Acta physiol. scand. 1975. 93. 563-565 From the Department of Pharmacology, University of Helsinki, and the Research Laboratories of the State Alcohol Monopoly (ALKO), Helsinki, Finland
Dopamine and Noradrenaline Content in the Brain of Rat Strains Selected for their Alcohol Intake BY
LIISAAHTEEand KALERVO ERIKSSON
Hereditary mechanisms are involved in the control of alcohol drinking in rats and mice (Mardones ef al. 1953, McLearn and Rodgers 1957). By outbreeding rats and selecting breeding animals that differ in their alcohol consumption Eriksson (1968, 1969, 1971) has developed 2 strains of rats, one of which in a free-choice situation prefers a 10% (v/v) ethanol solution to water while the other drinks more water than ethanol solution. Earlier we reported that the brain 5-hydroxytryptamine content is 15 to 20% higher in ethanolselecting than in water-selecting rats (Ahtee and Eriksson 1972, 1973). In the present work we have estimated the dopamine and noradrenaline content in the brain of the alcoholpreferring and water-preferring rats. The test animals were either ALKO, Alcohol (AA) or ALKO, Non-Alcohol (ANA) male and female rats of Wistar origin that had been selectively outbred for their alcohol consumption for 22 generations. These 2 rat strains have been described in detail by Eriksson (1969, 1971). In the present experiments the AA rats were divided into 2 groups and the ANA rats into 3 groups (see Table I). During the free-choice experiments (treatment 11) the rats were kept in individual cages. Initially, for a habituation period of 10 days, they had 10% (v/v) ethanol solution as the sole drinking fluid. After this time of habituation they were given a choice between water and 10% ethanol solution. In one series of experiments (treatment 111) the ANA rats were forced to drink only ethanol as 10% solution. The ethanol intake of the rats was measured daily. The ethanol consumption is expressed as percentage of calories from ethanol in relation to total calorie intake. The animals were killed by decapitation between 1 1 A.M. and 1 P.M. After decapitation the brains were rapidly removed, dissected on ice and weighed. Dopamine and noradrenaline were estimated in the same tissue sample by the method of Shellenberger and Gordon (1971). The results were corrected for the recovery of standard carried through the method. The recovery was for dopamine 89rf:1.5% (mean +S.E., 14 estimations) and for noradrenaline 8 6 k 1.5% (14 estimations). Table I shows that dopamine concentrations were 15 to 25% higher in the brain of Key words: Dopamine, noradrenaline, ethanol preference
563
564
LIlSA AHTEE AND KALERVO ERIKSSON
TABLE 1. The dopamine (DA) and noradrenaline (NA) content Ofg/g; mean f S . E . ) in the brain of alcohol preferring (AA) and water-preferring (ANA) rats before and during access to ethanol. The table also gives percentage proportion (mean fS.D.) of calories derived from ethanol/day in relation to total calorie intake. Strain
Sex
Treatment'
Number of rats
ANA ANA ANA AA AA
r3
I
I5
11
l3
Ill I I1
8 10 10 10
6k8.5 49f3 0 27f 10
AN A ANA AA AA
3
I
4 6 9 9
0 7+5 0 20f I5
s s
(3
P ?
11
I
3
II
Percentage of ethanol calories/day
0
DA
NA
0.77 f0.02 0.83 0.02 1.05 rf: 0.033 I .04+ 0.023
0.404_0.01 0.442 0.01 0.42t 0.00 0.45 5 0.00 0.47 0.0 I
0.77f0.05 0.79f 0.03 0.97+ 0.02' 0.93f0.02'
0.38 0.01 0.42 0.01 0.41 iO.01 0.41 :kO.OI
0.85_+0.02
+
I - Never ethanol, I 1 Free choice of ethanol, 111 = Forced ethanol drinking. Compared to corresponding ANA rats p i 0 . 0 1 . Compared to corresponding ANA rats p c 0.001. ~
ethanol preferring rats than in the brain of water preferring rats. The weight (mean f S.D. 1.5410.07 g) of the brain of the male A N A rats was 9Y0 higher than that (1.41 k0.07 g) of the male A A rats. Similarly, the brains (1.48 k0.06 g) of female A N A rats weighed 1 I no more than those (1.33 t0.05 g) of the female AA rats. However the dopamine concentrations were significantly higher in the brain of A A rats than in the brain of A N A rats if the total dopamine contents per brain rather than the concentrations were compared. Ethanol consumption either in a free-choice situation or in a forced situation did not change the brain dopamine concentration. The brain noradrenaline concentrations of the AA rats did not differ significantly from those of the A N A rats. As shown by Gordon and Shellenberger (1974) the noradrenaline concentration was slightly lower in the brain of female rats than in the brain of male rats. In conclusion these experiments show that the dopamine concentration but not the noradrenaline concentration is significantly higher in the brain of ethanol preferring rats than in the brain of water preferring rats. Whether this difference bears any relation to the ethanol selecting behaviour of these rats remains to be elucidated. This study was supported by the Finnish Foundation for Alcohol Studies.
