Role of the cholinergic muscarinic system in bipolar disorder and related mechanism of action of antipsychotic agents

PET imaging of M4 muscarinic acetylcholine receptors in rhesus macaques using [11C]MK-6884: Quantification with kinetic modeling and receptor occupancy by CVL-231 (emraclidine), a novel positive allosteric modulator

Stimulation of the M4 muscarinic acetylcholine receptor reduces striatal hyperdopaminergia, suggesting its potential as a therapeutic target for schizophrenia. Emraclidine (CVL-231) is a novel, highly selective, positive allosteric modulator (PAM) of M4 muscarinic acetylcholine receptors i.e. acts as a modulator that increases the response of these receptors. First, we aimed to further characterize the positron emission tomography (PET) imaging and quantification performance of a recently developed M4 PAM radiotracer, [11C]MK-6884, in non-human primates (NHPs). Second, we applied these results to determine the receptor occupancy of CVL-231 as a function of dose. Using paired baseline-blocking PET scans, we quantified total volume of distribution, binding potential, and receptor occupancy. Both blood-based and reference region-based methods quantified M4 receptor levels across brain regions. The 2-tissue 4-parameter kinetic model best fitted regional [11C]MK-6884-time activity curves. Only the caudate nucleus and putamen displayed statistically significant [11C]MK-6884 uptake and dose-dependent blocking by CVL-231. For binding potential and receptor occupancy quantification, the simplified reference tissue model using the grey cerebellum as a reference region was employed. CVL-231 demonstrated dose-dependent M4 receptor occupancy in the striatum of the NHP brain and shows promise for further development in clinical trials.

Common changes in rat cortical gene expression after valproate or lithium treatment particularly affect pre- and post-synaptic pathways that regulate four neurotransmitters systems

OBJECTIVES

We have postulated that common changes in gene expression after treatment with different therapeutic classes of psychotropic drugs contribute to their common therapeutic mechanisms of action.

METHODS

To test this hypothesis, we measured levels of cortical coding and non-coding RNA using GeneChip® Rat Exon 1.0 ST Array after treatment with vehicle (chow only), chow containing 1.8 g lithium carbonate/kg (n = 10) or chow containing 12 g sodium valproate/kg (n = 10) for 28 days. Differences in levels of RNA were identified using JMP Genomics 13 and the Panther Gene Ontology Classification System was used to identify potential consequences of RNA.

RESULTS

Compared to vehicle treatment, levels of cortical RNA for 543 and 583 coding and non-coding RNAs were different after treatment with valproate and lithium, respectively. Moreover, levels of 323 coding and non-coding RNAs were altered in a highly correlated way by treatment with valproate and lithium, changes that would impact on cholinergic, glutamatergic, serotonergic and dopaminergic neurotransmission as well as on voltage gated ion channels.

CONCLUSIONS

Our study suggests that treating with mood stabilisers cause many common changes in levels of RNA which will impact on CNS function, particularly affecting post-synaptic muscarinic receptor functioning and the release of multiple neurotransmitters.

Association of polygenic score and the involvement of cholinergic and glutamatergic pathways with lithium treatment response in patients with bipolar disorder

Lithium is regarded as the first-line treatment for bipolar disorder (BD), a severe and disabling mental health disorder that affects about 1% of the population worldwide. Nevertheless, lithium is not consistently effective, with only 30% of patients showing a favorable response to treatment. To provide personalized treatment options for bipolar patients, it is essential to identify prediction biomarkers such as polygenic scores. In this study, we developed a polygenic score for lithium treatment response (Li+PGS) in patients with BD. To gain further insights into lithium's possible molecular mechanism of action, we performed a genome-wide gene-based analysis. Using polygenic score modeling, via methods incorporating Bayesian regression and continuous shrinkage priors, Li+PGS was developed in the International Consortium of Lithium Genetics cohort (ConLi+Gen: N = 2367) and replicated in the combined PsyCourse (N = 89) and BipoLife (N = 102) studies. The associations of Li+PGS and lithium treatment response - defined in a continuous ALDA scale and a categorical outcome (good response vs. poor response) were tested using regression models, each adjusted for the covariates: age, sex, and the first four genetic principal components. Statistical significance was determined at P < 0.05. Li+PGS was positively associated with lithium treatment response in the ConLi+Gen cohort, in both the categorical (P = 9.8 × 10-12, R2 = 1.9%) and continuous (P = 6.4 × 10-9, R2 = 2.6%) outcomes. Compared to bipolar patients in the 1st decile of the risk distribution, individuals in the 10th decile had 3.47-fold (95%CI: 2.22-5.47) higher odds of responding favorably to lithium. The results were replicated in the independent cohorts for the categorical treatment outcome (P = 3.9 × 10-4, R2 = 0.9%), but not for the continuous outcome (P = 0.13). Gene-based analyses revealed 36 candidate genes that are enriched in biological pathways controlled by glutamate and acetylcholine. Li+PGS may be useful in the development of pharmacogenomic testing strategies by enabling a classification of bipolar patients according to their response to treatment.

Antidepressant efficacy of cariprazine in bipolar disorder and the role of its pharmacodynamic properties: A hypothesis based on data

The treatment of bipolar depression is one of the most challenging needs in contemporary psychiatry. Currently, only quetiapine, olanzapine-fluoxetine combination, lurasidone, cariprazine, and recently lumateperone have been FDA-approved to treat this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain elusive. The current study investigated whether the pharmacodynamic properties of cariprazine fit into a previously developed model which was the first to be derived based on the strict combination of clinical and preclinical data. The authors performed a systematic review of the literature to identify the pharmacodynamic properties of cariprazine. The original model suggests that a constellation of effects on different receptors is necessary and that serotonin reuptake inhibition does not appear to play a significant role in acute bipolar depression. On the contrary, norepinephrine activity seems to be necessary. Probably the early antidepressant effect can be achieved through an agonistic activity at 5HT-1A and antagonism at alpha1 noradrenergic and 5-HT2A receptors, but the presence of a norepinephrine reuptake inhibition appears essential to sustain it. Overall, the properties of cariprazine fit well the proposed model and add to its validity. A point that needs further clarification is norepinephrine reuptake inhibition which is not yet fully studied for cariprazine.

Basal Forebrain Cholinergic Innervation Induces Depression-Like Behaviors Through Ventral Subiculum Hyperactivation

Malfunction of the ventral subiculum (vSub), the main subregion controlling the output connections from the hippocampus, is associated with major depressive disorder (MDD). Although the vSub receives cholinergic innervation from the medial septum and diagonal band of Broca (MSDB), whether and how the MSDB-to-vSub cholinergic circuit is involved in MDD is elusive. Here, we found that chronic unpredictable mild stress (CUMS) induced depression-like behaviors with hyperactivation of vSub neurons, measured by c-fos staining and whole-cell patch-clamp recording. By retrograde and anterograde tracing, we confirmed the dense MSDB cholinergic innervation of the vSub. In addition, transient restraint stress in CUMS increased the level of ACh in the vSub. Furthermore, chemogenetic stimulation of this MSDB-vSub innervation in ChAT-Cre mice induced hyperactivation of vSub pyramidal neurons along with depression-like behaviors; and local infusion of atropine, a muscarinic receptor antagonist, into the vSub attenuated the depression-like behaviors induced by chemogenetic stimulation of this pathway and CUMS. Together, these findings suggest that activating the MSDB-vSub cholinergic pathway induces hyperactivation of vSub pyramidal neurons and depression-like behaviors, revealing a novel circuit underlying vSub pyramidal neuronal hyperactivation and its associated depression.

