Neuronal calcium-binding proteins and schizophrenia

Calcium-binding proteins (CBPs) such as calbindin, parvalbumin and calretinin are used as immunohistochemical markers for discrete neuronal subpopulations. They are particularly useful in identifying the various subpopulations of GABAergic interneurons that control output from prefrontal and cingulate cortices as well as from the hippocampus. The strategic role these interneurons play in regulating output from these three crucial brain regions has made them a focus for neuropathological investigation in schizophrenia. The number of pathological reports detailing subtle changes in these CBP-containing interneurons in patients with schizophrenia is rapidly growing. These proteins however are more than convenient neuronal markers. They confer survival advantages to neurons and can increase the neuron's ability to sustain firing. These properties may be important in the subtle pathophysiology of nondegenerative phenomena such as schizophrenia. The aim of this review is to introduce the reader to the functional properties of CBPs and to examine the emerging literature reporting alterations in these proteins in schizophrenia as well as draw some conclusions about the significance of these findings.

The increased activity of plasma manganese superoxide dismutase in tardive dyskinesia is unrelated to the Ala-9Val polymorphism

That tardive dyskinesia (TD) may have its origins in free-radical toxicity has stimulated investigations into one enzyme important in the control of oxidative free radicals: superoxide dismutase (SOD). The manganese-containing form of this enzyme (MnSOD) is the major superoxide scavenger in mitochondria; a weak association between a functional genetic polymorphism (Ala-9Val) in the mitochondrial targeting sequence (MTS) of this enzyme and TD has been reported in a Japanese population. We have undertaken to determine both the plasma activity of MnSOD and the association of the Ala-9Val polymorphism in a well-matched series of male Chinese schizophrenic patients with (n=42) and without (n=59) TD, and normal male controls (n=50). MnSOD activity was elevated in the TD subjects over those without TD (P<0.05) and normal controls (P<0.05), an effect that was independent of age, age at first antipsychotic treatment, drug dosage and duration of illness. A significant positive correlation between total AIMS score and MnSOD activity was also observed (P<0.0001). No significant reduction in the frequency of the Ala allele was observed in the TD group (0.14) below non-TD (0.18) or control subjects (0.17); nor was there any relationship between MnSOD activity and the polymorphism. There was no difference between the mean AIMS scores for the two genotypes (V/V and A/V) in the TD group. We conclude that while we have further evidence of a disturbance in the mechanisms regulating oxidative free radicals in TD, this effect is not under the control of the genetic polymorphism investigated here.

[Association of antipsychotic agent-induced weight gain with a polymorphism of the promotor region of the 5-HT2C receptor gene]

OBJECTIVE

To determine whether 5-hydroxytryptamine 2C (5-HT2C) receptor gene 759C/T polymorphism influences the weight gain following antipsychotic agents (APS) treatment in patient with schizophrenia.

METHODS

DNA was extracted from the peripheral blood of 117 Chinese first-episode patients of Han nationality with schizophrenia diagnosed according to CCMD-II-R criteria. PCR-RELP technique was used to analyse the frequencies of 5-HTR2C receptor gene 759C/T hemizygote (male) and genotype (female). Monotherapy with APS (chlorpromazine or rispperidone) was given for 10 weeks. The body weight was taken and body mass index (BMI) was calculated on admission and every week subsequently for each patient. The correlation of hemizygote or genotype and the BMI was analyzed.

RESULTS

Ten weeks after treatment, there was an average increase in body weight of (3.2 +/- 3.5) kg or (5.7 +/- 6.2)% of the baseline weight with a range of -7 kg approximately 12 kg or -7.8% approximately 32%. The frequency of mutant hemizygote was 58% among the 58 male subjects; the frequency of mutant homozygote was 0%, and the frequency of mutant heterozygote was 27.0% among the 59 female subjects. The body weight gain > 7% occurred in 53% of wild type hemizygote males and 47% of wild type homozygote females; and only 18% of mutant hemizygote males and 13% of mutant heterozygote females. The proportions of 759T hemizygote males or heterozygote females in those with body weight gain > 7% and those with body weight < 7% were significantly different (chi(2) = 22.35, v1, P = 0.000 1; chi(2) = 12.36, v1, P = 0.000 1). Patients without mutant allele were five to six times more likely to develop substantial weight gain (OR = 5.11, 6.68).

