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Persistence of cyclicity of the plasma dopamine metabolite. Homovanillic acid, in neuroleptic treated schizophrenic patients
Life Sciences, Vol. 44, pp. 1117-1121 Printed in the U.S.A.
Pergamon Press
PERSISTENCE OF CYCLICITY OF THE PLASMA DOPAMINE METABOLITE. HOMOVANILLIC ACID, IN NEUROLEPTIC TREATED SCHIZOPHRENIC PATIENTS R. Davila*. M. Zumarraga*. I. Andia*. A.J. Friedhoff.** * Direction de Investigation Neuroquimica. Servicio Vasco de Salud. Zamudio. Vizcaya. Spain. ** Millhauser Laboratories of the Department of Psychiatry, New York University School of Medicine, New York, N.Y. (Received in final form February 16, 1989) Summary The dopamine metabolite, homovanillic acid, decreases in concentration in plasma between 8:30 A.M. and 12:30 P.M. In patients with schizophrenia this cyclic change is attenuated by chronic neuroleptic treatment; however, if the 8 A.M. dose of neuroleptic is omitted, the decrease in level occurs. Presuming that neuroleptics attenuate the decline through a receptor mediated compensatory increase in dopamine release, it would appear that receptors are not fully occupied by neuroleptics even at therapeutically effective doses. The usual morning decrease in plasma cortisol levels was unaffected by neuroleptics.
Homovanillic Acid (HVA) is believed to be the principal metabolite of brain dopamine found in plasma (1). Inasmuch as antipsychotic drugs act by interfering with dopaminergic activity in the brain. the dopaminergic system has been of much interest in the study of psychosis. In rats. HVA derived from brain dopamine (DA) is believed to constitute about 35% of total plasma HVA (2.3). and the increase in HVA in rat plasma occurring after neuroleptic treatment has been found to be largely of central nervous system origin (2). Neuroleptics probably also produce an increase in plasma HVA in humans, but findings have not been entirely consistent (4.5.6.7). Bunney and Grace (8) have found that neuroleptics not only block dopamine receptors acutely, as has been reported earlier (9). but also, after long term treatment, produce depolarization blockade which leads to a marked reduction in DA release. It may be that both receptor blockade and depolarization blockade are involved in treatment response. Thus the delayed therapeutic response, usually seen in neuroleptic treatment. may occur because, although dopsmine receptor blockade occurs early in treatment. depolarization blockade occurs later, so that a maximum decrease in dopaminergic activity does not occur quickly. Recently, Bowers et al. (10) found that patients with schizophrenia who have low pretreatment plasma HVA levels had a poor response to antipsychotic drugs, while those with higher values had a better response. We had somewhat similar results (11.12.13). We found that an initial increase in plasma HVA after neuroleptics correlated positively with improvement (submitted for publication). In general, there has been agreement that declining plasma HVA has been positively correlated with decreasing psychopathology during neuroleptic treatment (5.6). There has been less agreement that an initial increase in plasma HVA occurs in humans in response to neuroleptic challenge 0024-3205189 $3.00 + .OO Copyright (c) 1989 Pergamon Press plc
1118
Persistence of Cyclicity of Plasma HVA
Vol. 44, No. 16, 1989
(5.6.7). although this compensatory increase has been consistently found to occur in rats (1.14.15). In previous experiments we and other authors found that. in a non-psychiatric population, there is a decrease in plasma HVA during the morning (16.17). Thus the contradictory findings may be related to fact that plasma HVA 3 levels change cyclically, so that time of sampling is important. In the present study we compared the change in plasma levels of HVA between 8:30 A.M. and 12:30 P.M. in normal individuals with that found in patients with chronic schizophrenia who had been under long term neuroleptic treatment. In the patients, samples for HVA assay were obtained from each subject on days when the usual neuroleptic was administered at 8:30 A.M.. and also on days when the usual 8:30 A.M. neuroleptic dose was omitted. We also studied plasma cortisol levels, which are known to fluctuate cyclically, to determine if these variations correlated with the variation in HVA.
