235
Drug and Alcohol Dependence, 4 (1979) 235 - 237 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
TETRAHYDROISOQUINOLINES
AND THE SEROTONERGIC
JEROME
A. COLLINS
J. HANNIGAN
and MICHAEL
Department of Biochemistry and Biophysics, Medicine, Maywood, IlIinois 60153 (U.S.A.)
Loyola
University
Stritch
SYSTEM
School of
Although its oxidation to acetate overwhelmingly predominates, acetaldehyde (ACH) formed during ethanol metabolism can be “trapped” by condensation with catecholamines (CAs) or DOPA. The condensation products, tetrahydroisoquinolines (TIQs), have been detected in the brains of mice chronically exposed to ethanol [l] and in the urine of alcoholics during detoxification [ 21. Catecholic TIQs are not without physiological effects. Several TIQs derived from dopamine or DOPA have been shown to promote ethanol consumption when infused centrally into alcohol-avoiding rats [ 31. The TIQ derived from ACH and DOPA (3-carboxysalsolinol) has an analgesic action in mice [ 41 . The neurochemical aspects underlying these recently described effects of TIQs have not been clarified. Since alterations in serotonin (5-HT) have been implicated in ethanol preference [ 51 and in drug-induced analgesia (antinociception) [6] , we decided to examine the effects of certain TIQs on the serotonergic system. In this communication, we report that intraperitoneal (i.p.) administration of Is, 3s(cis)3-carboxysalsolinol (cSAL) results in significant changes in brain 5-HT levels and/or metabolism.
Methods Acute and chronic experiments (see legends of Tables 1 and 2) were carried out with male Sprague-Dawley rats (120 - 380 g) which were sacrificed by decapitation one hour after the last i.p. dose of cSAL or isotonic saline. Striatal and hypothalamic regions were assayed for 5-HT and the CAs in the acute studies and for 5-HT, tryptophan, 5-hydroxyindoleacetic acid (5-HIAA) and CAs in the chronic experiment. A modification of the fluorometric method reported by Holman et at. [7] , employing separation on BioRex 70 resin, was used. Recoveries of compounds assayed ranged from 50 - 70%. Results and discussion Acute cSAL treatment in doses of 50 - 400 mg/kg (i.p.) caused 70 - 90% increases in striatal 5-HT concentrations (Table 1). Hypothalamic 5-HT
236
levels were somewhat depressed, but the changes were not significant to p < 0.05 levels. As reported elsewhere [8] , dopamine and noradrenaline levels in the striatum and hypothalamus were not significantly affected by acutely administered cSAL unless an aromatic amino-acid decarboxylase inhibitor was pre-administered. Marshall et al. [ 41 reported that &AL had one-fifth of the analgesic effect of morphine in mice. It is possible that an increase in striatal 5-HT underlies the cSAL-induced analgesia.
TABLE
1
Effect of a single injection and hypothalamus’ TIQ dose (mg/kg)
Control
of 3-carboxysalsolinol
on serotonin
levels in rat striatum
pg/g tissue * s.e.m. Striatum
Hypothalamus
0.524
+ 0.078
1.53
? 0.15
50
0.891
+ 0.160*
1.05
i 0.07
150
0.902
2 0.136*
1.29
f 0.14
400
0.992
i 0.112*
1.41
c 0.19
‘The TIQ was administered intraperitoneally in isotonic saline, and the rats were decapitated one hour afterward. Brain parts were removed and weighed, and 5-HT was analyzed as described in the text. 6 - 8 rats per group were used. *p < 0.01 compared to control striatal levels.
Following chronic administration, cSAL reduced 5-HT levels 52% in the striatum and 15% in the hypothalamus (Table 2). Changes in tryptophan and 5-HIAA were more variable. In the striatum, tryptophan levels were increased 21% while 5-HIAA, although increased, was not significantly different from controls; in the hypothalamus, tryptophan was unchanged and 5-HIAA levels were slightly decreased. Dopamine and noradrenaline were largely unchanged by the chronic treatment. Therefore the serotonergic neurons, rather than catecholaminergic systems, seem to be primarily altered by cSAL, and may, in fact, be the principal sites of TIQ action. Furthermore, the effect of cSAL is somewhat selective, being much more pronounced in the striatum than in the hypothalamus. When infused centrally, cSAL (and other TIQs) promoted alcohol drinking behavior [ 31. Its effects on the striatal serotonergic system that we have observed may in some way be related to the increased alcohol consumption. The mechanisms responsible for increased striatal 5-HT levels after a single cSAL injection and the decreased levels after chronic injections are not readily apparent. Other TIQs are being examined for their 5-HT effects.
