Brain-derived neurotrophic factor-deficient mice develop aggressiveness and hyperphagia in conjunction with brain serotonergic abnormalities

Persistent activation of select forebrain regions in aggressive, adolescent cocaine-treated hamsters

Hamsters repeatedly exposed to cocaine throughout adolescence display highly escalated offensive aggression compared to saline-treated littermates. The current study investigated whether adolescent cocaine exposure activated neurons in areas of hamster forebrain implicated in aggressive behavior by examining the expression of FOS, i.e., the protein product of the immediate early gene c-fos shown to be a reliably sensitive marker of neuronal activation. Adolescent cocaine-treated hamsters and saline-treated littermates were scored for offensive aggression and then sacrificed 1 day later and examined for the number of FOS immunoreactive (FOS-ir) cells in regions of the hamster forebrain important for aggression control. When compared with non-aggressive, saline-treated controls, aggressive cocaine-treated hamsters showed persistent increases in the number of FOS-ir cells in several aggression regions, including the anterior hypothalamus, nucleus circularis, lateral hypothalamus (i.e., the hypothalamic attack area), lateral septum, and medial and corticomedial amygdaloid nuclei. Conversely, aggressive cocaine-treated hamsters showed a significant decrease in FOS-ir cells in the medial supraoptic nucleus, bed nucleus of the stria terminalis, and central amygdala when compared with controls. However, no differences in FOS-ir cells were found in other areas implicated in aggression such as the paraventricular hypothalamic nucleus, or in a number of non-aggression areas. These results suggest that adolescent cocaine exposure may constitutively activate neurons in select forebrain areas critical for the regulation of aggression in hamsters. A model for how persistent activation of neurons in one of these brain regions (i.e., the hypothalamus) may facilitate the development of the aggressive phenotype in adolescent cocaine-exposed animals is presented.

Mutation screen of the brain derived neurotrophic factor gene (BDNF): identification of several genetic variants and association studies in patients with obesity, eating disorders, and attention-deficit/hyperactivity disorder

Several lines of evidence indicate an involvement of brain derived neurotrophic factor (BDNF) in body weight regulation and activity: heterozygous Bdnf knockout mice (Bdnf(+/-)) are hyperphagic, obese, and hyperactive; furthermore, central infusion of BDNF leads to severe, dose-dependent appetite suppression and weight loss in rats. We searched for the role of BDNF variants in obesity, eating disorders, and attention-deficit/hyperactivity disorder (ADHD). A mutation screen (SSCP and DHPLC) of the translated region of BDNF in 183 extremely obese children and adolescents and 187 underweight students was performed. Additionally, we genotyped two common polymorphisms (rs6265: p.V66M; c.-46C > T) in 118 patients with anorexia nervosa, 80 patients with bulimia nervosa, 88 patients with ADHD, and 96 normal weight controls. Three rare variants (c.5C > T: p.T2I; c.273G > A; c.*137A > G) and the known polymorphism (p.V66M) were identified. A role of the I2 allele in the etiology of obesity cannot be excluded. We found no association between p.V66M or the additionally genotyped variant c.-46C > T and obesity, ADHD or eating disorders. This article contains supplementary material, which may be viewed at the American Journal of Medical Genetics website at http://www.interscience.wiley.com/jpages/0148-7299:1/suppmat/index.html.

Loss of brain-derived neurotrophic factor gene allele exacerbates brain monoamine deficiencies and increases stress abnormalities of serotonin transporter knockout mice

To study the neurochemical and behavioral effects of altered brain-derived neurotrophic factor (BDNF) expression on a brain serotonin system with diminished serotonin transport capability, a double-mutant mouse model was developed by interbreeding serotonin transporter (SERT) knockout mice with BDNF heterozygous knockout mice (BDNF +/-), producing SERT -/- x BDNF +/- (sb) mice. Prior evidence implicates serotonin and SERT in anxiety and stress responses. Some studies have shown that BDNF supports serotonergic neuronal development, leading to our hypothesis that reduced BDNF availability during development might exaggerate the consequences of absent SERT function. In the present study, brain serotonin and 5-hydroxyindol acetic acid concentrations in male sb mice were significantly reduced in the hippocampus and hypothalamus compared with wild-type control SB mice, BDNF-deficient Sb mice, and serotonin transporter knockout sB mice. The sb mice had significantly increased anxiety-like behaviors compared with SB, Sb, and sB mice as measured on the elevated plus maze test. These sb mice also had significantly greater increases in plasma adrenocorticotrophic hormone than mice with other genotypes after a stressful stimulus. Analysis of neuronal morphology showed that hypothalamic and hippocampal neurons exhibited 25-30% reductions in dendrites in sb mice compared with SB control mice. These findings support the hypothesis that genetic changes in BDNF expression interact with serotonin and other circuits that modulate anxiety and stress-related behaviors. Thus, this double-mutant mouse model should prove valuable in studying other gene x gene consequences for brain plasticity as well as in evaluating epistatic interactions of BDNF and serotonin transporter gene polymorphisms in neuropsychiatric disorders.

Genetic alterations of the murine serotonergic gene pathway: the neurodevelopmental basis of anxiety

The relative contribution of genetic and environmental factors in the configuration of behavioral differences is among the most prolonged and contentious controversies in intellectual history. Although current views emphasize the joint influence of genes and environmental sources during early brain development, the physiological complexities of multiple gene-gene and gene-environment interactions in the developmental neurobiology of fear and anxiety remain elusive. Variation in genes coding for proteins that control serotonin (5-hydroxytryptamine, 5-HT) system development and plasticity, establish 5-HT neuron identity, and modulate 5-HT receptor-mediated signal transduction as well as cellular pathways have been implicated in the genetics of anxiety and related disorders. This review selects anxiety and avoidance as paradigmatic traits and behaviors, and it focuses on mouse models that have been modified by deletion of genes coding for key players of serotonergic neurotransmission. In particular, pertinent approaches regarding phenotypic changes in mice bearing inactivation mutations of 5-HT receptors, 5-HT transporter, and monoamine oxidase A and other genes related to 5-HT signaling will be discussed and major findings highlighted.

Association of BDNF with restricting anorexia nervosa and minimum body mass index: a family-based association study of eight European populations

Eating disorders (ED), such as anorexia nervosa (AN) and bulimia nervosa (BN), are complex psychiatric disorders where different genetic and environmental factors are involved. Several lines of evidence support that brain-derived neurotrophic factor (BDNF) plays an essential role in eating behaviour and that alterations on this neurotrophic system participates in the susceptibility to both AN and BN. Accordingly, intraventricular administration of BDNF in rats determines food starvation and body weight loss, while BDNF or its specific receptor NTRK2 knockout mice develop obesity and hyperphagia. Case-control studies also suggest a BDNF contribution in the aetiology of ED: we have previously reported a strong association between the Met66 variant within the BDNF gene, restricting AN (ANR) and minimum body mass index (minBMI) in a Spanish sample, and a positive association between the Val66Met and -270C/T BDNF SNPs and ED in six different European populations. To replicate these results, avoiding population stratification effects, we recruited 453 ED trios from eight European centres and performed a family-based association study. Both haplotype relative risk (HRR) and haplotype-based haplotype relative risk (HHRR) methods showed a positive association between the Met66 allele and ANR. Consistently, we also observed an effect of the Met66 variant on low minBMI and a preferential transmission of the -270C/Met66 haplotype to the affected ANR offspring. These results support the involvement of BDNF in eating behaviour and further suggest its participation in the genetic susceptibility to ED, mainly ANR and low minBMI.