Methods Eleven male patients between the ages of 18 and 45, mean 30, participated in the study. They were free of any medical illness, gave informed consent, and met the Research Diagnostic Criteria for diagnosis of chronic or subchronic schizophrenia. The duration of their illness ranged from 1.5 to 23 years. At the time of the study all were receiving neuroleptic treatment and had been under treatment for at least 18 months, and for at least 6 months before blood collection. Various neuroleptics were used for treatment. Two patients were receiving trifluoperazine. five, thioridazine and four, haloperidol. From inspection of the data, the nature of the neuroleptic did not appear to effect outcome. Control group consisted of 14 healthy males, ages 25-50. mean age 33. Blood samples were collected at 8:30 A.M. and again at 12:30 P.M. of the same day, the plasma was separated immediately after venipuncture. and stored in liquid nitrogen, until assay. Subjects remained sitting for 15 minutes before, and during blood collection. After the first venipuncture at 8:30 A.M. all patients received their usual neuroleptic does and blood was collected four hours later at 12:30 P.M. In a second trial blood was taken at the usual times, but the usual 8:30 A.M. neuroleptic dose was omitted. Free HVA in plasma was assayed by high performance liquid chromatography with electrochemical detection, as previously described (17). Cortisol was determined by a radioimmunoassay procedure (Diagnostic Products Corporation, Los Angeles, CA).
Results Means and standard errors of the plasma HVA and cortisol concentrations are presented in the Table and the data are presented graphically in Figure 1. Results of the paired t-test reflect the significance of the change in the measures from 8:30 A.M. to 12:30 P.M. It can be seen that there is a significant decrease, during the morning, in the concentration of plasma HVA in normal individuals. as we had previously reported (17). There is no such significant decrease in medicated patients with schizophrenia; however, the decrease is significant in patients with schizophrenia. undergoing continuous neuroleptic treatment, when the usual 8:30 A.M. dose is omitted.
Persistence of Cyclicity of Plasma HVA
Vol. 44, No. 16, 1989
1119
The well established decrease in cortisol during the morning (18) occurred in both controls and patients under both conditions. It was not significantly influenced by neuroleptic treatment (F=1.48). Table 1 ___
1N I I I 14 _ I 11
pHVA (ng/ml)
Control
-.----Patients with medication
--
--_25.71 (4.73)
14.68 (1.60)
I_ I 11
--_--
Same patients with medication omitted __-
8:30 A.M. mean (s.e)
15.86 (1.34)
____L
I I I I_ I 1 14 )
Cortisol (ng/ml)
IN
----Control --~ Patients with medication
8~30 A.M. mean (s.e.1
12:30 P.M. mean (s.e.1
19.59 (1.31)
15.73 (1.54) -__ 12.67 (1.09)
---
Same patients with medication omitted
I 12:30 P.M. I mean (s.e.1 I 1 15.58 (1.77) I -I 16.36 (2.02) I lI L1.56 (1.03) I I_----_
I 11 f 19.55 (1.38) I I_-I-_._-__ I 11 I 20.52 (1.06)
I t I I_--i 2.85 l-
P
c.02
I-l.04
N. S
LI 4.23
<.Ol
I-_ I t I I-I 3.09
<.Ol
II 4.74
c.001
P
I -Trmm-I
4.44
c.001
I I
_-__-I-
CORTISOL
HVA
30
205 -3 10
--Controls
Patients Medicoted
P”fEnts Medicated
u-w Controls
Potients Medicated
Potients Not Med icoted
Fig. 1 Treatment Effects on Plasma HVA and Cortisol
