Signaling: cellular insights into the pathophysiology of bipolar disorder

Valproic acid inhibits substance P-induced activation of protein kinase C epsilon and expression of the substance P receptor

The neuropeptide substance P (SP) has been hypothesized to be involved in the etiopathology of affective disorders. This hypothesis is based on the findings that neurokinin-1-receptor antagonists have antidepressant effects in depressed patients and that SP may worsen mood. In this study, we investigated the effect of the mood-stabilizing agents valproic acid (VPA), carbamazepine, and lithium on SP-induced gene expression. As a model system, we used primary rat astrocytes and human astrocytoma cells, which both express functional SP-receptors and, upon stimulation with SP, synthesize interleukin-6 (IL-6), a cytokine which has been shown to be elevated during the acute depressive state. We found that VPA dose-dependently inhibited SP-induced IL-6 synthesis which was seen with pre-incubation periods of 30 min, 3, 7 and 14 days, whereas carbamazepine and lithium showed no inhibitory effect. The inhibitory effect of VPA was not mediated by inhibition of the stress-regulated kinases p38 and p42/44 (Erk1/2) but by inhibition of protein kinase C epsilon activation. Furthermore, VPA down-regulated the expression of the substance P receptor (neurokinin(NK)-1-receptor) as assessed by real-time PCR. Whether both mechanisms contribute to the mood-stabilizing properties of VPA has to be evaluated in further studies.

Beta-1-adrenergic receptor gene in major depression: influence on antidepressant treatment response

Noradrenergic dysfunction has been implicated in the development of affective disorders. beta-adrenergic receptors (betaARs) mediate the response to norephinephrine, are coupled to the cAMP signaling cascade, supposed to be altered in their density and/or sensitivity in depression, and down regulated in several brain regions after long term treatment with different but not all antidepressants. A recently identified functional polymorphism in the beta(1)-adrenergic receptor (G1165C) leading to the amino acid variation Gly389Arg was associated with an enhanced coupling to the stimulatory G(s)-protein and increased adenylyl cyclase activation, disturbances which are often observed in affective disorders. Therefore, we investigated whether this beta(1)AR polymorphism is associated with major depression or with the response to antidepressant treatment in a sample of 259 patients compared to 206 healthy controls. Although we could not detect an association between the beta(1)AR polymorphism and major depression we found a tendency for a relation between CC homozygosity and a better and even faster response to antidepressant treatment in those patients, which were treated with antidepressants affecting directly or indirectly the beta(1)AR system (tricyclic antidepressants, noradrenergic and serotonergic specific agents, selective noradrenaline reuptake inhibitors) determined by the HAMD and CGI score (P = 0.05). However, after correction for multiple testing (Bonferroni) these results did not remain significant. Nevertheless, these findings suggest that the presence of the C allele might be an indicator for antidepressant treatment response.

Enhancing neuronal plasticity and cellular resilience to develop novel, improved therapeutics for difficult-to-treat depression

There is growing evidence from neuroimaging and ostmortem studies that severe mood disorders, which have traditionally been conceptualized as neurochemical disorders, are associated with impairments of structural plasticity and cellular resilience. It is thus noteworthy that recent preclinical studies have shown that critical molecules in neurotrophic signaling cascades (most notably cyclic adenosine monophosphate [cAMP] response element binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen activated protein [MAP] kinases) are long-term targets for antidepressant agents and antidepressant potentiating modalities. This suggests that effective treatments provide both trophic and neurochemical support, which serves to enhance and maintainnormal synaptic connectivity, thereby allowing the chemical signal to reinstate the optimal functioning of critical circuits necessary for normal affective functioning. For many refractory patients, drugs mimicking "traditional" strategies, which directly or indirectly alter monoaminergic levels, may be of limited benefit. Newer "plasticity enhancing" strategies that may have utility in the treatment of refractory depression include N-methyl-D-aspartate antagonists, alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA) potentiators, cAMP phosphodiesterase inhibitors, and glucocorticoid receptor antagonists. Small-molecule agents that regulate the activity f growth factors, MAP kinases cascades, and the bcl-2 family of proteins are also promising future avenues. The development of novel, nonaminergic-based therapeutics holds much promise for improved treatment of severe, refractory mood disorders.