Exploring the relationship between serotonin and brain-derived neurotrophic factor: analysis of BDNF protein and extraneuronal 5-HT in mice with reduced serotonin transporter or BDNF expression

Serotonin (5-HT) has been proposed to promote neuronal plasticity during the treatment of mood and anxiety disorders and following neurodegenerative insult by altering the expression of critical genes including brain-derived neurotrophic factor (BDNF). In this study, mice with constitutive reductions in the serotonin transporter (SERT) or BDNF were investigated to further assess the functional relationship between serotonin neurotransmission and BDNF expression. Using a modified extraction procedure and a commercial enzyme-linked immunosorbant assay, 50% decreases in BDNF protein in hippocampus, frontal cortex and brain stem were confirmed in 4-month-old mice lacking one copy of the BDNF gene (BDNF(+/-)). By contrast, 4-month-old male and female mice with partial (SERT(+/-)) or complete (SERT(-/-)) reductions in SERT expression showed no differences in BDNF protein levels compared to SERT(+/+) mice, although male SERT knockout mice of all genotypes had higher BDNF levels in hippocampus, frontal cortex, and brain stem than female animals. Microdialysis also was performed in BDNF(+/-) mice. In addition to other phenotypic aspects suggestive of altered serotonin neurotransmission, BDNF(+/-) mice show accelerated age-related degeneration of 5-HT forebrain innervation. Nevertheless, extracellular 5-HT levels determined by zero net flux microdialysis were similar between BDNF(+/+) and BDNF(+/-) mice in striatum and frontal cortex at 8-12 months of age. These data illustrate that a 50% decrease in BDNF does not appear to be sufficient to cause measurable changes in basal extracellular 5-HT concentrations and, furthermore, that constitutive reductions in SERT expression are not associated with altered BDNF protein levels at the ages and in the brain regions examined in this study.

A neural signaling triumvirate that influences ageing and age-related disease: insulin/IGF-1, BDNF and serotonin

The ageing process and its associated diseases all involve perturbed energy metabolism, oxidative damage, and an impaired ability of the organism and its cells to cope with adversity. We propose that some specific signaling pathways in the brain may be important determinants of health during ageing. Among such specific signaling modalities are those activated in neurons by insulin-like growth factors (IGFs), brain-derived neurotrophic factor (BDNF) and serotonin. This triumvirate may be particularly important because of their cooperative influence on energy metabolism, food intake, stress responses and cardiovascular function. The health benefits to the periphery and central nervous system of dietary restriction and exercise may be mediated by this triumvirate of signals in the brain. At the molecular level, BDNF, serotonin and IGFs can all stimulate the production of proteins involved in cellular stress adaptation, growth and repair, neurogenesis, learning and memory and cell survival. The importance of this triumvirate is emphasized when it is seen that their general roles in energy metabolism, stress adaptation and disease resistance are conserved among diverse organisms consistent with important roles in the ageing process.

No changes in serum ghrelin levels in female patients with bulimia nervosa

It has been reported that fasting plasma ghrelin levels may play a role in the pathophysiology of eating disorders. In this study, the authors examined whether serum levels of ghrelin were altered in the patients with bulimia nervosa (BN). We enrolled 18 female patients with BN, and 21 age-matched female controls for this study. Eating-related psychopathology, depressive symptoms were evaluated by using the Bulimic Investigatory Test, Edinburgh (BITE) and the 17-item Hamilton Depression Rating Scale (HDRS). Serum levels of ghrelin were measured by Ghrelin enzyme immunoassay kit. There were no significant differences in serum ghrelin levels between the patients with BN and normal controls. Furthermore, the authors did not found correlation between serum ghrelin levels and clinical parameters in the patients with BN. Our study suggests that serum ghrelin levels in the patients with BN were indistinguishable from normal controls. Therefore, it is unlikely that ghrelin plays a role in the pathophysiology of BN.

Dicyclohexylphthalate causes hyperactivity in the rat concomitantly with impairment of tyrosine hydroxylase immunoreactivity

Endocrine disruptors possibly exert effects on neuronal functions leading, in particular, to behavioural alterations. In this study, we examined the effects of dicyclohexylphthalate (DCHP), an endocrine disruptor, on rat behavioural and cellular responses. Single intracisternal administration of DCHP (0.87-87 nmol) into 5-day-old male Wistar rats caused significant hyperactivity at 4-5 weeks of age. It was about 1.4-fold more active in the nocturnal phase after administration of 87 nmol of DCHP than control rats (p < 0.001). The response had a tendency to be dose-dependent. Based on DNA macoarray analyses, DCHP down-regulated the levels of gene expression of the dopamine D4 receptor at 4 weeks old in both the midbrain and the striatum, and the dopamine transporter in the midbrain at 8 weeks old 1.7- to 2-fold. The gene expression of several subtypes of glutamate receptors was facilitated in the striatum at 4 weeks old and in the midbrain at 8 weeks old. Some normalization and/or compensatory changes seemed to occur in gene expression of GABA or glycine transmission. Furthermore, DCHP abolished immunoreactivity of tyrosine hydroxylase in the substantia nigra at 8 weeks of age, where TUNEL-positive cells were seen. We conclude that DCHP affected the developing rat brain, resulting in hyperactivity, probably as a result of degeneration of mesencephalic tyrosine hydroxylase rather than alteration of the level of gene expression.

The effect of escitalopram, desipramine, electroconvulsive seizures and lithium on brain-derived neurotrophic factor mRNA and protein expression in the rat brain and the correlation to 5-HT and 5-HIAA levels

The reported increase in brain-derived neurotrophic factor (BDNF) mRNA expression after antidepressant treatment is a cornerstone of the BDNF hypothesis of antidepressant action. However, if this increase becomes manifest on the BDNF protein level is unknown. In the present study we performed parallel measurements of BDNF mRNA and protein expression in the frontal cortex and hippocampus of the rat after chronic treatment with electroconvulsive seizures (ECS), lithium, desipramine or escitalopram. ECS increased BDNF mRNA and protein in the hippocampus and BDNF protein in the frontal cortex. Desipramine moderately increased BDNF mRNA expression in the dentate gyrus but did not change BDNF protein in neither region. Escitalopram did not affect BDNF mRNA expression, but decreased BDNF protein in the frontal cortex and the hippocampus. Lithium increased BDNF protein levels in the hippocampus and frontal cortex, but overall decreased BDNF mRNA expression. Thus, here we report a striking non-correspondence between changes in BDNF mRNA and protein expression induced by the antidepressant treatments and lithium. Further, increased expression of BDNF mRNA or protein was not a common action of the treatments. We also investigated if treatment-induced modulations of the tissue contents of 5-hydroxytryptamine (5-HT) and its metabolite, 5-hydroxy-indoleacetic acid (5-HIAA), were related to changes in BDNF mRNA or protein expression. No correlation was found. However, all treatments increased 5-HT levels in the hippocampus.

