The fibroblast growth factor system and mood disorders

Schizophrenia: a neurodevelopmental disorder--integrative genomic hypothesis and therapeutic implications from a transgenic mouse model

Schizophrenia is a neurodevelopmental disorder featuring complex aberrations in the structure, wiring, and chemistry of multiple neuronal systems. The abnormal developmental trajectory of the brain appears to be established during gestation, long before clinical symptoms of the disease appear in early adult life. Many genes are associated with schizophrenia, however, altered expression of no one gene has been shown to be present in a majority of schizophrenia patients. How does altered expression of such a variety of genes lead to the complex set of abnormalities observed in the schizophrenic brain? We hypothesize that the protein products of these genes converge on common neurodevelopmental pathways that affect the development of multiple neural circuits and neurotransmitter systems. One such neurodevelopmental pathway is Integrative Nuclear FGFR1 Signaling (INFS). INFS integrates diverse neurogenic signals that direct the postmitotic development of embryonic stem cells, neural progenitors and immature neurons, by direct gene reprogramming. Additionally, FGFR1 and its partner proteins link multiple upstream pathways in which schizophrenia-linked genes are known to function and interact directly with those genes. A th-fgfr1(tk-) transgenic mouse with impaired FGF receptor signaling establishes a number of important characteristics that mimic human schizophrenia - a neurodevelopmental origin, anatomical abnormalities at birth, a delayed onset of behavioral symptoms, deficits across multiple domains of the disorder and symptom improvement with typical and atypical antipsychotics, 5-HT antagonists, and nicotinic receptor agonists. Our research suggests that altered FGF receptor signaling plays a central role in the developmental abnormalities underlying schizophrenia and that nicotinic agonists are an effective class of compounds for the treatment of schizophrenia.

Fibroblast growth factors in neurodevelopment and psychopathology

In psychiatric disorders, the effect of genetic and environmental factors may converge on molecular pathways and brain circuits related to growth factor functioning. In this review, we describe how disturbances in fibroblast growth factors (FGFs) and their receptors influence behavior by affecting brain development. Recently, several studies reported associations of members of the FGF family with psychiatric disorders. FGFs are key candidates to modulate the impact of environmental factors, such as stress. Mutant mice for FGF receptor 1 show schizophrenia-like behaviors that are related to general loss of neurons and postnatal glia dysfunction. Mice lacking FGF2, a FGFR1 ligand, show similar reductions in brain volume and hyperactivity, as well as increased anxiety behaviors. FGFR2 and FGF17 are involved in the development of frontal brain regions and impairments in cognitive and social behaviors, respectively. Moreover, treatment with FGF2 was beneficial for depressive and cognitive measures in several animal studies and one human study. These findings indicate the importance of the FGF system with respect to developing novel etiology-directed treatments for psychopathology.

Somatic drugs for psychiatric diseases: aspirin or simvastatin for depression?

The evolution in the understanding of the neurobiology of most prevalent mental disorders such as major depressive disorder (MDD), bipolar disorder or schizophrenia has not gone hand in hand with the synthesis and clinical use of new drugs that would represent a therapeutic revolution such as that brought about by selective serotonin reuptake inhibitors (SSRIs) or atypical antipsychotics. Although scientists are still a long way from understanding its true aetiology, the neurobiological concept of depression has evolved from receptor regulation disorder, to a neurodegenerative disorder with a hippocampal volume decrease with the controversial reduction in neurotrophins such as BDNF, to current hypotheses that consider depression to be an inflammatory and neuroprogressive process. As regards antidepressants, although researchers are still far from knowing their true mechanism of action, they have gone from monoaminergic hypotheses, in which serotonin was the main protagonist, to emphasising the anti-inflammatory action of some of these drugs, or the participation of p11 protein in their mechanism of action.In the same way, according to the inflammatory hypothesis of depression, it has been proposed that some NSAIDS such as aspirin or drugs like simvastatin that have an anti-inflammatory action could be useful in some depressive patients. Despite the fact that there may be some data to support their clinical use, common sense and the evidence advise us to use already tested protocols and wait for the future to undertake new therapeutic strategies.

The fibroblast growth factor family: neuromodulation of affective behavior

In this review, we propose a broader view of the role of the fibroblast growth factor (FGF) family in modulating brain function. We suggest that some of the FGF ligands together with the FGF receptors are altered in individuals with affective disorder and modulate emotionality in animal models. Thus, we propose that members of the FGF family may be genetic predisposing factors for anxiety, depression, or substance abuse; that they play a key organizing role during early development but continue to play a central role in neuroplasticity in adulthood; and that they work not only over extended time frames, but also via rapid signaling mechanisms, allowing them to exert an "on-line" influence on behavior. Therefore, the FGF family appears to be a prototype of "switch genes" that are endowed with organizational and modulatory properties across the lifespan, and that may represent molecular candidates as biomarkers and treatment targets for affective and addictive disorders.

Depression and treatment response: dynamic interplay of signaling pathways and altered neural processes

Since the 1960s, when the first tricyclic and monoamine oxidase inhibitor antidepressant drugs were introduced, most of the ensuing agents were designed to target similar brain pathways that elevate serotonin and/or norepinephrine signaling. Fifty years later, the main goal of the current depression research is to develop faster-acting, more effective therapeutic agents with fewer side effects, as currently available antidepressants are plagued by delayed therapeutic onset and low response rates. Clinical and basic science research studies have made significant progress towards deciphering the pathophysiological events within the brain involved in development, maintenance, and treatment of major depressive disorder. Imaging and postmortem brain studies in depressed human subjects, in combination with animal behavioral models of depression, have identified a number of different cellular events, intracellular signaling pathways, proteins, and target genes that are modulated by stress and are potentially vital mediators of antidepressant action. In this review, we focus on several neural mechanisms, primarily within the hippocampus and prefrontal cortex, which have recently been implicated in depression and treatment response.

The genetic association of DUSP6 with bipolar disorder and its effect on ERK activity

The dual-specificity phosphatase 6 (DUSP6) gene resides at chromosome location 12q22-23, which is one of the candidate loci for susceptibility to bipolar disorder and which encodes a phosphatase selective for extracellular signal-regulated kinase (ERK). Previously, we reported a positive association between the functional Leu114Val polymorphism (rs2279574) in DUSP6 and bipolar disorder. Given that the association between DUSP6 and the reported down-regulation of DUSP6 transcript in bipolar postmortem brains were sex-dimorphic, showing significance in women but not men, we performed two independent analyses in homogenous samples of male and female Korean patients with bipolar disorder or schizophrenia using samples enlarged from our previous report. Among the examined DUSP6 SNPs, five (rs769700, rs704076, rs770087, rs808820, and rs2279574) showed positive allelic associations, with the frequency of minor alleles (C, T, G, G, and G) in each SNP significantly increased in women with BD. Consequently, the "C-T-G-G-G" haplotype was significantly over-represented (P=0.016; OR=3.242), whereas the "T-G-T-A-T" haplotype was significantly under-represented (P=0.014; OR=0.697). We found no significant associations with DUSP6 SNPs in men with bipolar disorder or schizophrenia. We also investigated the functions of the functional SNPs' positive associations and found that Leu114Val (rs2279574; T/G) and Ser144Ala (rs770087; T/G) mutations in DUSP6 proteins reduced lithium-induced ERK1/2 phosphorylation in vitro, implicating the dominant active functions. Thus, DUSP6 may not only play important roles in the pathogenesis of bipolar disorder, particularly in women, but also affect the therapeutic response to lithium through modulating lithium's effects on intracellular signaling.

