Monoaminergic synapses and schizophrenia: 45 years of neuroleptics

How the Cerebellum and Prefrontal Cortex Cooperate During Trace Eyeblinking Conditioning

Several data have demonstrated that during the widely used experimental paradigm for studying associative learning, trace eye blinking conditioning (TEBC), there is a strong interaction between cerebellum and medial prefrontal cortex (mPFC). Despite this evidence, the neural mechanisms underlying this interaction are still not clear. Here, we propose a neurophysiologically plausible computational model to address this issue. The model is constrained on the basis of two critical anatomo-physiological features: (i) the cerebello-cortical organization through two circuits, respectively, targeting M1 and mPFC; (ii) the different timing in the plasticity mechanisms of these parallel circuits produced by the granule cells time sensitivity according to which different subpopulations are active at different moments during conditioned stimuli. The computer simulations run with the model suggest that these features are critical to understand how the cooperation between cerebellum and mPFC supports motor areas during TEBC. In particular, a greater trace interval produces greater plasticity changes at the slow path synapses involving mPFC with respect to plasticity changes at the fast path involving M1. As a consequence, the greater is the trace interval, the stronger is the mPFC involvement. The model has been validated by reproducing data collected through recent real mice experiments.

Psychobiotics

Psychobiotics are live bacteria that directly and indirectly produce positive effects on neuronal functions by colonizing into the intestinal flora. Preliminary studies, although in limited numbers, have found that these bacteria have anxiolytic and antidepressant activities. No research has yet been published on the antipsychotic efficacy of psychobiotics. However, these preliminary studies have opened up new horizons and raised the idea that a new class is emerging in psychopharmacology. About 70 years have passed since the discovery of chlorpromazine, and while the synaptic transmission is understood in almost all details, there seems to be a paradigm shift in psychopharmacology. In recent years, the perspective has shifted from synapse to intestinal microbiota. In this respect, germ-free and conventional animal experiments and few human studies were examined in a comprehensive manner. In this article, after a brief look at the history of contemporary psychopharmacology, the mechanisms of the gut-brain relationship and the evidence of metabolic, systemic, and neuropsychiatric activities of psychobiotics were discussed in detail. In conclusion, psychobiotics seem to have the potential for treatment of neuropsychiatric disorders in the future. However, there are many questions and we do not know the answers yet. We anticipate that the answer to these questions will be given in the near future.

Antipsychotics: Mechanisms underlying clinical response and side-effects and novel treatment approaches based on pathophysiology

Antipsychotic drugs are central to the treatment of schizophrenia and other psychotic disorders but are ineffective for some patients and associated with side-effects and nonadherence in others. We review the in vitro, pre-clinical, clinical and molecular imaging evidence on the mode of action of antipsychotics and their side-effects. This identifies the key role of striatal dopamine D2 receptor blockade for clinical response, but also for endocrine and motor side-effects, indicating a therapeutic window for D2 blockade. We consider how partial D2/3 receptor agonists fit within this framework, and the role of off-target effects of antipsychotics, particularly at serotonergic, histaminergic, cholinergic, and adrenergic receptors for efficacy and side-effects such as weight gain, sedation and dysphoria. We review the neurobiology of schizophrenia relevant to the mode of action of antipsychotics, and for the identification of new treatment targets. This shows elevated striatal dopamine synthesis and release capacity in dorsal regions of the striatum underlies the positive symptoms of psychosis and suggests reduced dopamine release in cortical regions contributes to cognitive and negative symptoms. Current drugs act downstream of the major dopamine abnormalities in schizophrenia, and potentially worsen cortical dopamine function. We consider new approaches including targeting dopamine synthesis and storage, autoreceptors, and trace amine receptors, and the cannabinoid, muscarinic, GABAergic and glutamatergic regulation of dopamine neurons, as well as post-synaptic modulation through phosphodiesterase inhibitors. Finally, we consider treatments for cognitive and negative symptoms such dopamine agonists, nicotinic agents and AMPA modulators before discussing immunological approaches which may be disease modifying. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Therapeutic Potential of the Microbiome in the Treatment of Neuropsychiatric Disorders

