Brurn Rcwirc,i~ Bullefm, Vol. 2X. pp. 493-496. Printed in the USA.
1992 Copyright
+
0361.9230/1)2 $5.00t .OO 1492 Pergamon Press Ltd.
RAPID COMMUNICATION
Long-Lasting Suppression of Alcohol Preference in Rats Following Serotoni~ Receptor Blockade by Ritanserin IZABELA
PANOCKA
AND MAURI210
MASSI”’
~epart~~ent of Behavioral P~~sju~ug~, institute of Genetics and A?~imai Breeding Polish Academy of Sciences, Jastszebiec, 05-551 Mrokow, Poland “Institute of Pharmacology, Universit’v of Camerino, 62032 Camerino. ftuly Received 7 June 1991 PANOCKA. I. AND M. MASSI. Long-lasting suppwssion ~~f‘nk~~ho~ prt$wntv in tim ./i)/kwing .seroionin rwplor hhckadt~ hj’ rmn.wrin. BRAIN RES BULL 28(3) 493-499, 199?.-Rats with developed preference for 3 % ethanol were injected subcutaneously (SC) with 10 mgikg of the 5HTZ antagonist ritanserin for 9 days. This resulted in a marked and significant suppression of alcohol preference, as compared to controls. The effect was very hong-las~ng, as shown by the fact that it was still evident up to 20 days after the end of the treatment. Since ritanserin shows some affinity also for D,-dopaminergic receptors (even though much lower than for 5HT, receptors). for comparison, other rats were injected SC for 9 days with 0.0625 mgkg of haloperidol or with its vehicle. The effect of haloperidol treatment was low and short-lasting. Depletion of endogenous serotonin by p-chlorophenylalanine (600 mg/kg x 3 days) completely abolished the suppression of alcohol preference by ritanserin. These results suggest that: I) the ritanserin-induced reduction of alcohol preference is not due to dopaminergic blockade, 2) that the effect of ritanserin is completely dependent on the endo~enous serotoninergic mechanisms. Ritanserm
Haloperidol
Alcohol preference -
p-Chlorophenylalanine
METHOD
A large body of evidence indicates that serotonin is involved in alcohol preference and in the maintainence of volitional alcohol intake (8. 17, 20). Serotonin uptake inhibitors, such as zimeldine and fluoxetine, which increase 5-HT concentration at ~stsyna~t~c level, as well as 5-W’ agonists are known to inhibit alcohol intake in rats and in humans (1, 5, 14, 19.
Animals Male Wistat rats (Charles River, Calco Co., Italy) weighing 300~0~ g were employed. They were kept in individu~ cages on a 12: 12 h light-dark cycle and fed ad lib (diet No. 4RF18, Mucedola, Settimo Milanese, Italy).
21. 23, 24).
However, it was recently shown that reduction of 3% alcohol intake in rats and decrease of alcohol intake in humans can also be achieved by the 5-HT receptor antagonist ritanserin (l&18). The present study was aimed to further evaluate the effect of ritanserin on alcohol intake in the rat, and to verify whether its effect is just dependent on its 5-HT blocking activity or on other aspects of the pharmacological profile of the molecule. Although ritanserin is highly selective for S-HT, and 5-HT,, receptors, it binds with lower affinity also to Hi-histamine and D,-dopamine receptors (10,12). Particular interest on the affinity of ritanserin for D2 receptors comes from the notion that the dopaminergic system is involved in the rewarding aspects of alcohol intake (3, 4, 9). ‘Requests for reprints Camerino (MC), Italy.
should be addressed
to Dr. Maurizio
Massi.
D?%@ I) Ritanserin was a generous gift of Janssen Pharmaceutics (Beerse, Belgium); 2) haloperidol (Haldol, Janssen Farmaceutici, Rome, Italy) and 3) p-chlorophenylalanine (PCPA; SIGMA, Milan, Italy) were purchased from commercial sources. Drug Administrati~?~ Ritanserin was dissolved at the concentration of 10 mg/ml in a vehicle containing 20% propylene glycol, 0.5% lactic acid and NaOH 2 N to adjust the pH to 5. Institute
493
of Pharmacology,
University
of Camerino,
Via Scalzino
5, 62032
494
PAhW’KA
w x z k
AND
MASS1
20-
o-,
1
I
,
1
I,
,
12345678
9 days
E
1
2
3
4
5
6
7
8
9
IO
days
FIG. 3. Alcohol preference in rats pretreated with FCPA (B and C) or with PCPA vehicle (A) and then treated with ritanserin (B) or its vehicle (A and C). Values are meanskS.E.M. of 5 rats (B) and 6 rats (A and C). Difference from controls as in Fig. I.
were given free choice between 3% alcohol and water (6,16).
011 I
Experimental Procedure I
I
I
I
3
5
I
1
I
7
I
I
9
1
,
1
11
13
I
1
15
1
1
I
17
I
I
19
days
FIG. 1. Alcohol preference in rats during (Panel A) and after (Panel B) treatment with ritanserin (BIT) or with its vehicle (CO). Values are means+ S.E.M. of 5 subjects. Statistical difference from controls: ‘p
1992 Copyright
+
0361.9230/1)2 $5.00t .OO 1492 Pergamon Press Ltd.