Hippocampal neurometabolite changes in depression treatment: a (1)H magnetic resonance spectroscopy study

Previous studies using magnetic resonance spectroscopy have related abnormalities in hippocampal metabolism to depression. Current evidence is consistent with the conclusion that the hippocampal formation plays an important role in the presentation of depressive symptoms. Eighteen adult patients with major depressive disorder, aged 20 to 60 years, underwent magnetic resonance spectroscopy of the hippocampus during a period of depressive symptomatology and after 7-11 weeks of antidepressant medication with at least 50% reduction in the Montgomery-Åsberg Depression Rating Scale ()MADRS score. During therapy, we found a significantly decreased Lac/Cr ratio in the left hippocampus. The Ins/Cr ratio showed a significant negative correlation with the severity of depression as assessed by the MADRS at baseline. Moreover, we found a negative association of NAA/Cho with age and a positive association of Cho/Cr with age, both on the left and right sides at baseline. In light of our findings and previous studies results we hypothesize that mitochondrial dysfunction leading to predominantly anaerobic glycolysis in connection with the intracellular signaling pathways disturbances and decreased astrocytic function/number might subsequently lead to decreased brain neuroplasticity in depression. These mechanisms could be positively influenced by antidepressant treatment with selective serotonin or norepineprine reuptake inhibitors, with potential effects on untimely neuronal aging in depression.

New drug targets in depression: inflammatory, cell-mediated immune, oxidative and nitrosative stress, mitochondrial, antioxidant, and neuroprogressive pathways. And new drug candidates--Nrf2 activators and GSK-3 inhibitors

This paper reviews new drug targets in the treatment of depression and new drug candidates to treat depression. Depression is characterized by aberrations in six intertwined pathways: (1) inflammatory pathways as indicated by increased levels of proinflammatory cytokines, e.g. interleukin-1 (IL-1), IL-6, and tumour necrosis factor α. (2) Activation of cell-mediated immune pathways as indicated by an increased production of interferon γ and neopterin. (3) Increased reactive oxygen and nitrogen species and damage by oxidative and nitrosative stress (O&NS), including lipid peroxidation, damage to DNA, proteins and mitochondria. (4) Lowered levels of key antioxidants, such as coenzyme Q10, zinc, vitamin E, glutathione, and glutathione peroxidase. (5) Damage to mitochondria and mitochondrial DNA and reduced activity of respiratory chain enzymes and adenosine triphosphate production. (6) Neuroprogression, which is the progressive process of neurodegeneration, apoptosis, and reduced neurogenesis and neuronal plasticity, phenomena that are probably caused by inflammation and O&NS. Antidepressants tend to normalize the above six pathways. Targeting these pathways has the potential to yield antidepressant effects, e.g. using cytokine antagonists, minocycline, Cox-2 inhibitors, statins, acetylsalicylic acid, ketamine, ω3 poly-unsaturated fatty acids, antioxidants, and neurotrophic factors. These six pathways offer new, pathophysiologically guided drug targets suggesting that novel therapies could be developed that target these six pathways simultaneously. Both nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activators and glycogen synthase kinase-3 (GSK-3) inhibitors target the six above-mentioned pathways. GSK-3 inhibitors have antidepressant effects in animal models of depression. Nrf2 activators and GSK-3 inhibitors have the potential to be advanced to phase-2 clinical trials to examine whether they augment the efficacy of antidepressants or are useful as monotherapy.

Review of pharmacological treatment in mood disorders and future directions for drug development

After a series of serendipitous discoveries of pharmacological treatments for mania and depression several decades ago, relatively little progress has been made for novel hypothesis-driven drug development in mood disorders. Multifactorial etiologies of, and lack of a full understanding of, the core neurobiology of these conditions clearly have contributed to these development challenges. There are, however, relatively novel targets that have raised opportunities for progress in the field, such as glutamate and cholinergic receptor modulators, circadian regulators, and enzyme inhibitors, for alternative treatment. This review will discuss these promising new treatments in mood disorders, the underlying mechanisms of action, and critical issues of their clinical application. For these new treatments to be successful in clinical practice, it is also important to design innovative clinical trials that identify the specific actions of new drugs, and, ideally, to develop biomarkers for monitoring individualized treatment response. It is predicted that future drug development will identify new agents targeting the molecular mechanisms involved in the pathophysiology of mood disorders.

Fibroblast growth factor receptor 1- 5-hydroxytryptamine 1A heteroreceptor complexes and their enhancement of hippocampal plasticity

BACKGROUND

The hippocampus and its 5-hydroxytryptamine transmission plays an important role in depression related to its involvement in limbic circuit plasticity.

METHODS

The analysis was made with bioluminescence resonance energy transfer, co-immunoprecipitation, in situ proximity ligation assay, binding assay, in cell western and the forced swim test.

RESULTS

Using bioluminescence resonance energy transfer analysis, fibroblast growth factor receptor 1 (FGFR1)-5-hydroxytryptamine 1A (5-HT1A) receptor complexes have been demonstrated and their specificity and agonist modulation characterized. Their presence based on co-immunoprecipitation and proximity ligation assay has also been indicated in hippocampal cultures and rat dorsal hippocampal formation showing a neuronal location. In vitro assays on extracellular signal-regulated kinases 1 and 2 phosphorylation have shown synergistic increases in signaling on coactivation with fibroblast growth factor 2 (FGF2) and a 5-HT1A agonist, and dependent on the heteroreceptor interface. In vitro and in vivo studies also revealed a 5-HT1A agonist induced phosphorylation of FGFR1 and extracellular signal-regulated kinase 1/2 in rat hippocampus without changing FGF2 levels. Co-activation of the heteroreceptor also resulted in synergistic increases in extensions of PC12 cells and neurite densities and protrusions in primary hippocampal cultures dependent on the receptor interface. The combined acute and repeated intracerebroventricular treatment with FGF2 and 8-OH-DPAT was found to produce evidence of highly significant antidepressant actions in the forced swim test.

CONCLUSIONS

The findings indicate that neurotrophic and antidepressant effects of 5-HT in brain may, in part, be mediated by activation of the 5-HT1A receptor protomer in the hippocampal FGFR1-5-HT1A receptor complex enhancing the FGFR1 signaling.