The search for rational treatment of neuropsychiatric disorders began with the discovery of chlorpromazine in 1951 and continues to evolve. Day by day, new details of the intestinal microbiota–brain axis are coming to light. As the role of microbiota in the etiopathogenesis of neuropsychiatric disorders is more clearly understood, microbiota-based (or as we propose, “fecomodulation”) treatment options are increasingly discussed in the context of treatment. Although their history dates back to ancient times, the importance of psychobiotics and fecal microbiota transplantation (FMT) has only recently been recognized. Despite there being few preclinical and clinical studies, the evidence gathered to this point suggests that consideration of the microbiome in the treatment of neuropsychiatric disorders represents an area of significant therapeutic potential. It is increasingly hoped that such treatment options will be more reliable in terms of their side effects, cost, and ease of implementation. However, there remains much to be researched. Questions will be answered through germ-free animal experiments and randomized controlled trials. In this article, the therapeutic potential of microbiota-based options in the treatment of neuropsychiatric disorders is discussed in light of recent research.

Effects of Antipsychotic Drugs on the Epigenetic Modification of Brain-Derived Neurotrophic Factor Gene Expression in the Hippocampi of Chronic Restraint Stress Rats

Recent studies have shown that antipsychotic drugs have epigenetic effects. However, the effects of antipsychotic drugs on histone modification remain unclear. Therefore, we investigated the effects of antipsychotic drugs on the epigenetic modification of the BDNF gene in the rat hippocampus. Rats were subjected to chronic restraint stress (6 h/d for 21 d) and then were administered with either olanzapine (2 mg/kg) or haloperidol (1 mg/kg). The levels of histone H3 acetylation and MeCP2 binding at BDNF promoter IV were assessed with chromatin immunoprecipitation assays. The mRNA levels of total BDNF with exon IV, HDAC5, DNMT1, and DNMT3a were assessed with a quantitative RT-PCR procedure. Chronic restraint stress resulted in the downregulation of total and exon IV BDNF mRNA levels and a decrease in histone H3 acetylation and an increase in MeCP2 binding at BDNF promoter IV. Furthermore, there were robust increases in the expression of HDAC5 and DNMTs. Olanzapine administration largely prevented these changes. The administration of haloperidol had no effect. These findings suggest that the antipsychotic drug olanzapine induced histone modification of BDNF gene expression in the hippocampus and that these epigenetic alterations may represent one of the mechanisms underlying the actions of antipsychotic drugs.

Sex differences in prolactin levels in emerging psychosis: Indication for enhanced stress reactivity in women

BACKGROUND

Hyperprolactinemia is a known side effect of antipsychotics. In recent reports it has also been shown in antipsychotic-naïve at-risk mental state (ARMS) and first-episode psychosis (FEP) patients. Prolactin is not only involved in reproduction and lactation, but is also synthesized in response to stress. As stress is thought to play an important role in the onset and relapse of schizophrenia, the aim of this study was to further elucidate the influence of prolactin in emerging psychosis.

METHODS

The data analysed in this study were collected within the prospective Früherkennung von Psychosen (FePsy) study. Blood sample collection took place under standardized conditions between 8 and 10am after an overnight fast and 30minutes of rest. All patients were antipsychotic-naïve and did not take any prolactin influencing medication.

RESULTS

Our sample consisted of 116 antipsychotic-naïve ARMS and 49 FEP patients. Hyperprolactinemia was shown in 32% of ARMS and 35% of FEP patients. After correction for the normal biological variation between the sexes, we still found higher average prolactin levels in female than in male patients (β=0.42; t=2.47; p=0.01) but no difference in prolactin levels between ARMS and FEP patients (β=-0.05; t=-0.30; p=0.76). The survival analysis revealed no significant predictive value for prolactin levels to predict transition to psychosis.

