Low HVA and normal 5HIAA CSF levels in drug-free schizophrenic patients compared to healthy volunteers: correlations to symptomatology and family history

Consensus on potential biomarkers developed for use in clinical tests for schizophrenia

Background

Schizophrenia is a serious mental illness affecting approximately 20 million individuals globally. Both genetic and environmental factors contribute to the illness. If left undiagnosed and untreated, schizophrenia results in impaired social function, repeated hospital admissions, reduced quality of life and decreased life expectancy. Clinical diagnosis largely relies on subjective evidence, including self-reported experiences, and reported behavioural abnormalities followed by psychiatric evaluation. In addition, psychoses may occur along with other conditions, and the symptoms are often episodic and transient, posing a significant challenge to the precision of diagnosis. Therefore, objective, specific tests using biomarkers are urgently needed for differential diagnosis of schizophrenia in clinical practice.

Aims

We aimed to provide evidence-based and consensus-based recommendations, with a summary of laboratory measurements that could potentially be used as biomarkers for schizophrenia, and to discuss directions for future research.

Methods

We searched publications within the last 10 years with the following keywords: ‘schizophrenia’, ‘gene’, ‘inflammation’, ‘neurotransmitter’, ‘protein marker’, ‘gut microbiota’, ‘pharmacogenomics’ and ‘biomarker’. A draft of the consensus was discussed and agreed on by all authors at a round table session.

Results

We summarised the characteristics of candidate diagnostic markers for schizophrenia, including genetic, inflammatory, neurotransmitter, peripheral protein, pharmacogenomic and gut microbiota markers. We also proposed a novel laboratory process for diagnosing schizophrenia in clinical practice based on the evidence summarised in this paper.

Conclusions

Further efforts are needed to identify schizophrenia-specific genetic and epigenetic markers for precise diagnosis, differential diagnosis and ethnicity-specific markers for the Chinese population. The development of novel laboratory techniques is making it possible to use these biomarkers clinically to diagnose disease.

A New Look on an Old Issue: Comprehensive Review of Neurotransmitter Studies in Cerebrospinal Fluid of Patients with Schizophrenia and Antipsychotic Effect on Monoamine's Metabolism

Neurotransmitters metabolism has a key role in the physiopathology of schizophrenia as demonstrated by studies measuring monoamine metabolites in patient’s cerebrospinal fluid (CSF) since the beginning of the antipsychotic use. This comprehensive review aims to understand the anomalies of CSF monoamines in schizophrenia and their correlation with clinical and paraclinical features. We also review the influence of antipsychotic treatment on CSF monoamines and discuss the connection with metabolic and inflammatory processes. Studies comparing CSF homovanillic acid (HVA) levels between patients and controls are miscellaneous, due to the heterogeneity of samples studies. However, low HVA is associated with more positive symptoms and a poorer outcome and negatively correlated with brain ventricle size. Based on humans and animals’ studies, antipsychotic treatments increase HVA during the first week of administration and decrease progressively over the time with a fall-off after withdrawal. 5‐hydroxyindolacetic acetic acid levels do not seem to be different in the patient’s CSF compared to controls. Considering metabolic co-factors of neurotrans-mitters synthesis, there is evidence supporting an increase of kynurenic acid in the CSF of patients with schizophrenia. Few studies explore folate metabolism in CSF. Literature also emphasizes the relationship between folate metabolism, inflammation and monoamine’s metabolism. Those results suggest that the CSF monoamines could be correlated with schizophrenia symptoms and treatment outcome. However, further studies, exploring the role of CSF monoamines as biomarkers of disease severity and response to treatment are needed. They should assess the antipsychotic prescription, inflammatory markers and folate metabolism as potential confounding factors.

Biological correlates of personality: considerations on the possible usefulness of central nervous system peripheral markers

Although a great deal of biological research has been carried out on several psychiatric disorders, it is disappointing to see how little progress has been made in the field of the biology of personality. The authors underline the methodological problems that arise in the investigation of biological substrates of human personality and review both currently available and putative peripheral markers of the central nervous system that might be used in further human studies.

No major influence of regular tobacco smoking on cerebrospinal fluid monoamine metabolite concentrations in patients with psychotic disorder and healthy individuals

Metabolism of the monoamines dopamine, serotonin and noradrenaline, is altered in the central nervous system of people with schizophrenia, and their major metabolites homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG), respectively, have been intensively studied as indirect measures of these neurotransmitters in cerebrospinal fluid (CSF). Regular tobacco smoking has been shown to alter neurotransmitter metabolism in the brain and studies have found CSF monoamine metabolite concentrations to be substantially lower in smokers. However, few studies investigating these monoamines in CSF have controlled for regular tobacco smoking. We investigated if regular tobacco smoking influences CSF HVA, 5-HIAA and MHPG concentrations in patients treated for psychotic disorders (n = 69) and healthy non-psychotic human volunteers (n = 200). After lumbar puncture CSF samples were analyzed with mass fragmentography. CSF HVA, 5-HIAA and MHPG concentrations did not significantly differ between smokers and non-smokers neither in patients, nor in healthy subjects, whereas back-length predicted HVA and 5-HIAA and antipsychotic medication MHPG concentrations. The results indicate that regular tobacco smoking has no significant effect on monoamine metabolite concentrations in CSF. This suggests that lack of controlling for regular tobacco smoking should not substantially violate the results in studies of the major monoamine metabolites in CSF.

Risk factors for suicide among patients with schizophrenia: a cohort study focused on cerebrospinal fluid levels of homovanillic acid and 5-hydroxyindoleacetic acid

BACKGROUND

The objective of this study was to investigate the association between 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) in cerebrospinal fluid (CSF), bullying, and later suicide among patients with schizophrenia.

METHODS

Ninety-nine patients with schizophrenia were included. Correlations of clinical factors, 5-HIAA and HVA, and later suicide were investigated.

RESULTS

Twelve patients committed suicide (12%) during a 28-year follow-up period. Later suicide was correlated to bullying in childhood (P=0.02) and a lower quotient of HVA/5-HIAA in CSF (P<0.05).

CONCLUSION

Suicide in schizophrenia is related to childhood exposedness and CSF neurotransmitter levels.

