BDNF protein expression in the hippocampus following exposure of rats to forced swimming stress

Sildenafil prevents chronic psychosocial stress-induced working memory impairment: Role of brain-derived neurotrophic factor

Background

Psychosocial stress, a common feature in modern societies, impairs cognitive functions. It is suggested that stress hormones and elevated excitatory amino acids during stress are responsible for stress-induced cognitive deficits. Reduced brain-derived neurotrophic factor (BDNF) levels, increased oxidative stress, and alteration of synaptic plasticity biomarkers are also possible contributors to the negative impact of stress on learning and memory. Sildenafil citrate is a selective phosphodiesterase type 5 (PDE5) inhibitor and the first oral therapy for the treatment of erectile dysfunction. It has been shown that sildenafil improves learning and memory and possesses antioxidant properties. We hypothesized that administering sildenafil to stressed rats prevents the cognitive deficit induced by chronic psychosocial stress.

Methods

Psychosocial stress was generated using the intruder model. Sildenafil 3 mg/kg/day was administered intraperitoneally to animals. Behavioral studies were conducted to test spatial learning and memory using the radial arm water maze. Then, the hippocampal BDNF level and several antioxidant markers were assessed.

Results

This study revealed that chronic psychosocial stress impaired short-term but not long-term memory. The administration of sildenafil prevented this short-term memory impairment. Chronic psychosocial stress markedly reduced the level of hippocampal BDNF (P˂0.05), and this reduction in BDNF was normalized by sildenafil treatment. In addition, neither chronic psychosocial stress nor sildenafil significantly altered the activity of measured oxidative parameters (P > 0.05).

Conclusion

Chronic psychosocial stress induces short-term memory impairment. The administration of sildenafil citrate prevented this impairment, possibly by normalizing the level of BDNF.

Cranial electrotherapy stimulation alleviates depression-like behavior of post-stroke depression rats by upregulating GPX4-mediated BDNF expression

To elucidate whether cranial electrotherapy stimulation (CES) improves depression-like behavior of post-stroke depression (PSD) via regulation of glutathione peroxidase 4 (GPX4)-mediated brain-derived neurotrophic factor (BDNF) expression. Middle cerebral artery occlusion (MCAO) and chronic unpredictable mild stress (CUMS) were used to develop a rat PSD model. CES was applied, and RAS-selective lethal 3 (RSL3) was injected into the hippocampus to inhibit GPX4 in PSD rats. The depression behavior was detected by sucrose preference and forced swimming tests. The structure and morphology of the hippocampus were observed and analyzed by histopathological hematoxylin-eosin (HE) staining. The mRNA and protein expressions of GPX4 and BDNF in the hippocampus were detected by qRT-PCR, western blot and immunohistochemical analysis.The degeneration and necrosis of hippocampal neurons, the depression-like behavior were severer and the expression of BDNF in the hippocampus were decreased in PSD rats than those in MCAO and control groups. CES promoted the hippocampal neuron repair, alleviated the depression-like behavior and increased the expression of BDNF in PSD rats. The inhibition of GPX4 by RSL3 exacerbated the depression-like behavior and decreased the expression of BDNF in PSD rats. In addition, we found that RSL3 disrupted the positive effects of CES on the PSD rats. Conclusion: CES improves depression-like behavior of PSD rats through upregulation of GPX4-mediated BDNF expression in the hippocampus.

Evaluation of the Effect of Hypericum triquetrifolium Turra on Memory Impairment Induced by Chronic Psychosocial Stress in Rats: Role of BDNF

BACKGROUND

Chronic psychosocial stress impairs memory function and leads to a depression-like phenotype induced by a persistent status of oxidative stress. Hypericum perforatum L. (St. John's wort) is widely used to relieve symptoms of anxiety and depression; however, its long-term use is associated with adverse effects. Hypericum triquetrifolium Turra is closely related to H. perforatum. Both plants belong to Hypericaceae family and share many biologically active compounds. Previous work by our group showed that methanolic extracts of H. triquetrifolium have potent antioxidant activity as well as high hypericin content, a component that proved to have stress-relieving and antidepressant effects by other studies. Therefore, we hypothesized that H. triquetrifolium would reduce stress-induced cognitive impairment in a rat model of chronic stress.

