- Email: [email protected]
The expression of the n-methyl-D -aspartate receptor subunit NR-I is decreased in schizophrenia
60
Defects in the limbic cortex associated with schizophrenia are indicated by reduced cerebral glucose utilization in the anterior cingulate cortex and by a decrease in the number of small interneurons in schizophrenic patients. The axon terminals of dopaminergic fibers projecting to the anterior cingulate cortex may also be structurally and functionally altered. This study examined the integrity of DA terminals in the anterior cingulate cortex of schizophrenic patients with an in vitro assay of [3H]GBR 12935 labeled dopamine transporter receptors (DATR). The anterior cingulate cortex was obtained from postmortem brains of 16 schizophrenic and 12 control subjects. Scatchard analysis of individual brain samples indicated a normal affinity (KD) but a 49% reduction in the density of [3H]GBR 12935 binding sites. [Mean (SD) Bmax=303.7 (139) controls; Bmax=156.3 (69) schizophrenics; t=3.69, p<0.001]. The reduction in DATR sites may be the consequence of morphological or functional changes in DA innervation to the anterior cingulate cortex.
THE NMDA RECEPTOR COMPLEX IN THE HIPPOCAMPUS IN SCHIZOPHRENIA
X.F. Huang*, G. Dixon, S.V. Catts, P.B. Ward, D. Wakefield, A. Lloyd
School of Psychiatry, University of NSW, Sydney, N S W 2052, Australia The NMDA (N-methyl-D-aspartate) receptor is a member of the glutamate receptor family and is a heteromeric complex of at least two protein subunits: the NMDAR1 protein plus one or more members of the four NMDAR2 proteins. Activation of NMDA receptors is central to memory acquisition and learning, as well as being critical in excitotoxic neuronal injury. We hypothesize that altered expression of the NMDA receptor complex may underly the pathogenesis of schizophrenia. In the rat, eight alternatively spliced isoforms of NMDAR 1 have been identified and shown to be developmentally regulated, regionally distributed, and functionally unique. We sought to characterize the alternatively spliced isoforms of NMDAR1 and the NMDAR2 subunit mRNAs in the adult human hippocampus. Human brains were obtained (postmortem delay of 4 to 24 h) from individuals without neurological disease, and from characterized cases of schizophrenia. Total RNA was prepared from specific regions of human hippocampal tissue. Reverse transcriptase polymerase chain reactions (RT-PCR) and specific oligonucleotide primers were used to amplify across the two predicted splice junctions of the NMDAR1 cDNA. The amplified cDNAs were characterised in Southern hybridisation using oligonucleotide probes specific for each of the unique splice sequences of NMDAR1. The distribution of the NMDAR1 splice isoforms and the NMDAR2A-D mRNAs was examined using in situ hybridization with specific oligonucleotide probes. Several alternatively spliced isoforms of the human NMDAR1 mRNA were identified. The NMDAR1 isoforms and NMDAR2 subunits are expressed heterogenously within the normal human hippocampus. These data provide the initial basis for understanding the unique composition of NMDA
receptor complexes in specific CNS regions, and may provide clues to the differential susceptibility to schizophrenia. These studies are currently being applied to tissue obtained from schizophrenic cases.
CLINICAL
DETECTION
PROSTAGLANDIN SCHIZOPHRENIA
OF ALTERED
FUNCTION
IN A
SUBTYPE
C.J. H u d s o n * , A. Lin, S. Cogan, J.J. W a r s h
Clarke Institute of Psychiatry, University of Toronto, Toronto, M5T 1R8 Canada The heterogeneity of schizophrenia has significantly impeded progress in understanding the pathophysiology of this illness(es). It may be possible, however, to delineate schizophrenia subtypes based on unique alterations in signal transduction. We propose that a schizophrenia subtype exists with either subsensitive prostaglandin receptors or impaired prostaglandin synthesis. In healthy subjects oral administration of niacin results in vasodilation as the result of large (300-400 fold) increases in serum prostaglandins which, in turn, lead to increased cAMP levels. Development of an analogue-to-digital system allowed for the degree of vasodilation in response to a niacin challenge to be measured with high sensitivity, specificity. We found a blunted response (no vasodilation) in 11/32 neuroleptic treatment whereas all healthy controls and all but 1 bipolar disorder controls (both on and off neuroleptic) demonstrated the expected vasodilation to the niacin challenge. These observations raise the question of whether the blunted response to niacin occurs as a result of and therefore is associated with abnormalities in phospholipid-derived messengers such as prostaglandins.