Cerebrospinal fluid monoamine metabolite concentrations as intermediate phenotypes between glutamate-related genes and psychosis

Glutamate-related genes have been associated with schizophrenia, but the results have been ambiguous and difficult to replicate. Homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) are the major degradation products of the monoamines dopamine, serotonin and noradrenaline, respectively, and their concentrations in the cerebrospinal fluid (CSF), mainly HVA, have been associated with schizophrenia. In the present study, we hypothesized that CSF HVA, 5-HIAA and MHPG concentrations represent intermediate phenotypes in the association between glutamate-related genes and psychosis. To test this hypothesis, we searched for association between 238 single nucleotide polymorphisms (SNPs) in ten genes shown to be directly or indirectly implicated in glutamate transmission and CSF HVA, 5-HIAA and MHPG concentrations in 74 patients with psychotic disease. Thirty-eight nominally significant associations were found. Further analyses in 111 healthy controls showed that 87% of the nominal associations were restricted to the patients with psychosis. Some of the psychosis-only-associated SNPs found in the d-amino acid oxidase activator (DAOA) and the kynurenine 3-monooxygenase (KMO) genes have previously been reported to be associated with schizophrenia. The present results suggest that CSF monoamine metabolite concentrations may represent intermediate phenotypes in the association between glutamate-related genes and psychosis.

Changes in gene expression and methylation in the blood of patients with first-episode psychosis

Schizophrenia is a severe mental health disorder with high heritability. The investigation of individuals during their first-episode psychosis (FEP), before the progression of psychotic disorders and especially before treatment with antipsychotic medications, is particularly helpful for understanding this complex disease and for the identification of potential biomarkers. In this study, we compared the expression of genes that are involved in neurotransmission and neurodevelopment of antipsychotic-naive FEP in the peripheral blood of patients (n=51) and healthy controls (n=51). In addition, we investigated the differentially expressed genes with respect to a) DNA methylation, b) the correlation between gene expression and clinical variables (PANSS), and c) gene expression changes after risperidone treatment. Expression levels of 11 genes were quantified with SYBR Green. For methylation analysis, bisulfite sequencing was performed. A significant decrease in GCH1 mRNA levels was observed in FEP patients relative to controls. Also, when we compare the FEP patients after risperidone treatment with controls, this difference remains significant, and no significant differences were observed in GCH1 mRNA levels when comparing patients before and after risperidone treatment. Additionally, although the differences were non-significant after Bonferroni correction, the expression of GCH1 seemed to be correlated with PANSS scores, and the GCH1 promoter region was more methylated in FEP than in controls, thus corroborating the results obtained at the mRNA level. Few studies have been conducted on GCH1, and future studies are needed to clarify its potential role in the progression of schizophrenia.

Neuropeptide Y, social function and long-term outcome in schizophrenia

There is a lack of biomarkers in schizophrenia and the mechanisms underlying the observed deficits in social functioning are poorly understood. This cohort study aimed to explore whether neurotransmitter neuropeptide Y (NPY) in cerebrospinal fluid (CSF) from patients with schizophrenia is correlated to social function and clinical variables. A further aim was to determine whether baseline levels of NPY were associated with subsequent 3-year outcome. Fifty-six consecutively admitted patients with schizophrenia were included and underwent lumbar puncture and symptom ratings before antipsychotic treatment. NPY levels in CSF were determined by radioimmunoassay. Social function (Social Competence and Social Interest) was assessed by Nurses' Observation Scale for Inpatient Evaluation while psychiatric symptoms were rated using the Comprehensive Psychopathological Rating Scale. Three-year outcome was assessed with the Strauss-Carpenter Outcome Scale. Cross-sectional analysis showed a correlation between level of NPY and Social Competence at index admission (r(s)=0.37, p<0.05). The longitudinal analysis (i.e., at the 3-year follow-up) indicated that, for each standard deviation increase in baseline NPY, there was an increased risk of being unemployed (odds ratio [OR] 2.02, 95% confidence interval [CI] 1.07-3.82), having moderate or severe symptoms (OR 3.09, CI 1.30-7.32) or being hospitalized at least 6 months the previous year (OR 3.24, CI 1.09-9.64). However, NPY was not correlated to Social Interest or clinical variables at index admission. In conclusion, NPY levels in CSF are correlated to Social Competence and seem to predict some aspects of longitudinal outcome in schizophrenia.

Presynaptic dopaminergic function: implications for understanding treatment response in psychosis

All current antipsychotic drugs block dopamine (DA) receptors, but the nature of the DA dysfunction in schizophrenia has not been clear. However, consistent evidence now shows that presynaptic dopaminergic function is altered in schizophrenia, specifically in terms of increased DA synthesis capacity, baseline synaptic DA levels, and DA release. Furthermore, presynaptic dopaminergic function is already elevated in prodromal patients who later developed the disorder. Currently available antipsychotics act on postsynaptic receptors, not targeting presynaptic DA abnormalities. This has implications for understanding response and developing new treatments. The lack of normalization of the abnormal presynaptic function could explain why discontinuation is likely to lead to relapse, because the major dopaminergic function persists, meaning that once treatment stops there is nothing to oppose the dysregulated dopamine function reinstating symptoms. Furthermore, it suggests that drugs that target presynaptic dopaminergic function may constitute new treatment possibilities for schizophrenic patients, in particular, for those in whom antipsychotics are poorly effective. In addition, the longitudinal changes with the onset of psychosis indicate the potential to target a defined dynamic neurochemical abnormality to prevent the onset of psychosis.

Toward a modern search for schizophrenia genes

Genetic epidemiology has provided consistent evidence that schizophrenia has a genetic component It is now clear that this genetic component is complex and polygenic, with several genes interacting in epistasis. Although molecular studies have failed to identify any DNA variant that clearly contributes to vulnerability to schizophrenia, several regions have been implicated by linkage studies. To overcome the difficulties in the search for schizophrenia genes, it is necessary (i) to use methods of analysis that are appropriate for complex multifactorial disorders; (ii) to gather large enough clinical samples; and (iii) in the absence of genetic validity of the diagnostic classification currently used, to apply new strategies in order to better define the affected phenotypes. For this purpose, we describe here two strategies: (i) the candidate symptom approach, which concerns affected subjects and uses proband characteristics as the affected phenotype, such as age at onset, severity, and negative/positive symptoms; and (ii) the endophenotypic approach, which concerns unaffected relatives and has already provided positive findings with phenotypes, such as P50 inhibitory gating or eye-movement dysfunctions.

Alterations in dopamine and glutamate neurotransmission in tetrahydrobiopterin deficient spr-/- mice: relevance to schizophrenia

Tetrahydrobiopterin (BH4) is a pivotal cofactor for enzymes responsible for the synthesis and release of monoamine neurotransmitters including dopamine (DA) and serotonin (5-HT) as well as the release of glutamate (Glu). Deficiencies in BH4 levels and reduced activities of BH(4)-associated enzymes have been recently reported in patients with schizophrenia. Accordingly, it is possible that abnormalities in the biochemical cascades regulated by BH(4) may alter DA, 5-HT and Glu neurotransmission, and consequently contribute to the pathophysiology of different neuropsychiatric diseases including schizophrenia. The development of a novel strain of mutant mice that is deficient in BH(4) by knocking out the expression of a functional sepiapterin reductase gene (spr -/-) has added new insights into the potential role of BH(4) in the pathophysiology and improved treatment of schizophrenia.

