Antipsychotic drugs, dopamine receptors, and schizophrenia

Clinical Neuroscience Research 1 (2001) 53±60

www.elsevier.nl/locate/clires

Antipsychotic drugs, dopamine receptors, and schizophrenia Philip Seeman* Departments of Pharmacology and Psychiatry, Medical Science Building, University of Toronto, 8 Taddle Creek Road, Toronto, Ontario, M5S 1A8 Canada

Abstract The clinical potencies of antipsychotic drugs are directly related to their af®nities for the dopamine D2 receptor. In addition, the concentrations of antipsychotic drugs (given at therapeutic maintenance doses) in the plasma water or in the spinal ¯uid are almost identical to the antipsychotic dissociation constants at the dopamine D2 receptor. A consistent 70±75% of brain D2 receptors are occupied by antipsychotic drugs, as calculated from the therapeutic concentration and the antipsychotic dissociation constant. The D3 and D4 dopamine receptors, however, are not consistently occupied by antipsychotic drugs, the occupancies being 0±85% for D3, and 0±95% for D4. Human brain imaging also reveals that therapeutic doses of antipsychotic drugs occupy ,70% of D2 receptors. Between 2 and 4 h after the daily oral dose, clozapine and quetiapine occupy high levels (,70%) of the dopamine D2 receptors in schizophrenia patients, with lower occupancies at 6 and 12 h. Although clozapine and quetiapine occupy low levels of D2 receptors many hours after the oral dose, the observed fraction of D2 receptors occupied by these drugs, however, depends on the radioligand used, with high occupancy seen when using [ 11C]raclopride, and low occupancy seen with [ 11C]methylspiperone (which is tightly bound to D2). This dependence on the radioligand occurs because clozapine and quetiapine are loosely bound to D2. The loose binding of clozapine and quetiapine to D2 permits endogenous dopamine to displace these antipsychotic drugs much more quickly than haloperidol. In addition, the small dose of radioactive raclopride injected (in brain imaging) can displace a little of the D2-bound clozapine. Hence, the observed low level of D2 occupancy by clozapine in patients may arise from a combination of the above three factors ± the ligand dependency, the endogenous dopamine, and the displacement by the imaging dose. Parkinsonism and extrapyramidal effects occur with antipsychotics which have a high af®nity for D2 and which are, therefore, tightly bound to D2. Clozapine and quetiapine have a low af®nity for D2, and, being readily displaced by endogenous dopamine, do not give rise to extrapyramidal effects. Because the loosely bound antipsychotics dissociate from D2 more rapidly, clinical relapse may occur earlier than that found with the tightly bound traditional antipsychotics. The dopamine hypothesis of schizophrenia is supported by the fact that D2 is the main target of antipsychotic action, that monomers of D2 appear elevated in schizophrenia, and that the synaptic levels of dopamine in schizophrenia are at least two-fold higher than in control subjects. q 2001 Association for Research in Nervous and Mental Disease. All rights reserved. Keywords: Antipsychotic drugs; Dopamine receptors; Schizophrenia

1. The clinical potencies of antipsychotic drugs correlate with the dissociation constants at D2 The clinical potencies of antipsychotics correlate with their ability to block dopamine D2 receptors [1±4]. The antipsychotic dissociation constants in Table 1 were obtained using [ 3H]raclopride and human cloned dopamine D2 receptors [5±9]. The average doses for controlling acute schizophrenia correlate with the dissociation constants (Kd values) at the dopamine D2 receptor for antipsychotic drugs, using the data in Table 1. Although chlorpromazine and thioridazine deviate from the overall correlation between the doses and the Kd values, the deviations for these two drugs, however, disappear when the spinal ¯uid concentrations (or the concentrations in the * Tel.: 11-416-978-4891; fax: 11-416-971-2445. E-mail address: [email protected] (P. Seeman).

plasma water) of the various antipsychotic drugs are used [5±9]. 2. Therapeutic concentrations of antipsychotics occupy ,70% of brain D2 receptors To determine whether D2 receptors are consistently occupied to the same extent for every antipsychotic drug, it is possible to calculate or to measure the proportion of D2 receptors occupied in the human brain. The proportion, f, of brain dopamine D2 receptors occupied by an antipsychotic drug, can be calculated, given the concentration, C, of the antipsychotic drug in the plasma water or the spinal ¯uid, and the inhibition (or dissociation) constant, Kd, of the antipsychotic drug, using the equation f ˆ C=…C 1 Kd†. The dissociation constant, however, depends on the radi-