231 TABLE
2
Effect of chronic 3-carboxysalsolinol treatment metabolites in rat striatum and hypothalamus’
on levels of biogenic
amines and
pg/g tissue * s.e.m. Striatum
Hypothalamus
Tryptophan Control Experimental
3.21 t 0.08 3.96 -r 0.17*
5.06 * 0.79 3.88 + 0.36
Serotonin Control Experimental
0.330 0.160
* 0.010 + 0.020*
0.367 0.301
* 0.003 * 0.014*
0.403 0.448
+ 0.047 + 0.058
0.771 0.588
* 0.035 2 0.007*
5-HIAA Control Experimental Dopamine Control Experimental
8.43 8.38
Noradrenaline Control Experimental
_ -
i 0.73 t 1.24
2.86 2.87
r 0.46 * 0.40
2.22 2.24
f 0.16 + 0.31
‘Carboxysalsolinol was given 3 times daily (50 mg/kg, i.p.) for 5 days, and rats were sacrificed one hour after the last injection. Twelve rats per group were used. *p < 0.01 compared to appropriate control.
Acknowledgement This work was supported by a grant (AA 00266) from the United States Public Health Service.
References 1 M. Hamilton, K. Blum and M. Hirst, Alcoholism: Clin. Exp. Res., 2 (1978) 133. 2 W. Nijm et al., in E. Usdin (ed.), Proceedings 4th International Catecholamine Symposium, Pergamon Press, New York, 1979, in press. 3 R. D. Myers and C. L. Melchior, Pharmacol. Biochem. Behav., 7 (1977) 381. 4 A. Marshall, M. Hirst and K. Blum, Experientia, 33 (1977) 754. 5 R. D. Myers and C. L. Melchior, Res. Commum. Chem. Pathol. Pharmacol., 10 (1975) 363. 6 T. Harvey, A. Schlosburg and L. M. Yunger, Fed. Proc., 29 (1975) 1796. 7 R. B. Holman, P. Angwin and J. D. Barchas, Neuroscience, 1 (1976) 147. 8 M. A. Collins, J. Hannigan and C. Weiner, in F. Seixas (ed.), Currents in Alcoholism, Vol. 5, Grune and Stratton, New York, 1979, in press.
Drug and Alcohol Dependence, 4 (1979) 235 - 237 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
TETRAHYDROISOQUINOLINES
AND THE SEROTONERGIC
JEROME
A. COLLINS
J. HANNIGAN
and MICHAEL
Department of Biochemistry and Biophysics, Medicine, Maywood, IlIinois 60153 (U.S.A.)
Loyola
University
Stritch
SYSTEM
School of
Although its oxidation to acetate overwhelmingly predominates, acetaldehyde (ACH) formed during ethanol metabolism can be “trapped” by condensation with catecholamines (CAs) or DOPA. The condensation products, tetrahydroisoquinolines (TIQs), have been detected in the brains of mice chronically exposed to ethanol [l] and in the urine of alcoholics during detoxification [ 21. Catecholic TIQs are not without physiological effects. Several TIQs derived from dopamine or DOPA have been shown to promote ethanol consumption when infused centrally into alcohol-avoiding rats [ 31. The TIQ derived from ACH and DOPA (3-carboxysalsolinol) has an analgesic action in mice [ 41 . The neurochemical aspects underlying these recently described effects of TIQs have not been clarified. Since alterations in serotonin (5-HT) have been implicated in ethanol preference [ 51 and in drug-induced analgesia (antinociception) [6] , we decided to examine the effects of certain TIQs on the serotonergic system. In this communication, we report that intraperitoneal (i.p.) administration of Is, 3s(cis)3-carboxysalsolinol (cSAL) results in significant changes in brain 5-HT levels and/or metabolism.
Methods Acute and chronic experiments (see legends of Tables 1 and 2) were carried out with male Sprague-Dawley rats (120 - 380 g) which were sacrificed by decapitation one hour after the last i.p. dose of cSAL or isotonic saline. Striatal and hypothalamic regions were assayed for 5-HT and the CAs in the acute studies and for 5-HT, tryptophan, 5-hydroxyindoleacetic acid (5-HIAA) and CAs in the chronic experiment. A modification of the fluorometric method reported by Holman et at. [7] , employing separation on BioRex 70 resin, was used. Recoveries of compounds assayed ranged from 50 - 70%. Results and discussion Acute cSAL treatment in doses of 50 - 400 mg/kg (i.p.) caused 70 - 90% increases in striatal 5-HT concentrations (Table 1). Hypothalamic 5-HT
236
levels were somewhat depressed, but the changes were not significant to p < 0.05 levels. As reported elsewhere [8] , dopamine and noradrenaline levels in the striatum and hypothalamus were not significantly affected by acutely administered cSAL unless an aromatic amino-acid decarboxylase inhibitor was pre-administered. Marshall et al. [ 41 reported that &AL had one-fifth of the analgesic effect of morphine in mice. It is possible that an increase in striatal 5-HT underlies the cSAL-induced analgesia.
