Central Brain-derived Neurotrophic Factor Levels Research Articles

The Gut-Brain Axis, BDNF, NMDA and CNS Disorders

Gastro-intestinal (GI) microbiota and the 'gut-brain axis' are proving to be increasingly relevant to early brain development and the emergence of psychiatric disorders. This review focuses on the influence of the GI tract on Brain-Derived Neurotrophic Factor (BDNF) and its relationship with receptors for N-methyl-D-aspartate (NMDAR), as these are believed to be involved in synaptic plasticity and cognitive function. NMDAR may be associated with the development of schizophrenia and a range of other psychopathologies including neurodegenerative disorders, depression and dementias. An analysis of the routes and mechanisms by which the GI microbiota contribute to the pathophysiology of BDNF-induced NMDAR dysfunction could yield new insights relevant to developing novel therapeutics for schizophrenia and related disorders. In the absence of GI microbes, central BDNF levels are reduced and this inhibits the maintenance of NMDAR production. A reduction of NMDAR input onto GABA inhibitory interneurons causes disinhibition of glutamatergic output which disrupts the central signal-to-noise ratio and leads to aberrant synaptic behaviour and cognitive deficits. Gut microbiota can modulate BDNF function in the CNS, via changes in neurotransmitter function by affecting modulatory mechanisms such as the kynurenine pathway, or by changes in the availability and actions of short chain fatty acids (SCFAs) in the brain. Interrupting these cycles by inducing changes in the gut microbiota using probiotics, prebiotics or antimicrobial drugs has been found promising as a preventative or therapeutic measure to counteract behavioural deficits and these may be useful to supplement the actions of drugs in the treatment of CNS disorders.

The role of brain‐derived neurotrophic factor in learned fear processing: an awake rat fMRI study

Brain‐derived neurotrophic factor (BDNF) signaling is implicated in the etiology of many psychiatric disorders associated with altered emotional processing. Altered peripheral (plasma) BDNF levels have been proposed as a biomarker for neuropsychiatric disease risk in humans. However, the relationship between peripheral and central BDNF levels and emotional brain activation is unknown. We used heterozygous BDNF knockdown rats (BDNF +/−) to examine the effects of genetic variation in the BDNF gene on peripheral and central BDNF levels and emotional brain activation as assessed by awake functional magnetic resonance imaging (fMRI). BDNF +/− and control rats were trained to associate a flashing light (conditioned stimulus; CS) with foot‐shock, and brain activation in response to the CS was measured 24 h later in awake rats using fMRI. Central and peripheral BDNF levels were decreased in BDNF +/− rats compared with control rats. Activation of fear circuitry (amygdala, periaqueductal gray, granular insular) was seen in control animals; however, activation of this circuitry was absent in BDNF +/− animals. Behavioral experiments confirmed impaired conditioned fear responses in BDNF +/− rats, despite intact innate fear responses. These data confirm a positive correlation [r = 0.86, 95% confidence interval (0.55, 0.96); P = 0.0004] between peripheral and central BDNF levels and indicate a functional relationship between BDNF levels and emotional brain activation as assessed by fMRI. The results demonstrate the use of rodent fMRI as a sensitive tool for measuring brain function in preclinical translational studies using genetically modified rats and support the use of peripheral BDNF as a biomarker of central affective processing.

Fucosterol, a sterol extracted from Sargassum fusiforme, shows antidepressant and anticonvulsant effects

We previously showed that extracts of Sargassum fusiforme significantly reduce immobility time in the forced swim test and tail suspension test, suggesting that these extracts possess antidepressant-like effects. Here, fucosterol extracted from S. fusiforme was evaluated for antidepressant and anticonvulsant activities in mice. Fucosterol (10, 20, 30 and 40mg/kg) significantly shortened immobility time in the forced swim test and tail suspension test for30min after treatment but had no effect on locomotor activity in the open field test. Fucosterol significantly increased serotonin, norepinephrine and the metabolite 5-hydroxyindoleacetic acid in mouse brain, suggesting that the effects of fucosterol may be mediated through these neurotransmitters. As assessed using maximal electroshock, fucosterol (20, 40, 100mg/kg) possessed anticonvulsant activity, whereas rotarod toxicity test results indicated that fucosterol did not induce neurotoxicity at the same dose levels in mice. Thus, fucosterol may be a useful antidepressant adjunct candidate for treating depression in patients with epilepsy. A significant increase in hippocampal brain-derived neurotrophic factor (BDNF) levels was found in the fucosterol 20mg/kg group (P<0.05). Our findings suggested that fucosterol may possess an antidepressant-like effect, which may be mediated by increasing central BDNF levels.

Hypothalamic-pituitary-adrenal system, neurotrophic factors and clozapine response: association with FKBP5 and NTRK2 genes.