Plasma homovanillic acid differences in clinical subgroups of first episode schizophrenic patients

This study evaluates the relationship between plasma homovanillic acid (pHVA) levels, which have been used to study the role of central dopamine in schizophrenia, and the positive/negative syndrome in first episode schizophrenic patients before and after antipsychotic treatment. Forty neuroleptic-naive first episode schizophrenic patients were monitored at baseline and on days 7, 14 and 28. Clinical status was evaluated with the Scale for the Assessment of Positive Symptoms (SAPS), the Scale for the Assessment of Negative Symptoms (SANS), and the Brief Psychotic Rating Scale. Plasma HVA levels were also measured. Patients were divided into predominantly positive or negative syndrome groups by subtracting SAPS from SANS scores, at baseline. A healthy control group was also enrolled. Schizophrenic patients as a group had significantly higher pHVA levels than controls at baseline (20.50+/-11.85 vs. 13.04+/-7.22 ng/ml). Moreover, 12 predominantly negative syndrome patients had similar mean baseline pHVA levels (21.30+/-12.36 ng/ml) to those of 28 predominantly positive syndrome patients (19.40+/-11.33 ng/ml). During follow-up, there was a different evolution of pHVA levels in the predominantly positive syndrome group than in the predominantly negative syndrome group, with a significantly greater global reduction of pHVA levels in the former. Although both groups showed clinical improvement following 4 weeks of treatment with risperidone, pHVA levels at endpoint were lower (13.29+/-5.91 ng/ml) than at baseline in patients in the predominantly positive syndrome group, while among those in the predominantly negative syndrome group there was no difference in pHVA levels before and after treatment (21.02+/-13.06 ng/ml). The different pHVA level profiles observed in predominantly positive and negative syndrome first episode patients after 4 weeks of treatment with risperidone suggest that each syndrome may have a different underlying neurobiology.

Cerebrospinal fluid kynurenic acid in male patients with schizophrenia - correlation with monoamine metabolites

BACKGROUND

The tryptophan metabolite kynurenic acid (KYNA) is an endogenous glutamate/nicotinic receptor antagonist. Previous studies have shown that the concentration of the compound is increased in cerebrospinal fluid (CSF) of patients with schizophrenia. Furthermore, it has been found that the CSF concentration of KYNA is positively correlated to CSF concentrations of the monoamine metabolites homovanillic acid (HVA) and 5-hydroxy indoleacetic acid (5-HIAA) in healthy control subjects.

OBJECTIVES

To study the correlations between KYNA and the monoamine metabolites HVA, 5-HIAA and 4-hydroxy-3-methoxyphenylglycol (HMPG) in CSF of male patients (n= 53, ranging from 20 to 48 years of age) with verified schizophrenia.

METHODS

CSF was obtained by lumbar puncture, and KYNA analysis was performed with an isocratic reversed-phase high-performance liquid chromatography system connected to a fluorescence detector. HVA, 5-HIAA and HMPG concentrations were measured by mass fragmentography with deuterium-labelled internal standards.

RESULTS

Positive intercorrelations were found between CSF KYNA, HVA and 5-HIAA, while CSF content of HMPG did not correlate to KYNA or any of the monoamine metabolites in CSF.

CONCLUSION

The results of this study suggest that increased KYNA formation is associated with an increased dopamine and serotonin turnover in male patients with schizophrenia.

Analysis of plasma biopterin levels in psychiatric disorders suggests a common BH4 deficit in schizophrenia and schizoaffective disorder

Tetrahydrobiopterin (BH4) is an essential cofactor for amine neurotransmitter synthesis. BH4 also stimulates and modulates the glutamatergic system, and regulates the synthesis of nitric oxide by nitric oxide synthases. A connection between BH4 deficiencies and psychiatric disorders has been previously reported; major depression and obsessive-compulsive disorder have been found in subjects with a BH4 deficiency disorder and more recently we have observed a robust plasma deficit of biopterin (a measure of BH4), in a large group of schizophrenic patients compared to control subjects. To extend our previous finding in schizophrenia, we analyzed plasma biopterin levels from patients with schizoaffective and bipolar disorders. A significant difference in biopterin was seen among the diagnostic groups (P < 0.0001). Post hoc analyses indicated significant biopterin deficits relative to the normal control group for the schizoaffective group, who had biopterin levels comparable to the schizophrenic group. Bipolar disorder subjects had plasma biopterin levels that were higher that the schizoaffective disorder group and significantly higher than the schizophrenic group. The demonstrated significant biopterin deficit in both schizophrenia and schizoaffective disorder, may suggest an etiological role of a BH4 deficit in these two disorders, via dysregulation of neurotransmitter systems.

Elevated levels of kynurenic acid in the cerebrospinal fluid of male patients with schizophrenia

Previous studies have shown that endogenous brain levels of kynurenic acid (KYNA), a glutamate receptor antagonist, are elevated in patients with schizophrenia. Here we analyse KYNA in the cerebrospinal fluid (CSF) from a large cohort, including male healthy controls (n=49) and male patients with schizophrenia (n=90). We found that male patients with schizophrenia had significantly higher levels of CSF KYNA compared to healthy male controls (1.45 nM+/-0.10 vs. 1.06 nM+/-0.06 in the control group). Furthermore, when the patients with schizophrenia were divided into subgroups we found that CSF KYNA levels were significantly elevated in drug-naïve, first episode patients (1.53 nM+/-0.19, n=37) and in patients undergoing treatment with antipsychotic drugs (1.53 nM+/-0.17, n=34) compared to healthy male controls. No elevated CSF KYNA levels were detected in drug-free patients with schizophrenia, i.e. patients previously undergoing antipsychotic medications but drug-free at time of sampling (1.16 nM+/-0.10, n=19). Present results confirm that CSF KYNA concentration is elevated in patients with schizophrenia and are consistent with the hypothesis that KYNA contributes to the pathophysiology of the disease.