Spreading depression induces long-lasting brain protection against infarcted lesion development via BDNF gene-dependent mechanism

Preconditioning the rat brain with spreading depression for 48 h induces potent ischemic tolerance (infarct tolerance) after an interval of 12-15 days, consequently reducing the infarcted lesion size in the acute phase following focal cerebral ischemia. However, persistence of the morphological and functional neuroprotection has not yet been proven. We tested whether tolerance-derived neuroprotection against focal cerebral ischemia persists or merely delays the progress of cerebral infarction. Prolonged spreading depression was induced in mice by placing a depolarized focus with intracerebral microinfusion of KCl for 24 h; after intervals of 3, 6, 9 or 12 days, temporary focal ischemia was imposed. In the analysis of the infarcted lesion volume 24 h after ischemia, groups with 6 or 9 day interval demonstrated significantly smaller lesion volume compared to time-matched vehicle control group (P=0.002). Significant reduction in cerebral infarction was also observed at the chronic phase, namely 14 days after ischemia (33% reduction) (P=0.021) accompanied with less severe neurological deficits (38% reduction) (P=0.020). Using this technique, we also investigated if the mice with targeted disruption of a single BDNF allele (heterozygous BDNF-deficient mice) can gain the same potency of tolerance as the wild mice. In the result on infarcted lesion volumes following temporary focal ischemia, potent tolerance developed in the wild type (35% reduction) (P=0.007) but not in the heterozygous BDNF-deficient mice (<19% reduction) (P=0.155), indicating that BDNF expression level following spreading depression is contributing to infarct tolerance development.

Opposite changes in the serum brain-derived neurotrophic factor in anorexia nervosa and obesity

OBJECTIVE

A role for the brain-derived neurotrophic factor (BDNF) in the regulation of eating behavior has been recently demonstrated. Therefore, the possibility exists that alterations in BDNF production and/or activity are involved in the pathophysiology of anorexia nervosa (AN) and obesity.

METHODS

We measured morning serum levels of BDNF in 22 women with AN, 24 women with obesity (body mass index [BMI] > 30 kg/m2), and 27 nonobese healthy women. All the subjects were drug-free and underwent a clinical assessment by means of rating scales measuring both eating-related psychopathology and depressive symptoms.

RESULTS

As compared with the nonobese healthy controls, circulating BDNF was significantly reduced in AN patients and significantly increased in obese subjects. No significant difference was observed in serum BDNF concentrations between AN women with or without a comorbid depressive disorder. Moreover, serum BDNF levels were significantly and positively correlated with the subjects' body weight and BMI.

CONCLUSION

The BDNF changes observed in AN and obesity are likely secondary adaptive mechanisms aimed at counteracting the change in energy balance that occurs in these syndromes.

Brain-derived neurotrophic factor

Since the purification of BDNF in 1982, a great deal of evidence has mounted for its central roles in brain development, physiology, and pathology. Aside from its importance in neural development and cell survival, BDNF appears essential to molecular mechanisms of synaptic plasticity. Basic activity-related changes in the central nervous system are thought to depend on BDNF modification of synaptic transmission, especially in the hippocampus and neocortex. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders.

p-Nitrotoluene causes hyperactivity in the rat

It has not been known which endocrine disruptors exert their effects on neuronal functions, particularly leading to behavioral alterations. To address this, we examined the effects of p-nitrotoluene, an endocrine disruptor, on rat behavior and gene expression. Single intracisternal administration of p-nitrotoluene (ca. 10 microg) into 5-day-old male Wistar rats caused significant hyperactivity at 4-5 weeks of age. They were about 1.4-fold more active in the nocturnal phase after administration of p-nitrotoluene than control rats. Based on DNA array analyses, p-nitrotoluene decreased more than two-fold the levels of gene expression of the mesencephalic dopamine transporter at 8 weeks old. Thus, it was demonstrated for the first time that p-nitrotoluene definitely affected the developing brain, resulting in hyperactivity in the rat.

Critical role of brain-derived neurotrophic factor in mood disorders

The purpose of this review is to integrate what is currently known about the role of brain-derived neurotrophic factor (BDNF) in the pathophysiology of mood disorders including major depressive disorder (MDD) and bipolar disorder (BD). We reviewed the pre-clinical and clinical papers demonstrating that BDNF plays a role in the pathophysiology of mood disorders and in the mechanism of action of therapeutic agents. Pre-clinical studies suggest that the expression of BDNF might be a downstream target of antidepressant treatments and mood stabilizers such as lithium and valproate, and that BDNF exerts antidepressant activity in animal models of depression. Furthermore, BDNF protects against stress-induced neuronal damage, and it might affect neurogenesis in the hippocampus, which is thought to be involved in the pathogenesis of mood disorders. Clinical studies have demonstrated that serum levels of BDNF in drug-naive patients with MDD are significantly decreased as compared with normal controls, and that BDNF might be an important agent for therapeutic recovery from MDD. Moreover, recent findings from family-based association studies have suggested that the BDNF gene is a potential risk locus for the development of BD. These findings suggest that BDNF plays a critical role in the pathophysiology of mood disorders and in the activity of therapeutic agents in patients with mood disorders. New agents capable of enhancing BDNF levels may lead aid the development of novel therapeutic drugs for patients with mood disorders.

Late onset loss of hippocampal 5-HT and NE is accompanied by increases in BDNF protein expression in mice co-expressing mutant APP and PS1

Transgenic mice expressing both mutant amyloid precursor protein (APPswe) and presenilin-1 (PS1DeltaE9) develop amyloid deposits as early as 4 months of age and preliminary evidence suggests that this may be associated with degenerative changes in serotonin axons innervating the dentate gyrus of the hippocampus. In the present investigation, which focused on further delineating the effects of amyloid deposition on hippocampal neurochemistry, decreases in serotonin neurotransmitter levels (-25%) were discovered to be present at 18 months in APP+/PS1+ mice, while norepinephrine was reduced in the hippocampus of 12- (-30%) and 18-month-old (-45%) APP+/PS1+ double mutants. In addition, brain-derived neurotrophic factor (BDNF) protein levels were investigated since changes in BDNF are reported to occur in AD, and BDNF has been shown to have trophic effects on serotonin and norepinephrine neurons. In doubly, but not singly mutant mice, hippocampal BDNF levels were increased at 12 (+70%) and 18 months (+170%). Furthermore, in a different model of serotonergic and noradrenergic degeneration, BDNF protein levels were similarly increased in response to depletions in hippocampal serotonin and norepinephrine caused by the chemical neurotoxin 1-methyl-4-(2'-aminophenyl)-1,2,3,6-tetrahydropyridine (2'-NH2-MPTP). These findings show that early amyloid deposition in mice expressing mutant human APP and PS-1 is associated with a progressive loss of serotonin and norepinephrine neurotransmitter levels in the hippocampus later in life. Furthermore, BDNF protein levels are increased in APP+/PS1+ and 2'-NH2-MPTP-treated mice, possibly as a compensatory response to serotonergic and noradrenergic neurodegeneration in a brain region important for learning and memory.

