole, injected i.c.v. 15 min before naloxone (6.25 mglkg) on acute morphine withdrawal. *P < 0.05; **P < 0.01. Treatment (mg mouse)
Mice jumping
Jumping episodes LX + S.E.)
Saline Dapiprazoie
12/16
30.8 -+ 5.89
++
(0.5) (1) (3)
11116 7116 lo/16
23.8 f 5.63 10.8 + 5.35* 11.4 f 3.97**
+ 0 0
Paw and head shakes
75 Effect of dapiprazole, clonidine and yohimbine Table III. injected i.p. 15 min before morphine, on acute morphine withdrawal in mice. *P < 0.05; **P< 0.001. Treatment
(mg/W
Saline Dapiprazole (5) (10) Clonidine (0.125) (0.5) Yohimbine (5)
Paw and head shakes
Mice jumping
Jumping episodes (x f S.E.)
14/16
36.3 f 7.11
-I-+
14/16 14/16
22.4 f 4.69 13.3 f 3.391
++ +
10/15 2/16
14.7 + 5.31* 2.2 f 1.89+*
++ +++
10/12
32.7 + 8.31
+
experiment. The data on yohimbine are the result of three distinct experiments because of the unexpected results. To explore whether the effect of dapiprazole was centrally mediated, we injected the drug i.c.v. and obtained a notable suppression of morphine withdrawal symptoms in a doserelated fashion similar to the effect of systemic administration (Table 111.Clonidine and yohimbine were not included in this kind of experiment as their central activities, at least regarding some withdrawal signs have been studied previously [22 - 241. Both dapiprazole and clonidine, when administered 15 min before morphine to ascertain the Effect of dapiprazole. clonidine and yohimbine Table IV. injected i.p. 1 h before morphine, on acute morphine withdrawal in mice. Treatment (mglkg)
Mice jumping
Jumping episodes (x f SE.)
Saline Dapiprazole (10) Clonidine (0.1251 to.51 Yobimbine (5)
8/10
32.3 f
6.68
++
8/10
37.2 + 13.53
++
8.10 8110
24.2 + 6.70 37.6 f 10.21
++ ++
6/10
20.1 f
+
4.65
Paw and head shakes
role of the adrenergic systems in the development of opiate dependence, were capable of decreasing jumping episodes subsequent to naloxone treatment. As shown in Table III, the jumping decrease is dose-related and statistically significant for the two clonidine doses used, whereas for dapiprazole statistical significance was reached only with the highest dose. Yohimbine administered 15 min before morphine had no effect on jumping, but reduced paw and head shakes as did dapiprazole. However, this sign was enhanced by the higher dose of clonidine. Table IV shows that neither dapiprazole, clonidine nor yohimbine, when injected 1 h before morphine, influenced the jumping behaviour in mice. Yohimbine seemed to reduce paw and head shakes. Discussion
In the present study we tried to assess whether the noradrenergic system could be involved in the development of morphine dependence. Few studies have been carried out on the effects of different transmitter systems on the development of morphine dependence [25,26]. The demonstration that dapiprazole and clonidine, injected 15 min prior to naloxone, decrease jumping behaviour and head and paw shakes further indicates the involvement of the adrenergic system in the naloxone-precipitated syndrome and is additional proof of the utility of the acute dependence model in studying the adapative changes produced by opiates. In fact, in this model dapiprazole depresses the signs of withdrawal as previously observed with chronically injected mice [12]. Since dapiprazole is a selective alpha-l adrenoceptor blocker [ll] its antiwithdrawal effect is unlikely to depend on other types of receptors as could occur with other drugs used in previous studies. It is difficult to explain the antiwithdrawal effect of yohimbine in this study, as this drug is known to counteract the effect of clonidine, including some signs of withdrawal in rats. Although our results are in agreement with
76