Evidence for a tetrahydrobiopterin deficit in schizophrenia

Tetrahydrobiopterin (BH(4)) is a vital cofactor maintaining availability of the amine neurotransmitters [dopamine (DA), noradrenaline (NA), and serotonin (5-HT)], regulating the synthesis of nitric oxide (NO) by nitric oxide synthase (NOS), and stimulating and modulating the glutamatergic system (directly and indirectly). These BH(4) properties and their potential relevance to schizophrenia led us to investigate the hypothesis of a study group (healthy controls, n=37; schizophrenics, n=154) effect on fasting plasma total biopterin levels (a measure of BH(4)). Study analysis showed a highly significant deficit of total biopterins for the schizophrenic sample after partialling out the effects of potential confounds of gender, age, ethnicity, neuroleptic use history and dose of current use, 24-hour dietary phenylalanine/protein ratio (a dietary variable relevant to BH(4) synthesis), and plasma phenylalanine (which stimulates BH(4) synthesis). A mean decrement of 34% in plasma total biopterins for schizophrenics from control values supports clinical relevance for the finding. In a subsample (21 controls and 23 schizophrenics), sequence analysis was done of the GTP cyclohydrolase I feedback regulatory gene and no mutations were found in the coding region of the gene. A deficiency of BH(4) could lead to hypofunction of the systems of DA, NA, 5-HT, NOS/NO, and glutamate, all of which have been independently implicated in schizophrenia psychopathology. Further, evidence has been accumulating which implicates the critical interdependence of these neurotransmitter systems in schizophrenia; this concept, along with the present study finding of a biopterin deficit, suggests that further study of the BH(4) system in schizophrenia is warranted and desirable.

Higher cerebrospinal fluid homovanillic acid levels in depressed patients with comorbid posttraumatic stress disorder

Major depression and posttraumatic stress disorder (PTSD) are often comorbid, resulting in more impairment compared than with either diagnosis alone. Both major depression and PTSD are thought to be associated with monoamine transmitter abnormalities. This study compared clinical features and cerebrospinal fluid (CSF) monoamine metabolites in drug-free depressed subjects with a current major depressive episode (MDE) without comorbid PTSD, subjects with a current MDE and comorbid PTSD, and healthy volunteers. Depressed subjects with comorbid PTSD had higher CSF homovanillic acid (HVA) levels compared with depressed subjects without comorbid PTSD or healthy volunteers. Higher HVA was present after adjustment for sex, lifetime aggression severity and depression scores, alcoholism, tobacco smoking, comorbid cluster B personality disorder, reported childhood abuse, and psychosis. We found no group difference in CSF 5-hydroxyindolacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) levels. Higher dopaminergic activity may contribute to alterations in memory and other cognitive functions, anhedonia, and hypervigilance observed in PTSD.

Lower CSF homovanillic acid levels in depressed patients with a history of alcoholism

Major depression and alcoholism are often comorbid, resulting in more impairment and more suicidal behavior compared with either diagnosis alone. This study compared clinical features and cerebrospinal fluid (CSF) monoamine metabolites in depressed subjects with and without a history of alcoholism and healthy volunteers. We hypothesized that depressed subjects with a history of alcoholism would be more aggressive, impulsive, and suicidal than depressed subjects without a history of alcoholism, and would have lower CSF monoamine metabolite levels. We compared 63 subjects with a current major depressive episode (MDE) and a history of alcoholism, 72 subjects with a current MDE but without a history of alcoholism, and 22 healthy volunteers. Participants with a history of alcoholism were in remission for at least 6 months. All subjects were free from prescribed medications known to affect brain serotonin, dopamine, or norepinephrine systems for a minimum of 14 days. Depressive symptoms, lifetime aggression, impulsivity, Axis II disorders, and suicidal behavior were assessed. CSF was sampled and homovanillic acid (HVA), 5-hydroxyindolacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) were assayed by high-performance lipid chromatography with electrochemical detection. Depressed subjects with a history of alcoholism did not differ from depressed subjects without a history of alcoholism in current severity of depressive symptoms, or in past suicidal behavior. Depressed subjects with a history of alcoholism had lower CSF HVA levels, and higher lifetime aggression and current suicide ideation scale scores and were more likely to be tobacco smokers compared with depressed subjects without a history of alcoholism. Low HVA was present after adjustment for sex, aggression and depression scores, cigarette smoking, antisocial and borderline personality disorders, psychomotor retardation, and delusions. Controls had CSF HVA levels intermediate between the two depressed groups. We found no group difference in CSF 5-HIAA and MHPG levels. In individuals with current MDE, those with a history of comorbid alcoholism had lower CSF HVA levels compared with those without a history of alcoholism. Low CSF HVA suggests that impaired dopaminergic activity is associated with a history of alcoholism in persons with current MDE.

Effects of estrogen on brain development and neuroprotection--implications for negative symptoms in schizophrenia

Increasing evidence during the last few years suggests that there are gender-specific differences in schizophrenia, influencing the age of onset, treatment outcome and the prevalence of negative symptoms. With respect to the latter in postmortem brain and cerebrospinal fluid of schizophrenic patients with negative symptoms a reduction of dopaminergic activity became evident. Measures of noradrenergic activity, dopamine beta-hydroxylase and the metabolite MHPG, appear to decrease with brain atrophy seen in patients with negative symptoms. Serotonergic activity tends to be low in patients with impaired cognitive function as is seen in negative schizophrenia. In these patients ventricular enlargement is associated with the severity of negative symptoms, low monoamine activity and low cerebral glucose metabolism. On the other hand atypical antipsychotic drugs that modulate also glutamate receptor activity, suggest an additional alternative mechanism of antipsychotic action beyond aminergic neurotransmitters. These drugs improve glutamatergic transmission and decrease negative symptoms; this suggests a glutamatergic deficiency as an extension of the dopamine model. The glutamate-dopamine interaction illustrates the importance of cross-talk between projections to the cortex, striatum, and lower brainstem for the expression of negative symptomatology. On the other hand, estradiol-17beta the most potent female sex hormone influences not only primary and secondary sexual characteristics but also embryonal and fetal growth as well as development of the brain aminergic networks, which are involved in schizophrenia. Estradiol-l7beta possesses neuroprotective properties, which are relevant for the course of schizophrenia and this may explain the pronounced gender differences with respect to progression and therapeutic response of schizophrenia. The present review attempts an update and synthesis of the information about the hormonal influence on neuronal pathways in negative symptoms of schizophrenia. It shows that estradiol-l7beta influences transporters and receptors as well as the morphological appearance of neuronal systems and that it may be an integral part of the neuroprotective system ameliorating schizophrenia.

Biological markers and schizophrenia

OBJECTIVE

The delivery of biological markers for schizophrenia would greatly assist preventative strategies by identifying at-risk individuals who could then be monitored and treated in a manner with a view to minimising subsequent morbidity. This paper aims to present a selection of biological measures that may indicate risk of schizophrenia.

METHOD

A selective and brief review is provided of intensively studied putative markers, including enlarged cerebral ventricles, dopamine D2 receptor density, amphetamine-stimulated central nervous system dopamine release, plasma homovanillic acid and smooth pursuit eye tracking dysfunction.

RESULTS

A number of biological measures have been reported to be correlated with schizophrenia.

