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Nicotine preferentially stimulates dopamine release in the limbic system of freely moving rats
European Journal of Pharmacology, 132 (1986) 337-338
337
Elsevier EJP 039RC
Rapid communication
Nicotine preferentially stimulates dopamine release in the limbic system of freely moving rats A s s u n t a I m p e r a t o , Angelina Mulas and G a e t a n o Di C h i a r a Institute of Experimental Pharmacology and Toxicology, Universi(v of Cagliari, Viale A. Diaz 182, 09100 Cagliari, Italy Received 10 November 1986, accepted 12 November 1986
We have recently observed that various substances of abuse such as ethanol (Imperato and Di Chiara, 1985), amphetamine, cocaine and morphine-like opiates (Di Chiara and Imperato, in press) preferentially stimulate dopamine (DA) release in the mesolimbic system. We now describe the effect of nicotine on the release and metabolism of DA as estimated by brain dialysis in the nucleus accumbens, the major target of the mesolimbic DA system and in the dorsal caudate, a terminal area of the nigrostriatal DA system. Male Sprague-Dawley rats (200-250 g) were implanted under halothane anaesthesia with two dialysis tubes (Vitafiber, Amicon) 200 /xm o.d., inserted transversally, one through the accumbens and the other through the dorsal caudate according to the technique extensively described by us (Imperato and Di Chiara, 1985). Ringer solution was pumped through the dialysis tube at a constant rate of 2/~l/min. DA and its main metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were estimated in 20 min samples of the dialysate by high performance liquid chromatography according to the procedure already reported (Imperato and Di Chiara, 1985). The behaviour of the rats was videotaped, then analyzed by recognizing certain specific behavioural items (see fig. 1) and expressed as the % of time spent by the rat for each behavioural item during every 20 min of observation. Experiments were performed 24 h after the implantation of the dialysis tube on rats moving freely in a Persepx cylinder (40 cm diameter x 40 cm height). The 0014-2999/86/$03.50 © 1986 Elsevier Science Publishers B.V.
basal output of DA, DOPAC and HVA 24 h after the implant was as follows (pmol/20 min, means _+ S.E.M. of 4 rats); nucleus accumbens: DA 0.14 _+ 0.01; DOPAC 24 _+ 2.5; HVA 17.5 _+ 1.6; dorsal caudate: DA 0.36 _+ 0.03; DOPAC 36 _+ 3.5; HVA 28.3 _+ 3.2. As shown in fig. 1, a dose of 0.6 m g / k g s.c. of nicotine (hydrogen tartrate, dissolved in saline 0.1 ml/100 g, expressed as the base), which has been shown to be rewarding in rats in a place preference test (Fudala et al., 1985), stimulated DA release maximally (by 100%) in the nucleus accumbens and by 50% in the dorsal caudate; it increased the output of DOPAC and of HVA only in the nucleus accumbens. The rats showed a complex syndrome of behavioural stimulation characterized by ambulation, grooming an exploratory activity. Nicotine-induced stimulation of DA release was dose-related and the EDs0 (mg/kg s.c.) with 95% confidence limits for this effect was about 5 times lower in -the accumbens (0.32, 0.24-0.41) as compared to the caudate (1.85, 1.42-2.4). The nonoverlapping 95% confidence limits of the EDs0s for stimulation of DA release in the two areas indicate that the difference is significant. In order to investigate the specificity and the mechanism of the stimulatory effect of nicotine on DA release, a dose of 0.6 m g / k g s.c. of nicotine was tested in rats pretreated with a centrally acting antagonist of nicotinic cholinergic receptors such as mecamylamine hydrochloride (1 m g / k g s.c., 40 min before nicotine). Another group of rats was
338 250. ACCUMBENS
1501
N ~'
__j
DA
r % ; HVA 100
-
"J00PAc
0
u~ 2oo CAUDATE rn Li_ o 150
IOO
~-" 0 Z w Q- 100
• C~(~MNG
[~LOCOHOT~N
L~
rl o
~e
pretreated with a peripheral nicotine receptor blocker such as hexamethonium bromide (1.0 m g / k g s.c., 40 min before nicotine). Pretreatment with mecamylamine completely prevented the stimulation of DA release induced by 0.6 m g / k g of nicotine in the accumbens while hexamethonium failed to significantly influence the stimulation (saline, 0.83 + 0.10; nicotine, 1.375 + 0.16 *; mecamylamine + nicotine, 0.92 _ 0.12n s; hexamethonium + nicotine, 1.425 __+0.18 *, DA output from the accumbens cumulated for 2 h and expressed in pmol; means + S.E.M. of the results obtained in 5 rats per group; * P < 0.05 versus saline; n s. not significantly different from saline). At the doses administered mecamylamine and hexamethonium failed to significantly influence DA release. It thus appears that the nicotine-induced stimulation of DA release arises from centrally located nicotinic cholinergic receptors. These results provide biochemical evidence for a role of limbic DA in the central actions of nicotine and suggest that, by analogy with other drugs of abuse (Di Chiara and Imperato, in press), the rewarding properties of nicotine are linked to stimulation of DA neurotransmission in the limbic system.