Transgenic mice overexpressing the full-length neurotrophin receptor trkB exhibit increased activation of the trkB-PLCgamma pathway, reduced anxiety, and facilitated learning

We have investigated the biochemical, physiological, and behavioral properties of transgenic mice overexpressing the full-length neurotrophin receptor trkB (trkB.TK+). The highest trkB.TK+ mRNA overexpression was achieved in the cerebral cortex and hippocampal subfields, both areas also showing strongly increased trkB.TK+ receptor protein expression and phosphorylation. Furthermore, as a result of trkB.TK+ overexpression, partial activation of trkB downstream signaling was observed. Phosphorylation of phospholipaseCgamma-1 was increased but unexpectedly, the expression and phosphorylation levels of signaling molecules Shc and mitogen-activated protein kinase (MAPK) were unaltered. Behavioral studies revealed improved learning and memory in the water maze, contextual fear conditioning, and conditioned taste aversion tests, and reduced anxiety in the elevated plus maze (EPM) and light-dark exploration tests in trkB.TK+ transgenic mice. Electrophysiological studies revealed a reduced long-term potentiation (LTP) at the Schaffer collateral-CA1 synapse in trkB.TK+ mice. Altogether, overexpression of the trkB.TK+ receptor postnatally leads to selective activation of trkB signaling pathways and enhanced learning and memory.

Essential role of brain-derived neurotrophic factor in adult hippocampal function

Brain-derived neurotrophic factor (BDNF) regulates neuronal development and function. However, it has been difficult to discern its role in the adult brain in influencing complex behavior. Here, we use a recently developed inducible knockout system to show that deleting BDNF in broad forebrain regions of adult mice impairs hippocampal-dependent learning and long-term potentiation. We use the inducible nature of this system to show that the loss of BDNF during earlier stages of development causes hyperactivity and more pronounced hippocampal-dependent learning deficits. We also demonstrate that the loss of forebrain BDNF attenuates the actions of desipramine, an antidepressant, in the forced swim test, suggesting the involvement of BDNF in antidepressant efficacy. These results establish roles for BDNF in the adult, and demonstrate the strength of this inducible knockout system in studying gene function in the adult brain.

Expression of the neurotrophin receptor trkB is regulated by the cAMP/CREB pathway in neurons

trkB as receptor for neurotrophins brain-derived neurotrophic factor (BDNF)/neurotrophin (NT)-4/5 plays a crucial role during development, maintenance of the adult brain, and its adaptation to injury or pathological conditions. In spite of this, very little is known about the mechanisms that regulate its expression. Here, we show that forskolin (Fk) rapidly stimulates the expression of both the full-length and truncated trkB isoforms in primary cultures of cortical neurons. Gel shift assays and transient transfection experiments demonstrate that this activation occurs via a protein kinase A (PKA)/cyclic AMP-responsive element-binding protein (CREB)-dependent mechanism. Activated CREB binds to the second cyclic AMP (cAMP)-responsive element (CRE) of the two CRE sites located within the P2 promoter of the trkB gene, which is able to confer cAMP responsiveness to a heterologous promoter. Our results illustrate that the trkB gene is a target for CREB regulation and explain the increase of trkB expression produced in different adaptative responses of the nervous system where CREB is participating.

Minireview: A hypothalamic role in energy balance with special emphasis on leptin

The hypothalamus is a major site for integration of central and peripheral signals that regulate energy homeostasis. Within the hypothalamus, neurons residing in the ARC (arcuate nucleus)-PVN (paraventricular)-PF/LH (perifornical/lateral hypothalamus) axis communicate among each other and are subjected to the influence of several peripheral factors, including leptin and insulin. Proper signaling in the hypothalamus by leptin, a long-sought peripheral factor that relays the status of fat stores, is critical to normal regulation of food intake and body weight. Leptin action in the hypothalamus is mediated by a large number of orexigenic and anorectic peptide-producing neurons of the ARC-PVN-PF/LH axis. Not only the classical JAK2 (Janus kinase 2)-STAT3 (signal transducer and activator of transcription 3) pathway, but also the phosphatidylinositol-3 kinase-phosphodiesterase 3B-cAMP pathway mediates hypothalamic leptin receptor signaling. It appears that hypothalamic leptin resistance, possibly due to defective nutritional regulation of leptin receptor expression and/or reduced STAT3 signaling in the hypothalamus, contributes to the development of obesity associated with high-fat feeding and aging. Interestingly, hypothalamic neurons may develop leptin resistance despite an intact JAK2-STAT3 signaling path. The role of suppressor of cytokine signaling 3 and other negative regulators of leptin signaling in central leptin resistance needs to be established, an important area of future investigation. Further understanding of the neural circuitry and leptin signaling in the hypothalamus is critical not only for the advancement of our knowledge on the hypothalamic role in energy balance but also for future development of drugs for the attenuation or treatment of obesity and related disorders in humans.

A mechanism underlying mature-onset obesity: evidence from the hyperphagic phenotype of brain-derived neurotrophic factor mutants

Mice deficient in brain-derived neurotrophic factor (BDNF) develop mature-onset obesity, primarily due to overeating. To gain insight into the mechanism of this hyperphagia, we characterized food intake, body weight, meal pattern, and meal microstructure in young and mature mice fed balanced or high-fat diets. Hyperphagia and obesity occurred in mature but not young BDNF mutants fed a balanced diet. This hyperphagia was mediated by increased meal number, which was associated with normal meal size, meal duration, and satiety ratio. In contrast, the high-fat diet induced premature development of hyperphagia and obesity in young BDNF mutants and a similar magnitude hyperphagia in mature mutants. This hyperphagia was supported by increased meal size and was accompanied by a reduced satiety ratio. Thus the mechanism underlying hyperphagia was present before significant weight gain, but whether it occurred, and whether meal frequency or meal size was altered to support it, was modulated by a process associated with aging and by diet properties. Meal pattern changes associated with the balanced diet suggested meal initiation, and the oropharyngeal positive feedback that drives feeding, were enhanced and might have contributed to overeating in BDNF mutants, whereas negative feedback was normal. Consistent with this hypothesis, meal microstructure revealed that all hyperphagic mutant groups exhibited increased intake rates at meal onset. Therefore, the central nervous system targets of BDNF actions may include orosensory brain stem neurons that process and transmit positive feedback or forebrain neurons that modulate its strength.

Association between the brain-derived neurotrophic factor 196G/A polymorphism and eating disorders

Several lines of evidence suggest that genetic factors might contribute to the pathogenesis of eating disorders and that brain-derived neurotrophic factor (BDNF) plays a role in the pathophysiology of eating disorders. To investigate the role of the BDNF gene in the susceptibility to eating disorders, we analyzed the BDNF 196G/A gene polymorphism in female patients with eating disorders and female normal controls. The difference in the genotype frequency between patients (n = 198) and normal controls (n = 222) was statistically significant (P = 0.029). Interestingly, a significant (P = 0.015) difference in the genotype frequency between normal controls and bulimia nervosa patients (n = 101) with binge-purging type was detected. This study suggests that the BDNF 196G/A gene polymorphism might be associated with a susceptibility to eating disorders.