CONCLUSION

Our findings support a possible role of prolactin in emerging psychosis and it could be speculated that stress, which can induce hyperprolactinemia, has a stronger effect on women than on men in emerging psychosis.

Selective genetic disruption of dopaminergic, serotonergic and noradrenergic neurotransmission: insights into motor, emotional and addictive behaviour

BACKGROUND

The monoaminergic transmitters dopamine (DA), noradrenaline (NE) and serotonin (5-HT) modulate cerebral functions via their extensive effects in the brain. Investigating their roles has led to the creation of vesicular monoaminergic transporter-2 (VMAT2) knockout (KO) mice. While this mutation results in postnatal death, VMAT2-heterozygous (HET) mice are viable and show a complex behavioural phenotype. However, the simultaneous alteration of the 3 systems prevents investigations into their individual functions.

METHODS

To assess the specific role of NE, 5-HT and DA, we genetically disrupted their neurotransmission by creating conditional VMAT2-KO mice with targeted recombination. These specific recombinations were obtained by breeding VMAT2(lox/lox) mice with DBHcre, SERTcre and DATcre mice, respectively. We conducted a complete neurochemical and behavioural characterization of VMAT2-HET animals in each system.

RESULTS

Conditional VMAT2-KO mice revealed an absence of VMAT2 expression, and a specific decrease in the whole brain levels of each monoamine. Although NE- and 5-HT-depleted mice are viable into adulthood, DA depletion results in postnatal death before weaning. Interestingly, alteration of the DA transmission fully accounted for the increased amphetamine response formerly observed in the VMAT2-HET mice, whereas alteration of the 5-HT system was solely responsible for the increase in cocaine response.

LIMITATIONS

We used VMAT2-HET mice that displayed a mild phenotype. Because the VMAT2-KO in DA neurons is lethal, it precluded a straightforward comparison of the full KOs in the 3 systems.

CONCLUSION

Given the intermingled functions of NE, 5-HT and DA in regulating cognitive and affective functions, this model will enhance understanding of their respective roles in the pathophysiology of psychiatric disorders.

Connecting the dots of the cerebro-cerebellar role in cognitive function: neuronal pathways for cerebellar modulation of dopamine release in the prefrontal cortex

Cerebellar involvement in autism, schizophrenia, and other cognitive disorders is typically associated with prefrontal cortical pathology. However, the underlying neuronal mechanisms are largely unknown. It has previously been shown in mice that stimulation of the dentate nucleus (DN) of the cerebellum evokes dopamine (DA) release in the medial prefrontal cortex (mPFC). Here, we investigated the neuronal circuitry by which the cerebellum modulates mPFC DA release. Fixed potential amperometry was used to determine the contribution of two candidate pathways by which the cerebellum may modulate mPFC DA release. In urethane anesthetized mice, DA release evoked by DN stimulation (50 Hz) was recorded in mPFC following local anesthetic lidocaine (0.02 μg) or ionotropic glutamate receptor antagonist kynurenate (0.5 μg) infusions into the mediodorsal or ventrolateral thalamic nucleus (ThN md; ThN vl), or the ventral tegmental area (VTA). Following intra-VTA lidocaine or kynurenate infusions, DA release was decreased by ∼50%. Following intra-ThN md and ThN vl infusions of either drug, DA release was decreased by ∼35% and 15%, respectively. Reductions in DA release following lidocaine or kynurenate infusions were not significantly different indicating that neuronal cells in the VTA and ThN were activated primarily if not entirely by glutamatergic inputs. The present study suggests that neuropathological changes in the cerebellum commonly observed in autism, schizophrenia, and other cognitive disorders could result in a loss of functionality of cerebellar-mPFC circuitry that is manifested as aberrant dopaminergic activity in the mPFC. Additionally, these results specifically implicate glutamate as a modulator of mPFC dopaminergic activity.