THE EXPRESSION OF THE N-METHYL-DASPARTATE RECEPTOR S U B U N I T N R - 1 IS DECREASED IN SCHIZOPHRENIA C.R. H u m p h r i e s * , L. Virgo, A. M o r t i m e r , T. Barnes, S. Hirsch, J. de Belleroche
Department of Biochemistry, Charing Cross and Westminster Medical School St. Dunstans Road, London, W6 8RF, UK As yet, no consistent markers of pathology have been established in schizophrenia, although studies have indicated abnormalities in frontal and temporal structures. We have established a brain-bank of schizophrenic patients for which full clinical assessments are available, and are using in situ hybridisation to quantitate levels of neurone specific messenger RNAs (mRNAs) in schizophrenic compared to control subjects. Our early work concentrated on cholecystokinin (CCK) mRNA as CCK-like immunoreactivity has been shown to be depleted in schizophrenia. Results obtained from 16 schizophrenic brains and age-matched controls revealed a significant decrease in
61
CCK mRNA in frontal cortex (BA10) and superior temporal cortex (BA22) in schizophrenia. Go ~-subunit mRNA was also measured for comparison, and no change was found in either region. More recent work has focused on the mRNA encoding a N-methyl-D-aspartate NMDA glutamate receptor subunit (NR-1). A significant decrease in NR-1 mRNA expression was seen in tissue extracts using slot hybridisation and similar results have been obtained from in situ fiybridisation. A possible correlation between changes in CCK and NR-1 mRNA expression and their regional specificity is currently being investigated.
DOPAMINE D3 RECEPTORS ARE ELEVATED IN SCHIZOPHRENIC BRAIN AND DECREASED BY NEUROLEPTIC TREATMENT J.N. Joyce*, E.V. Gurevich, H.F. Kung, M.-P. Kung, Y. Bordelon, R. Shapiro, S.E. A r n o l d , R.E. G u r
Department of PrTchiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6141, USA The cloning, pharmacological characterization and anatomy of novel members of the dopamine (DA) D2 receptor family, including D3 and D4, have led directly to the hypothesis that they may be targets of antipsychotic action. While D2 and D4 receptors are reported to be elevated in post-mortem schizophrenic brain, this may be due to the antipsychotic treatment itself. The pharmacological properties of the D3 receptor is similar to those of the D2 receptor and, thus, is a potential target for the atypical neuroleptics. Their anatomy in human brain suggest a high association with the mesolimbic DA system (Murray et al., PNAS, in press). Hence, its preferential involvement in the functions of the limbic striatum, which is thought to modulate emotional behavior and to be involved in the pathogenesis of schizophrenia. Our post-mortem study revealed elevations (45°/,,-56%) in the number of D3 receptors, labeled with [1251]trans-7-OH-PIPAT, in the basal ganglia and ventral forebrain of 16 chronically hospitalized schizophrenics as compared to 15 controls. Three way analysis by ANOVA showed that binding was significantly elevated in the caudate nucleus, dorsal putamen and ventral putamen of schizophrenic cases off of neuroleptics ( n = 8 ) at time of death while the group on neuroleptics at time of death ( n = 8 ) did not have values different from controls. Elevated binding in the internal and external divisions of the globus pallidus of the schizophrenic group did not differ between those on and off neuroleptics. Neuroleptics were not directly competing for the D3 receptor as there was no change in the affinity for the D3 receptor in the schizophrenic group. Thus, elevated levels of D3 receptors in schizophrenics may be acutely decreased by neuroleptic treatment. This differs from the D2 and D4 receptors that show elevations in patients on neuroleptics. Funding from US Federal Grants MH43880 and AG09215 and by an award from Scottish Rite Benevolent Foundation's Schizophrenia Research Program, N.M.J., USA.