Prenatal cocaine exposure decreases brain-derived neurotrophic factor proteins in the rat brain

The pregnant rats received daily sc injections of cocaine (30 mg/kg) or saline from the gestational day (GD) 7 to GD 20. At 1 week postnatal, all pups were killed and the hippocampus, cortex and striatum were dissected out. Levels of brain-derived neurotrophic factor (BDNF) under the basal condition and depolarization with high potassium (40 mM) were measured. The results showed that hippocampal BDNF levels under basal and depolarization conditions were all significantly lower in the pups prenatally exposed to cocaine than those exposed to saline. There were no significant differences in basal BDNF levels between the cocaine and saline groups in the cortex or striatum. However, the prenatally cocaine-treated pups showed significantly less BDNF release following high potassium depolarization than the saline-treated animals did in both these regions. The results support the suggestion that prenatal cocaine exposure decreases BDNF expression in the offspring.

New insights into the mechanisms of antidepressant therapy

Depressive disorders are among the most frequent psychiatric diseases in the Western world with prevalence numbers between 9% and 18%. They are characterized by depressed mood, a diminished interest in pleasurable activities, feelings of worthlessness or inappropriate guilt, decrease in appetite and libido, insomnia, and recurrent thoughts of death or suicide. Among other findings, reduced activity of monoaminergic neurotransmission has been postulated to play a role in the pathogenesis of depression. Consistent with this hypothesis, most antidepressive drugs exert their action by elevating the concentration of monoamines in the synaptic cleft. However, it is not the enhancement of monoaminergic signaling per se, but rather long-term, adaptive changes that may underlie the therapeutic effect. These include functional and structural changes that are discussed later. In addition, in the last years, evidence has emerged that remissions induced in patients using lithium or electroconvulsive therapy are accompanied by structural changes in neuronal networks thereby affecting synaptic plasticity in various regions of the brain.

Mice with reduced brain-derived neurotrophic factor expression show decreased choline acetyltransferase activity, but regular brain monoamine levels and unaltered emotional behavior

The "neurotrophin hypothesis" of depression predicts that depressive disorders in humans coincide with a decreased activity and/or expression of brain-derived neurotrophic factor (BDNF) in the brain. Therefore, we investigated whether mice with a reduced BDNF expression due to heterozygous gene disruption demonstrate depression-like neurochemical changes or behavioral symptoms. BNDF protein levels of adult BDNF(+/-) mice were reduced to about 60% in several brain areas investigated, including the hippocampus, frontal cortex, striatum, and hypothalamus. The content of monoamines (serotonin, norepinephrine, and dopamine) as well as of serotonin and dopamine degradation products was unchanged in these brain regions. By contrast, choline acetyltransferase activity was significantly reduced by 19% in the hippocampus of BDNF(+/-) mice, indicating that the cholinergic system of the basal forebrain is critically dependent on sufficient endogenous BDNF levels in adulthood. Moreover, BDNF(+/-) mice exhibited normal corticosterone and adrenocorticotropic hormone (ACTH) serum levels under baseline conditions and following immobilization stress. In a panel of behavioral tests investigating locomotor activity, exploration, anxiety, fear-associated learning, and behavioral despair, BDNF(+/-) mice were indistinguishable from wild-type littermates. Thus, a chronic reduction of BDNF protein content in adult mice is not sufficient to induce neurochemical or behavioral alterations that are reminiscent of depressive symptoms in humans.

Experimental gene interaction studies with SERT mutant mice as models for human polygenic and epistatic traits and disorders

Current evidence indicates that virtually all neuropsychiatric disorders, like many other common medical disorders, are genetically complex, with combined influences from multiple interacting genes, as well as from the environment. However, additive or epistatic gene interactions have proved quite difficult to detect and evaluate in human studies. Mouse phenotypes, including behaviors and drug responses, can provide relevant models for human disorders. Studies of gene-gene interactions in mice could thus help efforts to understand the molecular genetic bases of complex human disorders. The serotonin transporter (SERT, 5-HTT, SLC6A4) provides a relevant model for studying such interactions for several reasons: human variants in SERT have been associated with several neuropsychiatric and other medical disorders and quantitative traits; SERT blockers are effective treatments for a number of neuropsychiatric disorders; there is a good initial understanding of the phenotypic features of heterozygous and homozygous SERT knockout mice; and there is an expanding understanding of the interactions between variations in SERT expression and variations in the expression of a number of other genes of interest for neuropsychiatry and neuropharmacology. This paper provides examples of experimentally-obtained interactions between quantitative variations in SERT gene expression and variations in the expression of five other mouse genes: DAT, NET, MAOA, 5-HT(1B) and BDNF. In humans, all six of these genes possess polymorphisms that have been independently investigated as candidates for neuropsychiatric and other disorders in a total of > 500 reports. In the experimental studies in mice reviewed here, gene-gene interactions resulted in either synergistic, antagonistic (including 'rescue' or 'complementation') or more complex, quantitative alterations. These were identified in comparisons of the behavioral, physiological and neurochemical phenotypes of wildtype mice vs. mice with single allele or single gene targeted disruptions and mice with partial or complete disruptions of multiple genes. Several of the descriptive phenotypes could be best understood on the basis of intermediate, quantitative alterations such as brain serotonin differences. We discuss the ways in which these interactions could provide models for studies of gene-gene interactions in complex human neuropsychiatric and other disorders to which SERT may contribute, including developmental disorders, obesity, polysubstance abuse and others.

Bisphenol A causes hyperactivity in the rat concomitantly with impairment of tyrosine hydroxylase immunoreactivity

We examined the effects of bisphenol A, an endocrine disruptor, on rat behavioral and cellular responses. Single intracisternal administration of bisphenol A (0.2-20 microg) into 5-day-old male Wistar rats caused significant hyperactivity at 4-5 weeks of age. Rats were about 1.6-fold more active in the nocturnal phase after administration of both 2 and 20 microg of bisphenol A than were control rats. The response was dose-dependent. Based on DNA macroarray analyses of the midbrain, bisphenol A decreased by more than twofold gene expression levels of the dopamine D4 receptor at 4 weeks of age and the dopamine transporter at 8 weeks of age. Furthermore, bisphenol A decreased by more than twofold gene expression levels of the dopamine D4 receptor at 4 weeks of age and the dopamine transporter at 8 weeks of age. We conclude that bisphenol A affected central dopaminergic system activity, resulting in hyperactivity due most likely to a large reduction of tyrosine hydroxylase activity in the midbrain.

Brain-derived neurotrophic factor as a potential risk locus for bipolar disorder: evidence, limitations, and implications

Brain-derived neurotrophic factor (BDNF) plays an important role in promoting and modifying growth, development, and survival of neuronal populations, and, in the mature nervous system, is involved in activity-dependent neuronal plasticity. Based on several lines of evidence, BDNF has been hypothesized to play an important role in the pathogenesis of mood disorder and the therapeutic action of at least some effective treatments. The gene encoding BDNF lies on the short arm of chromosome 11 in a region where some linkage studies of bipolar disorder have reported evidence for a susceptibility gene. BDNF can, thus, be considered as an attractive candidate gene for involvement in the pathogenesis of bipolar disorder, and two recent family-based association studies have provided evidence that one or more sequence variants within or near the BDNF gene show an association with disease susceptibility. These findings are of great interest and may open up a new chapter in the understanding of the causation and treatment of bipolar disorder. However, it is still early in the genetic investigation of BDNF in bipolar disorder, and it is important that these findings are replicated in large independent samples and that functional studies can confirm and characterize the pathogenic relevance of this genetic variation.