CONCLUSION

The 5-HT2C-receptor gene -759C/T polymorphism is associated with APS-induced weight gain. 759C-->T may be a protective factor for the development of weight gain in Chinese schizophrenic patients of Han nationality.

Association of antipsychotic drug-induced weight gain with a 5-HT2C receptor gene polymorphism

A side-effect of treatment with antipsychotic drugs for schizophrenia is increased body fat, which leads to further morbidity and poor adherence to treatment. The 5-hydroxytryptamine 2C receptor (5-HT2C) has been associated with this effect; we aimed to establish whether a genetic polymorphism of the promoter region of this receptor affects weight gain after drug treatment in first-episode patients with schizophrenia. We noted significantly less weight gain in patients with the -759T variant allele (p=0.0003) than in those without this allele, who were more likely to have substantial (>7%) weight gain (p=0.002). We have identified a genetic factor that is associated with antipsychotic drug-induced weight gain.

A selective reduction in the relative density of parvalbumin-immunoreactive neurons in the hippocampus in schizophrenia patients

OBJECTIVES

To determine the relative densities of the GABAergic subpopulation defined by calcium-binding proteins and to further study the importance of changes in GABAergic interneurons on neuropathology in the hippocampus in schizophrenia cases.

METHODS

The relative densities and neuronal body size of cells immunoreactive for the calcium-binding proteins parvalbumin and calretinin as well as the area size of the hippocampal sub-fields were determined from the hippocampal tissue sections taken from schizophrenic patients and well-matched control subjects (15 per group).

RESULTS

No significant difference in the density of calretinin-immunoreactive neurons and the neuronal body size of calretinin-positive neurons was found between subject groups. Relative to normal controls, schizophrenic patients showed a significant and profound deficit in the relative densities of parvalbumin-immunoreactive neurons in all hippocampal sub-fields. These reductions were more apparent in male schizophrenic patients and were unrelated to antipsychotic drug treatment, age or duration of illness.

CONCLUSION

The findings provide further evidence to support a profound and selective abnormality of a sub- population of GABAergic neurons in the hippocampus in schizophrenia cases, and are consistent with the etiological hypothesis of the neurodevelopment of schizophrenia.

A selective decrease in the relative density of parvalbumin-immunoreactive neurons in the hippocampus in schizophrenia

Neuropathological studies have demonstrated deficits of GABAergic interneurons in the hippocampus in schizophrenia. and selective deficits in some GABAergic sub-populations defined by calcium-binding proteins (CBPs) have been reported in the cortex in schizophrenia. In the present study, the relative densities of cells immunoreactive for the CBPs parvalbumnin (PV) and calretinin (CR) were determined in hippocampal tissue sections taken from patients with schizophrenia, bipolar disorder and major depression and from matched control subjects (15 per group). No significant difference in the density of CR-immunoreactive neurons was found between subject groups. Relative to normal controls, schizophrenic patients showed a significant and profound deficit in the relative density of PV-immunoreactive neurons in all hippocampal sub-fields. These reductions were more apparent in male than female schizophrenic patients, and were unrelated to antipsychotic drug treatment, age or duration of illness. The density of PV-immunoreactive neurons did not differ significantly from controls in the depression group, although a trend toward decreased relative density of PV-immunoreactive neurons was apparent in bipolar disorder that reached significance in one sub-field. The findings provide further evidence to support a profound and selective abnormality of a sub-population of GABAergic neurons in the hippocampus in schizophrenia.

Understanding the neurotransmitter pathology of schizophrenia: selective deficits of subtypes of cortical GABAergic neurons

Research aimed at understanding the neurotransmitter pathology of schizophrenia has been underway for half a century, with much emphasis on the dopamine system. Although this approach has advanced our understanding of treatment mechanisms, identification of primary dopaminergic abnormalities in the disease has been elusive. The increasing emphasis on a neuronal pathology of schizophrenia has led to the identification of abnormalities in GABAergic and glutamatergic systems; and we have identified selective deficits in GABAergic interneurons containing the calcium binding proteins parvalbumin and calbindin. Here we report further evidence for a loss of parvalbumin-immunoreactive neurons in both dorsolateral prefrontal and medial temporal cortex, indicating that these deficits are consistent with a subtle neurodevelopmental pathogenesis and hypothesizing that they may contribute to a further degenerative process in schizophrenia.