those described by others for body shakes in rats [27], but in contrast with other data [28], it is not clear why both an alpha-2 antagonist and alpha-2 agonist suppress withdrawal signs. The dose of yohimbine, reported to be able to act on alpha-2 adrenoceptors and counteract clonidine effects [23] could be high enough to affect also alpha-l adrenoceptors, behaving like dapiprazole in this model. Different areas in the central nervous system, where alpha adrenoceptor subtypes are not identical [29], may play important roles in the abstinence syndrome. Although other properties of yohimbine may be implicated, a better understanding of the endogenous substances or their reciprocal influences, the release of which is regulated by alpha-2 and opioid receptors, could provide a more reasonable explanation of our result obtained with yohimbine. It has been suggested that the anti-withdrawal action of clonidine is mediated by alpha-2 receptors of the locus coeruleus, thereby reducing the increased noradrenaline turnover during withdrawal [30]. However, injections of clonidine produce a marked sympathomimetic and sympatholytic effect as well as an intensification of some signs in the withdrawal syndrome [22], due to the fact that clonidine as an adrenergic agonist has only specificity for alpha-2 receptors which control the various withdrawal symptoms in different ways [27,31]. This could explain why clonidine injected 15 min before morphine decreases jumping and increases paw and head shakes. The fact that mice treated with clonidine and dapiprazole 15 min before morphine show a lower incidence of jumping suggests that the noradrenergic system plays a role also in the development of dependence. The results with dapiprazole and clonidine are in contrast to those obtained in rats since the administration of phentolamine and clonidine concomitantly with morphine did not modify any of the withdrawal signs considered [25]. Most probably the difference in inducing morphine dependence and the animal species is responsible for this fact. The observation that neither dapiprazole nor
clonidine injected 1 h before morphine seem to affect the abstinence syndrome is probably due to their short half-life and indicates that the effect of an acute block or stimulation of alphaadrenoceptors prior to morphine do not modify the devleopment of dependence [32,33]. However, further studies with drugs known to affect other systems will ascertain whether the observed effect on dependence development is specific or not. Studies are in progress with drugs interfering with the serotonin system. While dapiprazole attenuates all signs of withdrawal, clonidine exacerbates paw and head shakes, when injected 15 min before morphine. Dapiprazole in certain situations seems to reduce the overall severity of the opiate withdrawal symptoms. These data suggest the involvment of the noradrenergic system not only in the withdrawal syndrome but also in the devleopment of dependence. The pharmacological features of dapiprazole may have interesting clinical implications. References 1 2 3 4 5 6 7 8 9 10 11 12
13
D.E. Redmond and J.H. Krystal, Ann. Rev. Neurosci., 7 (1984) 443-478. D.S. Charney, et al., Life Sci., 35 (1984) 1263- 1272. D. Clovet, in: A.J. Friedhoff (Ed.), Catecholamines and Behavior, Plenum, New York, 1975, p. 103. J. Hughes, H.W. Kosteriitz and F.M. Leslie, Br. J. Pharmacol., 53 (1975) 371-381. D.E. Redmond Jr., J. Clin. Psychiatry 43 (Suppl. 6) (1982). D.R. Meyer and S.B. Sparber, Pharmacologist, 18 (1976) 236 (Abs.). R. Laverly and R.H. Roth, Brain Res., 182 (1980) 482485. M.S. Gold, D.E. Redmond Jr. and H.B. Kleber, Lancet, ii (1978) 599 - 602. D.S. Charney et al., Arch. Gen. Psychiatry, 38 (1981) 1273- 1277. J.J. Buccafusco, D.C. Marshall and R.M. Turner, Life Sci.. 35 (1984) 1401- 1408. P. Valeri, M. Palmery and B. Silvestrini, Drugs Exp. Clin. Res., 14 (1988) 53- 58. B. Siivestrini and P. Valeri, in: G. Biggio et al., (Eds.), Modulation of Central and Peripheral Transmitter Function, Fidia Research Series, Liviana Press, Springer Verlag, Berlin, 1986. E. Sternieri et al., Cob. Int. Neuro-Psychopharmacol., Vol. 2 13th Congress, Jerusalem.
77
14 15 16 17 18 19 20 21 22 23 24
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