Lithium modulates expression of TRH receptors and TRH-related peptides in rat brain

Lithium is an established mood stabilizer and neuroprotective agent frequently used in the treatment of bipolar disorder and as an adjuvant in drug-resistant unipolar depression. The mechanisms underlying both the therapeutic efficacy of lithium and the exacerbation of symptoms following rapid withdrawal are not understood. From previous studies showing antidepressant and neuroprotective activities of thyrotropin releasing hormone (TRH) and TRH-related neuropeptides we hypothesized that lithium may have substantial effects on the expression and secretion of these peptides and/or their receptors in various rat brain regions involved in the regulation of mood. Chronic lithium effect on TRH receptor binding studies: The effect of 1 and 2 weeks of dietary lithium on [(3)H]3-Me-His-TRH binding to plasma membranes of nucleus accumbens, amygdala and pituitary of young adult male Wistar and the endogenously 'depressed' Wistar Kyoto (WKY) rats was measured by the method of Burt and Taylor [Burt, D.R., Taylor, R.L., Endocrinology 106 (1980) 1416-1423]. Acute, chronic and withdrawal effect of lithium on TRH and TRH-like peptide levels in young, adult male Sprague-Dawley rats: Rats were divided into four lithium treatment groups. Control animals received a standard laboratory rodent chow. The acute group received a single i.p. injection of 1.5 milli-equivalents of LiCl 2 h prior to killing. The chronic and withdrawal groups received standard rodent chow containing 1.7 g/kg LiCl for 2 weeks. Withdrawal rats were returned to standard chow 48 h prior to killing while the chronic animals continued on the LiCl diet. TRH, TRH-Gly (pGlu-His-Pro-Gly, a TRH precursor), EEP (pGlu-Glu-Pro-NH(2), a TRH-like peptide with antidepressant activity) and Ps4 (a prepro-TRH-derived TRH-enhancing decapeptide) immunoreactivity (IR) were measured in 13 brain regions. The remaining samples were pooled and fractionated by high-pressure liquid chromatography followed by EEP radioimmunoassay. Chronic lithium treatment increased [(3)H]3Me-TRH binding in the nucleus accumbens and amygdala about two-fold in both Wistar and WKY rats but no change was observed in pituitary binding. The most widespread changes in TRH and TRH-related peptide levels were observed in the withdrawal group compared to the controls. The direction of change for the total IR was consistent for all TRH-IR and TRH-related peptide-IR within a given tissue. For example, withdrawal increased all peptide levels in the pyriform cortex and striatum but decreased these levels in the anterior cingulate and lateral cerebellum. Both acute injection and chronic treatment with LiCl decreased TRH and TRH-related peptide levels in the entorhinal cortex. Acute injection and withdrawal both increased EEP-IR in striatum by more than two-fold. The acute effects are most likely due to changes in the release of these peptides since 2 h is not sufficient time for alterations in peptide biosynthesis. Chronic treatment increased levels of pGlu-Phe-Pro-NH(2) levels in hippocampus, pGlu-Leu-Pro-NH(2), and peak '2' in septum by more than four-fold. The present results are consistent with a component role for TRH and related peptides in the mood-altering effects of lithium administration and withdrawal frequently observed during treatment for depression and bipolar disorder.