References AHIEE,L. and K. ERIKSSON, 5-Hydroxytryptamine and 5-hydroxyindoleacetic acid content i n the brain of rat strains selected for preferring alcohol to water. Physiol. Bchm. 1972. 8. 123-126. Regional distribution of brain 5-hydroxytryptamine in rat strains selected AHTEE,L. and K. ERIKSSON, for their alcohol intake. Ann. N Y Acad. Sri. 1973. 215. 126-134. ERIKSSON, K., Genetic selection for voluntary alcohol consumption i n the albino rat. Science 1968. 15Y. 739-741.
BRAIN CATECHOLAMINES IN ETHANOL SELECTION
565
ERIKSSON, K., Factors affecting voluntary alcohol consumption in the albino rat. Ann. Zool. Fenn. 1969. 6. 227-265. K., Rat strains specially selected for their voluntary alcohol consumption. Ann. Med. exp. Fenn. ERIKSSON, 1971. 49. 67-72, GORDON, J. H. and M. K. SHELLENBERGER, Regional catecholamine content in the rat brain: Sex differences and correlation with motor activity. Neuropharmacology 1974. 13. 129-137. G. E. and D. A. RODGERS, Differences in alcohol preference among inbred strains of mice. MCLEARN, Quart. J. Stud. Alcohol 1959. 20. 691-695. J. R . , N. M. SEGOVIA and A. D. HEDERRA, Heredity of experimental alcohol preference in MARDONES, rats. 11. coefficient of heredity. Quart. J. Stud. Alcohol 1953. 14. 1-2. SHELLENBERGER, M. K. and J. H. GORDON, A rapid, simplified procedure for simultaneous assay of norepinephrine, dopamine, and 5-hydroxytryptarnine from discrete brain areas. Analyr. Biochem. 1971. 39. 356372.
Dopamine and Noradrenaline Content in the Brain of Rat Strains Selected for their Alcohol Intake BY
LIISAAHTEEand KALERVO ERIKSSON
Hereditary mechanisms are involved in the control of alcohol drinking in rats and mice (Mardones ef al. 1953, McLearn and Rodgers 1957). By outbreeding rats and selecting breeding animals that differ in their alcohol consumption Eriksson (1968, 1969, 1971) has developed 2 strains of rats, one of which in a free-choice situation prefers a 10% (v/v) ethanol solution to water while the other drinks more water than ethanol solution. Earlier we reported that the brain 5-hydroxytryptamine content is 15 to 20% higher in ethanolselecting than in water-selecting rats (Ahtee and Eriksson 1972, 1973). In the present work we have estimated the dopamine and noradrenaline content in the brain of the alcoholpreferring and water-preferring rats. The test animals were either ALKO, Alcohol (AA) or ALKO, Non-Alcohol (ANA) male and female rats of Wistar origin that had been selectively outbred for their alcohol consumption for 22 generations. These 2 rat strains have been described in detail by Eriksson (1969, 1971). In the present experiments the AA rats were divided into 2 groups and the ANA rats into 3 groups (see Table I). During the free-choice experiments (treatment 11) the rats were kept in individual cages. Initially, for a habituation period of 10 days, they had 10% (v/v) ethanol solution as the sole drinking fluid. After this time of habituation they were given a choice between water and 10% ethanol solution. In one series of experiments (treatment 111) the ANA rats were forced to drink only ethanol as 10% solution. The ethanol intake of the rats was measured daily. The ethanol consumption is expressed as percentage of calories from ethanol in relation to total calorie intake. The animals were killed by decapitation between 1 1 A.M. and 1 P.M. After decapitation the brains were rapidly removed, dissected on ice and weighed. Dopamine and noradrenaline were estimated in the same tissue sample by the method of Shellenberger and Gordon (1971). The results were corrected for the recovery of standard carried through the method. The recovery was for dopamine 89rf:1.5% (mean +S.E., 14 estimations) and for noradrenaline 8 6 k 1.5% (14 estimations). Table I shows that dopamine concentrations were 15 to 25% higher in the brain of Key words: Dopamine, noradrenaline, ethanol preference
563
564
LIlSA AHTEE AND KALERVO ERIKSSON
TABLE 1. The dopamine (DA) and noradrenaline (NA) content Ofg/g; mean f S . E . ) in the brain of alcohol preferring (AA) and water-preferring (ANA) rats before and during access to ethanol. The table also gives percentage proportion (mean fS.D.) of calories derived from ethanol/day in relation to total calorie intake. Strain
Sex
Treatment'
Number of rats
ANA ANA ANA AA AA
r3
I
I5
11
l3
Ill I I1
8 10 10 10
6k8.5 49f3 0 27f 10
AN A ANA AA AA
3
I
4 6 9 9
0 7+5 0 20f I5
s s
(3
P ?