1566-2772/01/$ - see front matter q 2001 Association for Research in Nervous and Mental Disease. All rights reserved. PII: S 1566-277 2(00)00007-4

2 0.66 0.72 44 ± 1.5 1000 0.32 0.35 0.4 5.2 50 0.094 6 3 2.7 0.16 0.06 1.2 0.64 1.6 30 0.3 78 1.6 1.9 0.065 5 0.4 0.96

Bromocriptine Chlorpromazine [ 3H]Chlorpromazine Clozapine [ 3H]Clozaplne Dopamine, D2high Dopamine, D2low Fluphenazine Haloperidol [ 3H]Haloperidol Loxapine Melperone [ 3H]Methylspiperone Molindone Olanzapine [ 3HlOlanzapine Perphenazine Pimozide Prochlorperazine Raclopride [ 3H]Raclopride Remoxipride Risperidone Seroquel Sertindole [ 3H]Sertindole [ 3H]Spiperone Sulplride-S Thioridazine Tri¯uperazine

2.8 1.3 ± 82 ± 2.8 2500 0.53 0.7 ± 9.8 105 ± 9.6 6.4 ± 0.26 0.13 1.7 1.6 ± 80 1 155 1.2 ± ± 8 1.1 1.6

Raclo

D2 (nM)

5 4.8 ± 180 ± 10 8000 1.2 2.9 ± 23 300 ± 15 21 ± 0.48 0.33 4 7.2 ± 800 4 680 6.5 ± ± 10 4 3.8

Spip

D2 (nM)

9 13 ± 385 ± 50 23000 1.9 9.5 ± 45 520 ± 31 45 ± 0.92 0.85 5.3 22 ± 900 19 1400 8.2 ± ± 20 18.5 6.8

Nem.

D2 (nM)

± 38 23 ± 0.58

± 35 14 ± 0.23 2.9 ± 960 3.5 240 3 ± ± 10 1.9 0.7

2 1.6 640 2.5 160 2.5 ± 0.32 6.4 1.5 0.45

4.8 ± 1600 3.6 520 2 ± ± 15 2.5 0.95

0.2 15 ± 28

0.17 8.8 ± 21

0.11 6.2 ± 18 160 ± 20 7.8 ± 0.13

1.8 ± 270 ±

Spip.

D3 (nM)

1.3 ± 190 ±

Raclo

D3 (nM)

0.84 ± 150 ±

None

D3 (nM)

7.9 ± 2500 5.2 780 3 ± ± 30 3.5 1.6

± 76 40 ± 1.1

0.3 23 ± 33

3 ± 340 ±

Nem.

D3 (nM)

30 2 ± 9 700 ± 3500 14 ± 32 70 2400 ± 2400 4.4 2000 9 ± ± 1000 10.5 39

5.4 620 ± 2800 0.25 3000 0.9 0.84 0.089 200 1.5 44

9.5 ± 22 ±

Spip.

D4 (nM)

50 0.84 0.84 7.8 410 ± 2400 1.6 1.6 17

1.2 1.15 1.6 1.6

None

D4 (nM)

Blank spaces, not done; hyphen, not possible; none, the ligand-independent K value obtained by extrapolating all the K values (see text).

None

[ 3H]ligand used

a

D2 (nM)

Human clone:

Table 1 Dissociation constants, K, of antipsychotics for human cloned dopamine and serotonin-2A receptors, using different radio-ligands a

140 4100 ± 2200 18 1600 16 ± ± 2000 26 40

23 2.9 ± 10 800 ± 4300 30 ± 48

23 ± 40 ±

Nem.

D4 (nM)

4400 ± 6600 0.2 135 0.28 ± ± 13 8.8

1.1 7.4

3.8 60 ± 2 180 ± 5200 3.4 ±

2 ± 4 ±

Ket.

S2A (nM)

4000 ± 5200 0.21 110 0.3 0.28 0.57

3.2 46 ± 1.9 150 ± 5800 3 1.6

1.8 ± 3.5 3.5

None

S2A (nM)

2.4 12

6500 ± l0000 0.19 200 0.26 ± ±

5.8 103 ± 2.5 290 ± 5000 4.9 ±

2.8 ± 5.2 ±

Spip.