Molecular basis of lithium action: integration of lithium-responsive signaling and gene expression networks

The clinical efficacy of lithium in the prophylaxis of recurrent affective episodes in bipolar disorder is characterized by a lag in onset and remains for weeks to months after discontinuation. Thus, the long-term therapeutic effect of lithium likely requires reprogramming of gene expression. Protein kinase C and glycogen synthase kinase-3 signal transduction pathways are perturbed by chronic lithium at therapeutically relevant concentrations and have been implicated in modulating synaptic function in nerve terminals. These signaling pathways offer an opportunity to model critical signals for altering gene expression programs that underlie adaptive responses of neurons to long-term lithium exposure. While the precise physiological events critical for the clinical efficacy of lithium remain unknown, we propose that linking lithium-responsive genes as a regulatory network will provide a strategy to identify signature gene expression patterns that distinguish between therapeutic and nontherapeutic actions of lithium.

Recent developments in the psychobiology and pharmacotherapy of depression: optimising existing treatments and novel approaches for the future

Effective antidepressants include monoamine oxidase inhibitors and tricyclic antidepressants, selective serotonin re-uptake inhibitors and novel agents, including serotonin and noradrenaline re-uptake inhibitors. Although effective, current treatments most often produce partial symptomatic improvement (response) rather than symptom resolution and optimal functioning (remission). While current pharmacotherapies target monoaminergic systems, different symptoms of major depressive disorder (MDD) may have distinct neurobiological underpinnings and other neurobiological systems are likely involved in the pathogenesis of MDD. In this article a review of current pharmacotherapeutic options for MDD, current understanding of the neurobiology and pathogenesis of MDD and a review of new and promising directions in pharmacological research will be provided. It is generally accepted that no single neurotransmitter or system is responsible for the dysregulation found in MDD. While agents that affect monoaminergic systems will likely continue to be first-line treatments for MDD for the foreseeable future, a number of new and novel agents, including corticotropin-releasing factor antagonists, substance P antagonists and antiglucocorticoids show considerable promise for refining treatment options. In order to better understand the neurobiology and treatment response of MDD, it is probable that more sophisticated theory-driven typologies of MDD will have to be developed.

Defining the caudal ventral striatum in primates: cellular and histochemical features

Afferents from the amygdala help to define the ventral striatum and mediate goal-directed behaviors. In addition to well known inputs to the classic ventral striatum, the amygdala also projects to the caudoventral striatum and amygdalostriatal area. We examined whether the primate caudoventral striatum and amygdalostriatal area can be considered part of the "ventral" striatum based on cellular and histochemical features found in the classic rostral ventral striatum. We used several histochemical stains, including calbindin-D28k, a marker of the shell compartment, acetylcholinesterase, substance P, tyrosine hydroxylase, and Bcl-2, a marker of immature neurons, to examine this question. Our results indicate that the lateral amygdalostriatal area and caudoventral striatum are "striatal like" based on intermediate to high acetylcholinesterase and tyrosine hydroxylase levels. The lateral amygdalostriatal area is chemically similar to the shell, whereas the caudoventral striatum more closely resembles the striatum outside the shell. In contrast, the medial amygdalostriatal area is more related to the central amygdaloid nucleus than to the striatum. Bcl-2 immunoreactivity is associated with granular islands and medium-sized cells in the vicinity of the ventral striatum both rostrally and caudally. Together, the caudal ventral striatum has a histochemical and cellular organization similar to that of the rostral ventral striatum, consistent with their common innervation by the amygdala and other ventral structures. In addition, Bcl-2 is expressed in and near both poles of the ventral striatum, suggesting that these areas maintain a heightened capacity for growth and plasticity compared with other striatal sectors.

Mood stabilizer psychopharmacology

Mood stabilizers represent a class of drugs that are efficacious in the treatment of bipolar disorder. The most established medications in this class are lithium, valproic acid, and carbamazepine. In addition to their therapeutic effects for treatment of acute manic episodes, these medications often are useful as prophylaxis against future episodes and as adjunctive antidepressant medications. While important extracellular effects have not been excluded, most available evidence suggests that the therapeutically relevant targets of this class of medications are in the interior of cells. Herein we give a prospective of a rapidly evolving field, discussing common effects of mood stabilizers as well as effects that are unique to individual medications. Mood stabilizers have been shown to modulate the activity of enzymes, ion channels, arachidonic acid turnover, G protein coupled receptors and intracellular pathways involved in synaptic plasticity and neuroprotection. Understanding the therapeutic targets of mood stabilizers will undoubtedly lead to a better understanding of the pathophysiology of bipolar disorder and to the development of improved therapeutics for the treatment of this disease. Furthermore, the involvement of mood stabilizers in pathways operative in neuroprotection suggests that they may have utility in the treatment of classical neurodegenerative disorders.