11
I
3
II
Percentage of ethanol calories/day
0
DA
NA
0.77 f0.02 0.83 0.02 1.05 rf: 0.033 I .04+ 0.023
0.404_0.01 0.442 0.01 0.42t 0.00 0.45 5 0.00 0.47 0.0 I
0.77f0.05 0.79f 0.03 0.97+ 0.02' 0.93f0.02'
0.38 0.01 0.42 0.01 0.41 iO.01 0.41 :kO.OI
0.85_+0.02
+
I - Never ethanol, I 1 Free choice of ethanol, 111 = Forced ethanol drinking. Compared to corresponding ANA rats p i 0 . 0 1 . Compared to corresponding ANA rats p c 0.001. ~
ethanol preferring rats than in the brain of water preferring rats. The weight (mean f S.D. 1.5410.07 g) of the brain of the male A N A rats was 9Y0 higher than that (1.41 k0.07 g) of the male A A rats. Similarly, the brains (1.48 k0.06 g) of female A N A rats weighed 1 I no more than those (1.33 t0.05 g) of the female AA rats. However the dopamine concentrations were significantly higher in the brain of A A rats than in the brain of A N A rats if the total dopamine contents per brain rather than the concentrations were compared. Ethanol consumption either in a free-choice situation or in a forced situation did not change the brain dopamine concentration. The brain noradrenaline concentrations of the AA rats did not differ significantly from those of the A N A rats. As shown by Gordon and Shellenberger (1974) the noradrenaline concentration was slightly lower in the brain of female rats than in the brain of male rats. In conclusion these experiments show that the dopamine concentration but not the noradrenaline concentration is significantly higher in the brain of ethanol preferring rats than in the brain of water preferring rats. Whether this difference bears any relation to the ethanol selecting behaviour of these rats remains to be elucidated. This study was supported by the Finnish Foundation for Alcohol Studies.
References AHIEE,L. and K. ERIKSSON, 5-Hydroxytryptamine and 5-hydroxyindoleacetic acid content i n the brain of rat strains selected for preferring alcohol to water. Physiol. Bchm. 1972. 8. 123-126. Regional distribution of brain 5-hydroxytryptamine in rat strains selected AHTEE,L. and K. ERIKSSON, for their alcohol intake. Ann. N Y Acad. Sri. 1973. 215. 126-134. ERIKSSON, K., Genetic selection for voluntary alcohol consumption i n the albino rat. Science 1968. 15Y. 739-741.
BRAIN CATECHOLAMINES IN ETHANOL SELECTION
565
ERIKSSON, K., Factors affecting voluntary alcohol consumption in the albino rat. Ann. Zool. Fenn. 1969. 6. 227-265. K., Rat strains specially selected for their voluntary alcohol consumption. Ann. Med. exp. Fenn. ERIKSSON, 1971. 49. 67-72, GORDON, J. H. and M. K. SHELLENBERGER, Regional catecholamine content in the rat brain: Sex differences and correlation with motor activity. Neuropharmacology 1974. 13. 129-137. G. E. and D. A. RODGERS, Differences in alcohol preference among inbred strains of mice. MCLEARN, Quart. J. Stud. Alcohol 1959. 20. 691-695. J. R . , N. M. SEGOVIA and A. D. HEDERRA, Heredity of experimental alcohol preference in MARDONES, rats. 11. coefficient of heredity. Quart. J. Stud. Alcohol 1953. 14. 1-2. SHELLENBERGER, M. K. and J. H. GORDON, A rapid, simplified procedure for simultaneous assay of norepinephrine, dopamine, and 5-hydroxytryptarnine from discrete brain areas. Analyr. Biochem. 1971. 39. 356372.