References
1
2
3hr
TIME AFTER NICOTINE
Fig. 1. Effect of nicotine (0.6 mg/kg s.c.) on the in vivo release of dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) from the nucleus accumbens and from the dorsal caudate and on spontaneous behaviour. Behaviour is expressed as the % of time spent by the rat every 20 min in performing the items indicated in the figure. N = 6; * P < 0.05, ** P < 0.001) versus the results obtained after saline.
Di Chiara, G. and A. Imperato, 1985, Ethanol preferentially stimulates dopamine release in the nucleus accumbens of freely moving rats, European J. Pharmacol. 115, 131 Di Chiara, G. and A. Imperato, Preferential stimulation of dopamine release in the nucleus accumbens by opiates, alcohol and barbiturates: studies with transcerebral dialysis in freely moving rats, Ann. N.Y. Acad. Sci. (in press). Fudala, P.J., K.W. Teoh, and E.T. Iwamoto, 1985, Pharmacologic characterization of nicotine-induced conditioned place preference, Pharmacol. Biochem. Behav. 22, 237. Imperato, A. and G. Di Chiara, 1985, Dopamine release and metabolism in awake rats after systemic neuroleptics as studied by trans-striatal dialysis, J. Neurosci. 5 (2), 297.
337
Elsevier EJP 039RC
Rapid communication
Nicotine preferentially stimulates dopamine release in the limbic system of freely moving rats A s s u n t a I m p e r a t o , Angelina Mulas and G a e t a n o Di C h i a r a Institute of Experimental Pharmacology and Toxicology, Universi(v of Cagliari, Viale A. Diaz 182, 09100 Cagliari, Italy Received 10 November 1986, accepted 12 November 1986
We have recently observed that various substances of abuse such as ethanol (Imperato and Di Chiara, 1985), amphetamine, cocaine and morphine-like opiates (Di Chiara and Imperato, in press) preferentially stimulate dopamine (DA) release in the mesolimbic system. We now describe the effect of nicotine on the release and metabolism of DA as estimated by brain dialysis in the nucleus accumbens, the major target of the mesolimbic DA system and in the dorsal caudate, a terminal area of the nigrostriatal DA system. Male Sprague-Dawley rats (200-250 g) were implanted under halothane anaesthesia with two dialysis tubes (Vitafiber, Amicon) 200 /xm o.d., inserted transversally, one through the accumbens and the other through the dorsal caudate according to the technique extensively described by us (Imperato and Di Chiara, 1985). Ringer solution was pumped through the dialysis tube at a constant rate of 2/~l/min. DA and its main metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were estimated in 20 min samples of the dialysate by high performance liquid chromatography according to the procedure already reported (Imperato and Di Chiara, 1985). The behaviour of the rats was videotaped, then analyzed by recognizing certain specific behavioural items (see fig. 1) and expressed as the % of time spent by the rat for each behavioural item during every 20 min of observation. Experiments were performed 24 h after the implantation of the dialysis tube on rats moving freely in a Persepx cylinder (40 cm diameter x 40 cm height). The 0014-2999/86/$03.50 © 1986 Elsevier Science Publishers B.V.