Behavioral abnormalities in synapsin II knockout mice implicate a causal factor in schizophrenia

Recent studies on the phosphoprotein synapsin II have revealed reduced expression in postmortem medial prefrontal cortex tissues from subjects with schizophrenia, and chronic antipsychotic drug treatment has resulted in concurrent increases in synapsin II mRNA and protein levels. Collectively, this research suggests a role of synapsin II in the pathophysiology of schizophrenia; however, whether synapsin II plays a causal role in this disease process still remains unclear. Therefore, the goal of this investigation was to examine whether synapsin II knockout mice display behavioral abnormalities commonly expressed in preclinical animal models of schizophrenia, namely deficits in prepulse inhibition (PPI), decreased social behavior, and locomotor hyperactivity. Results indicate that mice with knockout of the synapsin II gene demonstrate deficits in PPI at three prepulse intensities (67, 70, and 73 dB), along with deficits in habituation to startle to a 110 dB acoustic pulse. Knockout animals also expressed decreased social behavior and increased locomotor activity when compared to wildtype and heterozygous populations. Complete knockout of the synapsin II gene was confirmed in postmortem brain tissues via immunoblotting. In conclusion, these results confirm that synapsin II knockout mice display behavioral endophenotypes similar to established preclinical animal models of schizophrenia, and lend support to the notion that abnormalities in synapsin II expression may play a causal role in the underlying pathophysiological mechanisms of schizophrenia.

Combined antipsychotic treatment involving clozapine and aripiprazole

Treatment resistance is considered a challenging problem of antipsychotic pharmacotherapy. In such cases, combination approaches are commonly used, for instance the add-on of aripiprazole to clozapine. This review aims at giving an overview of the present knowledge on this strategy. We performed a keyword-based screening of databases (including November 2007) and evaluated the data in a systematic manner. The courses of 94 patients were reported in 11 publications. At a mean dosage of 20.5 mg/day, aripiprazole achieved clinical improvement of psychotic symptoms and facilitated a dose reduction of clozapine from 476.7 to 425.1 mg/day. In parallel, clozapine serum levels decreased from 611 to 523 ng/ml. No pharmacokinetic interactions were reported, and clozapine-induced side effects ameliorated. However, single cases of extrapyramidal side effects occurred. The combination of clozapine and aripiprazole follows a neurobiological rationale and appears to be effective and tolerable. The results of placebo-controlled trials might allow further insight into the benefits and risks of this strategy.

Loudness dependence of the auditory evoked N1/P2 component as an indicator of serotonergic dysfunction in patients with schizophrenia--a replication study

Serotonergic dysfunction appears to be involved in the pathogenesis of schizophrenia. The loudness dependence of auditory evoked potentials (LDAEP) has been suggested to be a valid indicator of the brain serotonin system's activity in humans. Patients with schizophrenia showed weaker LDAEP, indicating high serotonergic activity, in comparison to healthy controls. Thus, we were able again to demonstrate electrophysiological evidence for an upregulated serotonergic system in schizophrenia.

Nitric oxide inhibits metamorphosis in larvae of Crepidula fornicata, the slippershell snail

This paper concerns the role of nitric oxide (NO) in controlling metamorphosis in the marine gastropod Crepidula fornicata. Metamorphosis was stimulated by the nitric oxide synthase (NOS) inhibitors AGH (aminoguanidine hemisulfate) and SMIS (S-methylisothiourea sulfate) at concentrations of about 100-1000 micromol l(-1) and 50-200 micromol l(-1), respectively. Metamorphosis was not, however, induced by the NOS inhibitor l-NAME (l-N(G)-nitroarginine methyl ester) at even the highest concentration tested, 500 micromol l(-1). Moreover, pre-incubation with l-NAME at 20 and 80 micromol l(-1) did not increase the sensitivity of competent larvae to excess K(+), a potent inducer of metamorphosis in this species; we suggest that either l-NAME is ineffective in suppressing NO production in larvae of C. fornicata, or that it works only on the constitutive isoform of the enzyme. In contrast, metamorphosis was potentiated by the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-1-one) in response to a natural metamorphic inducer derived from conspecific adults. Because NO typically stimulates cGMP production through the activation of soluble guanylate cyclase, this result supports the hypothesis that NO acts as an endogenous inhibitor of metamorphosis in C. fornicata. The expression of NOS, shown by immunohistochemical techniques, was detected in the apical ganglion of young larvae but not in older larvae, further supporting the hypothesis that metamorphosis in C. fornicata is made possible by declines in the endogenous concentration of NO during development.