Factors contributing to neurotrophin-independent survival of adult sensory neurons

Dorsal root ganglion (DRG) sensory neurons become less dependent upon neurotrophins for their survival as they mature. DRG neurons from young adult rats were dissociated and cultured in vitro in serum-free defined medium. We show that adult DRG sensory neurons are able to survive for at least 2 weeks in culture in the absence of nerve growth factor (NGF). We then investigated potential mechanisms contributing to this apparent neurotrophin-independent survival in these neurons through the use of inhibitors of cellular signaling pathways. The phosphoinositide kinase-3 (PI 3-K) inhibitor LY294002, and a protein kinase C (PKC) inhibitor, chelerythrine resulted in significant decreases in neuronal survival. Neither the mitogen activated protein kinase kinase (MEK) inhibitor U0126 nor two other PKC inhibitors (bisindolylmaleimide and rottlerin) had any significant effect on survival. Our results point to the importance of PI 3-K and PKC signaling in the neurotrophin-independent survival of adult DRG neurons.

The Wnt signaling pathway in bipolar disorder

The Wnt signaling pathway is a highly conserved pathway critical for proper embryonic development. However, recent evidence suggests that this pathway and one of its key enzymes, glycogen synthase kinase 3beta, may play important roles in regulating synaptic plasticity, cell survival, and circadian rhythms in the mature CNS-all of which have been implicated in the pathophysiology and treatment of bipolar disorder. Furthermore, two structurally highly dissimilar medications used to treat bipolar disorder, lithium and valproic acid, exert effects on components of the Wnt signaling pathway. Together, these data suggest that the Wnt signaling pathway may play an important role in the treatment of bipolar disorder. Here, the authors review the modulation of the Wnt/GSK-3beta signaling pathway by mood-stabilizing agents, focusing on two therapeutically relevant aspects: neuroprotection and modulation of circadian rhythms. The future development of selective GSK-3beta inhibitors may have considerable utility not only for the treatment of bipolar disorder but also for a variety of classical neurodegenerative disorders.

The interface between depression and cerebrovascular disease--some hope but no hype

Medical complications after stroke are an important problem not only for patients, but also for their families and the clinicians who take care of them, thus representing a major public health problem. Among medical illnessess complicating stroke, in the last several years much efforts has been directed to determine the role of affective disorders. Although depression coexisting with stroke has been shown to increase levels of functional disability and reduce the effectiveness of rehabilitation, we still have much to learn about the clinical interface between such disorders. This review focuses on the data concerning the potential relationship between depression and cerebrovascular disease (CVD) and the emerging insights which may be relevant to provide directions for the development of novel research strategies on the pathogenesis and treatment of post-stroke depression.

Lithium in bipolar disorder: can drug concentrations predict therapeutic effect?