1120
Persistence of Cyclicity of Plasma HVA
vol. 44, No. 16, 1989
The change in HVA measures during the morning was significantly influenced by neuroleptic treatment (F=4.21. pc.025). The change in pHVA concentration during the morning when the patients received medication is significantly different from the change when the medication was omitted (t=-3.15. p<.Ol). The change in HVA concentration was found to be significantly different between the controls and patients when medicated (t=2.77. pc.02). There was, however, no significant difference in the change in HVA concentration between the controls and patients when the medication was omitted (t=1.42). Discussion It has been reported that after a few weeks of neuroleptic treatment, the concentration of HVA in plasma of patients with schizophrenia returns from initial higher values to pretreatment values or to values lower than baseline (19.20). This has been considered to be evidence of a developing tolerance to neuroleptic treatment, however, not all investigators have been able to find an initial increase in HVA. in either plasma or cerebrospinal fluid, after neuroleptic treatment is started (5.6.7.21.22.23). We had previously found in patients with acute schizophrenia. an increase in the concentration of HVA in plasma on the fourth day of treatment, and four hours after the first single dose of 5 mg of haloperidol (12.13). These results are comparable with the variation of HVA in plasma and brain of rats, recently reported by Chang (14). We, and other authors, have also found a tendency toward a decrease of HVA in plasma during the morning in normal unmedicated individuals (16.17). In the present study we have shown that this morning decline also occurs in patients with schizophrenia if their 8:30 A.M. medication is omitted. It is interesting that, after chronic neuroleptic treatment, administration of the usual first morning dose of neuroleptic is enough to attenuate the natural tendency of plasma HVA to decrease during the morning (8:30 A.M. to 12:30 P.M.). It appears that, during neuroleptic treatment, an equilibrium develops between the spontaneous decline and the compensatory increase in DA release, occurring in response to administration of the A.M. dose of a neuroleptic dopamine receptor blocker. From the finding that administration of a single A.M. dose produces an increased release of dopamine, it would seem that by 8:30 A.M. receptors are not saturated with neuroleptic received during the prior days treatment. It seems likely that the failure of some investigators to detect the HVA elevating effect of neuroleptic results from their not considering the daily rhythm of this plsma dopamine metabolite. Our own studies (submitted) and those of others (5.6.10) implicate adaptive changes in the dopaminergic system in the mediation of the therapeutic response. Cyclic changes in metabolite level reflect an adaptive aspect of the dopaminergic system. This adaptive process and the 24 hour cycle might be involved in the pathophysiology of the psychotic syndrome itself.
Acknowledgements Supported in part by Grant No. CCA-8411033 from the U.S.-Spain Joint Committee for Scientific Cooperation between the United States and Spain, and Grants No. MH 08618 & MH 35976 from the National Institute of Mental Health.