The role of dopamine in motor symptoms in the R6/2 transgenic mouse model of Huntington's disease

In both Huntington's disease (HD) patients and genetic mouse models of HD, there is a pre-symptomatic loss of dopamine (DA) receptors, suggesting that dysfunctional dopaminergic neurotransmission may be involved in early HD presentation. However, the role of DA in HD symptoms is not fully understood. In this study, we examined the possibility that dysfunctional dopaminergic neurotransmission contributes to the progressive decline in motor function of a transgenic mouse model of HD (R6/2 line). We found that R6/2 mice display an age-dependent abnormal behavioural response to (+)-methamphetamine (METH) and a dose-dependent increase in sensitivity to METH toxicity compared with wild-type (WT) mice. R6/2 mice also showed an attenuated response to cocaine, indicating that DA release may be compromised. Striatal DA levels were reduced in R6/2 mice by 9 weeks of age. Replacement of DA by chronic treatment with laevodopa (L-DOPA, administered as Sinemet) caused short-term improvements in activity and rearing behaviour, and abolished abnormal spontaneous hindlimb grooming. However, long-term treatment with L-DOPA had deleterious effects on survival and rotarod performance of R6/2 mice. These results suggest that dysfunctional DA neurotransmission contributes to phenotype development in R6/2 mice and thus also may be important in symptom progression in HD.

The atypical antipsychotic olanzapine enhances ingestive behaviour in the rat: a preliminary study

The weight gain associated with several antipsychotic drugs, most notably the newer 'atypical' compounds olanzapine and clozapine, introduces problems of compliance and morbidity in the treatment of schizophrenia. The mechanisms underlying this process have been little studied due to the lack of models of the effects of antipsychotic drugs on weight gain and/or feeding behaviour in vivo. Here, we report how the effects of olanzapine (0.5 mg/kg, i.p.) on ingestive behaviour were investigated in the food-deprived rat using a runway to food goal paradigm. Compared with vehicle-treated animals, olanzapine delayed the reductions in food intake and in running speed that occurred after the first trial blocks, without effects on starting speed. These results indicate that olanzapine can increase feeding behaviour through a suppression of satiety, suggesting a mechanism for its effects on weight gain and also providing an acute model for further assessment of the underlying pharmacology.

Phospholipid fatty acids and neurotoxicity in human neuroblastoma SH-SY5Y cells

The fatty acid composition of phospholipids from differentiated human neuroblastoma SH-SY5Y cells, human and rat brain tissue and rat brain synaptosomes was determined using high pressure liquid chromatography. Comparison of the fatty acid composition of the cells with that derived from brain tissue identified differences in the cells including a profound deficit of docosahexaenoic acid and an elevation of arachidonic acid. The phospholipid fatty acid content could be modified by addition of free fatty acids to the growth medium, and this was shown to influence the susceptibility of the SH-SY5Y cells to the cell death induced by a mitochondrial toxin, 3-nitropropionic acid.

Neurochemical correlates of cortical GABAergic deficits in schizophrenia: selective losses of calcium binding protein immunoreactivity

Deficits in a variety of different neurochemical species are consistent with a loss of cortical gamma-aminobutyric acid (GABA)ergic interneurons in schizophrenia. As well as neurochemical markers that indicate all neurons using GABA as a transmitter, and which include GABA uptake sites and glutamate decarboxylase, deficits of certain neuropeptides and calcium binding proteins coexisting with GABA have been reported. These abnormalities are indicative of losses specific to certain subtypes of GABAergic neurons. The calcium binding proteins in particular demonstrate selective deficits; we find losses of parvalbumin- and calbindin-, but not calretinin-immunoreactive cells in the prefrontal cortex in schizophrenia. These selective reductions in the density of parvalbumin- and calbindin-containing neurons could reflect functional loss of expression in intact cells or alternatively a deficit in the density of certain GABAergic neuronal subtypes. The latter interpretation is consistent with a neurodevelopmental pathogenesis involving neuronal damage at a time prior to the expression of these protective calcium-binding proteins. In this review we discuss the evidence for altered GABAergic transmission in schizophrenia.