The evidence is reviewed for effective serum lithium concentrations for the acute and prophylactic treatment of mania and depression in patients with bipolar disorder. The efficacy of lithium in the treatment of acute manic episodes has been recognised for several decades, primarily using concentrations in the range of 0.8 to 2 mmol/L. The number of patients responding increases as the serum lithium concentration increases, although individual patients may respond at lower concentrations (<0.8 mmol/L). Lithium doses and serum concentrations similar to those used to treat acute mania have been studied in bipolar depression, with no evaluation of a relationship between concentration and clinical response. Several prospective controlled trials have evaluated this relationship in the prophylactic treatment of bipolar disorder. Maintaining higher serum lithium concentrations (0.8 to 1 mmol/L) improves the likelihood of good effect in prophylactic treatment, although individual patients may do well on lower concentrations. Despite the paucity of evidence to specifically support the efficacy of lithium at lower serum lithium concentrations in the elderly, lower target ranges (0.5 to 0.8 mmol/L) are commonly recommended due to an increased sensitivity to adverse effects, particularly neurotoxicity. The serum lithium concentrations recommended in adults have been applied to children; however, this has not been studied. Overall, the evidence suggests a relationship between serum lithium concentration and therapeutic effect, although the exact nature of this relationship is not clear. For example, it is not known why some people respond to lower concentrations and others do not. There are many factors that influence studies trying to elucidate this relationship. Many of these factors are related to the interpretation of the serum lithium concentration. In summary, patients have an increased chance of responding to lithium if 12-hour serum lithium concentrations at steady state are above 0.8 mmol/L. Many patients will respond to lower concentrations (0.4 to 0.7 mmol/L), but we are unable to identify these patients a priori. The relationship between serum lithium concentrations and adverse effects is also very important in determining appropriate target lithium concentrations. The current best advice is to individualise the target serum lithium concentrations based on efficacy and tolerability and to optimise the interpretation of these concentrations by ensuring within-patient consistency with respect to dosage schedule, lithium preparation and the timing of blood sampling.

PKC, MAP kinases and the bcl-2 family of proteins as long-term targets for mood stabilizers

The complexity of the unique biology of bipolar disorder--which includes the predisposition to episodic, and often progressive, mood disturbance--and the dynamic nature of compensatory processes in the brain, coupled with limitations in experimental design, have hindered our ability to identify the underlying pathophysiology of this fascinating neuropsychiatric disorder. Although we have yet to identify the specific abnormal genes in mood disorders, recent studies have implicated critical signal transduction pathways as being integral to the pathophysiology and treatment of bipolar disorder. In particular, a converging body of preclinical data has shown that chronic lithium and valproate, at therapeutically relevant concentrations, regulate the protein kinase C signaling cascade. This has led to the investigation of the antimanic efficacy of tamoxifen (at doses sufficient to inhibit protein kinase C), with very encouraging preliminary results. A growing body of data also suggests that impairments of neuroplasticity and cellular resilience may also underlie the pathophysiology of bipolar disorder. It is thus noteworthy that mood stabilizers, such as lithium and valproate, indirectly regulate a number of factors involved in cell survival pathways--including cAMP response element binding protein, brain derived neurotrophic factor, bcl-2 and mitogen-activated protein kinases--and may thus bring about some of their delayed long-term beneficial effects via under-appreciated neurotrophic effects. The development of novel treatments, which more directly target molecules involved in critical central nervous system cell survival and cell death pathways, has the potential to enhance neuroplasticity and cellular resilience, thereby modulating the long-term course and trajectory of these devastating illnesses.

Valproate regulates GSK-3-mediated axonal remodeling and synapsin I clustering in developing neurons

Valproate (VPA) and lithium have been used for many years in the treatment of manic depression. However, their mechanisms of action remain poorly understood. Recent studies suggest that lithium and VPA inhibit GSK-3beta, a serine/threonine kinase involved in the insulin and WNT signaling pathways. Inhibition of GSK-3beta by high concentrations of lithium has been shown to mimic WNT-7a signaling by inducing axonal remodeling and clustering of synapsin I in developing neurons. Here we have compared the effect of therapeutic concentrations of lithium and VPA during neuronal maturation. VPA and, to a lesser extent, lithium induce clustering of synapsin I. In addition, lithium and VPA induce similar changes in the morphology of axons by increasing growth cone size, spreading, and branching. More importantly, both mood stabilizers decrease the level of MAP-1B-P, a GSK-3beta-phosphorylated form of MAP-1B in developing neurons, suggesting that therapeutic concentrations of these mood stabilizers inhibit GSK-3beta. In vitro kinase assays show that therapeutic concentrations of VPA do not inhibit GSK-3beta but that therapeutic concentrations of lithium partially inhibit GSK-3beta activity. Our results support the idea that both mood stabilizers inhibit GSK-3beta in developing neurons through different pathways. Lithium directly inhibits GSK-3beta in contrast to VPA, which inhibits GSK-3beta indirectly by an as-yet-unknown pathway. These findings may have important implications for the development of new strategies to treat bipolar disorders.