Mechanistic explanations how cell-mediated immune activation, inflammation and oxidative and nitrosative stress pathways and their sequels and concomitants play a role in the pathophysiology of unipolar depression

This paper reviews that cell-mediated-immune (CMI) activation and inflammation contribute to depressive symptoms, including anhedonia; anxiety-like behaviors; fatigue and somatic symptoms, e.g. illness behavior or malaise; and mild cognitive impairment (MCI). These effects are in part mediated by increased levels of pro-inflammatory cytokines (PICs), e.g. interleukin-1 (IL-1), IL-6 and tumor necrosis factor (TNF)α, and Th-1-derived cytokines, such as IL-2 and interferon (IFN)γ. Moreover, new pathways, i.e. concomitants and sequels of CMI activation and inflammation, were detected in depression: (1) Induction of indoleamine 2,3-dioxygenase (IDO) by IFNγ and some PICs is associated with depleted plasma tryptophan, which may interfere with brain 5-HT synthesis, and increased production of anxiogenic and depressogenic tryptophan catabolites. (2) Increased bacterial translocation may cause depression-like behaviors by activating the cytokine network, oxidative and nitrosative stress (O&NS) pathways and IDO. (3) Induction of O&NS causes damage to membrane ω3 PUFAs, functional proteins, DNA and mitochondria, and autoimmune responses directed against intracellular molecules that may cause dysfunctions in intracellular signaling. (4) Decreased levels of ω3 PUFAs and antioxidants, such as coenzyme Q10, glutathione peroxidase or zinc, are associated with an increased inflammatory potential; more oxidative damage; the onset of specific symptoms; and changes in the expression or functions of brain 5-HT and N-methyl-d-aspartate receptors. (5) All abovementioned factors cause neuroprogression, that is a combination of neurodegeneration, neuronal apoptosis, and lowered neurogenesis and neuroplasticity. It is concluded that depression may be the consequence of a complex interplay between CMI activation and inflammation and their sequels/concomitants which all together cause neuroprogression that further shapes the depression phenotype. Future research should employ high throughput technologies to collect genetic and gene expression and protein data from patients with depression and analyze these data by means of systems biology methods to define the dynamic interactions between the different cell signaling networks and O&NS pathways that cause depression.

Differential effects of prenatal stress in 5-Htt deficient mice: towards molecular mechanisms of gene × environment interactions

Prenatal stress (PS) has been shown to influence the development of the fetal brain and to increase the risk for the development of psychiatric disorders in later life. Furthermore, the variation of human serotonin transporter (5-HTT, SLC6A4) gene was suggested to exert a modulating effect on the association between early life stress and the risk for depression. In the present study, we used a 5-Htt×PS paradigm to investigate whether the effects of PS are dependent on the 5-Htt genotype. For this purpose, the effects of PS on cognition, anxiety- and depression-related behavior were examined using a maternal restraint stress paradigm of PS in C57BL6 wild-type (WT) and heterozygous 5-Htt deficient (5-Htt +/-) mice. Additionally, in female offspring, a genome-wide hippocampal gene expression profiling was performed using the Affymetrix GeneChip® Mouse Genome 430 2.0 Array. 5-Htt +/- offspring showed enhanced memory performance and signs of reduced anxiety as compared to WT offspring. In contrast, exposure of 5-Htt +/- mice to PS was associated with increased depressive-like behavior, an effect that tended to be more pronounced in female offspring. Further, 5-Htt genotype, PS and their interaction differentially affected the expression of numerous genes and related pathways within the female hippocampus. Specifically, MAPK and neurotrophin signaling were regulated by both the 5-Htt +/- genotype and PS exposure, whereas cytokine and Wnt signaling were affected in a 5-Htt genotype×PS manner, indicating a gene×environment interaction at the molecular level. In conclusion, our data suggest that although the 5-Htt +/- genotype shows clear adaptive capacity, 5-Htt +/- mice--particularly females--at the same time appear to be more vulnerable to developmental stress exposure when compared to WT offspring. Moreover, hippocampal gene expression profiles suggest that distinct molecular mechanisms mediate the behavioral effects of the 5-Htt genotype, PS exposure, and their interaction.

Effects of citalopram on serotonin and CRF systems in the midbrain of primates with differences in stress sensitivity

This chapter reviews the neurobiological effects of stress sensitivity and s-citalpram (CIT) treatment observed in our nonhuman primate model of functional hypothalamic amenorrhea (FHA). This type of infertility, also known as stress-induced amenorrhea, is exhibited by cynomolgus macaques. In small populations, some individuals are stress-sensitive (SS) and others are highly stress-resilient (HSR). The SS macaques have suboptimal secretion of estrogen and progesterone during normal menstrual cycles. SS monkeys also have decreased serotonin gene expression and increased CRF expression compared to HSR monkeys. Recently, we found that CIT treatment improved ovarian steroid secretion in SS monkeys, but had no effect in HSR monkeys. Examination of the serotonin system revealed that SS monkeys had significantly lower Fev (fifth Ewing variant, rodent Pet1), TPH2 (tryptophan hydroxylase 2), 5HT1A autoreceptor and SERT (serotonin reuptake transporter) expression in the dorsal raphe than SR monkeys. However, CIT did not alter the expression of either Fev, TPH2, SERT or 5HT1A mRNAs. In contrast, SS monkeys tended to have a higher density of CRF fiber innervation of the dorsal raphe than HSR monkeys, and CIT significantly decreased the CRF fiber density in SS animals. In addition, CIT increased CRF-R2 gene expression in the dorsal raphe. We speculate that in a 15-week time frame, the therapeutic effect of S-citalopram may be achieved through a mechanism involving extracellular serotonin inhibition of CRF and stimulation of CRF-R2, rather than alteration of serotonin-related gene expression.

Altered expression of glutamate signaling, growth factor, and glia genes in the locus coeruleus of patients with major depression

Several studies have proposed that brain glutamate signaling abnormalities and glial pathology have a role in the etiology of major depressive disorder (MDD). These conclusions were primarily drawn from post-mortem studies in which forebrain brain regions were examined. The locus coeruleus (LC) is the primary source of extensive noradrenergic innervation of the forebrain and as such exerts a powerful regulatory role over cognitive and affective functions, which are dysregulated in MDD. Furthermore, altered noradrenergic neurotransmission is associated with depressive symptoms and is thought to have a role in the pathophysiology of MDD. In the present study we used laser-capture microdissection (LCM) to selectively harvest LC tissue from post-mortem brains of MDD patients, patients with bipolar disorder (BPD) and from psychiatrically normal subjects. Using microarray technology we examined global patterns of gene expression. Differential mRNA expression of select candidate genes was then interrogated using quantitative real-time PCR (qPCR) and in situ hybridization (ISH). Our findings reveal multiple signaling pathway alterations in the LC of MDD but not BPD subjects. These include glutamate signaling genes, SLC1A2, SLC1A3 and GLUL, growth factor genes FGFR3 and TrkB, and several genes exclusively expressed in astroglia. Our data extend previous findings of altered glutamate, astroglial and growth factor functions in MDD for the first time to the brainstem. These findings indicate that such alterations: (1) are unique to MDD and distinguishable from BPD, and (2) affect multiple brain regions, suggesting a whole-brain dysregulation of such functions.

Modulation of neuroplastic molecules in selected brain regions after chronic administration of the novel antidepressant agomelatine

RATIONALE

Neuronal plasticity is associated with depression, probably as a result of modified expression of proteins important for cellular resiliency. It is therefore important to establish if and how antidepressant drugs may be able to regulate these mechanisms in order to achieve relevant clinical effects.

OBJECTIVE

We investigated the effects of chronic treatment with agomelatine (an MT(1)/MT(2) receptor agonist and 5-HT(2C) receptor antagonist) on the brain-derived neurotrophic factor (BDNF), fibroblast growth factor (FGF-2), and activity-regulated cytoskeleton-associated protein (Arc).

METHODS

Animals were treated for 21 days with agomelatine, venlafaxine, or a vehicle and sacrificed 1 h (6 p.m.) or 16 h after the last injection (9 a.m.) to evaluate the messenger RNA (mRNA) and protein expression of these neuroplastic markers in the hippocampus and prefrontal cortex.