TABLE
1
Effect of a single injection and hypothalamus’ TIQ dose (mg/kg)
Control
of 3-carboxysalsolinol
on serotonin
levels in rat striatum
pg/g tissue * s.e.m. Striatum
Hypothalamus
0.524
+ 0.078
1.53
? 0.15
50
0.891
+ 0.160*
1.05
i 0.07
150
0.902
2 0.136*
1.29
f 0.14
400
0.992
i 0.112*
1.41
c 0.19
‘The TIQ was administered intraperitoneally in isotonic saline, and the rats were decapitated one hour afterward. Brain parts were removed and weighed, and 5-HT was analyzed as described in the text. 6 - 8 rats per group were used. *p < 0.01 compared to control striatal levels.
Following chronic administration, cSAL reduced 5-HT levels 52% in the striatum and 15% in the hypothalamus (Table 2). Changes in tryptophan and 5-HIAA were more variable. In the striatum, tryptophan levels were increased 21% while 5-HIAA, although increased, was not significantly different from controls; in the hypothalamus, tryptophan was unchanged and 5-HIAA levels were slightly decreased. Dopamine and noradrenaline were largely unchanged by the chronic treatment. Therefore the serotonergic neurons, rather than catecholaminergic systems, seem to be primarily altered by cSAL, and may, in fact, be the principal sites of TIQ action. Furthermore, the effect of cSAL is somewhat selective, being much more pronounced in the striatum than in the hypothalamus. When infused centrally, cSAL (and other TIQs) promoted alcohol drinking behavior [ 31. Its effects on the striatal serotonergic system that we have observed may in some way be related to the increased alcohol consumption. The mechanisms responsible for increased striatal 5-HT levels after a single cSAL injection and the decreased levels after chronic injections are not readily apparent. Other TIQs are being examined for their 5-HT effects.
231 TABLE
2
Effect of chronic 3-carboxysalsolinol treatment metabolites in rat striatum and hypothalamus’
on levels of biogenic
amines and
pg/g tissue * s.e.m. Striatum
Hypothalamus
Tryptophan Control Experimental
3.21 t 0.08 3.96 -r 0.17*
5.06 * 0.79 3.88 + 0.36
Serotonin Control Experimental
0.330 0.160
* 0.010 + 0.020*
0.367 0.301
* 0.003 * 0.014*
0.403 0.448
+ 0.047 + 0.058
0.771 0.588
* 0.035 2 0.007*
5-HIAA Control Experimental Dopamine Control Experimental
8.43 8.38
Noradrenaline Control Experimental
_ -
i 0.73 t 1.24
2.86 2.87
r 0.46 * 0.40
2.22 2.24
f 0.16 + 0.31
‘Carboxysalsolinol was given 3 times daily (50 mg/kg, i.p.) for 5 days, and rats were sacrificed one hour after the last injection. Twelve rats per group were used. *p < 0.01 compared to appropriate control.
Acknowledgement This work was supported by a grant (AA 00266) from the United States Public Health Service.
References 1 M. Hamilton, K. Blum and M. Hirst, Alcoholism: Clin. Exp. Res., 2 (1978) 133. 2 W. Nijm et al., in E. Usdin (ed.), Proceedings 4th International Catecholamine Symposium, Pergamon Press, New York, 1979, in press. 3 R. D. Myers and C. L. Melchior, Pharmacol. Biochem. Behav., 7 (1977) 381. 4 A. Marshall, M. Hirst and K. Blum, Experientia, 33 (1977) 754. 5 R. D. Myers and C. L. Melchior, Res. Commum. Chem. Pathol. Pharmacol., 10 (1975) 363. 6 T. Harvey, A. Schlosburg and L. M. Yunger, Fed. Proc., 29 (1975) 1796. 7 R. B. Holman, P. Angwin and J. D. Barchas, Neuroscience, 1 (1976) 147. 8 M. A. Collins, J. Hannigan and C. Weiner, in F. Seixas (ed.), Currents in Alcoholism, Vol. 5, Grune and Stratton, New York, 1979, in press.