Identification and cloning of human astrocyte genes displaying elevated expression after infection with HIV-1 or exposure to HIV-1 envelope glycoprotein by rapid subtraction hybridization, RaSH

Neurodegeneration and dementia are common complications of AIDS caused by human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system. HIV-1 target cells in the brain include microglia, infiltrating macrophages and astrocytes, but rarely neurons. Astrocytes play an important role in the maintenance of the synaptic micro-environment and in neuronal signal transmission. To investigate potential changes in cellular gene expression associated with HIV-1 infection of astrocytes, we employed an efficient and sensitive rapid subtraction hybridization approach, RaSH. Primary human astrocytes were isolated from abortus brain tissue and low-passage cells were infected with HIV-1. To identify genes that display both early and late expression modifications after HIV-1 infection and to avoid cloning genes displaying normal cell cycle fluctuations in astrocytes, RNAs were isolated and pooled from 6, 12, 24 h and 3 and 7 day uninfected and infected cells and used for RaSH. Temporal cDNA libraries were prepared from double-stranded cDNAs that were enzymatically digested into small fragments, ligated to adapters, PCR amplified, and hybridized by incubation of tester and driver PCR fragments. By subtracting temporal cDNAs derived from uninfected astrocytes from temporal cDNAs made from HIV-1 infected cells, genes displaying elevated expression in virus infected cells, termed astrocyte elevated genes (AEGs), were identified. Both known and novel AEGs, not reported in current DNA databases, are described that display early or late expression kinetics following HIV-1 infection or treatment with recombinant HIV-1 envelope glycoprotein (gp120). For selected AEGs, expression of their protein products was also tested by Western blotting and found to display elevated expression following HIV-1 infection. The comparable pattern of regulation of the AEGs following HIV-1 infection or gp120 treatment suggest that HIV-1 exposure of astrocytes, even in the absence of productive infection, can induce changes in cellular gene expression.

Endophenotypes in bipolar disorder

The search for genes in bipolar disorder has provided numerous genetic loci that have been linked to susceptibility to developing the disorder. However, because of the genetic heterogeneity inherent in bipolar disorder, additional strategies may need to be employed to fully dissect the genetic underpinnings. One such strategy involves reducing complex behaviors into their component parts (endophenotypes). Abnormal neurophysiological, biochemical, endocrinological, neuroanatomical, cognitive, and neuropsychological findings are characteristics that often accompany psychiatric illness. It is possible that some of these may eventually be useful in subdefining complex genetic disorders, allowing for improvements in diagnostic assessment, genetic linkage studies, and development of animal models. Findings in patients with bipolar disorder that may eventually be useful as endophenotypes include abnormal regulation of circadian rhythms (the sleep/wake cycle, hormonal rhythms, etc.), response to sleep deprivation, P300 event-related potentials, behavioral responses to psychostimulants and other medications, response to cholinergics, increase in white matter hyperintensities (WHIs), and biochemical observations in peripheral mononuclear cells. Targeting circadian rhythm abnormalities may be a particularly useful strategy because circadian cycles appear to be an inherent evolutionarily conserved function in all organisms and have been implicated in the pathophysiology of bipolar disorder. Furthermore, lithium has been shown to regulate circadian cycles in diverse species, including humans, possibly through inhibition of glycogen synthase kinase 3-beta (GSK-3beta), a known target of lithium.