GABAergic neuronal subtypes in the human frontal cortex--development and deficits in schizophrenia

Recent studies have provided evidence for a deficit of GABA-containing interneurons in the frontal cortex in schizophrenia. That this deficit might be brought about during early foetal or neonatal life is a hypothesis consistent with the substantial indications for a neurodevelopmental aetiology of the disease. GABAergic neurons can be defined by the presence of one of three types of calcium binding proteins, which are thought to have neuroprotective properties. We have undertaken an investigation into the postnatal ontology of these neuronal subtypes and find that calretinin expression is relatively constant and present from before birth, calbindin expression is also present early but redistributes in the cortex over the first months of life, while parvalbumin-immunoreactivity is not observed until between 3 and 6 months of age. Investigation of frontal cortical tissue taken post mortem from a series of schizophrenic patients and matched control subjects revealed that parvalbumin-, but not calretinin-immunoreactive cells are significantly diminished in schizophrenia. These observations support the hypothesis that GABAergic deficits in schizophrenia may stem from toxic events occurring during cortical development which selectively target immature neurons before protection by parvalbumin is conferred.

Increased density of glutamate/N-methyl-D-aspartate receptors in superior temporal cortex in schizophrenia

Saturable radioligand binding of [(3)H]L-689,560 to the glycine site of the N-methyl-D-aspartate (NMDA) receptor was determined bilaterally in superior temporal cortex (BA22) and prefrontal cortex (BA10) taken post mortem from patients with schizophrenia and matched control subjects. A significant increase in NMDA receptor density above control values was found bilaterally in BA22 in schizophrenia, but not in BA10. The effect was greatest in those patients described as primarily type II, in whom the effect was significantly lateralized, with a greater elevation in the left hemisphere. A significant decrease in NMDA receptor density was found in rat frontal cortex following chronic antipsychotic drug administration, indicating that prior drug treatment was unlikely to have contributed to the differences in schizophrenia.

Antipsychotic drug use in neurodegenerative disease in the elderly: problems and potential from a pharmacological perspective

The past decade has seen the introduction of several new antipsychotics for the treatment of schizophrenia. These drugs demonstrate substantially lower levels of extrapyramidal side effects (EPS) than the classical antipsychotics, as well as having (often poorly supported) claims of increased efficacy at ameliorating certain schizophrenic syndromes. Increasingly, these 'atypical' drugs are being used in the treatment of psychotic or related behavioural disturbances in patients with neurodegenerative disease. Thus, some newer antipsychotics are particularly valuable in ameliorating the L-dopa-induced psychosis in Parkinson's disease, while behavioural problems in dementing disorders, such as those occurring in Alzheimer's disease, are also frequently treated by antipsychotic drugs. The relationship between drug pharmacology and neurotransmitter pathology is essential to understanding the relative efficacy of individual antipsychotic drugs in treating the psychotic and behavioural disturbances of neurodegenerative disorders.

Plasma homovanillic acid in untreated schizophrenia--relationship with symptomatology and sex

Plasma homovanillic acid (pHVA) concentrations are considered to reflect, in part, central dopamine metabolism and thus may be of value in assessing the role of dopamine neurotransmission in schizophrenia. Furthermore, some recent studies have suggested a relationship of pHVA with symptomatology. We have undertaken a study of pHVA in a large cohort of unmedicated DSM-IV schizophrenic patients in order to assess the relationship of pHVA to various clinical parameters. pHVA in 58 drug-free patients (10.11+/-0.52 ng/ml) was significantly elevated in comparison with 62 matched control subjects (8.77+/-0.39 ng/ml). pHVA was found to be higher in patients with a more negative syndrome. No significant correlation of pHVA with overall SAPS or SANS scores was apparent in the patients although, within the SANS subscales, a significant relationship to anhedonia-asociality was apparent. Interestingly, the male drug-free patients showed a correlation of pHVA with negative symptoms defined by SANS and several SANS subscales, while females showed no significant relationship with any SANS subscales. The results may suggest that an increased dopaminergic turnover is apparent in (male) schizophrenic patients with predominantly negative symptoms, providing some support for reports that this change in neuronal activity may be related to the neuropathological abnormalities seen in the disease, which may themselves differ between males and females. Such neuronal deficits of developmental or degenerative origin may thus result in an elevation/disinhibition of central dopamine metabolism in schizophrenia.