OBJECTIVE

To determine whether chronic treatment with H. triquetrifolium protects against stress-associated memory deficits and to investigate a possible mechanism.

METHODS

The radial arm water maze (RAWM) was used to test learning and memory in rats exposed to daily stress using the resident-intruder paradigm. Stressed and unstressed rats received chronic H. triquetrifolium or vehicle. We also measured levels of brain-derived neurotrophic factor (BDNF) in the hippocampus, cortex and cerebellum.

RESULTS

Neither chronic stress nor chronic H. triquetrifolium administration affected performance during acquisition. However, memory tests in the RAWM showed that chronic stress impaired different post-encoding memory stages. H. triquetrifolium prevented this impairment. Furthermore, hippocampal BDNF levels were markedly lower in stressed animals than in unstressed animals, and chronic administration of H triquetrifolium chronic administration protected against this reduction. No significant difference was observed in the effects of chronic stress and/or H. triquetrifolium treatment on BDNF levels in the cerebellum and cortex.

CONCLUSION

H. triquetrifolium extract can oppose stress-associated hippocampus-dependent memory deficits in a mechanism that may involve BDNF in the hippocampus.

Immobility behavior during the forced swim test correlates with BNDF levels in the frontal cortex, but not with cognitive impairments

The forced swim test (FST) is widely used to evaluate the antidepressant-like activity of compounds and is sensitive to stimuli that cause depression-like behaviors in rodents. The immobility behavior observed during the test has been considered to represent behavioral despair. In addition, some studies suggest that the FST impairs rats' performance on cognitive tests, but these findings have rarely been explored. Thus, we investigated the effects of the FST on behavioral tests related to neuropsychiatric diseases that involve different cognitive components: novel object recognition (NOR), the object location test (OLT) and prepulse inhibition (PPI). Brain-derived neurotrophic factor (BDNF) levels in the frontal cortex and hippocampus were evaluated. The rats were forced to swim twice (15-min session followed by a 5-min session 24h later) and underwent cognitive tests 24h after the last swimming exposure. The FST impaired the rats' performance on the OLT and reduced the PPI and acoustic startle responses, whereas the NOR was not affected. The cognitive impairments were not correlated with an immobility behavior profile, but a significant negative correlation between the frontal BDNF levels and immobility behavior was identified. These findings suggest a protective role of BDNF against behavioral despair and demonstrate a deleterious effect of the FST on spatial memory and pre-attentive processes, which point to the FST as a tool to induce cognitive impairments analogous to those observed in depression and in other neuropsychiatric disorders.

The Role of Neurotrophins in Major Depressive Disorder

Neurotrophins and other growth factors have been advanced as critical modulators of depressive behavior. Support for this model is based on analyses of knockout and transgenic mouse models, human genetic studies, and screens for gene products that are regulated by depressive behavior and/or antidepressants. Even subtle alteration in the regulated secretion of brain-derived neurotrophic factor (BDNF), for example, due to a single nucleotide polymorphism (SNP)-encoded Val-Met substitution in proBDNF that affects processing and sorting, impacts behavior and cognition. Alterations in growth factor expression result in changes in neurogenesis as well as structural changes in neuronal cytoarchitecture, including effects on dendritic length and spine density, in the hippocampus, nucleus accumbens, and prefrontal cortex. These changes have the potential to impact the plasticity and stability of synapses in the CNS, and the complex brain circuitry that regulates behavior. Here we review the role that neurotrophins play in the modulation of depressive behavior, and the downstream signaling targets they regulate that potentially mediate these behavioral pro-depressant and antidepressant effects.