Vol. 44, No. 16, 1989
Persistence of Cyclicity of Plasma HVA
1121
REFERENCES: 1.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
N.G. BACOPOULOS. S.E. HATTOX and R.H. ROTH, Eur. J. Pharmacol. -56 225-236 (1979). K.S. KENDLER. G.R. HENINGER and R.H. ROTH, Eur. J. Pharmacol. -71 321-326 (1981). D.E. STERNBERG. R.H. HENINGER. and R.H. ROTH, Life Sci. 32 - 2447-2452 (1983). R. DAVILA, M. ZUMARRAGA. C. PERFA. I. ANDIA. B. BARCENA. and E. PINILLA. Psiquis E 131-136 (1985). K.L. DAVIS, M. DAVIDSON, R.C. MONS. K.S. KENDLER, B.M. DAVIS. C.A. JOHNS, Y. DENIGRIS and T.B. HORVATH. Science 227 1601-1602 (1985). D. PICKAR, R. LABARCA. M. LINNOILA. A. ROY, D. HOMMER. D. EVERETT and S.M. PAUL, Science 225 954-957 (1984). D. PICKAR. R. LABARCA. D. PICKAR. R. LABARCA, A.R. DORAN. Arch. Gen. Psychiat. 43 669-679 (1986). B.S. BUNNEYand A.A. GRACE, Life Sci. 23 1715-1728 (1978). A. CARLSSON and M. LINDQVIST. Acta Pharmacol. et Toxicol. 20 140-144 (1963). M.B. BOWERS, M.E. SWIGAR. P.I. JATLOW and N. GOICOECHEA. J. Clin. Psychiat. 45 248-251 (1984). R. DAVILA. M. ZUMARRAGA. E. MANERO, I. ANDIA and C. CASO. Inf. Psiquiatr. 97 245-250 (1984). R. DAVILA. E. MANERO, C. PEREA. B. BARCENA and M.I. ZAMALLOA. I. Cong. Sot. Esp. Psiquiat 134-135 (1984). R. DAVILA. M. ZUMARRAGA. I. ANDIA. M.I. ZAMALLOA. E. MANERO and C. PEREA. Proc. IV World Cong. Biol Psychiat. Philadelphia (1985). W.H. CHANG. E.K. YEH. W.H. HU. Y.T. TSENG. M.C. CHUNG and H.F. CHANG. Biol. Psychiat. 21 374-381 (1986). K.S. KENDLER, G.c HENINGER and R.H. ROTH, Life Sci. 30 2063-2069 (1982). K.S. KENDLER. R.C. MOHS and K.L. DAVIS, Psychiat. Res. 8 215-223 (1983). M. ZUMARRAGA. I. ANDIA. B. BARCENA. M.I. ZAMALLOA and R. DAVILA, Clin. Chem. (in press). P.CUGINI. F. HALBERG. A. SCHARMM In: Chronobiol._. eds. E. Haus and H.F. Kabat. Karger. New York, pp. 319-324 (1984). M.B. BOWERS and A. ROZITIS. Eur. J. Pharmacol 38 109-115 (1976). N.G. BACOPOULOS. G. BUNTOS. D.E. REDMOND, J. BAULU and R.H. ROTH, Brain Res. 157 396-401 (1978). G. BADGI. A. PERENYI. E. FRECSKA. Psychopharmacology g 62-64 (1985). L. BJERKENSTEDT. G. EDMAN. L. HAGENFELDT. G. SEDVALL and F.A. WIESEL. Brit. J. Psychiat. 147 276-282 (1985). C.F. SALLER and A.I. SALAMA, Neuropharmacology 24 123-129 (1985).
Pergamon Press
PERSISTENCE OF CYCLICITY OF THE PLASMA DOPAMINE METABOLITE. HOMOVANILLIC ACID, IN NEUROLEPTIC TREATED SCHIZOPHRENIC PATIENTS R. Davila*. M. Zumarraga*. I. Andia*. A.J. Friedhoff.** * Direction de Investigation Neuroquimica. Servicio Vasco de Salud. Zamudio. Vizcaya. Spain. ** Millhauser Laboratories of the Department of Psychiatry, New York University School of Medicine, New York, N.Y. (Received in final form February 16, 1989) Summary The dopamine metabolite, homovanillic acid, decreases in concentration in plasma between 8:30 A.M. and 12:30 P.M. In patients with schizophrenia this cyclic change is attenuated by chronic neuroleptic treatment; however, if the 8 A.M. dose of neuroleptic is omitted, the decrease in level occurs. Presuming that neuroleptics attenuate the decline through a receptor mediated compensatory increase in dopamine release, it would appear that receptors are not fully occupied by neuroleptics even at therapeutically effective doses. The usual morning decrease in plasma cortisol levels was unaffected by neuroleptics.