Relationship of symptomatology, gender, and antipsychotic drug treatment with plasma homovanillic acid in schizophrenia

AIM

To study the role of dopamine neurotransmission in schizophrenia and its drug treatment by assessing the relationship of plasma homovanillic acid (pHVA), a major central dopamine metabolite to various clinical parameters in schizophrenic patients.

METHODS

pHVA was measured by high-performance liquid chromatography with electrochemical detection in a large cohort of both medicated and unmedicated DSM-IV schizophrenic patients. Prior to the measurement of pHVA, the patients were rated on the schedule for the assessment of positive and negative symptoms (PANSS).

RESULTS

(1) pHVA in 46 patients receiving antipsychotic drugs was decreased, and in 58 drug-free patients increased, (7.4+/-2.7) microg/L and (10+/-4) microg/L compared with a matched control group (9 microg/L+/-3 microg/L, n=62) (ANOVA F=8.57, df=2, P < 0.01), respectively. Within the drug-free group, pHVA was higher in the patients with a more negative symptom profile. (2) No significant correlation of pHVA with overall SAPS or SANS scores was apparent in the drug-free patients, although within the SANS subscales, a significant relationships to anhedonia-asociality (r=0.32, P < 0.05) was apparent. The male drug-free patients showed a positive correlation of pHVA with negative symptoms (r=0.42, P < 0.05) while females showed no significant relationship with any PANSS subscales.

CONCLUSION

The results suggest that an increased dopaminergic metabolism is apparent in (male) schizophrenic patients with predominantly negative symptoms, supporting reports that this change in neuronal activity may be related to the neuropathological abnormalities seen in the disease, which may differ between males and females. Such neuronal deficits of developmental origin may thus result in an elevation/disinhibition of central dopamine metabolism in schizophrenia.

The new antipsychotics--some pharmacological aspects of their problems and potential

The drug treatment of schizophrenia still offers many challenges, despite the efficacy of the classical antipsychotics. Although the more recently introduced drugs demonstrate a diminished incidence of certain side effects, notably extrapyramidal motor symptoms, it is clear that they do not adequately address all symptoms of the disease. In addition, weight gain remains a major problem following treatment with many older and newer antipsychotic drugs. Nevertheless, some progress has been made towards ameliorating negative, depressive and cognitive features of schizophrenia. The newer antipsychotics show differential effects against these and other symptoms and thus their pharmacological profiles provide us with clues as to the receptor mechanisms underlying their therapeutic and side effects.

Agonist-stimulated GTPgamma[35S] binding to 5-HT(1A) receptors in human post-mortem brain

In this study, we have demonstrated that the technique of agonist-stimulated guanosine-5'-O-(3-[35S]thio)-triphosphate (GTPgamma[35S]) binding can be successfully used to study the functional activity of the human 5-HT(1A) receptor in post-mortem tissue. Full agonist and antagonist actions of ligands specific for this site have been shown. Utilising 4-(2'-methoxy-phenyl)-1-[2'-(n-2''-pyridinyl)-p-fluorobenzamido]- ethyl-piperazine ([3H]MPPF), the affinity of several antipsychotics for the 5-HT(1A) receptor was determined; clozapine and quetiapine were found to have K(i) values at this receptor that, relative to their dopamine D(2) receptor affinities, indicated at least partial receptor occupancy at clinical doses. The agonist/antagonist activity of these two antipsychotics was studied using GTPgamma[35S] binding. Both compounds show partial agonism, and in addition, clozapine exhibited a larger degree of antagonism against 5-HT-stimulated binding than did quetiapine.

Deficits of NMDA receptors and glutamate uptake sites in the frontal cortex in AIDS

HIV infection frequently leads to neurological deficits and is associated with neuronal loss and damage. We have investigated two neurochemical indicators of the integrity of glutamatergic systems in brain tissue taken postmortem from the frontal cortex of AIDS patients and age-matched controls. NMDA receptor density was determined by saturation analysis of [3H]L-689,560 occupation of the glycine binding site, while saturable [3H]D-aspartate binding provided a marker of the glutamate uptake site. NMDA receptor density was significantly reduced by 33% in the AIDS group, an effect which was more profound in the demented patients, and ligand binding to the glutamate uptake site was significantly reduced by >50% in demented AIDS patients compared with the control group. These reported glutamatergic deficits are consistent with an NMDA-receptor mediated excitotoxic mechanism being responsible for the neuronal loss occurring in AIDS.