The "good enough" mood stabilizer: a review of the clinical evidence

A growing family of medications is used for mood stabilization in bipolar disorder. These medications fall into two broad categories according to likely mechanisms of action. Within the categories, specific drugs may vary in their efficacy for different phases of the disorder. The first category, including lithium, anticonvulsants, and some novel treatments, appears to have mechanisms related to intracellular second messengers. These medications have more pronounced antimanic than antidepressant effects, except for lamotrigine, which has antidepressant effects without precipitating mania. The second group of mood stabilizers is the atypical antipsychotics, which act through dopamine and other monoamines. Olanzapine and in all likelihood other drugs in the class possess marked, acute antimanic properties and possible antidepressant properties, but require further study before they can be used as routine options in long-term care. It is clear that the advent of multiple mood stabilizer candidates has not yet led to a single ideal therapy for bipolar disorder, but rather to options that can be flexibly tailored to the lifetime needs of individual patients, in sequences or combinations, and perhaps in conjunction with other classes of psychotropics.

Bipolar disorder

Bipolar, or manic-depressive, disorder is a frequent, severe, mostly recurrent mood disorder associated with great morbidity. The lifetime prevalence of bipolar disorder is 1.3 to 1.6%. The mortality rate of the disease is two to three times higher than that of the general population. About 10-20% of individuals with bipolar disorder take their own life, and nearly one third of patients admit to at least one suicide attempt. The clinical manifestations of the disease are exceptionally diverse. They range from mild hypomania or mild depression to severe forms of mania or depression accompanied by profound psychosis. Bipolar disorder is equally prevalent across sexes, with the exception of rapid cycling, a severe and difficult to treat variant of the disorder, which arises mostly in women. Because of the high risk of recurrence and suicide, long-term prophylactic pharmacological treatment is indicated. Lithium salts are the first choice long-term preventive treatment for bipolar disorder. They also possess well documented antisuicidal effects. Second choice prophylactic treatments are carbamazepine and valproate, although evidence of their effectiveness is weaker.

Gene expression differences in bipolar disorder revealed by cDNA array analysis of post-mortem frontal cortex

Previous studies have implicated a number of biochemical pathways in the etiology of bipolar disorder (BD). However, the precise abnormalities underlying this disorder remain to be established. To investigate novel factors that may be important in the pathophysiology of BD, we utilized cDNA expression arrays to examine differences in expression of up to 1200 genes known to be involved in potentially relevant biochemical processes. This investigation was undertaken in post-mortem samples of frontal cortex tissue from patients with BD and matched controls, obtained (n = 10/group) from the Stanley Foundation Neuropathology Consortium. Results include significant (greater than 35% change in signal intensity) differences between BD and controls in a number of genes (n = 24). Selected targets were analyzed by RT-PCR, which confirmed a decrease in transforming growth factor-beta1 (TGF-beta 1), and an increase in both caspase-8 precursor (casp-8) and transducer of erbB2 (Tob) expression in BD. We further observed a significant decrease of TGF-beta 1 mRNA levels in BD by RT-PCR in individual post-mortem samples. Given the neuroprotective role attributed to this inhibitory cytokine, our results suggest that the down-regulation of TGF-beta 1 may lead to various neurotoxic insults potentially involved in the etiology of certain mood disorders.

Proposed endophenotypes of dysthymia: evolutionary, clinical and pharmacogenomic considerations

Dysthymia is highly prevalent--though underdiagnosed--occurring in at least 3% of the population. We conceptualize it as the clinical extension of adaptive traits that have developed during evolution to cope with stress and failure. A classification of dysthymias into anxious and anergic subtypes--and their putative association to bipolarity--is proposed. We further posit neurochemical and neurophysiological substrates for the two subtypes. A better recognition and understanding of dysthymic subtypes and their respective place in the affective spectrum will increase the proportion of people that may benefit from targeted treatments. It would also expand the pool of subjects that may be enrolled in genetic and pharmacogenomic research studies.