Dopamine receptor signaling molecules are altered in elderly schizophrenic cortex

Alterations of molecules that mediate dopaminergic signal transduction have been found in schizophrenia, supporting the hypothesis of altered dopaminergic neurotransmission in this illness. To further explore this hypothesis, the authors measured transcript expression of three proteins involved in dopamine (DA) signaling in postmortem dorsolateral prefrontal and anterior cingulate cortex of elderly schizophrenic subjects and a comparison group. The transcript encoding calcyon, a protein that potentiates crosstalk between D1 DA receptors and Gq/11-linked receptors, was increased in schizophrenic prefrontal and cingulate cortex by 25%. Transcript levels of spinophilin, a protein enriched in dendritic spines that modulates excitatory neurotransmission, were increased 22% in dorsolateral prefrontal cortex but were unchanged in anterior cingulate cortex in schizophrenia. Levels of DARPP-32 mRNA, a downstream effector of dopaminergic neurotransmission, were similar in both groups for both cortical groups. These alterations in spinophilin and calcyon mRNA levels in schizophrenic prefrontal and cingulate cortex provide further evidence of altered dopaminergic neurotransmission in this illness.

Dopamine-D1 and -D2 receptors differentially regulate synapsin II expression in the rat brain

We previously demonstrated that chronic treatment with the dopamine-D2 receptor antagonist, haloperidol, increases mRNA and protein content of the phosphoprotein, synapsin II, in the rat striatum. Since dopamine-D2 receptor antagonism and dopamine-D1 receptor blockade can have opposing effects on gene expression, the present investigation compared the effects of haloperidol with those of the dopamine-D1 receptor antagonist, R-[+]-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH23390), on the expression of synapsin II protein. Haloperidol and SCH23390 respectively elevated and reduced concentrations of the molecule in mouse primary midbrain cell cultures. Additional experiments revealed that the dopamine-D1 receptor agonist, R-[+]-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzapezine-7,8-diol (SKF38393), upregulated the phosphoprotein in these cells. Furthermore, in vivo rat studies demonstrated that chronic haloperidol treatment increases synapsin II protein expression in the medial prefrontal cortex and nucleus accumbens, as was observed in the striatum. In contrast, chronic SCH23390 administration reduced concentrations of this protein in all of these regions, although the reductions seen in the medial prefrontal cortex were insignificant. Neither haloperidol nor the dopamine-D1 receptor antagonist affected synapsin I protein expression in any of the studied brain areas. Based on these findings, we propose dopamine receptors may specifically regulate synapsin II expression through a cyclic AMP-dependent pathway. Since synapsin II is involved in neurotransmitter release and synaptogenesis, and changes in synaptic efficacy and structure are suggested in schizophrenia as well as in haloperidol treatment, our findings offer insight into the mechanistic actions of the antipsychotic agent at the synaptic level.

Screening the receptorome reveals molecular targets responsible for drug-induced side effects: focus on ‘fen–phen’

The in vitro pharmacological profiling of drugs using a large panel of cloned receptors (e.g., G protein-coupled receptors, ligand-gated ion channels, Na(+)-dependent monoamine transporters), an approach that has come to be known as 'receptorome screening', has unveiled novel molecular mechanisms responsible for the actions and/or side effects of certain drugs. For instance, receptorome screening has been employed to uncover novel molecular targets involved in the actions of antipsychotic medications and the hallucinogenic mint extract salvinorin A. This review highlights the recent application of receptorome screening to discover why the anorexigen fenfluramine causes serious cardiopulmonary side effects. Receptorome screening has implicated N-deethylation of fenfluramine and serotonin 5-hydroxy-t-ryptamine 2B receptors in the adverse effects of the drug; subsequent studies corroborated this finding. The results discussed highlight the utility of determining the potential activity of drugs -- and, importantly, of their in vivo metabolites -- at as many molecular targets as possible in order to reliably predict side effect profiles. Receptorome screening represents one of the most effective methods for identifying potentially serious drug-related side effects at the preclinical stage, thereby avoiding significant economic and human health consequences.