Clozapine: Why Is It So Uniquely Effective in the Treatment of a Range of Neuropsychiatric Disorders?

Clozapine is superior to other antipsychotics as a therapy for treatment-resistant schizophrenia and schizoaffective disorder with increased risk of suicidal behavior. This drug has also been used in the off-label treatment of bipolar disorder, major depressive disorder (MDD), and Parkinson's disease (PD). Although usually reserved for severe and treatment-refractory cases, it is interesting that electroconvulsive therapy (ECT) has also been used in the treatment of these psychiatric disorders, suggesting some common or related mechanisms. A literature review on the applications of clozapine and electroconvulsive therapy (ECT) to the disorders mentioned above was undertaken, and this narrative review was prepared. Although both treatments have multiple actions, evidence to date suggests that the ability to elicit epileptiform activity and alter EEG activity, to increase neuroplasticity and elevate brain levels of neurotrophic factors, to affect imbalances in the relationship between glutamate and γ-aminobutyric acid (GABA), and to reduce inflammation through effects on neuron-glia interactions are common underlying mechanisms of these two treatments. This evidence may explain why clozapine is effective in a range of neuropsychiatric disorders. Future increased investigations into epigenetic and connectomic changes produced by clozapine and ECT should provide valuable information about these two treatments and the disorders they are used to treat.

Cortical biometals: Changed levels in suicide and with mood disorders

BACKGROUND

Changes in levels of metals have been suggested to contribute to the pathophysiologies of several neurodegenerative disorders but to our knowledge this is the first metallomic study in CNS from patients with mood disorders. The focus of this study was on cortical regions affected by the pathophysiologies of bipolar disorders and major depressive disorders.

METHODS

Levels of metals were measured using inductively coupled plasma mass spectrometry in Brodmann's areas (BA) 6, 10 and 17 from patients with major depressive disorders (n = 13), bipolar disorders (n = 12) and age / sex matched controls (n = 13).

RESULTS

There were lower levels of cortical strontium (BA 6 & 10), ruthenium (BA 6 & 17) and cadmium (BA 10) from patients with major depressive disorder as well as lower levels of strontium in BA 10 from patients with bipolar disorders. Unexpectedly, there were changes in levels of 16 metals in the cortex, mainly BA 6, from suicide completers compared to those who died of other causes.

LIMITATIONS

Cohort sizes were relatively small but comparable with many studies using human postmortem CNS. Like all studies on non-treatment naïve patients, drug treatment was a potential confound in our experiments.

CONCLUSIONS

Our exploratory study suggests changes in levels of metals in bipolar disorders and major depressive disorders could be affecting cortical oxidative balance in patients with mood disorders. Our data raises the possibility that measuring levels of specific biometals in the blood could be used as a biomarker for increased risk of suicide.

Old drug, new data

New data have emerged over the past 10 years regarding the efficacy and mechanisms of action of lithium. This article briefly summarises the evidence for the use of lithium to treat affective disorders and psychosis, reviews its putative anti-suicidal effect, highlights new research on its mechanism of action and provides an update on some important side-effects and consequences of its use.

Linking lipid peroxidation and neuropsychiatric disorders: focus on 4-hydroxy-2-nonenal

4-hydroxy-2-nonenal (HNE) is considered to be a strong marker of oxidative stress; the interaction between HNE and cellular proteins leads to the formation of HNE-protein adducts able to alter cellular homeostasis and cause the development of a pathological state. By virtue of its high lipid concentration, oxygen utilization, and the presence of metal ions participating to redox reactions, the brain is highly susceptible to the formation of free radicals and HNE-related compounds. A variety of neuropsychiatric disorders have been associated with elevations of HNE concentration. For example, increased levels of HNE were found in the cortex of bipolar and schizophrenic patients, while HNE plasma concentrations resulted high in patients with major depression. On the same line, high brain concentrations of HNE were found associated with Huntington's inclusions. The incidence of high HNE levels is relevant also in the brain and cerebrospinal fluid of patients suffering from Parkinson's disease. Intriguingly, in this case the increase of HNE was associated with an accumulation of iron in the substantia nigra, a brain region highly affected by the pathology. In the present review we recapitulate the findings supporting the role of HNE in the pathogenesis of different neuropsychiatric disorders to highlight the pathogenic mechanisms ascribed to HNE accumulation. The aim of this review is to offer novel perspectives both for the understanding of etiopathogenetic mechanisms that remain still unclear and for the identification of new useful biological markers. We conclude suggesting that targeting HNE-driven cellular processes may represent a new more efficacious therapeutical intervention.

Changes in Muscarinic M2 Receptor Levels in the Cortex of Subjects with Bipolar Disorder and Major Depressive Disorder and in Rats after Treatment with Mood Stabilisers and Antidepressants

BACKGROUND

Increasingly, data are implicating muscarinic receptors in the aetiology and treatment of mood disorders. This led us to measure levels of different muscarinic receptor-related parameters in the cortex from people with mood disorders and the CNS of rats treated with mood stabilisers and antidepressant drugs.

METHODS

We measured [(3)H]AF-DX 384 binding in BA 46 and BA 24 from subjects with bipolar disorders (n = 14), major depressive disorders (n = 19), as well as age- and sex-matched controls (n = 19) and the CNS of rats treated with fluoxetine or imipramine. In addition, we used Western blots to measure levels of CHRM2 protein and oxotremorine-M stimulated [(35)S]GTPγS binding as a measure of CHRM 2 / 4 signaling.

RESULTS

Compared with controls, [(3)H]AF-DX 384 binding was lower in BA 24 and BA 46 in bipolar disorders and major depressive disorders, while CHRM2 protein and oxotremorine-M stimulated [(35)S]GTPγS binding was only lower in BA 24. Compared with vehicle, treatment with mood stabilisers, antidepressant drugs for 10 days, or imipramine for 28 days resulted in higher levels of in [(3)H]AF-DX 384 binding select regions of rat CNS.

CONCLUSIONS

Our data suggest that levels of CHRM2 are lower in BA 24 from subjects with mood disorders, and it is possible that signalling by that receptor is also less in this cortical region. Our data also suggest increasing levels of CHRM2 may be involved in the mechanisms of action of mood stabilisers and tricyclic antidepressants.

Triple reuptake inhibitors as potential next-generation antidepressants: a new hope?

The current therapy for depression is less than ideal with remission rates of only 25-35% and a slow onset of action with other associated side effects. The persistence of anhedonia originating from depressed dopaminergic activity is one of the most treatment-resistant symptoms of depression. Therefore, it has been hypothesized that triple reuptake inhibitors (TRIs) with potency to block dopamine reuptake in addition to serotonin and norepinephrine transporters should produce higher efficacy. The current review comprehensively describes the development of TRIs and discusses the importance of evaluation of in vivo transporter occupancy of TRIs, which should correlate with efficacy in humans.

The role of glutamatergic, GABA-ergic, and cholinergic receptors in depression and antidepressant-like effect

Depression is one of the most common mental disorders and social issue worldwide. Although there are many antidepressants available, the effectiveness of the therapy is still a serious issue. Moreover, there are many limitations of currently used antidepressants, including slow onset of action, numerous side effects, or the fact that many patients do not respond adequately to the treatment. Therefore, scientists are searching for new compounds with different mechanisms of action. Numerous data indicate the important role of glutamatergic, GABA-ergic, and cholinergic receptors in the pathomechanism of major depressive disorder. This review presents the role of glutamatergic, GABA-ergic, and cholinergic receptors in depression and antidepressant-like effect.