Forebrain-specific trkB-receptor knockout mice: behaviorally more hyperactive than "depressive"

BACKGROUND

According to the neurotrophin hypothesis of depression, decreased activity of brain-derived neurotrophic factor (BDNF) contributes to behavioral and plasticity-related alterations in depressed patients. We investigated the hypothesis that mice with a forebrain-specific knockout of the trkB receptor, the main mediator of BDNF signaling, represent a genetic animal model for depression.

METHODS

Using the CRE-loxP system, we bred trkB(CaMKII-CRE) mice with a trkB-receptor disruption in the forebrain. We subjected trkB-mutant mice to a battery of behavioral tests, comprising open field, elevated zero maze, emergence test, novel object test, and forced swim. Additionally, we investigated the hypothalamic-pituitary-adrenal (HPA) axis immunohistochemically and by plasma analyses.

RESULTS

trkB(CaMKII-CRE) mice showed a stereotyped hyper-locomotion with reduced explorative activity, and impulsive reactions to novel stimuli. The trkB-mutant mice did not exhibit depressionlike behaviors such as increased "despair" in the forced swim test, increased anxiety in the elevated zero maze, or neophobia in the novel object test. Furthermore, no HPA dysregulation was observed under normal and stressful conditions.

CONCLUSIONS

trkB(CaMKII-CRE) mice cannot be regarded as a genetic mouse model of depression. Instead, the behavioral symptoms of trkB(CaMKII-CRE) mice, comprising hyper-locomotion, stereotyped behaviors, and cognitive impairments, are similar to those postulated for mouse models of attention-deficit disorder.

Selectivity in neurotrophin signaling: theme and variations

Neurotrophins are a family of growth factors critical for the development and functioning of the nervous system. Although originally identified as neuronal survival factors, neurotrophins elicit many biological effects, ranging from proliferation to synaptic modulation to axonal pathfinding. Recent data indicate that the nature of the signaling cascades activated by neurotrophins, and the biological responses that ensue, are specified not only by the ligand itself but also by the temporal pattern and spatial location of stimulation. Studies on neurotrophin signaling have revealed variations in the Ras/MAP kinase, PI3 kinase, and phospholipase C pathways, which transmit spatial and temporal information. The anatomy of neurons makes them particularly appropriate for studying how the location and tempo of stimulation determine the signal cascades that are activated by receptor tyrosine kinases such as the Trk receptors. These signaling variations may represent a general mechanism eliciting specificity in growth factor responses.

Anxiety-related traits in mice with modified genes of the serotonergic pathway

The neurobiology of anxiety is complex, reflecting the cumulative physiological effects of multiple genes. These genes are interactive with each other and with the environment in which they are expressed. Variation in genes coding for proteins that control serotonin (5-HT) system development and plasticity, establish 5-HT neuron identity, and modulate 5-HT receptor-mediated signal transduction and cellular pathways have been implicated in the genetics of anxiety and related disorders. Here, we selected anxiety and avoidance as paradigmatic traits and behavior and cover both traditional studies with inbred murine strains and selected lines which have been modified by gene knockout technologies. The design of a mouse model partially or completely lacking a gene of interest during all stages of development (constitutive knockout) or in a spatio-temporal context (conditional knockout) is among the prime strategies directed at elucidating the role of genetic factors in fear and anxiety. In many cases, knockout mice have been able to confirm what has already been anticipated based on pharmacological studies. In other instances, knockout studies have changed views of the relevance of 5-HT homeostasis in brain development and plasticity as well as processes underlying emotional behavior. In this review, we discuss the pertinent literature regarding phenotypic changes in mice bearing inactivation mutations of 5-HT receptors, 5-HT transporter, monoamine oxidase A and other components of the serotonergic pathway. Finally, we attempt to identify future directions of genetic manipulation in animal models to advance our understanding of brain dysregulation characteristic of anxiety disorders.

Brain-derived neurotrophic factor-dependent unmasking of "silent" synapses in the developing mouse barrel cortex

Brain-derived neurotrophic factor (BDNF) is a critical modulator of central synaptic functions such as long-term potentiation in the hippocampal and visual cortex. Little is known, however, about its role in the development of excitatory glutamatergic synapses in vivo. We investigated the development of N-methyl-D-aspartate (NMDA) receptor (NMDAR)-only synapses (silent synapses) and found that silent synapses were prominent in acute thalamocortical brain slices from BDNF knockout mice even after the critical period. These synapses could be partially converted to alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-containing ones by adding back BDNF alone to the slice or fully converted to together with electric stimulation without affecting NMDAR transmission. Electric stimulation alone was ineffective under the BDNF knockout background. Postsynaptically applied TrkB kinase inhibitor or calcium-chelating reagent blocked this conversion. Furthermore, the AMPAR C-terminal peptides essential for interaction with PDZ proteins postsynaptically prevented the unmasking of silent synapses. These results suggest that endogenous BDNF and neuronal activity synergistically activate AMPAR trafficking into synaptic sites.

Brain-derived neurotrophic factor is required for the maintenance of cortical dendrites

Brain-derived neurotrophic factor (BDNF) is thought to be involved in neuronal survival, migration, morphological and biochemical differentiation, and modulation of synaptic function in the CNS. In the rodent cortex, postnatal BDNF expression is initially low but subsequently increases to reach maximal levels around weaning. Thus, BDNF expression peaks at a time when both structural and functional maturation of cortical circuitry occurs. Although the function of BDNF has been probed using many approaches, its requirements during this phase of life have not previously been examined genetically. To test the in vivo requirements for BDNF during this important phase of development we generated early-onset forebrain-specific BDNF mutant mice. Although these mice undergo forebrain-restricted deletion of BDNF by Cre-mediated recombination during embryogenesis, they are healthy, and we did not detect the loss of specific cortical excitatory or inhibitory neurons. However, the neocortex of 5-week-old mice was thinner, attributable at least partly to neuronal shrinkage. Importantly, although visual cortical layer 2/3 neurons in the mutants initially developed normal dendrite structure, dendritic retraction became apparent by 3 weeks of age. Thus, our observations suggest that cortically expressed BDNF functions to support the maintenance of cortical neuron size and dendrite structure rather than the initial development of these features. This is consistent with a role for BDNF in stabilizing the "survival" of circuitry during the phase of activity-dependent reorganization of cortical connectivity.