CONCLUSIONS

Presently, none of these measures has satisfactory performance characteristics in terms of predictive validity, noninvasiveness, ease of testing and low cost that would enable their widespread use. However, a few have potential for further investigation and development.

The potent, selective mGlu2/3 receptor agonist LY379268 increases extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindole-3-acetic acid in the medial prefrontal cortex of the freely moving rat

Previous work has shown that the potent, selective metabotropic glutamate mGlu2/3 receptor agonist LY379268 acts like the atypical antipsychotic clozapine in behavioral assays. To investigate further the potential antipsychotic actions of this agent, we examined the effects of LY379268 using microdialysis in awake, freely moving rats, on extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) in rat medial prefrontal cortex. Systemic LY379268 increased extracellular levels of dopamine, DOPAC, HVA, and 5-HIAA in a dose-dependent, somewhat delayed manner. LY379268 (3 mg/kg s.c. ) increased levels of dopamine, DOPAC, HVA, and 5-HIAA to 168, 170, 169, and 151% of basal, respectively. Clozapine (10 mg/kg) also increased dopamine, DOPAC, and HVA levels, with increases of 255, 262, and 173%, respectively, but was without effect on extracellular 5-HIAA levels by 3 mg/kg LY379268 were reversed by the selective mGlu2/3 receptor antagonist LY341495 (1 mg/kg). Furthermore, LY379268 (3 mg/kg)-evoked increases in DOPAC and HVA were partially blocked and the increase in 5-HIAA was completely blocked by local application of 3 microM tetrodotoxin. Therefore, we have demonstrated that mGlu2/3 receptor agonists activate dopaminergic and serotonergic brain pathways previously associated with the action of atypical antipsychotics such as clozapine and other psychiatric agents.

Increased dopamine synthesis rate in medial prefrontal cortex and striatum in schizophrenia indicated by L-(beta-11C) DOPA and PET

BACKGROUND

The aim of the present study was to investigate dopamine synthesis in the brain of drug-free schizophrenic patients, not only in the striatum but also in extrastriatal areas like the prefrontal cortex, brain areas that for a long time has been in focus of interest in the pathophysiology of schizophrenia.

METHODS

PET was performed in 12 drug-free (10 drug-naive) psychotic schizophrenic patients and 10 healthy volunteers matched for age and gender using 11C-labelled L-DOPA as the tracer. The time-radioactivity curve from occipital cortex (located within Brodman area 17 and 18) was used as input function to calculate L-DOPA influx rate, Ki images, that were matched to a common brain atlas. A significant overall increase of the Ki values was found in the schizophrenic group as compared with healthy controls.

RESULTS

In particular, significantly higher Ki were found in the schizophrenic patients compared to the controls in the caudate nucleus, putamen and in parts of medial prefrontal cortex (Brod 24). The Ki value reflect an increased utilization of L-DOPA, presumably due to increased activity of the amino acid decarboxylate enzyme.

CONCLUSIONS

The results indicate that the synthesis of dopamine is elevated within the striatum and parts of medial prefrontal cortex in schizophrenia.

Genetic antecedents of dopamine dysfunction in schizophrenia

BACKGROUND

Relatives of schizophrenic probands frequently manifest attenuated features of this illness including the negative symptoms and the milder positive psychotic symptoms. These two symptom dimensions are hypothesized to be associated with decreased and increased brain dopamine (DA) functions, respectively, raising the possibility that DA abnormalities may be present in the relatives of schizophrenic probands.

METHODS

Plasma homovanillic acid (HVA), the major DA metabolite and an indicator of brain DA activity, was measured in nonpsychotic, physically healthy first-degree relatives (n = 55) of schizophrenic probands and in normal subjects (n = 20) without a family history of schizophrenia.

RESULTS

Plasma HVA inversely correlated with negative symptoms and positively correlated with attenuated positive symptoms. Also, relatives had decreased plasma HVA compared to normal subjects, consistent with the fact that these relatives are characterized by negative symptoms. These findings were not related to major peripheral factors that could affect plasma HVA suggesting that the findings may reflect changes in brain DA activity.

CONCLUSIONS

Negative symptoms indicating a genetic diathesis to schizophrenia in relatives may have a biologic basis in reduced DA activity and the DA dysfunction of schizophrenia may have genetic antecedents. This opens an important new avenue for further study of DA in this illness.

CSF levels of HVA and 5-HIAA in drug-free schizophrenic patients and healthy controls: a prospective study focused on their predictive value for outcome in schizophrenia

The CSF levels of HVA and 5-HIAA were determined in 90 drug-free DSM-III-R schizophrenic patients and 47 healthy control subjects, and their predictive value for 5-year outcome was evaluated. CSF was collected by lumbar puncture at index admission, and in 37 of the patients a second sample was drawn after approx. 7 weeks of neuroleptic treatment. Outcome was rated prospectively 5 years after index admission by means of the Strauss-Carpenter outcome scale. Schizophrenic patients had significantly lower levels of HVA in the CSF than the control group, but no difference was found for 5-HIAA. The CSF-amine metabolite levels were not correlated with age at admission, age at first symptoms or duration of the disorder. Neither HVA nor 5-HIAA correlated with the total outcome scores at a 1- and 5-year follow-up evaluation. First-admitted previously untreated patients with the poorest 5-year outcome had significantly lower HVA/5-HIAA quotients than those with a good outcome. Furthermore, patients still having a low HVA/5-HIAA quotient after treatment with neuroleptics had a poorer 5-year outcome than patients with an increased quotient. The data indicate that both HVA and 5-HIAA in the CSF, and especially their sensitivity to neuroleptic treatment, have a predictive value for the prognosis in schizophrenia.

Effects of antipsychotics, vitamin E, and MK-801 on dopamine dynamics in the rat brain following discontinuation of cocaine

Cocaine, 10 mg/kg, I.P., twice daily, was given to rats for 1 week. At 1 and 4 weeks following discontinuation of cocaine, the initial rate of 3,4-dihydroxyphenylacetic acid (DOPAC) formation was assessed. The initial rate of DOPAC formation was found to be decreased in the frontal and cingulate cortices at 1 week, but was only decreased in the frontal cortex at 4 weeks. When administered in conjunction with cocaine, haloperidol, clozapine, and vitamin E, but not MK-801, were found to prevent cocaine's effects. In addition to the potential value these findings have for further understanding cocaine abuse, it is proposed that the alteration in dopamine metabolism produced by cocaine, and the ability of haloperidol, clozapine and vitamin E to decrease cocaine's effects, model some biochemical aspects of schizophrenia.