RESULTS

Agomelatine, but not venlafaxine, produced major transcriptional changes in the hippocampus, where significant up-regulations of BDNF and FGF-2 were observed. Both drugs up-regulated the Arc transcription levels. No effects were observed in the prefrontal cortex. Instead, the levels of BDNF protein were elevated by agomelatine in both regions: the effects of the drug on mRNA levels in the hippocampus and cortex are different, while the effects on the protein seem to have the same cumulative result, suggesting different modulatory mechanisms in the two regions.

CONCLUSIONS

Our data provide new information regarding the molecular mechanisms that contribute to the chronic effects of the new antidepressant agomelatine on brain function. The ability of agomelatine to modulate the expression of these neuroplastic molecules, which follows a circadian rhythm, may contribute to its antidepressant action.

Cytokines mediated inflammation and decreased neurogenesis in animal models of depression

In patients with major depression or in animal models of depression, significantly increases in the concentrations of pro-inflammatory cytokines have been consistently reported. Proinflammatory cytokines can stimulate the hypothalamic-pituitary-adrenal (HPA) axis to release stress hormone, glucocorticoids. As a consequence of excessive inflammatory response triggered by pro-inflammatory cytokines in the periphery, free radicals, oxidants and glucocorticoids are over-produced, which can affect glial cell functions and damage neurons in the brain. Indeed, decreased neurogenesis and the dysfunction of neurotrophic system (up- or down-regulations of neurotrophins and their receptors) have been recently found. Effective treatments for depressive symptoms, such as antidepressants and omega-3 fatty acids can increase or modulate neurotrophic system and enhance neurogenesis. However, the relationship between glial cells; microglia (mostly involved in neuroinflammation) and astrocytes (producing neurotrophins), and the contribution of inflammation to decreased neurogenesis and dysfunction of neurotrophic system are almost unknown. This review first introduces changes in behavior, neurotransmitter, cytokine and neurogenesis aspects in depressed patients and several animal models of depression, secondly explores the possible relationship between pro- and anti-inflammatory cytokines and neurogenesis in these models, then discusses the effects of current treatments on inflammation, neurotrophic system and neurogenesis, and finally pointes out the limitations and future research directions.

Vascular pathology and blood-brain barrier disruption in cognitive and psychiatric complications of type 2 diabetes mellitus

Vascular pathology is recognized as a principle insult in type 2 diabetes mellitus (T2DM). Co-morbidities such as structural brain abnormalities, cognitive, learning and memory deficits are also prevailing in T2DM patients. We previously suggested that microvascular pathologies involving blood-brain barrier (BBB) breakdown results in leakage of serum-derived components into the brain parenchyma, leading to neuronal dysfunction manifested as psychiatric illnesses. The current postulate focuses on the molecular mechanisms controlling BBB permeability in T2DM, as key contributors to the pathogenesis of mental disorders in patients. Revealing the mechanisms underlying BBB dysfunction and inflammatory response in T2DM and their role in metabolic disturbances, abnormal neurovascular coupling and neuronal plasticity, would contribute to the understanding of the mechanisms underlying psychopathologies in diabetic patients. Establishing this link would offer new targets for future therapeutic interventions.

Fibroblast growth factors in schizophrenia

A large association study by O'Donovan et al recently suggested that genetic variation in fibroblast growth factor receptor (FGFR) 2 increases the risk for developing schizophrenia. Fibroblast growth factors (FGFs) are part of the family of glial growth factors; they control the growth and patterning of specific brain structures and regulate the maintenance and repair of neuronal tissues. In addition, a direct interaction was recently found between FGFRs and adenosine A(2A) receptors, leading to corticostriatal plasticity and antagonizing the signaling pathway of dopamine D(2) receptors. These findings make FGFs plausible candidate genes for schizophrenia. Here, we review the role of FGFs in schizophrenia and combine evidence from studies on variations in FGF genes, RNA expression, protein levels, and FGF administration, as well as the effects of medication and environmental risk factors for schizophrenia. These data suggest that changes in the FGF system contribute to schizophrenia and possibly to a wider range of psychiatric disorders. The role of FGFs in schizophrenia and related disorders needs to be studied in more detail.

The expression of VGF is reduced in leukocytes of depressed patients and it is restored by effective antidepressant treatment

Major depression is a disease characterized by an inability of neuronal systems to show appropriate adaptive plasticity especially under challenging conditions, such as stress. Conversely, pharmacological intervention may normalize such defects through the modulation of factors that might act in concert for the functional recovery of depressed patients, like the neuropeptide VGF, which has previously shown to possess antidepressant like activity. We analyzed VGF mRNA levels in the brain of rodents exposed to stress or treated with antidepressant drugs. In addition, we assessed VGF expression in leukocytes obtained from 25 drug-free depressed patients before and during antidepressant treatment. We found a persistent reduction of VGF expression after exposure to prenatal stress and an upregulation of its levels following chronic treatment with different antidepressant drugs. Moreover, VGF mRNA levels were significantly reduced in drug-free depressed patients, as compared with controls, and were modulated in response to effective antidepressant treatment. Our data provide further support to the role of VGF in mood disorders and suggest that VGF could be a more specific biomarker for treatment responsiveness.

Effects of FGF receptor peptide agonists on animal behavior under normal and pathological conditions

Hexafins are recently identified low-molecular-weight peptide agonists of the fibroblast growth factor receptor (FGFR), derived from the beta6-beta7 loop region of various FGFs. Synthetic hexafin peptides have been shown to bind to and induce tyrosine phosphorylation of FGFR1, stimulate neurite outgrowth, and promote neuronal survival in vitro. Thus, the pronounced biological activities of hexafins in vitro make them attractive compounds for pharmacological studies in vivo. The present study investigated the effects of subcutaneous administration of hexafin1 and hexafin2 (peptides derived from FGF1 and FGF2, respectively) on social memory, exploratory activity, and anxiety-like behavior in adult rats. Treatment with hexafin1 and hexafin2 resulted in prolonged retention of social memory. Furthermore, rats treated with hexafin2 exhibited decreased anxiety-like behavior in the elevated plus maze. Employing an R6/2 mouse model of Huntington's disease (HD), we found that although hexafin2 did not affect the progression of motor symptoms, it alleviated deficits in activity related to social behavior, including sociability and social novelty. Thus, hexafin2 may have therapeutic potential for the treatment of HD.

Uncovering the molecular basis of positive affect using rough-and-tumble play in rats: a role for insulin-like growth factor I

Positive emotional states have been shown to confer resilience to depression and anxiety in humans, but the molecular mechanisms underlying these effects have not yet been elucidated. In laboratory rats, positive emotional states can be measured by 50-kHz ultrasonic vocalizations (hedonic USVs), which are maximally elicited by juvenile rough-and-tumble play behavior. Using a focused microarray platform, insulin-like growth factor I (IGFI) extracellular signaling genes were found to be upregulated by hedonic rough-and-tumble play but not depressogenic social defeat. Administration of IGFI into the lateral ventricle increased rates of hedonic USVs in an IGFI receptor (IGFIR)-dependent manner. Lateral ventricle infusions of an siRNA specific to the IGFIR decreased rates of hedonic 50-kHz USVs. These results show that IGFI plays a functional role in the generation of positive affective states and that IGFI-dependent signaling is a potential therapeutic target for the treatment of depression and anxiety.