Interaction of nitric oxide and serotonin in aggressive behavior

Nitric oxide (NO) modulates many behavioral and neuroendocrine responses. Genetic or pharmacological inhibition of the synthetic enzyme that produces NO in neurons evokes elevated and sustained aggression in male mice. Recently, the excessive aggressive and impulsive traits of neuronal NO synthase knockout (nNOS-/-) mice were shown to be caused by reductions in serotonin (5-HT) turnover and deficient 5-HT1A and 5-HT1B receptor function in brain regions regulating emotion. The consistently high levels of aggression observed in nNOS-/- mice could be reversed by 5-HT precursors and by treatment with specific 5-HT1A and 5-HT1B receptor agonists. The expression of the aggressive phenotype of nNOS-/- knockout mice requires isolated housing prior to testing. The effects of social factors such as housing condition and maternal care can affect 5-HT and aggression, but the interaction among extrinsic factors, 5-HT, NO, and aggression remains unspecified. Taken together, NO appears to play an important role in normal brain 5-HT function and may have significant implications for the treatment of psychiatric disorders characterized by aggressive and impulsive behaviors.

The role of the extracellular signal-regulated kinase signaling pathway in mood modulation

The neurobiological underpinnings of mood modulation, molecular pathophysiology of manic-depressive illness, and therapeutic mechanism of mood stabilizers are largely unknown. The extracellular signal-regulated kinase (ERK) pathway is activated by neurotrophins and other neuroactive chemicals to produce their effects on neuronal differentiation, survival, regeneration, and structural and functional plasticity. We found that lithium and valproate, commonly used mood stabilizers for the treatment of manic-depressive illness, stimulated the ERK pathway in the rat hippocampus and frontal cortex. Both drugs increased the levels of activated phospho-ERK44/42, activated phospho-ribosomal protein S6 kinase-1 (RSK1) (a substrate of ERK), phospho-CREB (cAMP response element-binding protein) and phospho-B cell lymphoma protein-2 antagonist of cell death (substrates of RSK), and BDNF. Inhibiting the ERK pathway with the blood-brain barrier-penetrating mitogen-activated protein kinase (MAP kinase)/ERK kinase (MEK) kinase inhibitor SL327, but not with the nonblood-brain barrier-penetrating MEK inhibitor U0126, decreased immobility time and increased swimming time of rats in the forced-swim test. SL327, but not U0126, also increased locomotion time and distance traveled in a large open field. The behavioral changes in the open field were prevented with chronic lithium pretreatment. SL327-induced behavioral changes are qualitatively similar to the changes induced by amphetamine, a compound that induces relapse in remitted manic patients and mood elevation in normal subjects. These data suggest that the ERK pathway may mediate the antimanic effects of mood stabilizers.

Decreased levels of serum brain-derived neurotrophic factor in female patients with eating disorders

BACKGROUND

Several lines of evidence suggest that brain-derived neurotrophic factor (BDNF) plays a role in the regulation of eating behavior. Because of its role in eating behavior, which is especially relevant to eating disorders, BDNF is an attractive candidate for investigation of potential biological markers of eating disorders such as bulimia nervosa (BN) and anorexia nervosa (AN).

METHODS

We enrolled 18 female patients with BN, 12 female patients with AN, and 21 age-matched female normal control subjects in this study. Eating-related psychopathology and depressive symptoms were evaluated using the Bulimic Investigatory Test, Edinburgh (BITE) and the Hamilton Depression Rating Scale (HDRS). Serum BDNF levels were measured by a sandwich enzyme-linked immunosorbent assay.

RESULTS

Serum levels of BDNF in the patients with AN or BN were significantly (p<.0001) decreased compared with those of normal control subjects, and serum BDNF levels in the patients with AN were significantly (p=.027) lower than those in patients with BN. A significant positive correlation (r=.378, p=.006) between serum BDNF levels and body mass index in all of the subjects was detected. Furthermore, there was a significant positive correlation (r=.435, p=.015) between the BITE symptom scale score and HDRS in these patients.

CONCLUSIONS

The present study suggests that BDNF may play a role in the pathophysiology of eating disorders.

The role of the extracellular signal-regulated kinase signaling pathway in mood modulation

The neurobiological underpinnings of mood modulation, molecular pathophysiology of manic-depressive illness, and therapeutic mechanism of mood stabilizers are largely unknown. The extracellular signal-regulated kinase (ERK) pathway is activated by neurotrophins and other neuroactive chemicals to produce their effects on neuronal differentiation, survival, regeneration, and structural and functional plasticity. We found that lithium and valproate, commonly used mood stabilizers for the treatment of manic-depressive illness, stimulated the ERK pathway in the rat hippocampus and frontal cortex. Both drugs increased the levels of activated phospho-ERK44/42, activated phospho-ribosomal protein S6 kinase-1 (RSK1) (a substrate of ERK), phospho-CREB (cAMP response element-binding protein) and phospho-B cell lymphoma protein-2 antagonist of cell death (substrates of RSK), and BDNF. Inhibiting the ERK pathway with the blood-brain barrier-penetrating mitogen-activated protein kinase (MAP kinase)/ERK kinase (MEK) kinase inhibitor SL327, but not with the nonblood-brain barrier-penetrating MEK inhibitor U0126, decreased immobility time and increased swimming time of rats in the forced-swim test. SL327, but not U0126, also increased locomotion time and distance traveled in a large open field. The behavioral changes in the open field were prevented with chronic lithium pretreatment. SL327-induced behavioral changes are qualitatively similar to the changes induced by amphetamine, a compound that induces relapse in remitted manic patients and mood elevation in normal subjects. These data suggest that the ERK pathway may mediate the antimanic effects of mood stabilizers.

Reduced behavioral effects of cocaine in heterozygous brain-derived neurotrophic factor (BDNF) knockout mice

Brain-derived neurotrophic factor (BDNF) affects the development of brain neurotransmitter systems, including dopamine and serotonin systems that are important for cocaine's rewarding and locomotor stimulatory properties. Human genomic markers within or near the BDNF locus have been linked to or associated with substance abuse. Post-mortem human brain specimens reveal individual differences in the levels of BDNF mRNA and in mRNA splicing patterns. To assess the effects of lifelong alterations in the levels of BDNF expression on a measure of psychostimulant reward, we have compared locomotor stimulant and rewarding effects of cocaine in heterozygous BDNF knockout mice with effects in their wild-type littermates. Heterozygous BDNF knockout mice displayed less locomotion during habituation and less locomotion after cocaine injections. Cocaine-conditioned place preferences were reduced in the BDNF heterozygotes. These mice displayed no significant difference from saline control values at a dose of 10 mg/kg s.c. cocaine, although they exhibited cocaine-induced preference at a 20 mg/kg dose. These data confirm important roles for BDNF in psychostimulant actions, presumably via neurotrophic effects on dopamine and serotonin systems. Furthermore, these data support suggestions that differences in human BDNF expression may underlie associations between markers near the human BDNF gene locus and drug addiction.

The role of estrogen in mood disorders in women

Major depression is twice as common in women as men and depressive episodes appear to be more common in women with bipolar disorder. There is accumulating evidence that, in at least some women, reproductive-related hormonal changes may play a role in increasing the risk of depressive symptoms premenstrually, postpartum and in the perimenopausal period. In this review, the evidence for the role of hormonal fluctuations, specifically estrogen, in triggering depressive symptoms in a subgroup of women is summarized. In addition, the potential role of estrogen in triggering depressive symptoms via its effects on the serotonergic system, brain-derived neurotrophic factor and Protein Kinase C is reviewed.