Enrichment pathway analysis. The inflammatory genetic background in Bipolar Disorder

INTRODUCTION

The pathophysiology of Bipolar Disorder (BD) is yet to be fully characterized. In the last years attention was focused on neurodevelopment or neurodegenerative events. In this context, hyper- and hypo- activation of inflammatory cascades may play a role in modulating the architecture and function of neuronal tissues. In the present paper we tested the enrichment of molecular pathways related to inflammatory cascades (IL-1, IL-2, IL-6, IL-8, TNF and INF) testing whether genes related to these systems hold more variations associated with the risk for BD than expected.

METHODS

~7000 bipolar patients and controls with genome-wide data available from NIMH dataset were analyzed. SNPs were imputed, checked for quality control, pruned and tested for association (0.01<p). Fisher test was conducted to test the enrichment within the pathways and the association was permutated (10(5) times) to limit false positive findings.

RESULTS

As a result, IL-6, IL-8 and IFN related pathways held twice to thrice the number of expected variants associated with BD. These tests resisted the permutation analysis.

LIMITATIONS

The restricted number of inflammatory components included in the analysis and the lack of functional consequences for some of the SNPs analyzed may be biased; however, these choices helped the authors to lighten the statistical computational load for the analyses and at the same time included possibly hidden SNPs in linkage disequilibrium with the analyzed variations.

CONCLUSIONS

We bring evidence that the inflammatory cascades may be genetically varied in Bipolar patients. This genetic background may explain part of the pathophysiology of the disorder.

The muscarinic system, cognition and schizophrenia

An increasing body of evidence has implicated the central muscarinic system as contributing to a number of symptoms of schizophrenia and serving as a potential target for pharmaceutical interventions. A theoretical review is presented that focuses on the central muscarinic system's contribution to the cognitive symptoms of schizophrenia. The aim is to bridge the void between pertinent neuropsychological and neurobiological research to provide an explanatory account of the role that the central muscarinic system plays in the symptoms of schizophrenia. First, there will be a brief overview of the relevant neuropsychological schizophrenia literature, followed by a concise introduction to the central muscarinic system. Subsequently, we will draw from animal, neuropsychological and pharmacological literature, and discuss the findings in relation to cognition, schizophrenia and the muscarinic system. Whilst unifying the multiple domains of research into a concise review will act as a useful line of enquiry into the central muscarinic systems contribution to the symptoms of schizophrenia, it will be made apparent that more research is needed in this field.

The pharmacodynamic properties of lurasidone and their role in its antidepressant efficacy in bipolar disorder

The treatment of bipolar depression is one of the most challenging issues in contemporary psychiatry. Currently only quetiapine, the olanzapine-fluoxetine combination and recently lurasidone are officially FDA-approved against this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain elusive. The current study investigated whether the pharmacodynamic properties of lurasidone fit to a previously developed model which was the first to be derived on the basis of the strict combination of clinical and preclinical data with no input from theory or opinion. The authors performed a complete and systematic review of the literature to identify the pharmacodynamic properties of lurasidone. The original model suggests that a constellation of effects on different receptors are necessary but the serotonin reuptake inhibition does not seem to play a significant role for bipolar depression. On the contrary norepinephrine activity seems to be very important. Probably the early antidepressant effect can be achieved through an agonistic activity at 5HT-1A and antagonism at alpha1 noradrenergic and 5-HT2A receptors, but the presence of a norepinephrine reuptake inhibition is essential in order to sustain it. Overall the properties of lurasidone fit well the model and add to its validity. A point that needs clarification is norepinephrine reuptake inhibition which is not yet studied for lurasidone.

Olanzapine: a 5-year perspective

Olanzapine is a novel antipsychotic, approved for the acute and maintenance treatment of schizophrenia and bipolar I disorder. Despite the publicity regarding reported adverse events with the novel antipsychotics, such as weight gain and Type II diabetes mellitus, olanzapine remains a useful and important medicine. It is a selective monoaminergic antagonist with high-affinity binding to a number of receptors thought to be implicated in some psychotic and mood symptoms. The complex pharmacology of olanzapine has lead to studies exploring its use in treating substance abuse, aggression/violence, borderline personality disorder, schizotypal personality disorder, obsessive-compulsive disorder and as a neuroprotective agent in schizophrenia. As the pharmacology of olanzapine and other novel antipsychotics becomes better understood, future effective treatment strategies are likely to match an individual's genetic makeup and receptor profiles to the most compatible agent.

Second generation antipsychotic-induced type 2 diabetes: a role for the muscarinic M3 receptor

Second generation antipsychotics (SGAs) are widely prescribed to treat various disorders, most notably schizophrenia and bipolar disorder; however, SGAs can cause abnormal glucose metabolism that can lead to insulin-resistance and type 2 diabetes mellitus side-effects by largely unknown mechanisms. This review explores the potential candidature of the acetylcholine (ACh) muscarinic M3 receptor (M3R) as a prime mechanistic and possible therapeutic target of interest in SGA-induced insulin dysregulation. Studies have identified that SGA binding affinity to the M3R is a predictor of diabetes risk; indeed, olanzapine and clozapine, SGAs with the highest clinical incidence of diabetes side-effects, are potent M3R antagonists. Pancreatic M3Rs regulate the glucose-stimulated cholinergic pathway of insulin secretion; their activation on β-cells stimulates insulin secretion, while M3R blockade decreases insulin secretion. Genetic modification of M3Rs causes robust alterations in insulin levels and glucose tolerance in mice. Olanzapine alters M3R density in discrete nuclei of the hypothalamus and caudal brainstem, regions that regulate glucose homeostasis and insulin secretion through vagal innervation of the pancreas. Furthermore, studies have demonstrated a dynamic sensitivity of hypothalamic and brainstem M3Rs to altered glucometabolic status of the body. Therefore, the M3R is in a prime position to influence glucose homeostasis through direct effects on pancreatic β-cells and by potentially altering signalling in the hypothalamus and brainstem. SGA-induced insulin dysregulation may be partly due to blockade of central and peripheral M3Rs, causing an initial disruption to insulin secretion and glucose homeostasis that can progressively lead to insulin resistance and diabetes during chronic treatment.

Evaluation of acetylcholinesterase in an animal model of mania induced by D-amphetamine

The present study aims to investigate the effects of mood stabilizers, lithium (Li) and valproate (VPA), on acetylcholinesterase (AChE) activity in the brains of rats subjected to an animal model of mania induced by D-amphetamine (D-AMPH). In the reversal treatment, Wistar rats were first given D-AMPH or saline (Sal) for 14 days. Between days 8 and 14, the rats were treated with Li, VPA, or Sal. In the prevention treatment, rats were pretreated with Li, VPA, or Sal. AChE activity was measured in the brain structures (prefrontal cortex, hippocampus, and striatum). Li, alone in reversion and prevention treatments, increased AChE activity in the brains of rats. VPA, alone in prevention treatment, increased AChE activity in all brain regions evaluated; in the reversion, only in the prefrontal. However, D-AMPH decreased activity of AChE in the striatum of rats in both the reversion and prevention treatments. VPA was able to revert and prevent this AChE activity alteration in the rat striatum. Our findings further support the notion that the mechanisms of mood stabilizers also involve changes in AChE activity, thus reinforcing the need for more studies to better characterize the role of acetylcholine in bipolar disorder.