basal output of DA, DOPAC and HVA 24 h after the implant was as follows (pmol/20 min, means _+ S.E.M. of 4 rats); nucleus accumbens: DA 0.14 _+ 0.01; DOPAC 24 _+ 2.5; HVA 17.5 _+ 1.6; dorsal caudate: DA 0.36 _+ 0.03; DOPAC 36 _+ 3.5; HVA 28.3 _+ 3.2. As shown in fig. 1, a dose of 0.6 m g / k g s.c. of nicotine (hydrogen tartrate, dissolved in saline 0.1 ml/100 g, expressed as the base), which has been shown to be rewarding in rats in a place preference test (Fudala et al., 1985), stimulated DA release maximally (by 100%) in the nucleus accumbens and by 50% in the dorsal caudate; it increased the output of DOPAC and of HVA only in the nucleus accumbens. The rats showed a complex syndrome of behavioural stimulation characterized by ambulation, grooming an exploratory activity. Nicotine-induced stimulation of DA release was dose-related and the EDs0 (mg/kg s.c.) with 95% confidence limits for this effect was about 5 times lower in -the accumbens (0.32, 0.24-0.41) as compared to the caudate (1.85, 1.42-2.4). The nonoverlapping 95% confidence limits of the EDs0s for stimulation of DA release in the two areas indicate that the difference is significant. In order to investigate the specificity and the mechanism of the stimulatory effect of nicotine on DA release, a dose of 0.6 m g / k g s.c. of nicotine was tested in rats pretreated with a centrally acting antagonist of nicotinic cholinergic receptors such as mecamylamine hydrochloride (1 m g / k g s.c., 40 min before nicotine). Another group of rats was
338 250. ACCUMBENS
1501
N ~'
__j
DA
r % ; HVA 100
-
"J00PAc
0
u~ 2oo CAUDATE rn Li_ o 150
IOO
~-" 0 Z w Q- 100
• C~(~MNG
[~LOCOHOT~N
L~
rl o
~e
pretreated with a peripheral nicotine receptor blocker such as hexamethonium bromide (1.0 m g / k g s.c., 40 min before nicotine). Pretreatment with mecamylamine completely prevented the stimulation of DA release induced by 0.6 m g / k g of nicotine in the accumbens while hexamethonium failed to significantly influence the stimulation (saline, 0.83 + 0.10; nicotine, 1.375 + 0.16 *; mecamylamine + nicotine, 0.92 _ 0.12n s; hexamethonium + nicotine, 1.425 __+0.18 *, DA output from the accumbens cumulated for 2 h and expressed in pmol; means + S.E.M. of the results obtained in 5 rats per group; * P < 0.05 versus saline; n s. not significantly different from saline). At the doses administered mecamylamine and hexamethonium failed to significantly influence DA release. It thus appears that the nicotine-induced stimulation of DA release arises from centrally located nicotinic cholinergic receptors. These results provide biochemical evidence for a role of limbic DA in the central actions of nicotine and suggest that, by analogy with other drugs of abuse (Di Chiara and Imperato, in press), the rewarding properties of nicotine are linked to stimulation of DA neurotransmission in the limbic system.
References
1
2
3hr
TIME AFTER NICOTINE
Fig. 1. Effect of nicotine (0.6 mg/kg s.c.) on the in vivo release of dopamine (DA), dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) from the nucleus accumbens and from the dorsal caudate and on spontaneous behaviour. Behaviour is expressed as the % of time spent by the rat every 20 min in performing the items indicated in the figure. N = 6; * P < 0.05, ** P < 0.001) versus the results obtained after saline.
Di Chiara, G. and A. Imperato, 1985, Ethanol preferentially stimulates dopamine release in the nucleus accumbens of freely moving rats, European J. Pharmacol. 115, 131 Di Chiara, G. and A. Imperato, Preferential stimulation of dopamine release in the nucleus accumbens by opiates, alcohol and barbiturates: studies with transcerebral dialysis in freely moving rats, Ann. N.Y. Acad. Sci. (in press). Fudala, P.J., K.W. Teoh, and E.T. Iwamoto, 1985, Pharmacologic characterization of nicotine-induced conditioned place preference, Pharmacol. Biochem. Behav. 22, 237. Imperato, A. and G. Di Chiara, 1985, Dopamine release and metabolism in awake rats after systemic neuroleptics as studied by trans-striatal dialysis, J. Neurosci. 5 (2), 297.