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Down-regulation of β-adrenergic activity in astroglia by chronic treatment with an antidepressant drug
European Journal of Pharmacology, 72 (1981) 267--268
267
Elsevier/North-Holland Biomedical Press
Rapid communication DOWN-REGULATION OF ~-ADRENERGIC ACTIVITY IN ASTROGLIA BY CHRONIC TREATMENT WITH AN ANTIDEPRESSANT DRUG L. H E R T Z
*, S. M U K E R J I
* and J.S. R I C H A R D S O N
*,**
Dept. of Pharmacology * and Dept. of Psychiatry **, Universityof Saskatchewan, Sashatoon, Saskatchewan S T N O W O , Canada Received 7 May 1981, accepted 11 May 1981
A considerable a m o u n t of evidence indicates that adenylate cyclase related dopaminergic, serotoninergic and fi-adrenergic receptors are found on normal astrocytes, a type of glial cell, which constitutes about one-third of the brain cortical volume {e.g., Hertz, 1981). Since destruction o f a major part of the neurons in rat neostriatum by kainic acid causes an increase in isoproterenol iduced accumulation of cyclic AMP (Minneman et al., 1978}, and since development o f ~adrenergic receptor sites in cultures coincides with glial proliferation (McCarthy and Harden, 1981), it is even likely that most fi-adrenergic receptor sites are found on astrocytes. Chronic, but not acute administration of any antidepressant therapy (drugs, electroconvulsive treatment) causes a down regulation of /~-adrenergic receptor function in the rodent brain (Sulser, 1979). This observation is of considerable significance for two reasons: It provides a c o m m o n denominator for all types of antidepressant therapy and it is seen only after prolonged treatment, which mimics the slow onset of the therapeutic antidepressant effect in patients. However, if most ~-adrenergic receptor sites are located on astrocytes, this d o w n regulation might at least as well occur in astrocytes as in neurons. To explore this possibility, we have investigated whether chronic exposure to amitriptyline causes a reduction of the isoproterenol-induced accumulation of cyclic AMP in mouse astrocytes in primary cultures. This preparation consitutes an excellent
model for normal astrocytes and is devoid of neurons (for references, see Hertz et al., 1980). The cultures were grown for the first 2 weeks in a modified Eagle medium with 10% horse serum. Subsequently, some cultures were fed a similar medium which in addition contained 1 pM amitriptyline, whereas the remaining cultures were fed normal medium. Accumulation of cyclic AMP was determined, in individual cultures which w e r e incubated with or without isoproterenol and amitriptyline (table 1) for 10 rain at 37°C in 150 mM Tris buffer, pH 7.4, with 0.5 mM isobutylmethylxanthine (IBMX). Cyclic AMP was measured by a conventional binding method, using Amersham's cyclic AMP assay kit, and protein by the Lowry method. Culturing with amitriptyline for 5 days had no significant effect on accumulation of cyclic AMP (results not presented). Exposure to the drug for 12 days also did not affect the accumulation of cyclic AMP in the absence of isoproterenol, but the enhanced accumulation in the presence of 1 ~ isoproterenol was reduced by 30% (table 1). This cannot be a result of traces of amitriptyllne which might remain in the medium, since the presence of a considerably higher amitriptyline concentration (5 ~M) during only the assay period had no effect on the accumulation of cyclic AMP. It is also probably not due to an intracellular accumulation of amitriptyline since the reduction in cyclic AMP accumulation was, if anything, smaller in cultures which had been
0 014-2999/81/0000--0000/$02.50 © Elsevier/North-Holland Biomedical Press
268 TA BL E 1 Accumulation of cyclic AMP (pmol/mg) protein) in primary cultures of mouse astrocytes during 10 rain of incubation in the presence of 0.5 mM IBMX and isoproterenol and amitriptyline as indicated. The cultures had been grown for the last 12 days in the presence or absence of 1 /2M amitriptyline; the statistical significance of the differences between the two groups of cultures are indicated. All cultures were from the same batch but the results were confirmed in cultures from a different batch. Isoproterenol Amitriptyline
0 0
1 ]~M 0
1 ~M 5 ~M
Grown without drug Grown with amitriptyline (1 pM) Statistical significance
102.8 _+10.4 (3) 120.2 _+11.1 (3) N.S.