Acute mood effect of donepezil in young, healthy volunteers

OBJECTIVE

Chronic use of the acetylcholinesterase inhibitor donepezil has been found to improve mood or to induce mania/hypomania in many neuropsychiatric patients with altered cholinergic and dopaminergic tone. Our aim was to determine whether acutely administered donepezil would alter mood in volunteers with no such alterations.

METHODS

This investigation was a double-blind, crossover design study of 15 young, healthy male participants who were allocated in random order to three oral treatments: placebo and 5-mg and 7.5-mg donepezil (doses which exert clinical and acute cognitive effects without considerable peripheral side effects). At the theoretical peak-plasma concentrations of donepezil, volunteers rated how they felt on validated questionnaires, which included various dimensions of subjective feelings. We also assessed changes in brain-derived neurotrophic factor (BDNF), which is increased by donepezil after chronic regimes and is related to modulation of mood.

RESULTS

Donepezil significantly increased ratings of vigour and anxiety symptoms (medium effect sizes). No changes in bodily symptoms or BDNF were observed.

CONCLUSIONS

Acute donepezil administration in participants with unaltered cholinergic and dopaminergic tone led to positive and negative changes in affect. These results call for further research on the direct mood effects of donepezil.

Propylisopropylacetic acid (PIA), a constitutional isomer of valproic acid, uncompetitively inhibits arachidonic acid acylation by rat acyl-CoA synthetase 4: a potential drug for bipolar disorder

BACKGROUND

Mood stabilizers used for treating bipolar disorder (BD) selectively downregulate arachidonic acid (AA) turnover (deacylation-reacylation) in brain phospholipids, when given chronically to rats. In vitro studies suggest that one of these, valproic acid (VPA), which is teratogenic, reduces AA turnover by inhibiting the brain long-chain acyl-CoA synthetase (Acsl)4 mediated acylation of AA to AA-CoA. We tested whether non-teratogenic VPA analogues might also inhibit Acsl4 catalyzed acylation, and thus have a potential anti-BD action.

METHODS

Rat Acsl4-flag protein was expressed in Escherichia coli, and the ability of three VPA analogues, propylisopropylacetic acid (PIA), propylisopropylacetamide (PID) and N-methyl-2,2,3,3-tetramethylcyclopropanecarboxamide (MTMCD), and of sodium butyrate, to inhibit conversion of AA to AA-CoA by Acsl4 was quantified using Michaelis-Menten kinetics.

RESULTS

Acsl4-mediated conversion of AA to AA-CoA in vitro was inhibited uncompetitively by PIA, with a Ki of 11.4mM compared to a published Ki of 25mM for VPA, while PID, MTMCD and sodium butyrate had no inhibitory effect.

CONCLUSIONS

PIA's ability to inhibit conversion of AA to AA-CoA by Acsl4 in vitro suggests that, like VPA, PIA may reduce AA turnover in brain phospholipids in unanesthetized rats, and if so, may be effective as a non-teratogenic mood stabilizer in BD patients.

Receptor targets for antidepressant therapy in bipolar disorder: an overview

The treatment of bipolar depression is one of the most challenging issues in contemporary psychiatry. Currently only quetiapine and the olanzapine-fluoxetine combination are officially approved by the FDA against this condition. The neurobiology of bipolar depression and the possible targets of bipolar antidepressant therapy remain relatively elusive. We performed a complete and systematic review to identify agents with definite positive or negative results concerning efficacy followed by a second systematic review to identify the pharmacodynamic properties of these agents. The comparison of properties suggests that the stronger predictors for antidepressant efficacy in bipolar depression were norepinephrine alpha-1, dopamine D1 and histamine antagonism, followed by 5-HT2A, muscarinic and dopamine D2 and D3 antagonism and eventually by norepinephrine reuptake inhibition and 5HT-1A agonism. Serotonin reuptake which constitutes the cornerstone in unipolar depression treatment does not seem to play a significant role for bipolar depression. Our exhaustive review is compatible with a complex model with multiple levels of interaction between the major neurotransmitter systems without a single target being either necessary or sufficient to elicit the antidepressant effect in bipolar depression.

Bipolar affective disorder, type II, apparently precipitated by donepezil

There is considerable evidence that pro-cholinergic agents can cause depressed mood. However, there are also published case reports of a rare association between cholinesterase inhibitors and mood elevation in patients with pre-existing major functional psychiatric disorders, or organic disorders other than dementia. This report adds to the literature by describing a case of mood elevation in a patient without pre-existing psychiatric disorder.

Muscarinic receptors: their roles in disorders of the central nervous system and potential as therapeutic targets

Phylogenetically, acetylcholine is an ancient neurochemical. Therefore, it is not surprising that cholinergic neurons project extensively throughout the central nervous system, innervating a wide range of structures within the brain. In fact, acetylcholine is involved in processes that underpin some of our most basic central functions. Both muscarinic and nicotinic receptor families, which mediate cholinergic transmission, have been implicated in the pathophysiology of psychiatric and neurological disorders. The question that remains to be definitively answered is whether or not these receptors are viable targets for the development of future therapeutic agents.

The role of the aminergic systems in the pathophysiology of bipolar disorder

Bipolar disorder (BPD) is a major medical and social burden, but little is known about the specific pathophysiology of BPD. The key biogenic amines in the aminergic system include serotonin (5-HT), norepinephrine (NE), dopamine (DA), and acetylcholine (ACh). By analyzing these neurotransmitters, this chapter highlights three hypotheses in the pathophysiology of BPD: the biogenic amine hypothesis, the cholinergic-aminergic balance hypothesis, and the permissive hypothesis. Evidence from select studies of cerebrospinal fluid, postmortem subjects, neuroimaging, genetic factors, and pharmacological agents will be used to reconcile these hypotheses. Possible explanations for discrepancies in these hypotheses are given, and directions for future studies are suggested.

Projection-specific neuromodulation of medial prefrontal cortex neurons

Mnemonic persistent activity in the prefrontal cortex (PFC) constitutes the neural basis of working memory. To understand how neuromodulators contribute to the generation of persistent activity, it is necessary to identify the intrinsic properties of the layer V pyramidal neurons that transfer this information to downstream networks. Here we show that the somatic dynamic and integrative properties of layer V pyramidal neurons in the rat medial PFC depend on whether they project subcortically to the pons [corticopontine (CPn)] or to the contralateral cortex [commissural (COM)]. CPn neurons display low temporal summation and accelerate in firing frequency when depolarized, whereas COM neurons have high temporal summation and display spike frequency accommodation. In response to dynamic stimuli, COM neurons act as low-pass filters, whereas CPn neurons act as bandpass filters, resonating in the theta frequency range (3-6 Hz). The disparate subthreshold properties of COM and CPn neurons can be accounted for by differences in the hyperpolarization-activated cyclic nucleotide gated cation h-current. Interestingly, neuromodulators hypothesized to enhance mnemonic persistent activity affect COM and CPn neurons distinctly. Adrenergic modulation shifts the dynamic properties of CPn but not COM neurons and increases the excitability of CPn neurons significantly more than COM neurons. In response to cholinergic modulation, CPn neurons were much more likely to display activity-dependent intrinsic persistent firing than COM neurons. Together, these data suggest that the two categories of projection neurons may subserve separate functions in PFC and may be engaged differently during working memory processes.