Homovanillic Acid (HVA) is believed to be the principal metabolite of brain dopamine found in plasma (1). Inasmuch as antipsychotic drugs act by interfering with dopaminergic activity in the brain. the dopaminergic system has been of much interest in the study of psychosis. In rats. HVA derived from brain dopamine (DA) is believed to constitute about 35% of total plasma HVA (2.3). and the increase in HVA in rat plasma occurring after neuroleptic treatment has been found to be largely of central nervous system origin (2). Neuroleptics probably also produce an increase in plasma HVA in humans, but findings have not been entirely consistent (4.5.6.7). Bunney and Grace (8) have found that neuroleptics not only block dopamine receptors acutely, as has been reported earlier (9). but also, after long term treatment, produce depolarization blockade which leads to a marked reduction in DA release. It may be that both receptor blockade and depolarization blockade are involved in treatment response. Thus the delayed therapeutic response, usually seen in neuroleptic treatment. may occur because, although dopsmine receptor blockade occurs early in treatment. depolarization blockade occurs later, so that a maximum decrease in dopaminergic activity does not occur quickly. Recently, Bowers et al. (10) found that patients with schizophrenia who have low pretreatment plasma HVA levels had a poor response to antipsychotic drugs, while those with higher values had a better response. We had somewhat similar results (11.12.13). We found that an initial increase in plasma HVA after neuroleptics correlated positively with improvement (submitted for publication). In general, there has been agreement that declining plasma HVA has been positively correlated with decreasing psychopathology during neuroleptic treatment (5.6). There has been less agreement that an initial increase in plasma HVA occurs in humans in response to neuroleptic challenge 0024-3205189 $3.00 + .OO Copyright (c) 1989 Pergamon Press plc
1118
Persistence of Cyclicity of Plasma HVA
Vol. 44, No. 16, 1989
(5.6.7). although this compensatory increase has been consistently found to occur in rats (1.14.15). In previous experiments we and other authors found that. in a non-psychiatric population, there is a decrease in plasma HVA during the morning (16.17). Thus the contradictory findings may be related to fact that plasma HVA 3 levels change cyclically, so that time of sampling is important. In the present study we compared the change in plasma levels of HVA between 8:30 A.M. and 12:30 P.M. in normal individuals with that found in patients with chronic schizophrenia who had been under long term neuroleptic treatment. In the patients, samples for HVA assay were obtained from each subject on days when the usual neuroleptic was administered at 8:30 A.M.. and also on days when the usual 8:30 A.M. neuroleptic dose was omitted. We also studied plasma cortisol levels, which are known to fluctuate cyclically, to determine if these variations correlated with the variation in HVA.
Methods Eleven male patients between the ages of 18 and 45, mean 30, participated in the study. They were free of any medical illness, gave informed consent, and met the Research Diagnostic Criteria for diagnosis of chronic or subchronic schizophrenia. The duration of their illness ranged from 1.5 to 23 years. At the time of the study all were receiving neuroleptic treatment and had been under treatment for at least 18 months, and for at least 6 months before blood collection. Various neuroleptics were used for treatment. Two patients were receiving trifluoperazine. five, thioridazine and four, haloperidol. From inspection of the data, the nature of the neuroleptic did not appear to effect outcome. Control group consisted of 14 healthy males, ages 25-50. mean age 33. Blood samples were collected at 8:30 A.M. and again at 12:30 P.M. of the same day, the plasma was separated immediately after venipuncture. and stored in liquid nitrogen, until assay. Subjects remained sitting for 15 minutes before, and during blood collection. After the first venipuncture at 8:30 A.M. all patients received their usual neuroleptic does and blood was collected four hours later at 12:30 P.M. In a second trial blood was taken at the usual times, but the usual 8:30 A.M. neuroleptic dose was omitted. Free HVA in plasma was assayed by high performance liquid chromatography with electrochemical detection, as previously described (17). Cortisol was determined by a radioimmunoassay procedure (Diagnostic Products Corporation, Los Angeles, CA).
Results Means and standard errors of the plasma HVA and cortisol concentrations are presented in the Table and the data are presented graphically in Figure 1. Results of the paired t-test reflect the significance of the change in the measures from 8:30 A.M. to 12:30 P.M. It can be seen that there is a significant decrease, during the morning, in the concentration of plasma HVA in normal individuals. as we had previously reported (17). There is no such significant decrease in medicated patients with schizophrenia; however, the decrease is significant in patients with schizophrenia. undergoing continuous neuroleptic treatment, when the usual 8:30 A.M. dose is omitted.