BASAL AND HALOPERIDOL-STIMULATED PROLACTIN IN FIRST DEGREE
RELATIVES
OF SCHIZOPHRENIC
PROBANDS B a r b a r a M. M a t h e s o n , Nicholas A. Keks*, David L. C o p o l o v
Mental Health Research Institute of Victoria and Monash Department of Psychological Medicine, Private Bag 3, P 0 Parkville Victoria 3052, Australia Dopaminergic dysfunction is implicated in the pathophysiology of schizophrenia. Dopamine has a key role in control of prolactin secretion. We have reported abnormalities in basal and haloperidol-stimulated prolactin in some patients with psychoses, particularly those with Kraepalinian schizophrenia (Keks et al., Biol. Psychiatry 32: 426, 1992) and with formal thought disorder in the absence of mood disturbance (Biol. Psychiatry, in press). It is possible that these findings may reflect a trait, rather than a state-dependent dopaminergic dysfunction. In view of the genetic findings in schizophrenia, these abnormalities may also be evident in unaffected first degree relatives schizophrenic probands. Here we report initial findings from 15 relatives and 9 controls of similar age and sex. Basal prolactin was determined in 3 plasma samples over 45 min post-cannulation, 0.5 mg haloperidol was then given intravenously and prolactin concentrations were determined in samples over a further 180 mins. Basal prolactin concentrations were 76.2+10.9 mU/L in relatives and 149+22.7mU/L in controls (p<0.01). There were no differences in prolactin response to haloperidol between relatives and controls, but women as a group had a significantly greater response than men. The results so far have demonstrated the feasibility of the research strategy, and suggest the possibility that a measure of brain dopamine activity may be abnormal in first degree relatives of schizophrenic probands.
MODULATION OF PSYCHOTIC BEHAVIOUR MODELS AND TARDIVE DYSKINESIA BY DNA ANTISENSE OLIGONUCLEOTIDE TO DOPAMINE RECEPTORS
T. Sasaki, A. Vicente, H.H.M. Van Tol, J.N. Nobrega, J.L. Kennedy*
Clarke Institute of Psychiatry, Toronto, Ontario, Canada M5T IR8 Although dopamine D2 family receptors, now classified into D2, D3, and D4, seem to be directly involved in the treatment of psychosis, the specific role of each subtype is unknown. We are investigating the respective roles of these dopamine receptors, by using antisense oligonucleotide injection into rat brain, which allows the specific suppression of each receptor. We are employing disruption of prepulse inhibition of startle response
Defects in the limbic cortex associated with schizophrenia are indicated by reduced cerebral glucose utilization in the anterior cingulate cortex and by a decrease in the number of small interneurons in schizophrenic patients. The axon terminals of dopaminergic fibers projecting to the anterior cingulate cortex may also be structurally and functionally altered. This study examined the integrity of DA terminals in the anterior cingulate cortex of schizophrenic patients with an in vitro assay of [3H]GBR 12935 labeled dopamine transporter receptors (DATR). The anterior cingulate cortex was obtained from postmortem brains of 16 schizophrenic and 12 control subjects. Scatchard analysis of individual brain samples indicated a normal affinity (KD) but a 49% reduction in the density of [3H]GBR 12935 binding sites. [Mean (SD) Bmax=303.7 (139) controls; Bmax=156.3 (69) schizophrenics; t=3.69, p<0.001]. The reduction in DATR sites may be the consequence of morphological or functional changes in DA innervation to the anterior cingulate cortex.
THE NMDA RECEPTOR COMPLEX IN THE HIPPOCAMPUS IN SCHIZOPHRENIA
X.F. Huang*, G. Dixon, S.V. Catts, P.B. Ward, D. Wakefield, A. Lloyd
School of Psychiatry, University of NSW, Sydney, N S W 2052, Australia The NMDA (N-methyl-D-aspartate) receptor is a member of the glutamate receptor family and is a heteromeric complex of at least two protein subunits: the NMDAR1 protein plus one or more members of the four NMDAR2 proteins. Activation of NMDA receptors is central to memory acquisition and learning, as well as being critical in excitotoxic neuronal injury. We hypothesize that altered expression of the NMDA receptor complex may underly the pathogenesis of schizophrenia. In the rat, eight alternatively spliced isoforms of NMDAR 1 have been identified and shown to be developmentally regulated, regionally distributed, and functionally unique. We sought to characterize the alternatively spliced isoforms of NMDAR1 and the NMDAR2 subunit mRNAs in the adult human hippocampus. Human brains were obtained (postmortem delay of 4 to 24 h) from individuals without neurological disease, and from characterized cases of schizophrenia. Total RNA was prepared from specific regions of human hippocampal tissue. Reverse transcriptase polymerase chain reactions (RT-PCR) and specific oligonucleotide primers were used to amplify across the two predicted splice junctions of the NMDAR1 cDNA. The amplified cDNAs were characterised in Southern hybridisation using oligonucleotide probes specific for each of the unique splice sequences of NMDAR1. The distribution of the NMDAR1 splice isoforms and the NMDAR2A-D mRNAs was examined using in situ hybridization with specific oligonucleotide probes. Several alternatively spliced isoforms of the human NMDAR1 mRNA were identified. The NMDAR1 isoforms and NMDAR2 subunits are expressed heterogenously within the normal human hippocampus. These data provide the initial basis for understanding the unique composition of NMDA
receptor complexes in specific CNS regions, and may provide clues to the differential susceptibility to schizophrenia. These studies are currently being applied to tissue obtained from schizophrenic cases.