S2A (nM)

54 P. Seeman / Clinical Neuroscience Research 1 (2001) 53±60

P. Seeman / Clinical Neuroscience Research 1 (2001) 53±60

oligand, as shown in Table 1 [6±8,10]. This is because a higher concentration of antipsychotic drug must be used to compete with a ligand of high fat-solubility, such as [ 3H]spiperone or [ 3H]nemonapride, compared to a ligand of low fat-solubility, such as [ 3H]raclopride. The lowest Kd value is closest to the true Kd value. The lowest Kd values are the ligand-independent ones. These values exactly match the Kd values which were directly obtained using the [ 3H]antipsychotic drug [6±8,10]. The lowest Kd values in Table 1 may be used to calculate the antipsychotic drug occupancies of the D2, D3 and D4 receptors. Such calculations indicate that dopamine D2 receptors are consistently occupied at ,70±75% by therapeutic maintenance doses for all the antipsychotic drugs. This ®nding does not hold for either the D3 receptor (,43% occupied, with remoxipride occupying 0%, and haloperidol having 20% occupancy) or the D4 dopamine receptor (,20% occupied, with values ranging from 0% occupancy by molindone, raclopride, remoxipride and perphenazine, to 95% for clozapine). (The therapeutic concentrations of antipsychotic drugs used to derive the receptor occupancies have been summarized elsewhere [6±10], with data for clozapine from [11]. The average D2-blocking concentration of clozapine (including norclozapine in clozapine equivalents) in the spinal ¯uid is about 230 nM.) The D2 receptors are also ,70% occupied by therapeutic doses of antipsychotics, when directly measured by positron emission tomography or SPET (single photon emission tomography) [12±19] in the human striatum (i.e. the caudate nucleus and/or the putamen). The antipsychotics with low D2 occupancy are clozapine and quetiapine (see later). 3. Endogenous dopamine raises the antipsychotic concentration needed for D2 blockade Because the antipsychotic drug competes with dopamine within the synaptic space, the antipsychotic therapeutic concentration needed to block dopamine receptors in the presence of dopamine will be higher than that in the absence of dopamine, where C50% ˆ Kd‰1 1 D=D2High Š, where D is the dopamine concentration in the synaptic space, and where D2High is the dissociation constant, 1.5 nM, of dopamine at the functional high-af®nity state of the dopamine D2 receptor [20]. The basal level of synaptic dopamine in the rat nucleus accumbens has been estimated to be 4 nM [21]. Hence, although the synaptic average concentration of dopamine, D, is not known, it appears that D is of the same order of magnitude as the dopamine Kd for D2High. Hence, with this single assumption that D , D2High, the above equation of C50% ˆ Kd‰1 1 D=D2High Š reduces to C50% , 2Kd. Moreover, the fraction, f, of D2 receptors occupied by an antipsychotic at a concentration C is C/(C 1 Kd). Thus, it may be shown that the concentration of antipsychotic drug needed to occupy 75% of the D2 receptors (i.e. C75%) is