Effects of excitotoxic lesions of the rat prefrontal cortex on CREB regulation and presynaptic markers of dopamine and amino acid function in the nucleus accumbens

The present study investigated the effects of excitotoxic lesions of the prefrontal cortex (PFC) on dopamine (DA) and excitatory amino acid (EAA) function in the nucleus accumbens core using in vivo microdialysis in freely moving rats. As a postsynaptic marker of neuronal function, the nuclear levels of the transcriptional factor CREB and its active phosphorylated form, CREB-P, were measured in the ventral tegmental area (VTA), and in the core and shell subregions of the nucleus accumbens of sham and lesioned animals. PFC-lesioned animals exhibited a greater locomotor response to novelty and amphetamine administration (125-500 microg/kg i.v.). No change was observed in extracellular levels of glutamate or saturable d-aspartate binding (a marker for the high-affinity EAA transporter) in the nucleus accumbens of PFC-lesioned animals. Extracellular levels of DA were comparable in sham and lesioned animals under tonic conditions, however, following amphetamine administration, DA efflux was significantly attenuated in lesioned animals. No correlation was observed between microdialysate levels of amino acids and the attenuated dopaminergic response to amphetamine in lesioned animals. Further, no effect of the lesion was found on nuclear CREB protein in saline- and amphetamine-treated rats. The density of CREB-P immunoreactive nuclei, while remaining unchanged in the VTA, increased in the nucleus accumbens shell following amphetamine treatment in lesioned animals. The results show that an important modulatory role of the PFC on the behavioural response to novelty and amphetamine is associated with the level of immediate-early gene regulation rather than levels of extracellular DA and amino acids in the ventral striatum.

Brain neurotransmitter deficits in mice transgenic for the Huntington's disease mutation

Huntington's disease (HD) is associated with an expansion in the CAG repeat sequence of a gene on chromosome 4, resulting in a neurodegenerative process particularly affecting the striatum and with profound but selective changes in content of various neurotransmitters. Recently, transgenic mice expressing a fragment of the human HD gene containing a large CAG expansion have been generated; these mice exhibit a progressive neurological phenotype that includes motor disturbances, as well as neuronal deficits. To investigate their underlying neurotransmitter pathology, we have determined concentrations of GABA, glutamate, and the monoamine neurotransmitters in several brain regions in these mice and control animals at times before and after the emergence of the behavioural phenotype. In contrast to the findings in HD, striatal GABA was unaffected, although a deficit was observed in the cerebellum, consistent with a dysfunction of Purkinje cells. Losses of the monoamine transmitters were observed, some of which are not seen in HD. Thus, 5-hydroxytryptamine and, to a greater extent, 5-hydroxyindoleacetic acid levels were diminished in all brain regions studied, and noradrenaline was particularly affected in the hippocampus. Dopamine was decreased in the striatum in older animals, parallelling evidence for diminished dopaminergic activity in HD.

Antipsychotic drug affinities at alpha2-adrenoceptor subtypes in post-mortem human brain

Although there is substantial interest in the possible role of alpha2-adrenoceptors in the antipsychotic efficacy of clozapine, there has so far been no systematic investigation of antipsychotic drug affinities for alpha2-adrenoceptor subtypes in the human brain. We have assessed the ability of three classical and four 'atypical' antipsychotic drugs to displace binding of [3H]RX821002 to alpha2-adrenoceptors in human post-mortem brain tissue. All seven drugs displaced radioligand from an apparent single site in the frontal cortex, consistent with the sole presence of the alpha2A-subtype in this region. In the caudate nucleus, all drugs except risperidone differentiated two sites, of which one was equivalent to the cortical alpha2A-subtype and the second, accounting for approximately two-thirds of specific radioligand binding, showed higher affinity for the antipsychotics. This second site, on the basis of prazosin's relatively high affinity, is consistent with an alpha2B-adrenoceptor identity. The new antipsychotic quetiapine showed the greatest selectivity for this receptor site; both quetiapine and clozapine had affinities for the alpha2B site which were greater than their affinities for human D2 dopamine receptors. The possible role of this site in the mechanisms underlying aspects of antipsychotic drug atypicality is discussed.