Clozapin-Augmentation mit atypischen Antipsychotika

Typical antipsychotic medications have considerably improved clinical outcome of patients suffering from schizophrenic psychoses, but up to 40% of the cases show treatment resistant symptoms. Even therapy with atypical antipsychotic drugs such as risperidone, quetiapine, olanzapine, sulpiride, amisulpride, and ziprasidone often fails to reach complete remission due to resistant, positive or negative symptoms or dose-limiting side effects. As this also holds true in the case of monotherapy with clozapine, a substance known to be effective against treatment-resistant schizophrenia, increasing numbers of patients receive atypical antipsychotic drugs in addition to clozapine. This review systematically evaluates case reports and clinical investigations on the use of clozapine combined with risperidone, olanzapine, quetiapine, sulpiride, amisulpride, or ziprasidone. Details on indication, methodology, and effects of the investigations are summarized. Only one double blind, placebo-controlled trial on the combination with sulpiride exists within a number of altogether 31 publications about 1182 treatments. Favorable effects on positive and/or negative symptoms or improvements of clozapine-induced side effects were described for every combination approach. In some cases pharmacokinetic interactions or serious unfavorable effects occurred. In conclusion it might be accepted that most of the combination therapies follow a neurobiological rational. There a major differences in the level of evidence that they are safe, tolerable and effective. We discuss criteria for the indication for augmenting clozapine therapy and the differential indication for existing alternatives. Additional randomized prospective trials are needed in order to evaluate these strategies systematically.

Distinct temporal phases in the behavioral pharmacology of LSD: dopamine D2 receptor-mediated effects in the rat and implications for psychosis

RATIONALE

The effect of LSD in humans has been described as occurring in two temporal phases. The behavioral effects in rats also occur in two temporal phases: an initial suppression of exploration followed by increased locomotor activity.

OBJECTIVES

We decided to investigate this phenomenon from the perspective that the pharmacology might have relevance to the neurochemical mechanisms underlying psychosis.

METHODS

Twenty-five male Sprague-Dawley rats were trained to discriminate LSD (186 nmol/kg, 0.08 mg/kg, i.p.) with a 30-min preinjection time (LSD-30, N=12) and LSD (372 nmol/kg, 0.16 mg/kg, i.p.) with a 90-min preinjection time (LSD-90, N=13) from saline, using a two-lever, food-reinforced operant conditioning task.

RESULTS

LSD (186 or 372 nmol/kg, 0.08 or 0.16 mg/kg) given 30 min prior to training produced a cue that was completely antagonized by 5-HT2A antagonists and lasted no longer than 1 h. LSD (372 nmol/kg, 0.16 mg/kg) injected 90 min before training produced a cue that was not fully blocked by 5-HT2A antagonists, but instead was significantly inhibited by haloperidol. In these rats, substitution no longer occurred with the 5-HT2 agonists DOI or LSD (30 min preinjection), but full substitution was obtained with the D2 agonists apomorphine, N-propyldihydrexidine, and quinelorane.

CONCLUSION

The discriminative stimulus effect of LSD in rats occurs in two phases, and these studies provide evidence that the later temporal phase is mediated by D2 dopamine receptor stimulation. A second temporal phase that involves dopaminergic pathways would be consistent with the widespread belief that excessive dopaminergic activity may be an underlying cause of paranoid psychosis.