55

about three times higher than that required to occupy 50% of the receptors, C50%. That is, C75% ˆ 3C50%, or C75% ˆ 6 Kd. Therefore, using the radioligand-independent Kd values in Table 1, the antipsychotic C75% concentrations have been calculated according to the latter equation and found to be virtually identical to the therapeutic concentrations of the antipsychotic drugs in the cerebrospinal ¯uid or in the plasma water (i.e. corrected for drug binding to the plasma proteins). These calculations, therefore, further con®rm the D2 receptor as the main antipsychotic target, and that D2 receptors are 75% occupied at therapeutic maintenance concentrations of antipsychotic drugs. 4. Clozapine and quetiapine have apparently low D2 occupancies In patients taking therapeutically effective antipsychotic doses of clozapine, this drug only occupies between 0 and ,50% of brain dopamine D2 receptors, as measured by a variety of radioligands using either positron tomography [12,13,16,17,22±28], or single photon tomography [29±34]. However, the majority or almost all of these imaging studies have examined schizophrenia patients between 6 and 12 h after the oral administration of clozapine or quetiapine. Recent data by Kapur and colleagues have shown that clozapine and quetiapine occupy high levels (,70%) of the dopamine D2 receptors between 2 and 4 h after the daily oral dose, with lower occupancies at 6 and 12 h [35,36]. The apparently low occupancy of D2 by clozapine at 6 and 12 h after dosing could suggest that D2 is not the major antipsychotic target for clozapine [13,22,37]. However, there are several factors which may account for the apparently low occupancy of D2 by clozapine and quetiapine. First, the fraction of receptors occupied by a drug depends on the radioligand used to measure that receptor [6± 8,10,38]. For example, clozapine occupies ,50% of D2 receptors when using [ 11C]raclopride, but only 20±45% when using the more fat-soluble [ 123I]iodobenzamide. Quetiapine, moreover, occupies ,40±50% when using [ 11C]raclopride, but only ,4% when using the more fatsoluble [ 11C]methylspiperone. Second, we have observed that low concentrations of raclopride and iodobenzamide can displace an appreciable amount of [ 3H]clozapine and [ 3H]quetiapine which are prebound to D2 receptors, but do not displace the more tightly bound antipsychotic [ 3H]ligands, such as [ 3H]haloperidol, [ 3H]chlorpromazine, [ 3H]olanzapine, [ 3H]raclopride, or [ 3H]sertindole [39]. This ®nding suggests that clozapine is loosely bound to the D2 receptor, and that the injected radioactive ligand at its peak concentration may displace a little of the D2-bound clozapine, resulting in an apparently low occupancy of D2 receptors. Therefore, under clinical brain imaging conditions with [ 11C]raclopride, the D2 occupancies by clozapine and by quetiapine may be a little higher

56

P. Seeman / Clinical Neuroscience Research 1 (2001) 53±60

than currently estimated. The same applies for brain imaging with [ 123I]iodobenzamide. Third, a pulse of an endogenous concentration of 100 nM dopamine [21] displaces D2-bound [ 3H]clozapine or [ 3H]quetiapine at least one hundred times faster than D2bound [ 3H]haloperidol or [ 3H]chlorpromazine [39]. Thus, the rapid release of clozapine and quetiapine from dopamine D2 receptors by endogenous dopamine may contribute to low D2 receptor occupancy. 5. `Atypical antipsychotic drugs' which elicit little or no Parkinsonism The blockade of D2 receptors by antipsychotic drugs elicits Parkinsonism and other extrapyramidal signs. Clozapine and quetiapine, however, cause little or no extrapyramidal signs. Other antipsychotics may also cause few extrapyramidal signs if the dose is kept low. A key factor in determining whether a particular antipsychotic drug elicits Parkinsonism is whether it binds more tightly or more loosely than dopamine at the high-af®nity state of the dopamine D2 receptor. The antipsychotic drugs which tend to elicit little or no extrapyramidal signs are those which have Kd values higher than 1.5 nM, which is the Kd for dopamine at the highaf®nity state of D2 (see Table 1). Thus, dopamine binds more tightly to D2 than these `atypical drugs', and the high endogenous dopamine in the human striatum appears to `out-compete' the loosely bound antipsychotic at the D2 receptor. The endogenous dopamine in the limbic brain regions (e.g. frontal cortex, cingulate gyrus), however, is of the order of one-tenth that in the striatum, and so the lower synaptic endogenous dopamine in the limbic regions would not be as effective in out-competing the administered antipsychotic drug. Thus, the D2 occupancy in the human limbic regions would be expected to be somewhat higher than that in the human striatum. That is, the higher output of endogenous dopamine in the striatum readily displaces more D2-bound clozapine in the striatum, compared to the lower output of dopamine in the cerebral cortex. In fact, [40] have found that clozapine occupies more D2 receptors in the cerebral cortex of patients than in the striatum. In avoiding extrapyramidal signs, it appears that the rapid displacement of clozapine by endogenous dopamine may be important. While dopamine can also displace other antipsychotic drugs [41], such as raclopride [42±44], or [ 3H]chlorpromazine [39], such action is not suf®ciently rapid, because these drugs are more tightly bound to D2, compared to clozapine. The separation of antipsychotic drugs into `loose' and `tight' binding to D2, relative to that for dopamine, is consistent with the ®ndings by [45]. These authors were able to reverse catalepsy induced by olanzapine and loxapine (both more loosely bound than dopamine), but were not