Persistence of Cyclicity of Plasma HVA
Vol. 44, No. 16, 1989
1119
The well established decrease in cortisol during the morning (18) occurred in both controls and patients under both conditions. It was not significantly influenced by neuroleptic treatment (F=1.48). Table 1 ___
1N I I I 14 _ I 11
pHVA (ng/ml)
Control
-.----Patients with medication
--
--_25.71 (4.73)
14.68 (1.60)
I_ I 11
--_--
Same patients with medication omitted __-
8:30 A.M. mean (s.e)
15.86 (1.34)
____L
I I I I_ I 1 14 )
Cortisol (ng/ml)
IN
----Control --~ Patients with medication
8~30 A.M. mean (s.e.1
12:30 P.M. mean (s.e.1
19.59 (1.31)
15.73 (1.54) -__ 12.67 (1.09)
---
Same patients with medication omitted
I 12:30 P.M. I mean (s.e.1 I 1 15.58 (1.77) I -I 16.36 (2.02) I lI L1.56 (1.03) I I_----_
I 11 f 19.55 (1.38) I I_-I-_._-__ I 11 I 20.52 (1.06)
I t I I_--i 2.85 l-
P
c.02
I-l.04
N. S
LI 4.23
<.Ol
I-_ I t I I-I 3.09
<.Ol
II 4.74
c.001
P
I -Trmm-I
4.44
c.001
I I
_-__-I-
CORTISOL
HVA
30
205 -3 10
--Controls
Patients Medicoted
P”fEnts Medicated
u-w Controls
Potients Medicated
Potients Not Med icoted
Fig. 1 Treatment Effects on Plasma HVA and Cortisol
1120
Persistence of Cyclicity of Plasma HVA
vol. 44, No. 16, 1989
The change in HVA measures during the morning was significantly influenced by neuroleptic treatment (F=4.21. pc.025). The change in pHVA concentration during the morning when the patients received medication is significantly different from the change when the medication was omitted (t=-3.15. p<.Ol). The change in HVA concentration was found to be significantly different between the controls and patients when medicated (t=2.77. pc.02). There was, however, no significant difference in the change in HVA concentration between the controls and patients when the medication was omitted (t=1.42). Discussion It has been reported that after a few weeks of neuroleptic treatment, the concentration of HVA in plasma of patients with schizophrenia returns from initial higher values to pretreatment values or to values lower than baseline (19.20). This has been considered to be evidence of a developing tolerance to neuroleptic treatment, however, not all investigators have been able to find an initial increase in HVA. in either plasma or cerebrospinal fluid, after neuroleptic treatment is started (5.6.7.21.22.23). We had previously found in patients with acute schizophrenia. an increase in the concentration of HVA in plasma on the fourth day of treatment, and four hours after the first single dose of 5 mg of haloperidol (12.13). These results are comparable with the variation of HVA in plasma and brain of rats, recently reported by Chang (14). We, and other authors, have also found a tendency toward a decrease of HVA in plasma during the morning in normal unmedicated individuals (16.17). In the present study we have shown that this morning decline also occurs in patients with schizophrenia if their 8:30 A.M. medication is omitted. It is interesting that, after chronic neuroleptic treatment, administration of the usual first morning dose of neuroleptic is enough to attenuate the natural tendency of plasma HVA to decrease during the morning (8:30 A.M. to 12:30 P.M.). It appears that, during neuroleptic treatment, an equilibrium develops between the spontaneous decline and the compensatory increase in DA release, occurring in response to administration of the A.M. dose of a neuroleptic dopamine receptor blocker. From the finding that administration of a single A.M. dose produces an increased release of dopamine, it would seem that by 8:30 A.M. receptors are not saturated with neuroleptic received during the prior days treatment. It seems likely that the failure of some investigators to detect the HVA elevating effect of neuroleptic results from their not considering the daily rhythm of this plsma dopamine metabolite. Our own studies (submitted) and those of others (5.6.10) implicate adaptive changes in the dopaminergic system in the mediation of the therapeutic response. Cyclic changes in metabolite level reflect an adaptive aspect of the dopaminergic system. This adaptive process and the 24 hour cycle might be involved in the pathophysiology of the psychotic syndrome itself.