Clozapine is an atypical antipsychotic drug known as being more effective compared with traditional antipsychotics for patients with poor response or resistance to treatment. It has been demonstrated that clozapine modulates hypothalamic-pituitary-adrenal activity and affects central brain-derived neurotrophic factor levels, which could explain part of its therapeutic efficacy. In this study, we investigated the role of genes related to the hypothalamic-pituitary-adrenal axis (FKBP5 and NR3C1) and neurotrophic factors (BDNF and NTRK2) in clinical response to clozapine in 591 schizophrenia patients. We found significant allelic and genotype associations between FKBP5-rs1360780, NTRK2-rs1778929 and NTRK2-rs10465180 polymorphisms and clozapine response. The haplotypes composed of rs1360780-rs3777747-rs17542466-rs2766533 (FKBP5) and rs1619120-rs1778929-rs10465180 (NTRK2) were also nominally significant. Our results suggest that genetic variability in FKBP5 and NTRK2 genes may partially explain clinical response to clozapine. Further studies are needed to clarify the involvement of these genes in clinical response to atypical antipsychotics.

Plasma brain-derived neurotrophic factor in women after bariatric surgery: a pilot study

Eighteen morbidly obese women had plasma brain-derived neurotrophic factor (BDNF) measured before bariatric surgery and 3 months postoperatively. We analyzed plasma BDNF levels in all the participants then subdivided according to menopausal status and type of surgery. Brain-derived neurotrophic factor decreased significantly in all the participants and in the premenopausal group when looked at in isolation.

Potential antidepressant properties of cysteamine on hippocampal BDNF levels and behavioral despair in mice

Several studies have demonstrated that antidepressants increase central brain-derived neurotrophic factor (BDNF) levels, suggesting that BDNF signaling is important for the therapeutic mechanism of antidepressants. Recent work has found that cysteamine and its related agent, cystamine, are neuroprotective in Huntington's disease mice, and act by enhancing the secretion of central BDNF. In the present study, the potential antidepressant effects of cysteamine were examined by behavioral paradigms and biochemical assay. Male BALB/CByJ mice were given a single dose of normal saline, 10 mg/kg of imipramine or either 50, 100 or 200 mg/kg of cysteamine (i.p.) 30 min before undergoing the forced-swimming test (FST) or the tail suspension test (TST). Other groups of mice treated with the same drugs and doses, without behavioral tests, were sacrificed for hippocampal BDNF measurements. We found that, compared with the control group, the cysteamine 200-mg/kg group showed a significant reduction in immobility time in the FST ( P < 0.01) and TST ( P < 0.01), and showed lower activity in the open field test ( P < 0.01). A significant increase in hippocampal BDNF levels was found in the cysteamine 200-mg/kg group ( P < 0.05). Our findings suggested that cysteamine may possess an antidepressant-like effect, which may be mediated by increasing central BDNF levels.

Cysteamine-related agents could be potential antidepressants through increasing central BDNF levels

Major depressive disorder (MDD) is a common mental disease, but with an unknown etiology. Antidepressants are the main biological treatment for MDD. However, current antidepressive agents have a slow onset of effect and a substantial proportion of MDD patients do not clinically improve, despite maximal medication. Thus, the exploration for new antidepressants with novel strategies may help to develop faster and more effective antidepressant agents. Studies in the recent decades have demonstrated that antidepressants increase central brain-derived neurotrophic factor (BDNF) levels and activating the BDNF-signaling pathway may play an important role in their therapeutic mechanism. Cysteamine is a natural product of cells and constitutes the terminal region of the CoA molecule. Recent work has found that cysteamine and a related agent, cystamine, have neuroprotective effects in Huntington's disease (HD) mice, through enhancing central BDNF levels. Furthermore, cystamine or cysteamine injection could increase serum BDNF levels in wild-type mice as well as HD mice. Since activation of the BDNF-dependent pathway plays an important role in the mechanism of antidepressant therapeutic action, cystamine or its derivatives could have potential antidepressant therapeutic effects. Among these agents, pantethine may be one of the most promising agents. It is a naturally occurring compound which can be administered orally with negligible side effects, and is metabolized to cysteamine. Further evaluation of the therapeutic and toxic effects of these cysteamine-related antidepressant agents in MDD animal models is needed before any clinical application.

Possible involvement of the BDNF-dependent pathway in treatment-emergent suicidality or decreased response to antidepressants

Antidepressants are the main biological treatment for major depression. However, a substantial proportion of depressed patients do not improve clinically despite appropriate treatment and, in rare cases, antidepressants can induce or increase suicidal tendencies. These phenomena are more commonly found in young patients. The causes underlying treatment-emergent suicidality or poor response to antidepressants are still unknown. Animal and postmortem studies have demonstrated that antidepressants increase central brain-derived neurotrophic factor (BDNF) levels and activate the BDNF-tyrosine kinase receptor B (TrkB) pathway, which plays an important role in their therapeutic mechanism. In this report, several possible mechanisms relating to the BDNF-dependent pathway are proposed to account for treatment-emergent suicidality and poor response to antidepressants. These include: (1) antidepressant-induced reduction in central BDNF expression acutely; (2) antidepressant dose-dependent effect on central BDNF levels; (3) age-related effect of antidepressants on BDNF expression; (4) overexpression of truncated TrkB or underexpression of full-length TrkB; (5) TrkB pathway dysfunction and (6) antidepressant-induced mania due to increased central BDNF levels. Further exploration of these hypotheses would help to design specific treatment strategies for depressed patients who have experienced unfavourable responses to antidepressant treatment.