able to reverse that by haloperidol (O.H. Kalkman and M.D. Tricklebank, personal communication). 6. The blockade of serotonin receptors does not alleviate catalepsy It has often been suggested that the blockade of serotonin2A receptors may alleviate the catalepsy or Parkinsonism caused by D2 blockade, but most data do not support this hypothesis. For example, selective serotonin-2A receptor blockade enhances the catalepsy of submaximal doses of raclopride (M.-L.G. Wadenburg et al., personal communication). Second, there is no correlation between the cataleptic doses of neuroleptics and the ratio of the antipsychotic dissociation constants at the D2 and at the serotonin-2A receptors, using the values in Table 1. Third, a high degree of serotonin-2A receptor occupancy (95%) by risperidone (6 mg/day) did not prevent extrapyramidal signs in six out of seven patients [46,47]. Fourth, ritanserin (2 mg/kg s.c.) had no effect on raclopride-induced catalepsy, using either maximal (4 mg/kg s.c.) or sub-maximal (0.2 mg/kg s.c.) doses of raclopride [48]. Serotonin-2A receptors, moreover, have little, if any, role in the antipsychotic process, because the blockade of serotonin-2A receptors `is not a prerequisite for the antipsychotic effect' [46,47,49]. In fact, full block of serotonin-2A receptors occurs at markedly subtherapeutic doses of risperidone, olanzapine and clozapine, indicating that serotonin2A block has little or no antipsychotic action [18]. The threshold doses of traditional antipsychotic drugs (for treating ®rst-episode schizophrenia patients) occupy 65± 70% of dopamine D2 receptors. This is true, for example, for haloperidol which does not occupy serotonin-2A receptors in patients. While olanzapine and risperidone fully occupy serotonin-2A receptors at sub-clinical doses, the threshold antipsychotic occupancies of D2 by these two medications are also 65%, despite the high serotonin receptor blockade. This latter ®nding [50] indicates the negligible clinical role of serotonin-2A receptor blockade in alleviating psychosis. Moreover, because clozapine is 20±50-fold more potent in blocking muscarinic acetylcholine receptors than blocking dopamine D2 receptors, clozapine is an extremely potent anticholinergic drug. Clozapine blocks muscarinic receptors between 1.5 and 36 nM, possibly contributing to the absence of Parkinsonism by clozapine. 7. D2 block a necessary minimum for antipsychotic action The consistent ®nding that all antipsychotic drugs, including clozapine, occupy high levels of D2 receptors, suggests that the blockade of D2 is an essential minimal

P. Seeman / Clinical Neuroscience Research 1 (2001) 53±60

requirement for clinical antipsychotic action in those patients who respond to neuroleptics. It is also true, however, that many schizophrenia patients may not clinically improve despite high occupancy (.75%) of their D2 receptors. Although clozapine is selective for the dopamine D4 receptor (Table 1), the clinical antipsychotic action of clozapine appears to be in its D2-blocking ability with its loose block of D2 at 44 nM. This conclusion is based on the ®nding that clozapine ®ts the rule of high levels of D2 block for clinical antipsychotic action, if one allows for the ligand-dependency artifact mentioned above, and if one accepts that a `transient' antipsychotic action of 2±4 h is suf®cient to treat psychotic patients [36]. It has been stated that D2 block is not adequate to explain the antipsychotic action of clozapine because clozapine has a low occupancy of D2, and, second, because clozapine is effective in 30% of patients who are resistant to haloperidol and similar traditional D2-blocking drugs [51]. Such treatment-resistant patients, however, also respond (often dramatically) to remoxipride [52±54], which is extremely selective for D2 (Table 1). In fact, remoxipride clinically improves at least 30% of treatment-resistant schizophenia patients [52±54]. This experience with remoxipride indicates that treatment-resistant patients may still improve via D2-block when using a low potency drug such as clozapine (K ˆ 44 nM at D2) or remoxipride (K ˆ 30 nM at D2). 8. The relapse of patients who stop taking clozapine Patients taking clozapine often relapse within days of stopping clozapine [55,56]. Because clozapine is loosely bound to the dopamine D2 receptor (Kd ˆ 44 nM), clozapine is readily displaced by any sudden pulse of endogenous dopamine arising from emotional or physical activity. In fact, both Conley in [55] and Pickar et al. [57] observed that the D2 occupancy by clozapine readily decreased upon clozapine withdrawal, in contrast to the two weeks or more of residual occupancy of D2 by traditional neuroleptics [58]. Any sudden surge of impulse-triggered release of endogenous dopamine will quickly displace any residual clozapine and may lead to a sudden clinical relapse. 9. Low doses of clozapine or remoxipride are effective in treating l-DOPA psychosis l-DOPA psychosis in Parkinson's disease can be treated by low doses of either clozapine [59±63] or remoxipride [64]. The average dose for clozapine is 55 mg/day, while that for remoxipride is 150 mg/day, much lower than that used in schizophrenia for either drug. Such lower doses follow from the fact that .95% of the brain dopamine has been depleted in Parkinson's disease. Thus, there is virtually no endogenous dopamine to compete against clozapine or remoxipride. The low dose of clozapine