CLINICAL
DETECTION
PROSTAGLANDIN SCHIZOPHRENIA
OF ALTERED
FUNCTION
IN A
SUBTYPE
C.J. H u d s o n * , A. Lin, S. Cogan, J.J. W a r s h
Clarke Institute of Psychiatry, University of Toronto, Toronto, M5T 1R8 Canada The heterogeneity of schizophrenia has significantly impeded progress in understanding the pathophysiology of this illness(es). It may be possible, however, to delineate schizophrenia subtypes based on unique alterations in signal transduction. We propose that a schizophrenia subtype exists with either subsensitive prostaglandin receptors or impaired prostaglandin synthesis. In healthy subjects oral administration of niacin results in vasodilation as the result of large (300-400 fold) increases in serum prostaglandins which, in turn, lead to increased cAMP levels. Development of an analogue-to-digital system allowed for the degree of vasodilation in response to a niacin challenge to be measured with high sensitivity, specificity. We found a blunted response (no vasodilation) in 11/32 neuroleptic treatment whereas all healthy controls and all but 1 bipolar disorder controls (both on and off neuroleptic) demonstrated the expected vasodilation to the niacin challenge. These observations raise the question of whether the blunted response to niacin occurs as a result of and therefore is associated with abnormalities in phospholipid-derived messengers such as prostaglandins.
THE EXPRESSION OF THE N-METHYL-DASPARTATE RECEPTOR S U B U N I T N R - 1 IS DECREASED IN SCHIZOPHRENIA C.R. H u m p h r i e s * , L. Virgo, A. M o r t i m e r , T. Barnes, S. Hirsch, J. de Belleroche
Department of Biochemistry, Charing Cross and Westminster Medical School St. Dunstans Road, London, W6 8RF, UK As yet, no consistent markers of pathology have been established in schizophrenia, although studies have indicated abnormalities in frontal and temporal structures. We have established a brain-bank of schizophrenic patients for which full clinical assessments are available, and are using in situ hybridisation to quantitate levels of neurone specific messenger RNAs (mRNAs) in schizophrenic compared to control subjects. Our early work concentrated on cholecystokinin (CCK) mRNA as CCK-like immunoreactivity has been shown to be depleted in schizophrenia. Results obtained from 16 schizophrenic brains and age-matched controls revealed a significant decrease in
61
CCK mRNA in frontal cortex (BA10) and superior temporal cortex (BA22) in schizophrenia. Go ~-subunit mRNA was also measured for comparison, and no change was found in either region. More recent work has focused on the mRNA encoding a N-methyl-D-aspartate NMDA glutamate receptor subunit (NR-1). A significant decrease in NR-1 mRNA expression was seen in tissue extracts using slot hybridisation and similar results have been obtained from in situ fiybridisation. A possible correlation between changes in CCK and NR-1 mRNA expression and their regional specificity is currently being investigated.