1430.8 _+79.9 (4) 1014.5 -+ 46.3 (4) P < 0.01
1458.7 + 121.5 (3) 1108.3 _+83.7 (3) P < 0.1
grown in the presence of amitriptyline and, in addition, were exposed to 5 pM amitriptyline during the assay period (table 1). This is in spite of the fact that exposure to relatively high concentrations of antidepressants during the cycic AMP accumulation period alone does counteract the isoproterenol induced accumulation of cyclic AMP (Hertz et al., 1980). It seems therefore that chronic exposure of astrocytes to antidepressant drugs leads to a down regulation of ~-adrenergic function, a response which is quantitatively and temporally similar to that in the brain in vivo (Sulser, 1979). The present results, together with a previous demonstration of astrocytic binding sites for doxepin, another tricyclic antidepressant (Hertz et al., 1980), suggest that at least part of the action of antidepressant therapy is exerted on glial cells.
Acknowledgement The Saskatchewan Health thanked for financial support.
Research
Board
is
References Hertz, L., 1981, Astrocytes, in: Handbook of Neurochemistry, 2nd edn., ed. A. Lajtha (Plenum Press, New York) (in press). Hertz, L., J.S. Richardson and S. Mukerji, 1980, Doxepin, a tricyclic antidepressant, binds to normal, intact astroglial cells in cultures and inhibits the isoproterenol induced increase in cyclic AMP production, Can. J. Physiol. Pharmacol. 58, 1515. McCarthy, K.D. and T.K. Harden, 1981, Identification of two benzodiazepine binding sites on cells cultured from rat cerebral cortex, J. Pharmacol. Exp. Ther. 216,183. Minneman, K.P., M. Quik and P.C. Emson, 1978, Receptor-linked cyclic AMP systems in rat neostriaturn: differential localization revealed by kainic acid injection, Brain Res. 1 5 1 , 5 0 7 . Sulser, F., 1979, New perspectives on the mode of action of antidepressant drugs, Trends Pharmacol. Sci. 1, 92.
267
Elsevier/North-Holland Biomedical Press
Rapid communication DOWN-REGULATION OF ~-ADRENERGIC ACTIVITY IN ASTROGLIA BY CHRONIC TREATMENT WITH AN ANTIDEPRESSANT DRUG L. H E R T Z
*, S. M U K E R J I
* and J.S. R I C H A R D S O N
*,**
Dept. of Pharmacology * and Dept. of Psychiatry **, Universityof Saskatchewan, Sashatoon, Saskatchewan S T N O W O , Canada Received 7 May 1981, accepted 11 May 1981
A considerable a m o u n t of evidence indicates that adenylate cyclase related dopaminergic, serotoninergic and fi-adrenergic receptors are found on normal astrocytes, a type of glial cell, which constitutes about one-third of the brain cortical volume {e.g., Hertz, 1981). Since destruction o f a major part of the neurons in rat neostriatum by kainic acid causes an increase in isoproterenol iduced accumulation of cyclic AMP (Minneman et al., 1978}, and since development o f ~adrenergic receptor sites in cultures coincides with glial proliferation (McCarthy and Harden, 1981), it is even likely that most fi-adrenergic receptor sites are found on astrocytes. Chronic, but not acute administration of any antidepressant therapy (drugs, electroconvulsive treatment) causes a down regulation of /~-adrenergic receptor function in the rodent brain (Sulser, 1979). This observation is of considerable significance for two reasons: It provides a c o m m o n denominator for all types of antidepressant therapy and it is seen only after prolonged treatment, which mimics the slow onset of the therapeutic antidepressant effect in patients. However, if most ~-adrenergic receptor sites are located on astrocytes, this d o w n regulation might at least as well occur in astrocytes as in neurons. To explore this possibility, we have investigated whether chronic exposure to amitriptyline causes a reduction of the isoproterenol-induced accumulation of cyclic AMP in mouse astrocytes in primary cultures. This preparation consitutes an excellent