57

corresponds to a low spinal ¯uid concentration of clozapine and norclozapine, estimated to be of the order of 60 nM, given that the unbound clozapine is 20% of the total plasma clozapine [11] (P.Seeman et al. unpublished data). Under these conditions, the fraction of D2 receptors occupied would be about 60% (Where C/(C 1 K) is 60 nM/(60 nM 1 44 nM) ˆ 60% of D2). 10. The dopamine hypothesis of schizophrenia The dopamine hypothesis of schizophrenia is supported by the following. First, the D2 receptor is the common target of antipsychotic drugs. Second, the density of dopamine D2 receptors is elevated in post-mortem schizophrenia tissues [65], as well as in schizophrenia patients, as measured by [ 11C]methylspiperone [22,66], but not by [ 11C]raclopride [67]. The different ®ndings with [ 11C]methylspiperone and [ 11C]raclopride suggests that the two radioligands may bind differently to the D2 receptor. A partial explanation is provided by the observation that D2 receptors can exist as either monomers or dimers in human and rat brain tissue [68], with radiospiperone labeling the monomer, while radio-nemonapride labels both forms of D2, a situation similar to that for cloned D2 receptors which exist in monomer and dimer forms [69± 71]. Thus, if the two benzamides (nemonapride and raclopride) have similar properties, the ®ndings of Wong et al. [66] may suggest that the D2 monomers (labeled by [ 11C]methylspiperone) are elevated in schizophrenia, but that the total population of monomers and dimers of D2 (labeled by [ 11C]raclopride) are the same as in control subjects. The elevation of D2 monomers in schizophrenia [65,66] may arise from the fact that the dopamine in the synaptic space in post-mortem schizophrenia tissues is virtually absent [65], as indicated by the lack of effect of guanine nucleotide on the density of [ 3H]raclopride sites [65]. Third, although the concentration of dopamine in the extracellular synaptic space in post-mortem schizophrenia tissue is low, as just noted, the synaptic level of dopamine in schizophrenia, in the presence of a resting level of neurone ®ring, is at least two-fold higher than in control subjects [42,44,72]. In addition, amphetamine causes a two-fold higher release of dopamine in schizophrenia, compared to control subjects [43,73]. Fourth, the dopamine D1 receptor in¯uences the dopamine D2 receptor, possibly by reducing the proportion of high-af®nity states of D2. This D1±D2 link is reduced or absent in post-mortem tissues from individuals who have died with psychosis in schizophrenia or in Huntington's disease, but not in those who died with either Alzheimer's disease or with non-neurological disorders [74]. Thus, the reduced link could result in more D2 receptors to be in the

58

P. Seeman / Clinical Neuroscience Research 1 (2001) 53±60

high-af®nity state and, therefore, to mediate or enhance the psychotic state, because the high-af®nity state of D2 is the physiological active state [20]. Future research on the dopamine hypothesis of schizophrenia must examine the role that various genes have in expressing or in¯uencing the dopamine system.

[14]

[15]

Acknowledgements Supported by Mr and Mrs Robert Peterson of The Peterson Foundation (University Park, FL) and NARSAD (National Alliance for Research in Schizophrenia and Depression), the Ontario Mental Health Foundation, the Medical Research Council of Canada, the Medland family (J. Aubrey and Helen Medland, Pamela and Desmond O'Rorke, Janet Marsh and David Medland), the National Institute on Drug Abuse, USA, the Stanley Foundation of the NAMI Research Institute, and the Schizophrenia Society of Canada.

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