Construct validity of negative symptoms: an empirical and conceptual review

The construct validity of negative symptoms is reviewed, and findings on deficit negative symptoms are also incorporated. A valid negative symptom construct should: (a) have replicable relationships with observable phenomena and other constructs; (b) have good reliability, temporal stability, and homogeneity; and (c) predict prognosis and response to treatment, possess convergent and discriminant validity, and be useful to clinicians. Although a number of well-replicated findings provide support for the validity of the construct, modification is warranted. Specifically, the data suggest that there is a highly correlated set of negative symptoms, which includes flat affect, alogia, anhedonia, and avolition. Primary and enduring symptoms from this set have good predictive and discriminant validity and can be studied in the context of the deficit syndrome, as well as with current negative symptom rating scales. Future studies should examine whether deficit negative symptoms are better conceptualized as a dimension or a category, elucidate the relationship between deficit symptoms and additional clinical and behavioral variables (e.g., response to newer neuroleptic medications and diminished emotional responding), and explore differences between the pattern of correlates of deficit symptoms and those of the positive and thought disorder symptoms.

Dopamine-related genes and their relationships to monoamine metabolites in CSF

Monoamine metabolite (MM) levels in lumbar cerebrospinal fluid (CSF) are extensively used as indirect estimates of monoamine turnover in the brain. In this study we investigated genotypes for DNA polymorphisms in the D2 (DRD2), D3 (DRD3), and D4 (DRD4) dopamine receptor and tyrosine hydroxylase (TH) genes and their relationships to CSF MM in healthy volunteers (n = 66). Concentrations of homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylglycol (MHPG), and 5-hydroxyindoleacetic acid (5-HIAA) were corrected for back length, a confounding variable. Corrected MM levels were not related to age, gender, height, weight heredity, season or atmospheric pressure at sampling. Individuals with specific DRD2 and TH allele and genotype configurations significantly differed in HVA and MHPG concentrations. DRD3 homo- and heterozygotic genotypes had significantly different CSF 5-HIAA levels. DRD4 genotypes were not related to MM concentrations. The results suggest that specific DRD2, DRD3, and TH genotypes participate in the regulation of monoamine turnover in the central nervous system. Accordingly monoamine receptors and synthesizing enzyme genotypes appear to be variance factors influencing MM concentrations in CSF. The relationships found in this study support MM concentrations as markers for monoamine transmission in the human brain.

Blink rate, neurocognitive impairments, and symptoms in schizophrenia

This study addresses the relationship between blink rate (as a measure of central dopaminergic activity), symptoms, neuropsychological performance, as well as neurological signs in schizophrenia. Blink rate between schizophrenic patients and a matched control group was compared in both "relaxed" and "attentive" conditions. Blink rate was increased in schizophrenic patients in the "relaxed" condition but not in the "attentive" condition. The relationship between blink rate and clinical variables was examined in a larger sample of 204 patients. In both "relaxed" and "attentive" conditions, blink rate was related to "hallucinations," "anxiety," negative symptoms, and neuroleptic dosage. Attention was a significant predictor only in the "relaxed" condition. No other significant correlation was found between blink rate, neuropsychological impairments, and neurological signs. These findings suggest that blink rate is not related to neurocognitive impairments in schizophrenia.

Effects of haloperidol and SCH 23390 on acoustic startle in animals depleted of dopamine as neonates: implications for neuropsychiatric syndromes

Animals depleted of dopamine (DA) in the neonatal period and tested in adulthood exhibit some similarities to patients with schizophrenia, including increased sensitivity to DA agonists, altered sensitivity to DA receptor antagonists, and abnormalities of the acoustic startle response (ASR). In this study, we examined the contributions of D1-like and D2-like DA receptors to ASR measures in animals depleted of DA as neonates. Male rat pups received intracerebroventricular injections of 6-hydroxydopamine (DA depleted) or its vehicle (controls) at 3 days of age. Animals underwent startle testing as adults (60-75 days of age) after administration of DA antagonists (haloperidol: 0.1 or 0.3 mg/kg, SCH 23390:0.01 or 0.05 mg/kg) with and without DA agonist administration (apomorphine 0.5 mg/kg). ASR amplitude and prepulse inhibition (PPI: percentage decrease in startle amplitude due to a low intensity prepulse) were measured. DA depleted animals showed increased ASR amplitude and reduced PPI compared to controls. Administration of D1-like or D2-like DA antagonists significantly reduced overall ASR and increased PPI in both control and DA depleted animals, with DA depleted animals showing a relatively greater sensitivity to the D1-like antagonist SCH 23390. Findings are discussed in terms of the role of residual DA in mediating ASR phenomena in depleted animals, differences between D1/D2 DA receptor mediation of ASR compared to other behaviors in DA depleted animals, and potential implications for neuropsychiatric syndromes such as schizophrenia.

On the concentration of 5-hydroxyindoleacetic acid in schizophrenia: a meta-analysis

A meta-analysis was performed on the results of a number of investigations of concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid, serum, or urine of acute and chronic schizophrenic patients. Only those studies were chosen in which some degree of age and gender matching were achieved and in which the comparison subjects were healthy normal volunteers. Fisher's procedure and a weighted Liptak method revealed no significant differences between normal subjects and schizophrenic patients, indicating that disturbances of serotonergic turnover do not, in general or essentially, contribute to the etiology of schizophrenia.

Schizophrenic patients with deficit syndrome have higher plasma homovanillic acid concentrations and ventricular enlargement

In order to investigate the biological characteristics of deficit syndrome in schizophrenia (Carpenter et al 1988), we examined cerebroventricular ratios (CVRs) and plasma concentrations of homovanillic acid (HVA) in a group of schizophrenic inpatients with deficit syndrome (n = 20) and in a control group of age- and sex-matched schizophrenic inpatients without deficit syndrome (n = 20). Symptoms and intelligence levels were measured using the Brief Psychiatric Rating Scale (BPRS) and the Wechsler Adult Intelligence Scale (WAIS), respectively. Patients in the deficit group had significantly higher CVRs as well as significantly elevated plasma HVA concentrations when compared with patients in the nondeficit group. We also found that the mean total WAIS score in the deficit group was significantly lower than that in the nondeficit group. These findings suggest the biological heterogeneity of schizophrenia. Increased central dopaminergic turnover, as indicated by higher plasma HVA concentrations, may partially account for the pathogenesis of deficit syndrome.

Effect of clozapine on d-fenfluramine-evoked neuroendocrine responses in schizophrenia and its relationship to clinical improvement

BACKGROUND

Clozapine is an effective antipsychotic that has high affinity for serotonin type 2 (5-HT2) receptors. The importance of 5-HT antagonism in the overall clinical efficacy of clozapine is unclear. Using a neuroendocrine strategy we tested the hypothesis that clinical response to clozapine is related to alteration in 5-HT function.