Abnormalities in the dopamine system in schizophrenia may lie in altered levels of dopamine receptor-interacting proteins

BACKGROUND

Dopamine receptor-interacting proteins constitute a part of the dopamine system that is involved in regulation of dopamine receptor-associated intracellular signaling. Previously, we demonstrated that two such proteins, the D1 receptor-interacting protein calcyon and the D2 receptor-interacting protein neuronal calcium sensor-1 (NCS-1), were elevated in the prefrontal cortex of schizophrenia cases from the Stanley Foundation Neuropathology Consortium.

METHODS

The aim of this study was to confirm and expand these findings. We employed Western blot and real-time reverse transcriptase polymerase chain reaction analyses to compare prefrontal (area 46) and occipital (area 17) cortical levels of calcyon and NCS-1 proteins and mRNAs between schizophrenia (n = 37) and control (n = 30) cohorts from the Brain Collection of the Mount Sinai Medical School/Bronx Veterans Administration Medical Center.

RESULTS

The schizophrenia cohort showed significant up-regulation of calcyon protein and message levels in both prefrontal and occipital cortical regions, both of which also displayed schizophrenia-associated up-regulation of NCS-1 message. Protein levels of NCS-1 were elevated only in the prefrontal cortex. All increases in protein levels were correlated with those of corresponding messages. Furthermore, schizophrenia-associated alterations in the levels of calcyon and NCS-1 messages were correlated.

CONCLUSIONS

Up-regulation of calcyon and NCS-1 in the second schizophrenia cohort strengthens the proposition that abnormalities of the dopamine system in this disease may lie in altered levels of dopamine receptor-interacting proteins. Also, up-regulation of both calcyon and NCS-1 in the cortex of schizophrenia patients can be attributed largely to an enhanced transcription or reduced degradation of their messages. Finally, our findings suggest that elevations in the expressions of calcyon and NCS-1 in schizophrenia may have the same underlying cause.

Molecular basis for catecholaminergic neuron diversity

Catecholaminergic neurons control diverse cognitive, motor, and endocrine functions and are associated with multiple psychiatric and neurodegenerative disorders. We present global gene-expression profiles that define the four major classes of dopaminergic (DA) and noradrenergic neurons in the brain. Hypothalamic DA neurons and noradrenergic neurons in the locus coeruleus display distinct group-specific signatures of transporters, channels, transcription, plasticity, axon-guidance, and survival factors. In contrast, the transcriptomes of midbrain DA neurons of the substantia nigra and the ventral tegmental area are closely related with <1% of differentially expressed genes. Transcripts implicated in neural plasticity and survival are enriched in ventral tegmental area neurons, consistent with their role in schizophrenia and addiction and their decreased vulnerability in Parkinson's disease. The molecular profiles presented provide a basis for understanding the common and population-specific properties of catecholaminergic neurons and will facilitate the development of selective drugs.

Serotonergic dysfunction in schizophrenia assessed by the loudness dependence measure of primary auditory cortex evoked activity

Increased serotonergic activity is discussed as an important pathogenetic factor in schizophrenia. Further support for this hypothesis is difficult to obtain due to the lack of valid indicators of the brain's serotonin system. A great deal of evidence discovered through human and animal studies suggests that a weak loudness dependence of auditory evoked potentials (LDAEP) indicates high serotonergic activity and vice versa. The LDAEP is a measure of auditory cortex activity, reflecting increase or decrease of auditory evoked potential amplitudes with increasing tone loudness, which is probably modulated by the serotonergic innervation there. This is true only for the LDAEP of the primary auditory cortex, since this region is more highly innervated by serotonergic fibers than the secondary auditory cortex. The LDAEP (N1/P2 component) of 25 inpatients with schizophrenia free of medication and 25 healthy controls matched by age and gender, were recorded. Using dipole source analysis, the LDAEP of primary (tangential dipole) and this of secondary auditory cortex (radial dipole) was separately analyzed. Following a 4-week treatment with the 5-HT(2) antagonists clozapine or olanzapine, patients were once again studied. The LDAEP of the primary, but not of the secondary auditory cortex, was significantly weaker in the patients with schizophrenia than in healthy volunteers, indicating enhanced serotonergic neurotransmission. After treatment with the 5-HT(2) antagonists, the LDAEP (of the right hemisphere) tended to be increased, indicating normalization of serotonergic function in the patients with schizophrenia. These results suggest that the loudness dependence of primary auditory cortex evoked activity is well suitable to assess serotonergic dysfunction in schizophrenia.