Neuronal plasticity: a link between stress and mood disorders

Although stress represents the major environmental element of susceptibility for mood disorders, the relationship between stress and disease remains to be fully established. In the present article we review the evidence in support for a role of neuronal plasticity, and in particular of neurotrophic factors. Even though decreased levels of norepinephrine and serotonin may underlie depressive symptoms, compelling evidence now suggests that mood disorders are characterized by reduced neuronal plasticity, which can be brought about by exposure to stress at different stages of life. Indeed the expression of neurotrophic molecules, such as the neurotrophin BDNF, is reduced in depressed subjects as well as in experimental animals exposed to adverse experience at early stages of life or at adulthood. These changes show an anatomical specificity and might be sustained by epigenetic mechanisms. Pharmacological intervention may normalize such defects and improve neuronal function through the modulation of the same factors that are defective in depression. Several studies have demonstrated that chronic, but not acute, antidepressant treatment increases the expression of BDNF and may enhance its localization at synaptic level. Antidepressant treatment can normalize deficits in neurotrophin expression produced by chronic stress paradigms, but may also alter the modulation of BDNF under acute stressful conditions. In summary, there is good agreement in considering neuronal plasticity, and the expression of key proteins such as the neurotrophin BDNF, as a central player for the effects of stress on brain function and its implication for psychopathology. Accordingly, effective treatments should not limit their effects to the control of neurotransmitter and hormonal dysfunctions, but should be able to normalize defective mechanisms that sustain the impairment of neuronal plasticity.

Stress sensitive female macaques have decreased fifth Ewing variant (Fev) and serotonin-related gene expression that is not reversed by citalopram

Female cynomolgus monkeys exhibit different degrees of reproductive dysfunction with moderate metabolic and psychosocial stress. When stressed with a paradigm of relocation and diet for 60 days or two menstrual cycles, highly stress resilient monkeys (HSR) continued to ovulate during the stress cycles whereas stress sensitive monkeys (SS) did not. After cessation of stress, monkeys characterized as HSR or SS were administered placebo (PL) or S-citalopram (CIT) for 15 weeks at doses that normalized ovarian steroid secretion in the SS animals and that maintained blood CIT levels in a therapeutic range. After euthanasia, the brain was perfused with 4% paraformaldehyde. The pontine midbrain was blocked and sectioned at 25 microm. The expression of four genes pivotal to serotonin neural function was assessed in the four groups of monkeys (n=4/group). Fev (fifth Ewing variant) ETS transcription factor, tryptophan hydroxylase 2 (TPH2), the serotonin reuptake transporter (SERT), and the 5HT1A autoreceptor were determined at 7-8 levels of the dorsal raphe nucleus with in situ hybridization (ISH) using radiolabeled- and digoxygenin-incorporated riboprobes. Positive pixel area and cell number were measured with Slidebook 4.2 in the digoxigenin assay for Fev. Optical density (OD) and positive pixel area were measured with NIH Image software in the radiolabeled assays for TPH2, SERT and 5HT1A. All data were analyzed with two-way ANOVA. SS monkeys had significantly fewer Fev-positive cells and lower Fev-positive pixel area in the dorsal raphe than HSR monkeys. SS monkeys also had significantly lower levels of TPH2, SERT and 5HT1A mRNAs in the dorsal raphe nucleus than HSR monkeys. However, CIT did not alter the expression of either Fev, TPH2, SERT or 5HT1A mRNAs. These data suggest that SS monkeys have fewer serotonin (5-HT) neurons than HSR monkeys, and that they have deficient Fev expression, which in turn, leads to deficient TPH2, SERT and 5HT1A expression. In addition, the therapeutic effect of CIT is probably achieved through mechanisms other than alteration of 5-HT-related gene expression.

New approaches to the pharmacological management of major depressive disorder

Despite effective and safe therapies for major depressive disorder (MDD), the current arsenal of antidepressant therapies does not fully satisfy the needs of patients or physicians. Many patients are only partial responders or are treatment resistant and side effects interfere with compliance. The majority of antidepressants directly affect monoamine neurotransmission within the central nervous system. Moving beyond this mechanism has been a challenge because of the lack of knowledge about the underlying etiology and pathophysiology of MDD. Provided in this report is a review of some of the major new advances in MDD research that suggest the possibility of novel and improved future therapeutic options. Emphasis is placed on studies of unipolar, but not bipolar, depression. New therapies include dual and triple monoamine uptake inhibitors, non-conventional antidepressants such as tianeptine, and a number of augmentation strategies. In addition, studies are underway on a number of mechanisms of action that might yield the next therapeutic advance. These include agents that interact with endocannabiniod systems, examination of natural products, and compounds that influence neuropeptide systems such as galanin and melanin-concentrating hormone, and growth and neurotrophic factors. Epigenetic mechanisms involving histone modification are also being explored. An area of intensive investigation is glutamate neurotransmission. Data support the hypothesis that NMDA receptor antagonists are effective in MDD individuals resistant to conventional therapies. The potential of metabotropic glutamate receptors as novel targets is also discussed. Accumulating evidence supports the idea that amplification of AMPA receptor function is a critical link in the transduction processes involved antidepressant effects.

NCAM-mimetic, FGL peptide, restores disrupted fibroblast growth factor receptor (FGFR) phosphorylation and FGFR mediated signaling in neural cell adhesion molecule (NCAM)-deficient mice

Neural cell adhesion molecule (NCAM) is a membrane-bound glycoprotein expressed on the surface of neuronal and glial cells. Previous in vitro studies have demonstrated that NCAM promotes neuronal functions largely via three main interaction partners: the fibroblast growth factor receptor (FGFR), a member of Src family of tyrosine kinases, Fyn and Raf1 kinase which all activate different intracellular signaling pathways. The objective was to clarify, which signaling pathways are being disrupted in NCAM knockout mice and whether FGL peptide is able to restore observed disruptions. Therefore we compared the levels of phosphorylation of FGFR1, Src kinase Fyn, Raf1 kinase, MAP kinases, Akt kinase and calcium/calmodulin-dependent kinases II and IV (CaMKII and CaMKIV) in the hippocampus of NCAM knockout mice to their wild-type littermates. The data of our study show that mice constitutively deficient in all isoforms of NCAM have decreased basal phosphorylation levels of FGFR1 and CaMKII and CaMKIV. Furthermore, NCAM-mimetic, FGL peptide, is found to be able to restore FGFR1, CaMKII and CaMKIV phosphorylation levels and thereby mimic the interactions of NCAM at this receptor in NCAM deficient mice. Also, we found that Fyn(Tyr530), Raf1, MAP kinases and Akt kinase phosphorylation in adult animals is not affected by NCAM deficiency but interestingly, we found an over-expression of another cell adhesion molecule L1. We conclude that in NCAM deficient mice FGFR1-dependent signaling is disrupted and it can be restored by FGL peptide.

Suicide neurobiology

In this review, we examine the history of the neurobiology of suicide, as well as the genetics, molecular and neurochemical findings in suicide research. Our analysis begins with a summary of family, twin, and adoption studies, which provide support for the investigation of genetic variation in suicide risk. This leads to an overview of neurochemical findings restricted to neurotransmitters and their receptors, including recent findings in whole genome gene expression studies. Next, we look at recent studies investigating lipid metabolism, cell signalling with a particular emphasis on growth factors, stress systems with a focus on the role of polyamines, and finally, glial cell pathology in suicide. We conclude with a description of new ideas to study the neurobiology of suicide, including subject-specific analysis, protein modification assessment, neuroarchitecture studies, and study design strategies to investigate the complex suicide phenotype.