Depression and antidepressants: molecular and cellular aspects

Clinical depression is viewed as a physical and psychic disease process having a neuropathological basis, although a clear understanding of its ethiopathology is still missing. The observation that depressive symptoms are influenced by pharmacological manipulation of monoamines led to the hypothesis that depression results from reduced availability or functional deficiency of monoaminergic transmitters in some cerebral regions. However, there are limitations to current monoamine theories related to mood disorders. Recently, a growing body of experimental data has showed that other classes of endogenous compounds, such as neuropeptides and amino acids, may play a significant role in the pathophysiology of affective disorders. With the development of neuroscience, neuronal networks and intracellular pathways have been identified and characterized, describing the existence of the interaction between monoamines and receptors in turn able to modulate the expression of intracellular proteins and neurotrophic factors, suggesting that depression/antidepressants may be intermingled with neurogenesis/neurodegenerative processes.

Increased oxidative stress in the anterior cingulate cortex of subjects with bipolar disorder and schizophrenia

BACKGROUND

Recent studies indicate the presence of mitochondrial dysfunction in brains of subjects with bipolar disorder (BD). Because the mitochondrial electron transport chain is a major source for production of reactive oxygen species that cause oxidative stress, we sought to determine in the present study if BD is associated with oxidative stress.

METHODS

Postmortem anterior cingulate brain sections from subjects with BD, major depressive disorder (MDD), or schizophrenia, and from nonpsychiatric, non-neurologic comparison controls were generously provided by the Stanley Foundation Neuropathology Consortium. Oxidative stress was determined by analyzing 4-hydroxynonenal (4-HNE), a major product of lipid peroxidation. The level of 4-HNE was determined by measuring 4-HNE protein adducts using immunohistochemistry.

RESULTS

We found that 4-HNE levels were significantly increased by 59% in BD subjects and by 47% in schizophrenia subjects, but not in MDD subjects, when compared with controls. Levels of 4-HNE were negatively correlated with pH in all 60 subjects. When pH was used as covariate, 4-HNE levels were still significantly increased in BD subjects when compared with controls. Further, 4-HNE levels were significantly correlated with pH values only in BD subjects, but not in MDD, schizophrenia, or control subjects.

CONCLUSIONS

Oxidative damage in the brain may contribute in part to the pathological process in BD and schizophrenia. This finding also suggests antioxidative stress as a probable alternative approach to the pharmacological treatment of these psychiatric disorders.

Bipolar disorder and mechanisms of action of mood stabilizers

Bipolar disorder (BD) is a major medical and social burden, whose cause, pathophysiology and treatment are not agreed on. It is characterized by recurrent periods of mania and depression (Bipolar I) or of hypomania and depression (Bipolar II). Its inheritance is polygenic, with evidence of a neurotransmission imbalance and disease progression. Patients often take multiple agents concurrently, with incomplete therapeutic success, particularly with regard to depression. Suicide is common. Of the hypotheses regarding the action of mood stabilizers in BD, the "arachidonic acid (AA) cascade" hypothesis is presented in detail in this review. It is based on evidence that chronic administration of lithium, carbamazepine, sodium valproate, or lamotrigine to rats downregulated AA turnover in brain phospholipids, formation of prostaglandin E(2), and/or expression of AA cascade enzymes, including cytosolic phospholipase A(2), cyclooxygenase-2 and/or acyl-CoA synthetase. The changes were selective for AA, since brain docosahexaenoic or palmitic acid metabolism, when measured, was unaffected, and topiramate, ineffective in BD, did not modify the rat brain AA cascade. Downregulation of the cascade by the mood stabilizers corresponded to inhibition of AA neurotransmission via dopaminergic D(2)-like and glutamatergic NMDA receptors. Unlike the mood stabilizers, antidepressants that increase switching of bipolar depression to mania upregulated the rat brain AA cascade. These observations suggest that the brain AA cascade is a common target of mood stabilizers, and that bipolar symptoms, particularly mania, are associated with an upregulated cascade and excess AA signaling via D(2)-like and NMDA receptors. This review presents ways to test these suggestions.

A double-blind, placebo-controlled pilot study of galantamine to improve cognitive dysfunction in minimally symptomatic bipolar disorder

OBJECTIVE

There is increasing evidence that cognitive impairment is common in patients with bipolar disorder. The purpose of this study was to determine whether galantamine augmentation improved cognition in patients with euthymic bipolar disorder. In addition, the effect of galantamine on clinical measures of functioning and psychopathology was assessed.

METHOD

This study was a randomized double-blind, placebo-controlled, parallel design examining the impact of galantamine augmentation on cognition and other clinical measures in 30 patients during the course of 3 months. Sixteen subjects who completed baseline and follow-up second neuropsychological testing were evaluable (10 with galantamine and 6 with placebo).

RESULTS

The galantamine group showed improved performance on the California Verbal Learning Test total learning and the placebo group showed improved performance on the 2 Delis-Kaplan Executive Functioning System trail-making conditions and category fluency.

CONCLUSIONS

Episodic memory performance was improved in the galantamine treatment group but did not improve in the placebo group. In contrast, performance on 2 of the processing speed measures showed significant improvement in the placebo condition, whereas that of the patients treated with galantamine did not improve. Galantamine may thus have specific benefits for episodic memory, but not processing speed, in patients with cognitive impairment as part of bipolar disorder.

Chronic administration of valproic acid reduces brain NMDA signaling via arachidonic acid in unanesthetized rats

Evidence that brain glutamatergic activity is pathologically elevated in bipolar disorder suggests that mood stabilizers are therapeutic in the disease in part by downregulating glutamatergic activity. Such activity can involve the second messenger, arachidonic acid (AA, 20:4n - 6). We tested this hypothesis with regard to valproic acid (VPA), when stimulating glutamatergic N-methyl-D: -aspartate (NMDA) receptors in rat brain and measuring AA and related responses. An acute subconvulsant dose of NMDA (25 mg/kg i.p.) or saline was administered to unanesthetized rats that had been treated i.p. daily with VPA (200 mg/kg) or vehicle for 30 days. Quantitative autoradiography following intravenous [1-(14)C]AA infusion was used to image regional brain AA incorporation coefficients k*, markers of AA signaling. In chronic vehicle-pretreated rats, NMDA compared with saline significantly increased k* in 41 of 82 examined brain regions, many of which have high NMDA receptor densities, and also increased brain concentrations of the AA metabolites, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TXB(2)). VPA pretreatment reduced baseline concentrations of PGE(2) and TXB(2), and blocked the NMDA induced increases in k* and in eicosanoid concentrations. These results, taken with evidence that carbamazepine and lithium also block k* responses to NMDA in rat brain, suggest that mood stabilizers act in bipolar disorder in part by downregulating glutamatergic signaling involving AA.

Reciprocal effects of combined administration of serotonin, noradrenaline and dopamine reuptake inhibitors on serotonin and dopamine levels in the rat prefrontal cortex: the role of 5-HT1A receptors

The purpose of the present study was to examine, by in vivo microdialysis technique, the effects of triple acting monoamine reuptake inhibitors, constructed by combinations of a selective serotonin reuptake inhibitor citalopram with a noradrenaline/dopamine reuptake inhibitor methylphenidate and a serotonin/noradrenaline reuptake inhibitor venlafaxine with a dopamine reuptake inhibitor GBR12909, on extracellular levels of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in the prefrontal cortex (PFC) of anaesthetized rats. At the highest dose tested, adjunctive methylphenidate (10 mg/kg s.c.) to citalopram markedly attenuated by 63% the extracellular levels of 5-HT as compared to the levels induced by citalopram (5 mg/kg i.p.) alone, whereas the overall DA concentrations significantly increased to about 149% of those induced by methylphenidate alone. Similarly, the combination of venlafaxine with GBR12909 (10 mg/kg s.c.) caused a reduction of 5-HT levels to 66% of the levels induced by venlafaxine (10 mg/kg i.p.) alone, whereas the overall DA levels increased to 151% of the venlafaxine-treated group. The extracellular levels of NA were only marginally affected by the treatments with combined reuptake inhibitors compared to the effects induced by methylphenidate or venlafaxine alone. The modulatory effects of combined administration of the DA/NA reuptake inhibitors with the 5-HT reuptake inhibitors (citalopram and venlafaxine) on potentiation of DA and attenuation of 5-HT efflux were completely reversed by a pre-treatment with the 5-HT(1A) receptor antagonist WAY-100635. These findings suggest a crucial role played by the 5-HT(1A) receptors in balancing the reuptake inhibitory efficacy for the enhancement of 5-HT and DA transmission in the PFC by the drugs combining the reuptake inhibition of all three monoamines.