METHOD

Ten treatment-resistant schizophrenic subjects were treated with clozapine for a mean of 10.3 (s.e. 0.9) weeks; d-fenfluramine (DFEN) challenge tests were performed before and after treatment with concurrent clinical ratings (BPRS, SAPS, SANS) made at the time of testing.

RESULTS

All patients showed clinical improvement following treatment with clozapine. In addition, clozapine produced a significant attenuation of prolactin (PRL) and cortisol (CRT) response to DFEN challenge. Change in symptom ratings correlated significantly with reduction in PRL response to DFEN challenge.

CONCLUSIONS

These data show that functional alterations occur in the 5-HT system following response to clozapine and lend support to studies suggesting that 5-HT is an important component to the spectrum of action of clozapine.

Longitudinal changes in symptoms and plasma homovanillic acid levels in chronically medicated schizophrenic patients

A correlation has been noted between the changes in plasma homovanillic acid concentrations and changes in psychiatric symptoms induced by neuroleptic treatment. Our objective was to determine whether plasma homovanillic acid concentration changed in accordance with the changes in symptoms over time. Twenty-eight chronically medicated schizophrenic inpatients received the same treatment regimen for 1 year. Symptoms and plasma homovanillic acid concentrations were examined every month and whenever conditions deteriorated. Plasma homovanillic acid concentrations were significantly higher in the patients in the worst condition than in the patients in the best condition. Further, when comparing the best and worst conditions of both the positive and negative symptoms, the change in psychiatric rating of positive and negative symptoms was correlated significantly with the change in plasma homovanillic acid level. These results suggest that a change in plasma homovanillic acid concentration can be produced not only by neuroleptic-induced dopaminergic blocking but also by a change in positive and negative symptoms of schizophrenia.

Noradrenergic and dopaminergic interrelation in schizophrenia

Growth hormone (GH) and prolactin (PRL) responses to the acute administration of clonidine (150 micrograms) and apomorphine (0.5 mg) were investigated in parallel in 20 drug-free subchronic and chronic schizophrenic patients and in nine control subjects. Neither basal levels of the two hormones nor their mean responses to both stimuli differed significantly between the two groups. However, eight patients had blunted GH responses to clonidine and seven to apomorphine; only two patients showed blunted GH responses to both stimuli. The blunted GH response to apomorphine correlated with the chronicity of the disorder. A greater than normal GH response to clonidine stimulation was observed in paranoid patients. Significant correlations were observed between negative symptoms and GH responses to clonidine (negative), between negative symptoms and PRL responses to apomorphine (positive), and between positive symptoms and PRL responses to apomorphine (negative).

A multidimensional approach to analysis of cerebrospinal fluid biogenic amines in schizophrenia: I. Comparisons with healthy control subjects and neuroleptic-treated/unmedicated pairs analyses

Recent hypotheses and findings indicate that measurements of interactions between cerebrospinal fluid (CSF) biogenic amine systems, rather than measurement of CSF biogenic amine metabolites, better correlate with clinically important findings in schizophrenia. To test hypotheses, we used a recent technological advance in high performance liquid chromatography with electrochemical detection and combined it with multivariate statistical analyses to study biogenic amine concentrations in CSF in schizophrenia. This approach enabled the study of the interactions of several metabolites of each of the three major neurotransmitter pathways (dopaminergic, noradrenergic, and serotonergic) to test existing hypotheses regarding the neurobiochemical basis of schizophrenia. Twenty biogenic amines, their metabolites, and other compounds from 24 medication-free schizophrenic patients and 12 normal control subjects were simultaneously measured using a recently developed technique of gradient high performance liquid chromatography coupled with a 16-channel electrochemical array detector. After covariation for storage time, results of a stepwise discriminant function analysis comparing the control and patient groups identified tryptophan, tryptophol, and epinephrine as discriminating variables. Hotelling's paired T2 test from a subgroup of schizophrenic patients studied while they were and were not receiving neuroleptic treatment did not yield any significant differences between subgroups. A discussion of the findings and a comparison with previous studies of CSF biogenic amines in schizophrenia are presented.

A multidimensional approach to analysis of cerebrospinal fluid biogenic amines in schizophrenia: II. Correlations with psychopathology

As part of a multidimensional study of cerebrospinal fluid biogenic amine metabolites in schizophrenia, the relationship between neurochemical measures and psychopathology assessed using the Psychiatric Symptom Assessment Scale (PSAS) was analyzed. In a group of 20 unmedicated patients, 3,4-dihydroxyphenylacetic acid (DOPAC) was a predictor of symptom severity in a stepwise multiple regression model. Values of 3-hydroxykynurenine and metanephrine in the unmedicated state predicted clinical response in a stepwise multiple regression model, as measured by improvement in PSAS mean item score following 6 weeks on a standard dose of neuroleptic. In a subgroup of 14 patients in whom both off- and on-medication concentrations of cerebrospinal fluid biogenic amines and metabolites were measured, change in 3-hydroxykynurenine predicted clinical outcome in a multiple regression model. These findings point toward the need to examine the role of the kynurenine pathway of tryptophan metabolism in the pathophysiology of schizophrenia.

A meta-analysis of homovanillic acid concentrations in schizophrenia

The results of several experiments in which homovanillic acid (HVA) concentrations were measured, mainly in the cerebrospinal fluid, of schizophrenics are examined using Fisher's combination procedure. It is found that the data does not support the claim that the level of this dopamine catabolite is raised whereas some evidence strongly supports the claim that it is actually lowered. This finding is discussed in relation to the hypothesis of dopaminergic neuronal hyperactivity in schizophrenia.

Serum homovanillic acid levels in schizophrenic patients and normal control subjects

Schizophrenic patients with an early age at onset of illness had low baseline levels of homovanillic acid (HVA) in serum compared with schizophrenic patients with a late age at onset. After adjustments were made for age at onset, there was a significant partial correlation between positive symptoms and serum HVA. The relationship between positive symptom scores and serum HVA was shifted to the left in the early onset patients, suggesting a relatively increased sensitivity of dopamine-associated response. Patients with severe negative symptoms also had an earlier age at onset and a trend toward lower serum HVA. This study found no difference between mean serum HVA values in schizophrenic patients and normal control subjects.

Prefrontal cortex regulates burst firing and transmitter release in rat mesolimbic dopamine neurons studied in vivo

The influence of the medial prefrontal cortex (PFC) on mesolimbic dopamine activity was studied with electrophysiological techniques and in vivo voltammetry in the chloral hydrate-anesthetized male rat. Glutamate injected into the PFC selectively increased burst firing of single dopamine cells in the ventral tegmental area and enhanced the release of dopamine from nerve terminals in the nucleus accumbens. PFC injection of the local anesthetic lidocaine produced the opposite effects on burst firing and terminal release. This selective modulation of the dynamic activity of mesolimbic dopamine neurons by the prefrontal cortex might be important in motivation, learning and schizophrenia.