Structure and function of dendritic spines within the hippocampus

Most excitatory input in the hippocampus impinges on dendritic spines. Therefore, the dendritic spines are likely to be of major importance for neural processing. The morphology of dendritic spines is very diverse and changes in spine size as well as in their density are thought to reflect changes in the strength of synaptic transmission. Thus, alterations in dendritic spine densities or shape are suspected to be morphological manifestations of psychopathological, pathophysiological, physiological and/or behavioural changes. However, in spite of a long history of research, the specific function of dendritic spines within the hippocampal formation is still not well understood. This review will shed light on the hippocampal dendritic spines, their ultrastructure and morphology, as well as their supposed roles in neuronal plasticity and in certain mental illnesses.

Chronic but not acute foot-shock stress leads to temporary suppression of cell proliferation in rat hippocampus

Stressful experiences, especially when prolonged and severe are associated with psychopathology and impaired neuronal plasticity. Among other effects on the brain, stress has been shown to negatively regulate hippocampal neurogenesis, and this effect is considered to be exerted via glucocorticoids. Here, we sought to determine the temporal dynamics of changes in hippocampal neurogenesis after acute and chronic exposure to foot-shock stress. Rats subjected to a foot-shock procedure showed strong activation of the hypothalamic-pituitary-adrenal (HPA) axis, even after exposure to daily stress for 3 weeks. Despite a robust release of corticosterone, acute foot-shock stress did not affect the rate of hippocampal cell proliferation. In contrast, exposure to foot-shock stress daily for 3 weeks led to reduced cell proliferation 2 hours after the stress procedure. Interestingly, this stress-induced effect did not persist and was no longer detected 24 hours later. Also, while chronic foot-shock stress had no impact on survival of hippocampal cells that were born before the stress procedure, it led to a decreased number of doublecortin-positive granule neurons that were born during the chronic stress period. Thus, whereas a strong activation of the HPA axis during acute foot-shock stress is not sufficient to reduce hippocampal cell proliferation, repeated exposure to stressful stimuli for prolonged period of time ultimately results in dysregulated neurogenesis. In sum, this study supports the notion that chronic stress may lead to cumulative changes in the brain that are not seen after acute stress. Such changes may indicate compromised brain plasticity and increased vulnerability to neuropathology.

A new role for FGF2 as an endogenous inhibitor of anxiety

Human postmortem studies have demonstrated that fibroblast growth factor-2 (FGF2) expression is decreased in the brain of depressed individuals. It remained unclear, however, whether this is a consequence of the illness or whether FGF2 plays a primary role in the control of mood and emotions. In this series of studies, we first ask whether endogenous FGF2 expression correlates with spontaneous anxiety, a trait associated with vulnerability to severe mood disorders in humans. This is tested in two genetically distinct groups of rats selectively bred to differ dramatically in their response to novelty and anxiety-provoking conditions (HRs = low anxiety/high response to novelty vs LRs = high anxiety/low response to novelty). We demonstrate that high-anxiety LRs have significantly lower levels of hippocampal FGF2 mRNA relative to low-anxiety HRs. We then demonstrate that FGF2 expression is modifiable by environmental factors that alter anxiety--thus, environmental complexity reduces anxiety behavior and induces FGF2 expression in hippocampus, particularly in high-anxiety LRs. Finally, we directly test the role of FGF2 as an anxiolytic and show that a 3 week treatment regimen of peripherally administered FGF2 is highly effective at blunting anxiety behavior, specifically in high-anxiety LRs. This treatment is accompanied by an increase in survival of adult-born hippocampal cells, both neurons and astrocytes, most clearly in LRs. These findings implicate hippocampal FGF2 as a central integrator of genetic and environmental factors that modify anxiety, point to hippocampal neurogenesis and gliogenesis as key in this modulation, and underscore FGF2's potential as a new target for treatment of depression and anxiety disorders.

Proton MR spectroscopy of the hippocampus at 3 T in patients with unipolar major depressive disorder: correlates and predictors of treatment response

Various lines of research suggest that neurotrophic processes in the hippocampus are key mechanisms in major depressive disorder and are of relevance for response to antidepressive treatment. We performed proton magnetic resonance spectroscopy (1H-MRS) of the hippocampus at 3 T in 18 unmedicated subjects with unipolar major depressive episodes and in 10 age- and gender-matched healthy volunteers. Thirteen patients underwent a second examination after 8 wk treatment with either citalopram (n=7) or nortriptyline (n=6). Of these patients, 11 MRS datasets could be used for the assessment of treatment correlates. In the cross-sectional comparison, we observed a significant reduction of the metabolic ratios Glx/Cr (Glx=glutamine, glutamate and gamma-aminobutyric acid) and glutamine (Gln)/Cr in the patient group. The Gln/Glx ratio also showed a trend towards significant reduction. The individual effect of treatment correlated with an increase in the absolute concentrations of N-acetylaspartate (NAA) and of choline compounds (Cho). Low baseline NAA and Cho levels predicted positive treatment effects. There was no difference in any clinical or metabolic measure, either at baseline or at follow-up between the two treatment groups (citalopram, nortriptyline). Our data provide first evidence for a reduction of Gln in the hippocampus of subjects with major depression. Furthermore, we provide first evidence in patients with major depression for neurorestorative effects in the hippocampus by pharmacological treatment expressed by a correlation of NAA and Cho increases with treatment response. This accounts in particular for those patients with low NAA and Cho baseline levels.

The FGF family: biology, pathophysiology and therapy

The family of fibroblast growth factors (FGFs) regulates a plethora of developmental processes, including brain patterning, branching morphogenesis and limb development. Several mitogenic, cytoprotective and angiogenic therapeutic applications of FGFs are already being explored, and the recent discovery of the crucial roles of the endocrine-acting FGF19 subfamily in bile acid, glucose and phosphate homeostasis has sparked renewed interest in the pharmacological potential of this family. This Review discusses traditional applications of recombinant FGFs and small-molecule FGF receptor kinase inhibitors in the treatment of cancer and cardiovascular disease and their emerging potential in the treatment of metabolic syndrome and hypophosphataemic diseases.

The inflammatory & neurodegenerative (I&ND) hypothesis of depression: leads for future research and new drug developments in depression

Despite extensive research, the current theories on serotonergic dysfunctions and cortisol hypersecretion do not provide sufficient explanations for the nature of depression. Rational treatments aimed at causal factors of depression are not available yet. With the currently available antidepressant drugs, which mainly target serotonin, less than two thirds of depressed patients achieve remission. There is now evidence that inflammatory and neurodegenerative (I&ND) processes play an important role in depression and that enhanced neurodegeneration in depression may-at least partly-be caused by inflammatory processes. Multiple inflammatory-cytokines, oxygen radical damage, tryptophan catabolites-and neurodegenerative biomarkers have been established in patients with depression and these findings are corroborated by animal models of depression. A number of vulnerability factors may predispose towards depression by enhancing inflammatory reactions, e.g. lower peptidase activities (dipeptidyl-peptidase IV, DPP IV), lower omega-3 polyunsaturated levels and an increased gut permeability (leaky gut). The cytokine hypothesis considers that external, e.g. psychosocial stressors, and internal stressors, e.g. organic inflammatory disorders or conditions, such as the postpartum period, may trigger depression via inflammatory processes. Most if not all antidepressants have specific anti-inflammatory effects, while restoration of decreased neurogenesis, which may be induced by inflammatory processes, may be related to the therapeutic efficacy of antidepressant treatments. Future research to disentangle the complex etiology of depression calls for a powerful paradigm shift, i.e. by means of a high throughput-high quality screening, including functional genetics and genotyping microarrays; established and novel animal and ex vivo-in vitro models for depression, such as new transgenic mouse models and endophenotype-based animal models, specific cell lines, in vivo and ex vivo electroporation, and organotypic brain slice culture models. This screening will allow to: 1) discover new I&ND biomarkers, both at the level of gene expression and the phenotype; and elucidate the underlying molecular I&ND pathways causing depression; and 2) identify new therapeutic targets in the I&ND pathways; develop new anti-I&ND drugs for these targets; select existing anti-I&ND drugs or substances that could augment the efficacy of antidepressants; and predict therapeutic response by genetic I&ND profiles.