No evidence for association between 19 cholinergic genes and bipolar disorder

Cholinergic dysfunction has been proposed for the pathogenesis of bipolar disorder (BD), and we have therefore performed a systematic association study of cholinergic system genes in BD (including schizoaffective disorder bipolar type). We genotyped 93 single nucleotide polymorphisms (SNPs) in 19 genes (CHAT, CHRM1-5, CHRNA1-7, CHRNA9, CHRNA10, and CHRNB1-4) in two series of samples: the National Institute of Mental Health (NIMH) Genetics Initiative pedigrees with 474 samples from 152 families, and the Clinical Neurogenetics (CNG) pedigrees with 83 samples from 22 multiplex families. Sib-transmission/disequilibrium test (sib_TDT) analysis showed nominally significant transmission bias for four SNPs (CHRNA2: rs7017417, P = 0.024; CHRNA5: rs514743, P = 0.031; CHRNB1: rs2302762, P = 0.049; CHRNB4: rs1948, P = 0.031). Haploview analyses showed nominally significant transmission bias of several haplotypes in CHRNA2, CHRNA7, CHRNB1, and CHRNB4, respectively. However, none of these associations reached gene-wide significance after correction by permutation. Alcohol dependence (including alcohol abuse) was not a significant covariate in the present genetic association analysis. Thus, it is unlikely that these 19 cholinergic genes play a major role in the pre-disposition to BD in these pedigrees.

Brain neurotransmitter receptor-binding characteristics in rats after oral administration of haloperidol, risperidone and olanzapine

The present study was conducted to characterize the binding of neurotransmitter receptors (dopamine D(2), serotonin 5-HT(2), histamine H(1), adrenaline alpha(1) and muscarine M(l) receptors) in the rat's brain after the oral administration of haloperidol, risperidone, and olanzapine. Haloperidol at 1 and 3 mg/kg displayed significant activity to bind the D(2) receptor (increase in the Kd value for [(3)H]raclopride binding) in the corpus striatum with little change in the activity toward the 5-HT(2) receptor (binding parameters for [(3)H]ketanserin). In contrast, risperidone (0.1-3 mg/kg) showed roughly 30 times more affinity for the 5-HT(2) receptor than D(2) receptor. Also, olanzapine (1-10 mg/kg) was most active toward the H(1) receptor in the cerebral cortex, corpus striatum, and hippocampus, was less active in binding 5-HT(2) and D(2) receptors, and showed the least affinity for alpha(1) and M(1) receptors. In conclusion, haloperidol and risperidone administered orally selectively bind D(2) and 5-HT(2) receptors, respectively, in the rat brain, while olanzapine binds H(1), 5-HT(2), and D(2) receptors more than alpha(1) and M(1) receptors.

Beneficial metabolic effects of M3 muscarinic acetylcholine receptor deficiency

Most animal models of obesity and hyperinsulinemia are associated with increased vagal cholinergic activity. The M3 muscarinic acetylcholine receptor subtype is widely expressed in the brain and peripheral tissues and plays a key role in mediating the physiological effects of vagal activation. Here, we tested the hypothesis that the absence of M3 receptors in mice might protect against various forms of experimentally or genetically induced obesity and obesity-associated metabolic deficits. In all cases, the lack of M3 receptors greatly ameliorated impairments in glucose homeostasis and insulin sensitivity but had less robust effects on overall adiposity. Under all experimental conditions tested, M3 receptor-deficient mice showed a significant elevation in basal and total energy expenditure, most likely due to enhanced central sympathetic outflow and increased rate of fatty-acid oxidation. These findings suggest that the M3 receptor may represent a potential pharmacologic target for the treatment of obesity and associated metabolic disorders.

The cholinergic system in Down's syndrome

The cholinergic system is one of the most important modulatory neurotransmitter systems in the brain. Alterations of the transmission communicators are accompanied by reduction of the cortical activity, which is associated with a learning and memory deficit. Down's syndrome is a pathological condition characterized by a high number of abnormalities that involve the brain. The cholinergic system is involved in alterations of the neurological system such as severe learning difficulties. To explain these alterations, important results are obtained from studies about murine trisomy 16 (animal model of Down's syndrome). The results obtained provide useful elements in the improvement of knowledge about the neurological and neurotransmissional alterations that are responsible for the neurobiological characteristics of Down's syndrome. These data potentially justify, in these patients, the therapeutic use of drugs that are principally administered to improve the severe learning difficulties of people with Alzheimer's disease, and suggest a trend which generates a hypothesis worthy of further exploration.

Chronic lithium chloride administration attenuates brain NMDA receptor-initiated signaling via arachidonic acid in unanesthetized rats

It has been proposed that lithium is effective in bipolar disorder (BD) by inhibiting glutamatergic neurotransmission, particularly via N-methyl-D-aspartate receptors (NMDARs). To test this hypothesis and to see if the neurotransmission could involve the NMDAR-mediated activation of phospholipase A2 (PLA2), to release arachidonic acid (AA) from membrane phospholipid, we administered subconvulsant doses of NMDA to unanesthetized rats fed a chronic control or LiCl diet. We used quantitative autoradiography following the intravenous injection of radiolabeled AA to measure regional brain incorporation coefficients k* for AA, which reflect receptor-mediated activation of PLA2. In control diet rats, NMDA (25 and 50 mg/kg i.p.) compared with i.p. saline increased k* significantly in 49 and 67 regions, respectively, of the 83 brain regions examined. The regions affected were those with reported NMDARs, including the neocortex, hippocampus, caudate-putamen, thalamus, substantia nigra, and nucleus accumbens. The increases could be blocked by pretreatment with the specific noncompetitive NMDA antagonist MK-801 ((5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate) (0.3 mg/kg i.p.), as well by a 6-week LiCl diet sufficient to produce plasma and brain lithium concentrations known to be effective in BD. MK-801 alone reduced baseline values for k* in many brain regions. The results show that it is possible to image NMDA signaling via PLA2 activation and AA release in vivo, and that chronic lithium blocks this signaling, consistent with its suggested mechanism of action in BD.

Chronic lithium chloride administration to rats elevates glucose metabolism in wide areas of brain, while potentiating negative effects on metabolism of dopamine D2-like receptor stimulation

RATIONALE AND OBJECTIVES

The regional cerebral metabolic rate for glucose (rCMRglc) can be imaged in vivo as a marker of brain functional activity. The effects of chronic lithium administration on baseline values of rCMRglc and values in response to administration of dopamine D2-like receptor agonists have not been examined in humans or rats. Knowing these effects may elucidate and localize the therapeutic action of lithium in bipolar disorder.