The cAMP-dependent protein kinase substrate Rap1 in platelets from patients with obsessive compulsive disorder or schizophrenia

Previous studies have reported that the cAMP-dependent protein kinase and one of its substrates, namely Rap1, are altered in patients with affective disorders. Abnormalities in the cAMP-dependent protein kinase have also been reported in platelets of patients with obsessive compulsive disorder and schizophrenia. However, it remains to be determined whether abnormalities in Rap1 are specifically related to affective disorders or may also be present in schizophrenia and obsessive compulsive disorder. Thus, we investigated Rap1 in platelets from 12 drug-free patients with obsessive compulsive disorder, ten drug-free patients with schizophrenia, and 20 healthy subjects. While no difference was observed in the levels of Rap1 between groups, the phosphorylation state of Rap1 was significantly lower in patients with obsessive compulsive disorder than in schizophrenic patients and controls. These data further support the idea that abnormalities of cAMP signalling pathway could be associated, albeit in a somewhat different way, with several psychiatric disorders.

The cellular neurobiology of depression

Major depressive disorders, long considered to be of neurochemical origin, have recently been associated with impairments in signaling pathways that regulate neuroplasticity and cell survival. Agents designed to directly target molecules in these pathways may hold promise as new therapeutics for depression.

Implications of the cAMP signaling pathway in psychiatric disorders: a systematic review of the evidence

The last decade has seen a shift in the theoretical framework addressing the pathophysiology of psychiatric disorders. During this period, research endeavors have been directed toward investigating the biochemical mechanisms involved in the transduction of information from the cell surface to the cell interior. The emerging picture, supported by growing evidence, is that in addition to neurotransmitters and their receptors, various signal transduction pathways may be linked to the pathophysiology of major psychiatric disorders. In this review, the role of one such pathway--the cyclic adenosine monophosphate (cAMP) signaling pathway--will be highlighted. We review data suggesting the involvement of the upstream and downstream components of this system in the pathophysiology of psychiatric disorders.

Post-receptor signaling pathways in the pathophysiology and treatment of mood disorders

The molecular medicine revolution has resulted in a more complete understanding about the etiology and pathophysiology of a variety of illnesses. This remarkable progress reflects in large part the elucidation of the basic mechanisms of signal transduction, and the application of the powerful tools of molecular biology to the study of human disease. Although we have yet to identify the specific abnormal genes in mood disorders, recent studies have implicated signal transduction pathways, in particular the stimulatory guanine nucleotide binding protein (Gs)/cyclic AMP and protein kinase C pathways, in the pathophysiology and treatment of mood disorders. Recent studies have also shown that mood stabilizers exert neurotrophic and neuroprotective effects not only in preclinical paradigms, but also in humans. Together, these studies suggest that mood disorders may be associated with impaired neuroplasticity and cellular resiliency, findings that may have major implications for our understanding of mood disorders, and for the development of improved therapeutics.

Neuroplasticity and cellular resilience in mood disorders

Although mood disorders have traditionally been regarded as good prognosis diseases, a growing body of data suggests that the long-term outcome for many patients is often much less favorable than previously thought. Recent morphometric studies have been investigating potential structural brain changes in mood disorders, and there is now evidence from a variety of sources demonstrating significant reductions in regional CNS volume, as well as regional reductions in the numbers and/or sizes of glia and neurons. Furthermore, results from recent clinical and preclinical studies investigating the molecular and cellular targets of mood stabilizers and antidepressants suggest that a reconceptualization about the pathophysiology and optimal long-term treatment of recurrent mood disorders may be warranted. It is proposed that impairments of neuroplasticity and cellular resilience may underlie the pathophysiology of mood disorders, and further that optimal long-term treatment for these severe illnesses may only be achieved by the early and aggressive use of agents with neurotrophic/neuroprotective effects. It is noteworthy that lithium, valproate and antidepressants indirectly regulate a number of factors involved in cell survival pathways including CREB, BDNF, bcl-2 and MAP kinases, and may thus bring about some of their delayed long-term beneficial effects via underappreciated neurotrophic effects. The development of novel treatments which more directly target molecules involved in critical CNS cell survival and cell death pathways have the potential to enhance neuroplasticity and cellular resilience, and thereby modulate the long-term course and trajectory of these devastating illnesses.