DOPAMINE D3 RECEPTORS ARE ELEVATED IN SCHIZOPHRENIC BRAIN AND DECREASED BY NEUROLEPTIC TREATMENT J.N. Joyce*, E.V. Gurevich, H.F. Kung, M.-P. Kung, Y. Bordelon, R. Shapiro, S.E. A r n o l d , R.E. G u r
Department of PrTchiatry, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6141, USA The cloning, pharmacological characterization and anatomy of novel members of the dopamine (DA) D2 receptor family, including D3 and D4, have led directly to the hypothesis that they may be targets of antipsychotic action. While D2 and D4 receptors are reported to be elevated in post-mortem schizophrenic brain, this may be due to the antipsychotic treatment itself. The pharmacological properties of the D3 receptor is similar to those of the D2 receptor and, thus, is a potential target for the atypical neuroleptics. Their anatomy in human brain suggest a high association with the mesolimbic DA system (Murray et al., PNAS, in press). Hence, its preferential involvement in the functions of the limbic striatum, which is thought to modulate emotional behavior and to be involved in the pathogenesis of schizophrenia. Our post-mortem study revealed elevations (45°/,,-56%) in the number of D3 receptors, labeled with [1251]trans-7-OH-PIPAT, in the basal ganglia and ventral forebrain of 16 chronically hospitalized schizophrenics as compared to 15 controls. Three way analysis by ANOVA showed that binding was significantly elevated in the caudate nucleus, dorsal putamen and ventral putamen of schizophrenic cases off of neuroleptics ( n = 8 ) at time of death while the group on neuroleptics at time of death ( n = 8 ) did not have values different from controls. Elevated binding in the internal and external divisions of the globus pallidus of the schizophrenic group did not differ between those on and off neuroleptics. Neuroleptics were not directly competing for the D3 receptor as there was no change in the affinity for the D3 receptor in the schizophrenic group. Thus, elevated levels of D3 receptors in schizophrenics may be acutely decreased by neuroleptic treatment. This differs from the D2 and D4 receptors that show elevations in patients on neuroleptics. Funding from US Federal Grants MH43880 and AG09215 and by an award from Scottish Rite Benevolent Foundation's Schizophrenia Research Program, N.M.J., USA.
BASAL AND HALOPERIDOL-STIMULATED PROLACTIN IN FIRST DEGREE
RELATIVES
OF SCHIZOPHRENIC
PROBANDS B a r b a r a M. M a t h e s o n , Nicholas A. Keks*, David L. C o p o l o v
Mental Health Research Institute of Victoria and Monash Department of Psychological Medicine, Private Bag 3, P 0 Parkville Victoria 3052, Australia Dopaminergic dysfunction is implicated in the pathophysiology of schizophrenia. Dopamine has a key role in control of prolactin secretion. We have reported abnormalities in basal and haloperidol-stimulated prolactin in some patients with psychoses, particularly those with Kraepalinian schizophrenia (Keks et al., Biol. Psychiatry 32: 426, 1992) and with formal thought disorder in the absence of mood disturbance (Biol. Psychiatry, in press). It is possible that these findings may reflect a trait, rather than a state-dependent dopaminergic dysfunction. In view of the genetic findings in schizophrenia, these abnormalities may also be evident in unaffected first degree relatives schizophrenic probands. Here we report initial findings from 15 relatives and 9 controls of similar age and sex. Basal prolactin was determined in 3 plasma samples over 45 min post-cannulation, 0.5 mg haloperidol was then given intravenously and prolactin concentrations were determined in samples over a further 180 mins. Basal prolactin concentrations were 76.2+10.9 mU/L in relatives and 149+22.7mU/L in controls (p<0.01). There were no differences in prolactin response to haloperidol between relatives and controls, but women as a group had a significantly greater response than men. The results so far have demonstrated the feasibility of the research strategy, and suggest the possibility that a measure of brain dopamine activity may be abnormal in first degree relatives of schizophrenic probands.
MODULATION OF PSYCHOTIC BEHAVIOUR MODELS AND TARDIVE DYSKINESIA BY DNA ANTISENSE OLIGONUCLEOTIDE TO DOPAMINE RECEPTORS
T. Sasaki, A. Vicente, H.H.M. Van Tol, J.N. Nobrega, J.L. Kennedy*
Clarke Institute of Psychiatry, Toronto, Ontario, Canada M5T IR8 Although dopamine D2 family receptors, now classified into D2, D3, and D4, seem to be directly involved in the treatment of psychosis, the specific role of each subtype is unknown. We are investigating the respective roles of these dopamine receptors, by using antisense oligonucleotide injection into rat brain, which allows the specific suppression of each receptor. We are employing disruption of prepulse inhibition of startle response