METHODS

In unanesthetized rats, we used the 2-deoxy-D-glucose (2-DG) technique to image the effects of a 6-week control diet or LiCl diet sufficient to produce a plasma lithium concentration therapeutically relevant to bipolar disorder, on rCMRglc at baseline and in response to the dopaminergic D2-like receptor agonist, quinpirole (1 mg/kg i.v.), or to i.v. saline.

RESULTS

Baseline rCMRglc was significantly elevated in 30 of 81 brain regions examined, in LiCl diet compared with control diet rats. Affected were visual and auditory structures, frontal cortex, amygdala, hippocampus, nucleus accumbens, caudate-putamen, interpeduncular nucleus, and substantia nigra. Acute quinpirole significantly decreased rCMRglc in four areas of the caudate-putamen in control diet rats, and in these and 19 additional brain areas in LiCl-fed rats.

CONCLUSIONS

In unanesthetized rats, chronic lithium administration widely upregulates baseline rCMRglc and potentiates the negative effects on rCMRglc of D2-like receptor stimulation. The baseline elevation may relate to lithium's reported ability to increase auditory and visual evoked responses in humans, whereas lithium's potentiation of quinpirole's negative effects on rCMRglc may be related to its therapeutic efficacy in bipolar disorder.

Neurochemical effects of olanzapine in first-hospitalization manic adolescents: a proton magnetic resonance spectroscopy study

We used proton magnetic resonance spectroscopy (1H MRS) to compare the in vivo effects of olanzapine on prefrontal N-acetyl-aspartate (NAA) levels in treatment remitters and nonremitters. Secondary aims of this study were to identify neurochemical predictors of successful olanzapine treatment and other neurochemical effects of olanzapine. In all, 20 adolescents admitted for their first hospitalization for bipolar disorder, type I, manic or mixed and 10 demographically matched healthy subjects were recruited. Manic adolescents were treated with olanzapine monotherapy and scanned at three time points (N = 19). Medial and left and right lateral ventral prefrontal NAA, choline, creatine/phosphocreatine, myo-inositol, and glutamate/glutamine were measured at baseline, prior to receiving medication, and on days 7 and 28 of treatment. Healthy subjects did not receive medication but underwent 1H MRS scans at the same time points to assess for normal variability in metabolites over time. Although there was no overall increase in NAA in manic adolescents following 28 days of treatment with olanzapine, olanzapine remitters (N = 11, 58%) exhibited a greater increase in medial ventral prefrontal NAA compared with nonremitters (N = 8, 42%, p = 0.006). Specifically, from baseline to end point, NAA levels decreased in nonremitters (p = 0.03) and increased in remitters (p = 0.05). Manic adolescents treated with olanzapine had an increase from baseline to day 7 in medial (p = 0.002) and right lateral (p = 0.02) ventral prefrontal choline. Baseline medial ventral prefrontal choline was greater in olanzapine remitters than in nonremitters (p = 0.001). Successful treatment of mania with olanzapine may lead to increased ventral prefrontal neuronal viability and/or function as compared to unsuccessful treatment with olanzapine. Additionally, olanzapine-induced increases in choline may lead to alteration of abnormalities in cell membrane metabolism or second messenger pathways that are thought to be involved in the pathophysiology of bipolar disorder.

A double-blind, placebo-controlled trial of adjunctive donepezil in treatment-resistant mania

INTRODUCTION

Because there is a high rate of partial response to standard thymoleptic medication, novel augmentation strategies for treatment-resistant bipolar disorder are needed. In an open trial, donepezil augmentation was associated with improvement in manic symptoms in 9 of 11 subjects.

METHOD

We conducted a 6-week, double-blind, placebo-controlled trial of donepezil for treatment-resistant bipolar mania. Eligible subjects had a Young Mania Rating Scale (YMRS) score of at least 15 despite two or more weeks of proven therapeutic levels of lithium or valproate. Subjects who completed the trial were eligible for an 8-week open trial of donepezil. Subjects were started on donepezil 5 mg/day and were eligible for dose increase to 10 mg/day after 4 weeks.

RESULTS

Twelve subjects were enrolled. Eleven subjects received at least 1 week of study medication and were included in the analysis. No subjects in the donepezil group (0/6) and 60% (3/5) in the placebo group met response criteria of >30% reduction in YMRS score (Fisher's Exact p = 0.061). YMRS scores were higher at trial endpoint in the donepezil group 20.17 (3.66) compared with the placebo group [11.20 (4.60), Z = -2.476, p = 0.01]. There were no differences at trial endpoint in Hamilton Rating Scale for Depression (HAM-D) or Brief Psychiatric Rating Scale (BPRS) scores in either the intent-to-treat or the completer analyses.

CONCLUSIONS

Donepezil does not appear to be an effective adjunctive treatment for refractory manic symptoms. The strength of the conclusion of this trial is limited by the possibility of a false-negative result due to the small sample.

The role of the extrapersonal brain systems in religious activity

The neuropsychology of religious activity in normal and selected clinical populations is reviewed. Religious activity includes beliefs, experiences, and practice. Neuropsychological and functional imaging findings, many of which have derived from studies of experienced meditators, point to a ventral cortical axis for religious behavior, involving primarily the ventromedial temporal and frontal regions. Neuropharmacological studies generally point to dopaminergic activation as the leading neurochemical feature associated with religious activity. The ventral dopaminergic pathways involved in religious behavior most closely align with the action-extrapersonal system in the model of 3-D perceptual-motor interactions proposed by . These pathways are biased toward distant (especially upper) space and also mediate related extrapersonally dominated brain functions such as dreaming and hallucinations. Hyperreligiosity is a major feature of mania, obsessive-compulsive disorder, schizophrenia, temporal-lobe epilepsy and related disorders, in which the ventromedial dopaminergic systems are highly activated and exaggerated attentional or goal-directed behavior toward extrapersonal space occurs. The evolution of religion is linked to an expansion of dopaminergic systems in humans, brought about by changes in diet and other physiological influences.

Gi/Go protein-dependent presynaptic mechanisms are involved in clozapine-induced down-regulation of tyrosine hydroxylase in PC12 cells

Although the clinical effects of antipsychotics have been extensively studied, the molecular mechanisms underlying their antipsychotic activity are unclear. Chronic clozapine has been reported to reduce significantly the expression of tyrosine hydroxylase (TH) in the mesolimbic system. To characterize the mechanisms of action of clozapine on TH expression, PC12 cells turned out to be a useful model, being by far less complex than the entire brain. Both the quantity of TH protein and the amount of TH mRNA in PC12 cells were found to be decreased during incubation of the cells in the presence of clozapine. This decline was followed by a decrease in the enzymatic activity of TH. The effect of clozapine was blocked by preincubation with N-ethylmaleimide, a sulphydryl-alkylating reagent that interferes in Gi/o protein-mediated second messenger pathways. Clozapine may thus decrease TH expression by interacting with Gi/o protein-coupled receptors, such as D2 and 5HT1A. Knowledge of the molecular mechanisms underlying the clinical effects of established antipsychotics will promote the development of new and more efficient antipsychotic drugs.