The P50 component of the auditory evoked potential and subtypes of schizophrenia

Decreased amplitude of the P50 component of the averaged evoked potential has been reported in schizophrenic patients. In an attempt to determine the relationship of this decrease to subtype diagnosis, we compared P50 amplitudes in 24 neuroleptic-free schizophrenic patients with paranoid (n = 13) versus nonparanoid (n = 11) subtype diagnoses. Eleven normal subjects and 11 cocaine users served as control groups. The schizophrenic patients were studied again after they had been treated with neuroleptics for 2 weeks. The control groups were studied again at least 2 weeks later. At baseline, the nonparanoid patients had significantly lower P50 amplitudes than did the normal subjects. The paranoid patients did not differ from the normal control subjects. The cocaine users had significantly decreased P50 amplitudes as compared with the normal control subjects. Neuroleptic treatment had no effect on P50 amplitudes in the paranoid patients but normalized amplitudes in the nonparanoid patients. The data suggest that P50 measurements may be useful in identifying subtypes of schizophrenia.

Cortical regulation of subcortical dopamine systems and its possible relevance to schizophrenia

A unique model of DA system regulation is presented, in which tonic steady-state DA levels in the ECF act to down-regulate the response of the system to pulsatile DA released by DA cell action potential generation. This type of regulation is similar in many respects to the phenomenon proposed to mediate the action of norepinephrine on target neurons; i.e., an increase in the "signal-to-noise" ratio as measured by postsynaptic cell firing (Freedman et al., 1977; Woodward et al., 1979). However, in this model the signal and the noise are neurochemical rather than electrophysiological. Furthermore, the "noise" (tonic DA in the ECF) actually down-regulates the "signal" (phasic DA release) directly, and thereby provides a "signal" of its own that affects the system over a longer time-course. Therefore, the difference between signal and noise may also depend on the time frame under which such determinations are made.

The depolarization block hypothesis of neuroleptic action: implications for the etiology and treatment of schizophrenia

Antipsychotic drugs are known to block dopamine receptors soon after their administration, resulting in an increase in dopamine neuron firing and dopamine turnover. Nonetheless, antipsychotic drugs must be administered repeatedly to schizophrenics before therapeutic benefits are produced. Recordings from dopamine neurons in rats have revealed that chronic antipsychotic drug treatment results in the time-dependent inactivation of dopamine neuron firing via over-excitation, or depolarization block. Furthermore, the clinical profile of the response to antipsychotic drugs appears to correspond to the dopamine system affected: antipsychotic drugs that exert therapeutic actions in schizophrenics inactivate dopamine neuron firing in the limbic-related ventral tegmental area, whereas drugs that precipitate extrapyramidal side effects cause depolarization block of the motor-related substantia nigra dopamine cells. One factor that remains unresolved with regard to the actions of antipsychotic drugs is the relationship between dopamine turnover and depolarization block--i.e., why does a significant level of dopamine release or turnover remain after antipsychotic drug treatment if dopamine cells are no longer firing? We addressed this question using an acute model of neuroleptic-induced depolarization block. In this model, dopamine cells recorded in rats one month after partial dopamine lesions could be driven into depolarization block by the acute administration of moderate doses of haloperidol. However, similar doses of haloperidol, which were effective at increasing dopamine levels in the striatum of intact rats, failed to change dopamine levels in lesioned rats. This is consistent with a model in which neuroleptic drugs exert their therapeutic effects in schizophrenics by causing depolarization block in DA cells, thereby preventing further activation of dopamine neuron firing in response to external stimuli. Thus, attenuating the responsivity of the dopamine system to stimuli may be more relevant to the therapeutic actions of antipsychotic drugs than receptor blockade or decreases in absolute levels of dopamine, which could presumably be circumvented by homeostatic adaptations in this highly plastic system.

Monoamines and CSF: relevance to neuropsychiatric disorders

Over the past 25 years much effort has been put into the research of the relationship between neuropsychiatric disorders and the concentrations of CSF-monoamine metabolites. Most of this research has beenfocused on the relation between CSF-concentrations of 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) and specific symptomatological entities, particularly schizophrenia, Alzheimer's dementia and endogenous depression. It appeared that specific relations between diseases and CSF-concentrations of monoamine metabolites cannot be longer maintained and that a more functional psychopathology should be considered as the future research strategy.

Akinesia: a syndrome common to parkinsonism, retarded depression, and negative symptoms of schizophrenia

A distinct hypokinetic syndrome appears to exist across several different neuropsychiatric diagnoses, involving (1) slowed motor activity with difficulty initiating and sustaining behaviors, (2) anhedonia with depressed mood and reduced affective range, and (3) cognitive impairment. Specifically, three well-recognized states--parkinsonism, retarded depression, and the negative symptoms of schizophrenia--prominently feature the components of this syndrome, and reduced dopamine turnover in the brain has been hypothesized to play a part in the pathophysiology of each. While aspects of this conceptualization remain controversial, it generates testable hypotheses that could have implications for the understanding and treatment of these states.

Sensory gating in rats depleted of dopamine as neonates: potential relevance to findings in schizophrenic patients

Based on a recent hypothesis of reduced subcortical dopaminergic tone, evidence of early neurodevelopmental deviation, and acoustic startle abnormalities in schizophrenia, we examined acoustic startle in adult animals depleted of dopamine (DA) as neonates. Male rat pups received intracerebroventricular injections of either 6-hydroxydopamine (6-OHDA, 100 micrograms) or its vehicle on postnatal day 3. At 60 days of age, baseline startle and prepulse inhibition (PPI) of startle were assessed in a no injection condition, with all other animals receiving injections of saline or the DA agonist, apomorphine. Acoustic startle was elicited using 120 db white noise bursts alone or preceded by prepulses of 75, 80, and 85 db. Animals treated with 6-OHDA exhibited a 93% depletion of striatal DA compared to vehicle-treated controls. Whereas DA depleted animals did not differ from controls in the no injection condition, they showed greater baseline startle and reduced PPI compared to controls after saline injections. Depleted animals also showed exaggerated responses to apomorphine, with greater increases in baseline startle, loss of habituation, and decreased PPI compared to controls. Findings indicate that neonatal DA depletions lead to increased baseline startle and impaired sensory gating in adulthood after saline injections and dopamine agonists compared to controls. These findings may be relevant to a subgroup of psychotic patients that exhibit similar startle abnormalities as well as signs of hypodopaminergic function.