RAPID COMMUNICATION
Long-Lasting Suppression of Alcohol Preference in Rats Following Serotoni~ Receptor Blockade by Ritanserin IZABELA
PANOCKA
AND MAURI210
MASSI”’
~epart~~ent of Behavioral P~~sju~ug~, institute of Genetics and A?~imai Breeding Polish Academy of Sciences, Jastszebiec, 05-551 Mrokow, Poland “Institute of Pharmacology, Universit’v of Camerino, 62032 Camerino. ftuly Received 7 June 1991 PANOCKA. I. AND M. MASSI. Long-lasting suppwssion ~~f‘nk~~ho~ prt$wntv in tim ./i)/kwing .seroionin rwplor hhckadt~ hj’ rmn.wrin. BRAIN RES BULL 28(3) 493-499, 199?.-Rats with developed preference for 3 % ethanol were injected subcutaneously (SC) with 10 mgikg of the 5HTZ antagonist ritanserin for 9 days. This resulted in a marked and significant suppression of alcohol preference, as compared to controls. The effect was very hong-las~ng, as shown by the fact that it was still evident up to 20 days after the end of the treatment. Since ritanserin shows some affinity also for D,-dopaminergic receptors (even though much lower than for 5HT, receptors). for comparison, other rats were injected SC for 9 days with 0.0625 mgkg of haloperidol or with its vehicle. The effect of haloperidol treatment was low and short-lasting. Depletion of endogenous serotonin by p-chlorophenylalanine (600 mg/kg x 3 days) completely abolished the suppression of alcohol preference by ritanserin. These results suggest that: I) the ritanserin-induced reduction of alcohol preference is not due to dopaminergic blockade, 2) that the effect of ritanserin is completely dependent on the endo~enous serotoninergic mechanisms. Ritanserm
Haloperidol
Alcohol preference -
p-Chlorophenylalanine
METHOD
A large body of evidence indicates that serotonin is involved in alcohol preference and in the maintainence of volitional alcohol intake (8. 17, 20). Serotonin uptake inhibitors, such as zimeldine and fluoxetine, which increase 5-HT concentration at ~stsyna~t~c level, as well as 5-W’ agonists are known to inhibit alcohol intake in rats and in humans (1, 5, 14, 19.
Animals Male Wistat rats (Charles River, Calco Co., Italy) weighing 300~0~ g were employed. They were kept in individu~ cages on a 12: 12 h light-dark cycle and fed ad lib (diet No. 4RF18, Mucedola, Settimo Milanese, Italy).
21. 23, 24).
However, it was recently shown that reduction of 3% alcohol intake in rats and decrease of alcohol intake in humans can also be achieved by the 5-HT receptor antagonist ritanserin (l&18). The present study was aimed to further evaluate the effect of ritanserin on alcohol intake in the rat, and to verify whether its effect is just dependent on its 5-HT blocking activity or on other aspects of the pharmacological profile of the molecule. Although ritanserin is highly selective for S-HT, and 5-HT,, receptors, it binds with lower affinity also to Hi-histamine and D,-dopamine receptors (10,12). Particular interest on the affinity of ritanserin for D2 receptors comes from the notion that the dopaminergic system is involved in the rewarding aspects of alcohol intake (3, 4, 9). ‘Requests for reprints Camerino (MC), Italy.
should be addressed
to Dr. Maurizio
Massi.
D?%@ I) Ritanserin was a generous gift of Janssen Pharmaceutics (Beerse, Belgium); 2) haloperidol (Haldol, Janssen Farmaceutici, Rome, Italy) and 3) p-chlorophenylalanine (PCPA; SIGMA, Milan, Italy) were purchased from commercial sources. Drug Administrati~?~ Ritanserin was dissolved at the concentration of 10 mg/ml in a vehicle containing 20% propylene glycol, 0.5% lactic acid and NaOH 2 N to adjust the pH to 5. Institute
493
of Pharmacology,
University
of Camerino,
Via Scalzino
5, 62032
494
PAhW’KA
w x z k
AND
MASS1
20-
o-,
1
I
,
1
I,
,
12345678
9 days
E
1
2
3
4
5
6
7
8
9
IO
days
FIG. 3. Alcohol preference in rats pretreated with FCPA (B and C) or with PCPA vehicle (A) and then treated with ritanserin (B) or its vehicle (A and C). Values are meanskS.E.M. of 5 rats (B) and 6 rats (A and C). Difference from controls as in Fig. I.
were given free choice between 3% alcohol and water (6,16).
011 I
Experimental Procedure I
I
I
I
3
5
I
1
I
7
I
I
9
1
,
1
11
13
I
1
15
1
1
I
17
I
I
19
days
FIG. 1. Alcohol preference in rats during (Panel A) and after (Panel B) treatment with ritanserin (BIT) or with its vehicle (CO). Values are means+ S.E.M. of 5 subjects. Statistical difference from controls: ‘p