model for normal astrocytes and is devoid of neurons (for references, see Hertz et al., 1980). The cultures were grown for the first 2 weeks in a modified Eagle medium with 10% horse serum. Subsequently, some cultures were fed a similar medium which in addition contained 1 pM amitriptyline, whereas the remaining cultures were fed normal medium. Accumulation of cyclic AMP was determined, in individual cultures which w e r e incubated with or without isoproterenol and amitriptyline (table 1) for 10 rain at 37°C in 150 mM Tris buffer, pH 7.4, with 0.5 mM isobutylmethylxanthine (IBMX). Cyclic AMP was measured by a conventional binding method, using Amersham's cyclic AMP assay kit, and protein by the Lowry method. Culturing with amitriptyline for 5 days had no significant effect on accumulation of cyclic AMP (results not presented). Exposure to the drug for 12 days also did not affect the accumulation of cyclic AMP in the absence of isoproterenol, but the enhanced accumulation in the presence of 1 ~ isoproterenol was reduced by 30% (table 1). This cannot be a result of traces of amitriptyllne which might remain in the medium, since the presence of a considerably higher amitriptyline concentration (5 ~M) during only the assay period had no effect on the accumulation of cyclic AMP. It is also probably not due to an intracellular accumulation of amitriptyline since the reduction in cyclic AMP accumulation was, if anything, smaller in cultures which had been
0 014-2999/81/0000--0000/$02.50 © Elsevier/North-Holland Biomedical Press
268 TA BL E 1 Accumulation of cyclic AMP (pmol/mg) protein) in primary cultures of mouse astrocytes during 10 rain of incubation in the presence of 0.5 mM IBMX and isoproterenol and amitriptyline as indicated. The cultures had been grown for the last 12 days in the presence or absence of 1 /2M amitriptyline; the statistical significance of the differences between the two groups of cultures are indicated. All cultures were from the same batch but the results were confirmed in cultures from a different batch. Isoproterenol Amitriptyline
0 0
1 ]~M 0
1 ~M 5 ~M
Grown without drug Grown with amitriptyline (1 pM) Statistical significance
102.8 _+10.4 (3) 120.2 _+11.1 (3) N.S.
1430.8 _+79.9 (4) 1014.5 -+ 46.3 (4) P < 0.01
1458.7 + 121.5 (3) 1108.3 _+83.7 (3) P < 0.1
grown in the presence of amitriptyline and, in addition, were exposed to 5 pM amitriptyline during the assay period (table 1). This is in spite of the fact that exposure to relatively high concentrations of antidepressants during the cycic AMP accumulation period alone does counteract the isoproterenol induced accumulation of cyclic AMP (Hertz et al., 1980). It seems therefore that chronic exposure of astrocytes to antidepressant drugs leads to a down regulation of ~-adrenergic function, a response which is quantitatively and temporally similar to that in the brain in vivo (Sulser, 1979). The present results, together with a previous demonstration of astrocytic binding sites for doxepin, another tricyclic antidepressant (Hertz et al., 1980), suggest that at least part of the action of antidepressant therapy is exerted on glial cells.
Acknowledgement The Saskatchewan Health thanked for financial support.
Research
Board
is
References Hertz, L., 1981, Astrocytes, in: Handbook of Neurochemistry, 2nd edn., ed. A. Lajtha (Plenum Press, New York) (in press). Hertz, L., J.S. Richardson and S. Mukerji, 1980, Doxepin, a tricyclic antidepressant, binds to normal, intact astroglial cells in cultures and inhibits the isoproterenol induced increase in cyclic AMP production, Can. J. Physiol. Pharmacol. 58, 1515. McCarthy, K.D. and T.K. Harden, 1981, Identification of two benzodiazepine binding sites on cells cultured from rat cerebral cortex, J. Pharmacol. Exp. Ther. 216,183. Minneman, K.P., M. Quik and P.C. Emson, 1978, Receptor-linked cyclic AMP systems in rat neostriaturn: differential localization revealed by kainic acid injection, Brain Res. 1 5 1 , 5 0 7 . Sulser, F., 1979, New perspectives on the mode of action of antidepressant drugs, Trends Pharmacol. Sci. 1, 92.