Depression-like behaviour in neural cell adhesion molecule (NCAM)-deficient mice and its reversal by an NCAM-derived peptide, FGL

The neural cell adhesion molecule (NCAM) plays a pivotal role in brain plasticity. Brain plasticity itself has a crucial role in the development of depression. The aim of this study was to analyze whether NCAM-deficient (NCAM(-/-)) mice exhibit depression-like behaviour and whether a peptide termed FGL, derived from the NCAM binding site for the fibroblast growth factor (FGF) receptor, is able to reverse the depression-like signs in NCAM(-/-) mice. Our study showed that NCAM(-/-) mice demonstrated increased freezing time in the tail-suspension test and reduced preference for sucrose consumption in the sucrose preference test, reduced adult neurogenesis in the dentate gyrus and reduced levels of the phosphorylated cAMP response element-binding protein (pCREB) in the hippocampus. FGL administered acutely or repeatedly reduced depression-like behaviour in NCAM(-/-) mice without having an effect on their wild-type littermates. Repeated administration of FGL enhanced survival of the newly born neurons in NCAM(-/-) mice and increased the levels of pCREB in both NCAM(+/+) and NCAM(-/-) mice. In conclusion, our data demonstrate that NCAM deficiency in mice results in a depression-like phenotype which can be reversed by the acute or repeated administration of FGL. The results also suggest a role of the deficit in NCAM signalling through the FGF receptor in depression.

Target identification for CNS diseases by transcriptional profiling

Gene expression changes in neuropsychiatric and neurodegenerative disorders, and gene responses to therapeutic drugs, provide new ways to identify central nervous system (CNS) targets for drug discovery. This review summarizes gene and pathway targets replicated in expression profiling of human postmortem brain, animal models, and cell culture studies. Analysis of isolated human neurons implicates targets for Alzheimer's disease and the cognitive decline associated with normal aging and mild cognitive impairment. In addition to tau, amyloid-beta precursor protein, and amyloid-beta peptides (Abeta), these targets include all three high-affinity neurotrophin receptors and the fibroblast growth factor (FGF) system, synapse markers, glutamate receptors (GluRs) and transporters, and dopamine (DA) receptors, particularly the D2 subtype. Gene-based candidates for Parkinson's disease (PD) include the ubiquitin-proteosome system, scavengers of reactive oxygen species, brain-derived neurotrophic factor (BDNF), its receptor, TrkB, and downstream target early growth response 1, Nurr-1, and signaling through protein kinase C and RAS pathways. Increasing variability and decreases in brain mRNA production from middle age to old age suggest that cognitive impairments during normal aging may be addressed by drugs that restore antioxidant, DNA repair, and synaptic functions including those of DA to levels of younger adults. Studies in schizophrenia identify robust decreases in genes for GABA function, including glutamic acid decarboxylase, HINT1, glutamate transport and GluRs, BDNF and TrkB, numerous 14-3-3 protein family members, and decreases in genes for CNS synaptic and metabolic functions, particularly glycolysis and ATP generation. Many of these metabolic genes are increased by insulin and muscarinic agonism, both of which are therapeutic in psychosis. Differential genomic signals are relatively sparse in bipolar disorder, but include deficiencies in the expression of 14-3-3 protein members, implicating these chaperone proteins and the neurotransmitter pathways they support as possible drug targets. Brains from persons with major depressive disorder reveal decreased expression for genes in glutamate transport and metabolism, neurotrophic signaling (eg, FGF, BDNF and VGF), and MAP kinase pathways. Increases in these pathways in the brains of animals exposed to electroconvulsive shock and antidepressant treatments identify neurotrophic and angiogenic growth factors and second messenger stimulation as therapeutic approaches for the treatment of depression.

Analysis of 10 independent samples provides evidence for association between schizophrenia and a SNP flanking fibroblast growth factor receptor 2

We and others have previously reported linkage to schizophrenia on chromosome 10q25-q26 but, to date, a susceptibility gene in the region has not been identified. We examined data from 3606 single-nucleotide polymorphisms (SNPs) mapping to 10q25-q26 that had been typed in a genome-wide association study (GWAS) of schizophrenia (479 UK cases/2937 controls). SNPs with P<0.01 (n=40) were genotyped in an additional 163 UK cases and those markers that remained nominally significant at P<0.01 (n=22) were genotyped in replication samples from Ireland, Germany and Bulgaria consisting of a total of 1664 cases with schizophrenia and 3541 controls. Only one SNP, rs17101921, was nominally significant after meta-analyses across the replication samples and this was genotyped in an additional six samples from the United States/Australia, Germany, China, Japan, Israel and Sweden (n=5142 cases/6561 controls). Across all replication samples, the allele at rs17101921 that was associated in the GWAS showed evidence for association independent of the original data (OR 1.17 (95% CI 1.06-1.29), P=0.0009). The SNP maps 85 kb from the nearest gene encoding fibroblast growth factor receptor 2 (FGFR2) making this a potential susceptibility gene for schizophrenia.

Neonatal FGF2 alters cocaine self-administration in the adult rat

The neurobiological bases of increased vulnerability to substance abuse remain obscure. We report here that rats that were selectively bred for greater drug-seeking behavior exhibited higher levels of FGF2 gene expression. We then asked whether a single FGF2 administration (20 ng/g, s.c.) on postnatal day 2 (PND2) can have a lifelong impact on drug-taking behavior, spatial and appetitive learning and the dopaminergic system. Indeed, early life FGF2 enhanced the acquisition of cocaine self-administration in adulthood. However, early life FGF2 did not alter spatial or operant learning in adulthood. Furthermore, early life FGF2 did not alter gene expression in the dopaminergic system in adulthood. These results suggest that elevated levels of FGF2 may lead to increased drug-taking behavior without altering learning. Thus, FGF2 may be an antecedent of vulnerability for drug-taking behavior and may provide clues to novel therapeutic approaches for the treatment of addiction.

Antidepressant-like effects of intracerebroventricular FGF2 in rats

The fibroblast growth factor (FGF) system is altered in post-mortem brains of individuals with major depressive disorder (MDD), but the functional relevance of this observation remains to be elucidated. To this end, we tested whether administering agents that act on FGF receptors would have antidepressant-like effects in rodents. We microinjected either FGF2 (200 ng, i.c.v.) or the FG loop (FGL) of neural cell adhesion molecule (NCAM) (5 microg, i.c.v.) into the lateral ventricle of rats and tested them on the forced swim test. Activating FGF receptors acutely had an antidepressant-like effect in the forced swim test. Furthermore, chronic FGF2 decreased depression-like behavior as assessed by two independent tests. Finally, the FGF system itself was altered after FGF2 administration. Specifically, there was an increase in FGFR1 mRNA in the dentate gyrus 24 h post-FGF2, suggesting the potential for self-amplification of the initial signal. These results support the potential therapeutic use of FGF2 or related molecules in the treatment of MDD and point to alternate mechanisms of neuronal remodeling that may be critical in this treatment.