Acknowledgements Supported in part by Grant No. CCA-8411033 from the U.S.-Spain Joint Committee for Scientific Cooperation between the United States and Spain, and Grants No. MH 08618 & MH 35976 from the National Institute of Mental Health.
Vol. 44, No. 16, 1989
Persistence of Cyclicity of Plasma HVA
1121
REFERENCES: 1.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23.
N.G. BACOPOULOS. S.E. HATTOX and R.H. ROTH, Eur. J. Pharmacol. -56 225-236 (1979). K.S. KENDLER. G.R. HENINGER and R.H. ROTH, Eur. J. Pharmacol. -71 321-326 (1981). D.E. STERNBERG. R.H. HENINGER. and R.H. ROTH, Life Sci. 32 - 2447-2452 (1983). R. DAVILA, M. ZUMARRAGA. C. PERFA. I. ANDIA. B. BARCENA. and E. PINILLA. Psiquis E 131-136 (1985). K.L. DAVIS, M. DAVIDSON, R.C. MONS. K.S. KENDLER, B.M. DAVIS. C.A. JOHNS, Y. DENIGRIS and T.B. HORVATH. Science 227 1601-1602 (1985). D. PICKAR, R. LABARCA. M. LINNOILA. A. ROY, D. HOMMER. D. EVERETT and S.M. PAUL, Science 225 954-957 (1984). D. PICKAR. R. LABARCA. D. PICKAR. R. LABARCA, A.R. DORAN. Arch. Gen. Psychiat. 43 669-679 (1986). B.S. BUNNEYand A.A. GRACE, Life Sci. 23 1715-1728 (1978). A. CARLSSON and M. LINDQVIST. Acta Pharmacol. et Toxicol. 20 140-144 (1963). M.B. BOWERS, M.E. SWIGAR. P.I. JATLOW and N. GOICOECHEA. J. Clin. Psychiat. 45 248-251 (1984). R. DAVILA. M. ZUMARRAGA. E. MANERO, I. ANDIA and C. CASO. Inf. Psiquiatr. 97 245-250 (1984). R. DAVILA. E. MANERO, C. PEREA. B. BARCENA and M.I. ZAMALLOA. I. Cong. Sot. Esp. Psiquiat 134-135 (1984). R. DAVILA. M. ZUMARRAGA. I. ANDIA. M.I. ZAMALLOA. E. MANERO and C. PEREA. Proc. IV World Cong. Biol Psychiat. Philadelphia (1985). W.H. CHANG. E.K. YEH. W.H. HU. Y.T. TSENG. M.C. CHUNG and H.F. CHANG. Biol. Psychiat. 21 374-381 (1986). K.S. KENDLER, G.c HENINGER and R.H. ROTH, Life Sci. 30 2063-2069 (1982). K.S. KENDLER. R.C. MOHS and K.L. DAVIS, Psychiat. Res. 8 215-223 (1983). M. ZUMARRAGA. I. ANDIA. B. BARCENA. M.I. ZAMALLOA and R. DAVILA, Clin. Chem. (in press). P.CUGINI. F. HALBERG. A. SCHARMM In: Chronobiol._. eds. E. Haus and H.F. Kabat. Karger. New York, pp. 319-324 (1984). M.B. BOWERS and A. ROZITIS. Eur. J. Pharmacol 38 109-115 (1976). N.G. BACOPOULOS. G. BUNTOS. D.E. REDMOND, J. BAULU and R.H. ROTH, Brain Res. 157 396-401 (1978). G. BADGI. A. PERENYI. E. FRECSKA. Psychopharmacology g 62-64 (1985). L. BJERKENSTEDT. G. EDMAN. L. HAGENFELDT. G. SEDVALL and F.A. WIESEL. Brit. J. Psychiat. 147 276-282 (1985). C.F. SALLER and A.I. SALAMA, Neuropharmacology 24 123-129 (1985).