Lithium differs from anticonvulsant mood stabilizers in prefrontal cortical and accumbal dopamine release: role of 5-HT(1A) receptor agonism

Anticonvulsant mood stabilizers, e.g., valproic acid and carbamazepine, and atypical antipsychotic drugs (APDs), e.g., clozapine, quetiapine, olanzapine, risperidone, and ziprasidone, have been reported to preferentially increase dopamine (DA) release in rat medial prefrontal cortex (mPFC), an effect partially or fully inhibited by WAY100635, a selective 5-HT(1A) antagonist. These atypical APDs have themselves been reported to be effective mood stabilizers, although the importance of increased cortical DA release to mood stabilization has not been established. The purpose of the present study was to determine whether zonisamide, another anticonvulsant mood stabilizer, as well as lithium, a mood stabilizer without anticonvulsant properties, also increases prefrontal cortical DA release and, if so, whether this release is also inhibited by 5-HT(1A) antagonism. As with valproic acid and carbamazepine, zonisamide (12.5 and 25 mg/kg) increased DA release in the mPFC, but not the NAC, an increase abolished by WAY100635 (0.2 mg/kg). However, lithium (100 and 250 mg/kg) decreased DA release in the NAC, an effect also attenuated by WAY100635 (0.2 mg/kg). Lithium itself had no effect in the mPFC but the combination of WAY100635 (0.2 mg/kg) and lithium (100 and 250 mg/kg) markedly increased DA release in the mPFC. Furthermore, M100907 (0.1 mg/kg), a selective 5-HT(2A) antagonist, abolished this increase in DA release in the mPFC. These results indicate that not all mood-stabilizing agents but only those, which have anticonvulsant mood-stabilizing properties, increase DA release in the cortex, and that the effect is dependent upon 5-HT(1A) receptor stimulation. However, the combination of lithium and 5-HT(1A) blockade may result in excessive 5-HT(2A) receptor stimulation, relative to 5-HT(1A) receptor stimulation, both of which can increase prefrontal cortical DA release.

Genetic tests of biologic systems in affective disorders

To liberate candidate gene analyses from criticisms of inexhaustiveness of examination of specific candidate genes, or incompleteness in the choice of candidate genes to study for specific neurobiological pathways, study of sizeable sets of genes pertinent to each putative pathophysiological pathway is required. For many years, genes have been tested in a 'one by one' manner for association with major affective disorders, primarily bipolar illness. However, it is conceivable that not individual genes but abnormalities in several genes within a system or in several neuronal, neural, or hormonal systems are implicated in the functional hypotheses for etiology of affective disorders. Compilation of candidate genes for entire pathways is a challenge, but can reasonably be carried out for the major affective disorders as discussed here. We present here five groupings of genes implicated by neuropharmacological and other evidence, which suggest 252 candidate genes worth examining. Inexhaustiveness of gene interrogation would apply to many studies in which only one polymorphism per gene is analyzed. In contrast to whole-genome association studies, a study of a limited number of candidate genes can readily exploit information on genomic sequence variations obtained from databases and/or resequencing, and has an advantage of not having the complication of an extremely stringent statistical criterion for association.

Chronic lithium chloride administration to unanesthetized rats attenuates brain dopamine D2-like receptor-initiated signaling via arachidonic acid

We studied the effect of lithium chloride on dopaminergic neurotransmission via D2-like receptors coupled to phospholipase A2 (PLA2). In unanesthetized rats injected i.v. with radiolabeled arachidonic acid (AA, 20:4 n-6), regional PLA2 activation was imaged by measuring regional incorporation coefficients k* of AA (brain radioactivity divided by integrated plasma radioactivity) using quantitative autoradiography, following administration of the D2-like receptor agonist, quinpirole. In rats fed a control diet, quinpirole at 1 mg/kg i.v. increased k* for AA significantly in 17 regions with high densities of D2-like receptors, of 61 regions examined. Increases in k* were found in the prefrontal cortex, frontal cortex, accumbens nucleus, caudate-putamen, substantia nigra, and ventral tegmental area. Quinpirole, 0.25 mg/kg i.v. enhanced k* significantly only in the caudate-putamen. In rats fed LiCl for 6 weeks to produce a therapeutically relevant brain lithium concentration, neither 0.25 mg/kg nor 1 mg/kg quinpirole increased k* significantly in any region. Orofacial movements following quinpirole were modified but not abolished by LiCl feeding. The results suggest that downregulation by lithium of D2-like receptor signaling involving PLA2 and AA may contribute to lithium's therapeutic efficacy in bipolar disorder.

Chronic lithium administration to rats selectively modifies 5-HT2A/2C receptor-mediated brain signaling via arachidonic acid

The effects of chronic lithium administration on regional brain incorporation coefficients k* of arachidonic acid (AA), a marker of phospholipase A2 (PLA2) activation, were determined in unanesthetized rats administered i.p. saline or 1 mg/kg i.p. (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), a 5-HT2A/2C receptor agonist. After injecting [1-(14)C]AA intravenously, k* (brain radioactivity/integrated plasma radioactivity) was measured in each of 94 brain regions by quantitative autoradiography. Studies were performed in rats fed a LiCl or a control diet for 6 weeks. In the control diet rats, DOI significantly increased k* in widespread brain areas containing 5-HT2A/2C receptors. In the LiCl-fed rats, the significant positive k* response to DOI did not differ from that in control diet rats in most brain regions, except in auditory and visual areas, where the response was absent. LiCl did not change the head turning response to DOI seen in control rats. In summary, LiCl feeding blocked PLA2-mediated signal involving AA in response to DOI in visual and auditory regions, but not generally elsewhere. These selective effects may be related to lithium's therapeutic efficacy in patients with bipolar disorder, particularly its ability to ameliorate hallucinations in that disease.

Serotonin receptors: their key role in drugs to treat schizophrenia

Serotonin (5-HT)-receptor-based mechanisms have been postulated to play a critical role in the action of the new generation of antipsychotic drugs (APDs) that are usually referred to as atypical APDs because of their ability to achieve an antipsychotic effect with lower rates of extrapyramidal side effects (EPS) compared to first-generation APDs such as haloperidol. Specifically, it has been proposed by Meltzer et al. [J. Pharmacol. Exp. Ther. 251 (1989) 238] that potent 5-HT2A receptor antagonism together with weak dopamine (DA) D2 receptor antagonism are the principal pharmacologic features that differentiate clozapine and other apparent atypical APDs from first-generation typical APD. This hypothesis is consistent with the atypical features of quetiapine, olanzapine, risperidone, and ziprasidone, which are the most common treatments for schizophrenia in the United States and many other countries, as well as a large number of compounds in various stages of development. Subsequent research showed that 5-HT1A agonism may be an important consequence of 5-HT2A antagonism and that substitution of 5-HT1A agonism for 5-HT2A antagonism may also produce an atypical APD drug when coupled with weak D2 antagonism. Aripiprazole, the most recently introduced atypical APD, and a D2 receptor partial agonist, may also owe some of its atypical properties to its net effect of weak D2 antagonism, 5-HT2A antagonism and 5-HT1A agonism [Eur. J. Pharmacol. 441 (2002) 137]. By contrast, the alternative "fast-off" hypothesis of Kapur and Seeman [Am. J. Psychiatry 158 (2001) 360] applies only to clozapine and quetiapine and is inconsistent with the "slow" off rate of most atypical APDs, including olanzapine, risperidone and ziprasidone. 5-HT2A and 5-HT1A receptors located on glutamatergic pyramidal neurons in the cortex and hippocampus, 5-HT2A receptors on the cell bodies of DA neurons in the ventral tegmentum and substantia nigra and GABAergic interneurons in the cortex and hippocampus, and 5-HT1A receptors in the raphe nuclei are likely to be important sites of action of the atypical APDs. At the same time, evidence has accumulated for the important modulatory role of 5-HT2C and 5-HT6 receptors for some of the effects of some of the current APDs. Thus, 5-HT has joined DA as a critical target for developing effective APDs and led to the search for novel drugs with complex pharmacology, ending the exclusive search for single-receptor targets, e.g., the D3 or D4 receptor, and drugs that are selective for them.