Experiential and genetic contributions to depressive- and anxiety-like disorders: clinical and experimental studies

Stressful events have been implicated in the precipitation of depression and anxiety. These disorders may evolve owing to one or more of an array of neuronal changes that occur in several brain regions. It seems likely that these stressor-provoked neurochemical alterations are moderated by genetic determinants, as well as by a constellation of experiential and environmental factors. Indeed, animal studies have shown that vulnerability to depressive-like behaviors involve mechanisms similar to those associated with human depression (e.g., altered serotonin, corticotropin releasing hormone and their receptors, growth factors), and that the effects of stressors are influenced by previous stressor experiences, particularly those encountered early in life. These stressor effects might reflect sensitization of neuronal functioning, phenotypic changes of processes that lead to neurochemical release or receptor sensitivity, or epigenetic processes that modify expression of specific genes associated with stressor reactivity. It is suggested that depression is a life-long disorder, which even after effective treatment, has a high rate of re-occurrence owing to sensitized processes or epigenetic factors that promote persistent alterations of gene expression.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

After Golgi-Cajal mapped neural circuits, the discovery and mapping of the central monoamine neurons opened up for a new understanding of interneuronal communication by indicating that another form of communication exists. For instance, it was found that dopamine may be released as a prolactin inhibitory factor from the median eminence, indicating an alternative mode of dopamine communication in the brain. Subsequently, the analysis of the locus coeruleus noradrenaline neurons demonstrated a novel type of lower brainstem neuron that monosynaptically and globally innervated the entire CNS. Furthermore, the ascending raphe serotonin neuron systems were found to globally innervate the forebrain with few synapses, and where deficits in serotonergic function appeared to play a major role in depression. We propose that serotonin reuptake inhibitors may produce antidepressant effects through increasing serotonergic neurotrophism in serotonin nerve cells and their targets by transactivation of receptor tyrosine kinases (RTK), involving direct or indirect receptor/RTK interactions. Early chemical neuroanatomical work on the monoamine neurons, involving primitive nervous systems and analysis of peptide neurons, indicated the existence of alternative modes of communication apart from synaptic transmission. In 1986, Agnati and Fuxe introduced the theory of two main types of intercellular communication in the brain: wiring and volume transmission (WT and VT). Synchronization of phasic activity in the monoamine cell clusters through electrotonic coupling and synaptic transmission (WT) enables optimal VT of monoamines in the target regions. Experimental work suggests an integration of WT and VT signals via receptor-receptor interactions, and a new theory of receptor-connexin interactions in electrical and mixed synapses is introduced. Consequently, a new model of brain function must be built, in which communication includes both WT and VT and receptor-receptor interactions in the integration of signals. This will lead to the unified execution of information handling and trophism for optimal brain function and survival.

Gliogenesis and glial pathology in depression

Recent research has changed the perception of glia from being no more than silent supportive cells of neurons to being dynamic partners participating in brain metabolism and communication between neurons. This discovery of new glial functions coincides with growing evidence of the involvement of glia in the neuropathology of mood disorders. Unanticipated reductions in the density and number of glial cells are reported in fronto-limbic brain regions in major depression and bipolar illness. Moreover, age-dependent decreases in the density of glial fibrillary acidic protein (GFAP) - immunoreactive astrocytes and levels of GFAP protein are observed in the prefrontal cortex of younger depressed subjects. Since astrocytes participate in the uptake, metabolism and recycling of glutamate, we hypothesize that an astrocytic deficit may account for the alterations in glutamate/GABA neurotransmission in depression. Reductions in the density and ultrastructure of oligodendrocytes are also detected in the prefrontal cortex and amygdala in depression. Pathological changes in oligodendrocytes may be relevant to the disruption of white matter tracts in mood disorders reported by diffusion tensor imaging. Factors such as stress, excess of glucocorticoids, altered gene expression of neurotrophic factors and glial transporters, and changes in extracellular levels of neurotransmitters released by neurons may modify glial cell number and affect the neurophysiology of depression. Therefore, we will explore the role of these events in the possible alteration of glial number and activity, and the capacity of glia as a promising new target for therapeutic medications. Finally, we will consider the temporal relationship between glial and neuronal cell pathology in depression.

Stress during development: Impact on neuroplasticity and relevance to psychopathology

Development represents a critical moment for shaping adult behavior and may set the stage to disease vulnerability later in life. There is now compelling evidence that stressful experiences during gestation or early in life can lead to enhanced susceptibility for mental illness. In this paper we review the data from experimental studies aimed at investigating behavioral, hormonal, functional and molecular consequences of exposure to stressful events during prenatal or early postnatal life that might contribute to later psychopathology. The use of the newest methodology in the field and the intensive efforts produced by researchers have opened the possibility to reveal the complex, finely tuned and previously unappreciated sets of molecular interactions between different factors that are critical for neurodevelopment thus leading to important discoveries regarding perinatal life. The major focus of our work has been to revise and discuss data from animal studies supporting the role of neuronal plasticity in the long-term effects produced by developmental adversities on brain function as well as the possible implications for disease vulnerability. We believe these studies might prove useful for the identification of novel targets for more effective pharmacological treatments of mental illnesses.

The mesolimbic dopamine reward circuit in depression

The neural circuitry that mediates mood under normal and abnormal conditions remains incompletely understood. Most attention in the field has focused on hippocampal and frontal cortical regions for their role in depression and antidepressant action. While these regions no doubt play important roles in these phenomena, there is compelling evidence that other brain regions are also involved. Here we focus on the potential role of the nucleus accumbens (NAc; ventral striatum) and its dopaminergic input from the ventral tegmental area (VTA), which form the mesolimbic dopamine system, in depression. The mesolimbic dopamine system is most often associated with the rewarding effects of food, sex, and drugs of abuse. Given the prominence of anhedonia, reduced motivation, and decreased energy level in most individuals with depression, we propose that the NAc and VTA contribute importantly to the pathophysiology and symptomatology of depression and may even be involved in its etiology. We review recent studies showing that manipulations of key proteins (e.g. CREB, dynorphin, BDNF, MCH, or Clock) within the VTA-NAc circuit of rodents produce unique behavioral phenotypes, some of which are directly relevant to depression. Studies of these and other proteins in the mesolimbic dopamine system have established novel approaches to modeling key symptoms of depression in animals, and could enable the development of antidepressant medications with fundamentally new mechanisms of action.

New approaches to antidepressant drug discovery: beyond monoamines

All available antidepressant medications are based on serendipitous discoveries of the clinical efficacy of two classes of antidepressants more than 50 years ago. These tricyclic and monoamine oxidase inhibitor antidepressants were subsequently found to promote serotonin or noradrenaline function in the brain. Newer agents are more specific but have the same core mechanisms of action in promoting these monoamine neurotransmitters. This is unfortunate, because only approximately 50% of individuals with depression show full remission in response to these mechanisms. This review summarizes the obstacles that have hindered the development of non-monoamine-based antidepressants, and provides a progress report on some of the most promising current strategies.