cDNA array reveals differential gene expression following chronic neuroleptic administration: implications of synapsin II in haloperidol treatment

The cDNA expression array is a recently developed scientific tool that can profile the differential expression of several hundreds of genes simultaneously and is therefore advantageous in the study of antipsychotic drug action at the genetic level. Using this technology, we discovered 14 genes in the rat striatum whose expression was changed by >/= 50% following chronic haloperidol treatment. Among them was the synapsin II gene, which was found to be significantly up-regulated after the treatment. Since recent studies have implicated this gene in schizophrenia, further experiments were performed to determine whether chronic haloperidol exposure resulted in concurrent increases in the expression of striatal synapsin II protein. Immunoblotting revealed that protein levels of both the a and b isoforms of synapsin II were also increased by comparable amounts following haloperidol treatment. This study is the first to show the regulation of synapsin II expression by haloperidol at the transcript and protein level in rat striatum. A possible mechanism for the observed haloperidol-induced increase in striatal synapsin II expression, along with the implications of this up-regulation in chronic haloperidol treatment, is presented.

Reduced prefrontal activity predicts exaggerated striatal dopaminergic function in schizophrenia

Both dopaminergic neurotransmission and prefrontal cortex (PFC) function are known to be abnormal in schizophrenia. To test the hypothesis that these phenomena are related, we measured presynaptic dopaminergic function simultaneously with regional cerebral blood flow during the Wisconsin Card Sorting Test (WCST) and a control task in unmedicated schizophrenic subjects and matched controls. We show that the dopaminergic uptake constant Ki in the striatum was significantly higher for patients than for controls. Patients had significantly less WCST-related activation in PFC. The two parameters were strongly linked in patients, but not controls. The tight within-patient coupling of these values, with decreased PFC activation predicting exaggerated striatal 6-fluorodopa uptake, supports the hypothesis that prefrontal cortex dysfunction may lead to dopaminergic transmission abnormalities.

Postmortem studies in schizophrenia

For over a century, postmortem studies have played a central part in the search for the structural and biochemical pathology of schizophrenia. However, for most of this time, little progress has been made. Recently, the situation has begun to change, helped by the emergence of more powerful methodologies and research designs, and by the availability of brain imaging to provide complementary information. As a result, it can now be clearly concluded that there are structural cerebral abnormalities in schizophrenia that are intrinsic to the disorder. The neuropathological process is not primarily degenerative, but involves a change in the normal cytoarchitecture of the brain, probably originating in development. Neurochemically, there is postmortem evidence for alterations in several transmitter systems including dopamine, glutamate, serotonin, and γ-aminobutyric acid (GABA). The cardinal findings are reviewed here, together with a consideration of the conceptual and methodological issues that face postmortem studies of schizophrenia.

Animal and plant members of a gene family with similarity to alkaloid-synthesizing enzymes

Here we describe novel members of a gene family which have similarity to strictosidine synthase (SS), one of the key enzymes in the production of monoterpene indole alkaloids. In addition to the first animal member of the family described previously (Drosophila hemomucin), a second Drosophila member has been identified, which appears to differ in subcellular distribution from hemomucin. In Arabidopsis, SS-like genes form a multigene family, compatible with a possible function as antifeedants and antibacterial compounds. In Caenorhabditis, two members have been identified and one member each in mouse and human. Interestingly, the human SS-like gene is strongly expressed in the brain, the very organ many of the indole alkaloids act upon.