Sequence variants of the brain-derived neurotrophic factor (BDNF) gene are strongly associated with obsessive-compulsive disorder

We evaluated a possible association between the brain-derived neurotrophic factor (BDNF) gene and susceptibility to obsessive-compulsive disorder (OCD) by genotyping a number of single-nucleotide polymorphisms (SNPs) and one microsatellite marker from the extended BDNF locus in 164 triads with OCD. Extensive background linkage disequilibrium was observed at this locus. Single-locus transmission-distortion tests revealed significant evidence of association with the disease for all the BDNF gene markers tested, including a Val66Met variation affecting the sequence of the proBDNF protein. Analysis of multi-SNP haplotypes provided similar results. Haplotype transmission comparisons in this and previous studies point to a functionally distinct BDNF haplotype uniquely marked by the rare Met66 allele, which is undertransmitted and likely confers a protective effect in OCD and other psychiatric disorders.

Brain-derived neurotrophic factor is required for the maintenance of cortical dendrites

Brain-derived neurotrophic factor (BDNF) is thought to be involved in neuronal survival, migration, morphological and biochemical differentiation, and modulation of synaptic function in the CNS. In the rodent cortex, postnatal BDNF expression is initially low but subsequently increases to reach maximal levels around weaning. Thus, BDNF expression peaks at a time when both structural and functional maturation of cortical circuitry occurs. Although the function of BDNF has been probed using many approaches, its requirements during this phase of life have not previously been examined genetically. To test the in vivo requirements for BDNF during this important phase of development we generated early-onset forebrain-specific BDNF mutant mice. Although these mice undergo forebrain-restricted deletion of BDNF by Cre-mediated recombination during embryogenesis, they are healthy, and we did not detect the loss of specific cortical excitatory or inhibitory neurons. However, the neocortex of 5-week-old mice was thinner, attributable at least partly to neuronal shrinkage. Importantly, although visual cortical layer 2/3 neurons in the mutants initially developed normal dendrite structure, dendritic retraction became apparent by 3 weeks of age. Thus, our observations suggest that cortically expressed BDNF functions to support the maintenance of cortical neuron size and dendrite structure rather than the initial development of these features. This is consistent with a role for BDNF in stabilizing the "survival" of circuitry during the phase of activity-dependent reorganization of cortical connectivity.

The anabolic-androgenic steroid nandrolone induces alterations in the density of serotonergic 5HT1B and 5HT2 receptors in the male rat brain

Anabolic-androgenic steroids (AAS) are partly misused by males in order to become brave and intoxicated and these agents are highly associated with psychosis, disinhibition, aggression and acts of violence. Since such behavioral states have been related to an imbalanced serotonergic system and the involvement of the serotonergic 5HT(1B) and the 5HT(2) receptors, it was important to discern the impact of AAS on these receptors. The objective of our study was to investigate the effects of 2 weeks of treatment with the AAS nandrolone decanoate at three different doses (1, 5, 15 mg/kg/day) on the total specific binding of the radioligands [(125)I]-(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (5HT(2) receptors) by autoradiography. All doses caused a significant down-regulation of the 5HT(1B) receptor density in the hippocampal CA(1) and in the medial globus pallidus and a significant up-regulation of the 5HT(2) receptor density in the nucleus accumbens shell. Alterations in receptor density were also observed in the lateral globus pallidus, ventromedial hypothalamus, the amygdala and in the intermediate layers of various cortex regions. In conclusion, serotonergic 5HT(1B) or 5HT(2) receptors are likely to play important roles in mediating observed emotional states and behavioral changes among AAS abusers.

Glial expression of Borna disease virus phosphoprotein induces behavioral and neurological abnormalities in transgenic mice

One hypothesis for the etiology of behavioral disorders is that infection by a virus induces neuronal cell dysfunctions resulting in a wide range of behavioral abnormalities. However, a direct linkage between viral infections and neurobehavioral disturbances associated with human psychiatric disorders has not been identified. Here, we show that transgenic mice expressing the phosphoprotein (P) of Borna disease virus (BDV) in glial cells develop behavioral abnormalities, such as enhanced intermale aggressiveness, hyperactivity, and spatial reference memory deficit. We demonstrate that the transgenic brains exhibit a significant reduction in brain-derived neurotrophic factor and serotonin receptor expression, as well as a marked decrease in synaptic density. These results demonstrate that glial expression of BDV P leads to behavioral and neurobiological disturbances resembling those in BDV-infected animals. Furthermore, the lack of reactive astrocytosis and neuronal degeneration in the brains indicates that P can directly induce glial cell dysfunction and also suggests that the transgenic mice may exhibit neuropathological and neurophysiological abnormalities resembling those of psychiatric patients. Our results provide a new insight to explore the relationship between viral infections and neurobehavioral disorders.

Neurotrophins

Nerve growth factor was the first identified protein with anti-apoptotic activity on neurons. This prototypic neurotrophic factor, together with the three structurally and functionally related growth factors brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3) and neurotrophin-4/5 (NT4/5), forms the neurotrophin protein family. Target T cells for neurotrophins include many neurons affected by neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and peripheral polyneuropathies. In addition, the neurotrophins act on neurons affected by other neurological and psychiatric pathologies including ischemia, epilepsy, depression and eating disorders. Work with cell cultures and animal models provided solid support for the hypothesis that neurotrophins prevent neuronal death. While no evidence exists that a lack of neurotrophins underlies the etiology of any neurodegenerative disease, these studies have spurred on hopes that neurotrophins might be useful symptomatic-therapeutic agents. However first clinical trials led to variable results and severe side effects were observed. For future therapeutic use of the neurotrophins it is therefore crucial to expand our knowledge about their physiological functions as well as their pharmacokinetic properties. A major challenge is to develop methods for their application in effective doses and in a precisely timed and localized fashion.

Temporal changes in the expression of brain-derived neurotrophic factor mRNA in the ventromedial nucleus of the hypothalamus of the developing rat brain

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family, which is important for the growth, differentiation, and survival of neurons during development. We have performed a detailed mapping of BDNF mRNA in the neonatal rat brain using a quantitative in situ hybridization technique. At postnatal day (PND) 4, hypothalamic structures showed only modest expression of BDNF mRNA, with the exception of the ventromedial nucleus (VMN), where expression was higher than that detected in the hippocampus. Abundant BDNF mRNA was also found in the bed nucleus of the anterior commissure, retrosplenial granular cortex, and the posteroventral part of the medial amygdaloid nucleus. Messenger RNAs encoding other neurotrophins, including nerve growth factor (NGF) and neurotrophin-3 (NT-3) and the BDNF receptor trkB, were not selectively localized in neonatal VMN. During subsequent developmental stages, BDNF mRNA expression in the VMN changed dynamically, peaking at PND 4 and falling to minimal levels in the adult brain. In contrast, the low levels of BDNF mRNA observed in the CA3 region of the hippocampus increased to adult levels following PND 10. As the VMN undergoes sexual differentiation, we compared BDNF, NGF, NT-3, and trkB mRNA expression in the VMN in males and females at embryonic day 20 and PND 4, but found no differences between them. These results suggest that localized and high level expression of BDNF mRNA in the neonatal VMN plays an important role in its neural organization and functional development.