Do two models of acute and chronic stress stimulation influence the amount of nerve growth factor (NGF) and its receptor TrkA in the hippocampal neurons of middle aged rats?

Antidepressant-like effects of Xiaochaihutang in a rat model of chronic unpredictable mild stress

ETHNOPHARMACOLOGICAL RELEVANCE

Xiaochaihutang (XCHT) has been used in China for thousands of years to treat "Shaoyang syndrome", which involves depressive-like symptoms. However, few studies have investigated its antidepressant effects and pharmacological mechanism of action. The present study was designed to confirm the antidepressant effect of XCHT using a chronic unpredictable mild stress (CUMS) model and explore its potential mechanism of action by investigating the monoamine neurotransmitters (dopamine and 5-hydroxytryptamine) and neurotrophins (BDNF and NGF).

MATERIALS AND METHODS

The CUMS model was established in rats, and the antidepressant effect of XCHT (0.6, 1.7 and 5mg/kg/day, given by gastric gavage for 4 weeks) was investigated using the open field test (OFT), food consumption test and sucrose preference test. The concentrations of 5-HT and DA in the hippocampus were measured by high performance liquid chromatography with electrochemical detection (HPLC-ECD). The expressions of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and their receptors tyrosine receptor kinase B (TrkB) and tyrosine receptor kinase A (TrkA) in the hippocampus were measured by immunohistochemical staining analysis.

RESULTS

CUMS caused a significant decrease in OFT, food consumption and sucrose preference in rats, and these depression-like behaviors were significantly improved by XCHT (1.7 and 5 g/kg/day). Moreover, XCHT significantly increased the concentrations of 5-HT (0.6 and 5 g/kg/day) and DA (5 g/kg/day), and improved the BDNF, NGF, TrkB and TrkA expressions in the hippocampus (1.7 and 5 g/kg/day), which was reduced in CUMS rats.

CONCLUSION

The results obtained suggested that XCHT may have therapeutic actions on depression-like behavior induced by CUMS in rats possibly mediated by increasing the monoamine neurotransmitter concentration and neurotrophin expression in the hippocampus.

Effects of exercise and diet change on cognition function and synaptic plasticity in high fat diet induced obese rats

Background

Nutritional imbalance-induced obesity causes a variety of diseases and in particular is an important cause of cognitive function decline. This study was performed on Sprague Dawley (SD) rats with 13-weeks of high fat diet-induced obesity in connection to the effects of regular exercise and dietary control for 8 weeks on the synaptic plasticity and cognitive abilities of brain.

Methods

Four weeks-old SD rats were adopted classified into normal-normal diet-sedentary (NNS, n = 8), obesity-high fat diet-sedentary (OHS, n = 8), obesity-high fat diet-training (OHT, n = 8), obesity-normal diet-sedentary (ONS, n = 8) and obesity- normal diet-training (ONT, n = 8). The exercise program consisted of a treadmill exercise administered at a speed of 8 m/min for 1–4 weeks, and 14 m/min for 5–8 weeks. The Western blot method was used to measure the expression of NGF, BDNF, p38MAPK and p-p38MAPK proteins in hippocampus of the brain, and expressions of NGF, BDNF, TrkA, TrkB, CREB and synapsin1 mRNA were analyzed through qRT-PCR.

Results

The results suggest cognitive function-related protein levels and mRNA expression to be significantly decreased in the hippocampus of obese rats, and synaptic plasticity as well as cognitive function signaling sub-pathway factors were also significantly decreased. In addition, 8-weeks exercises and treatment by dietary change had induced significant increase of cognitive function-related protein levels and mRNA expression as well as synaptic plasticity and cognitive function signaling sub-pathway factors in obese rats. In particular, the combined treatment had presented even more positive effect.

Conclusions

Therefore, it was determined that the high fat diet-induced obesity decreases plasticity and cognitive function of the brain, but was identified as being improved by exercises and dietary changes. In particular, it is considered that regular exercise has positive effects on memory span and learning capacity unlike dietary control.

Metabolic syndrome--from the neurotrophic hypothesis to a theory

Metabolic syndrome (MetS) is a complex and heterogeneous disease characterized by central obesity, impaired glucose metabolism, dyslipidemia, arterial hypertension, insulin resistance and high-sensitivity C-reactive protein. In 2006, a neurotrophic hypothesis of the etiopathogenesis of MetS was launched. This hypothesis considered the neurotrophins a key factor in MetS development. Chronic inflammatory and/or psychoemotional distress provoke a series of neuroimmunoendocrine interactions such as increased tissue and plasma levels of proinflammatory cytokines and neurotrophins, vegetodystonia, disbalance of neurotransmitters, hormones and immunity markers, activation of the hypothalamo-pituitary-adrenal axis, insulin resistance, and atherosclerosis. An early and a late clinical stage in the course of MetS are defined. Meanwhile, evidence of supporting results from the world literature accumulates. This enables the transformation of the definition of the neurotrophic hypothesis into a neurotrophic theory of MetS. The important role of two neurotrophic factors, i.e. the nerve growth factor and brain-derived neurotrophic factor as well as of the proinflammatory cytokines, neurotransmitters, adipokines and, especially, of leptin for the development of MetS, obesity and type 2 diabetes mellitus is illustrated. There are reliable scientific arguments that the metabotrophic deficit due to reduced neurotrophins could be implicated in the pathogenesis of MetS, type 2 diabetes mellitus, and atherosclerosis as well. A special attention is paid to the activity of the hypothalamo-pituitary-adrenal axis after stress. The application of the neurotrophic theory of MetS could contribute to the etiological diagnosis and individualized management of MetS by eliminating the chronic distress, hyponeurotrophinemia and consequent pathology. It helps estimating the risk, defining the prognosis and implementing the effective prevention of this socially significant disease as evidenced by the dramatic recent growth of the world publication output on this interdisciplinary topic.

Effects of Inhaled Lavender Essential Oil on Stress-Loaded Animals: Changes in Anxiety-Related Behavior and Expression Levels of Selected mRNAs and Proteins

Inhalation of various essential oils elicits behavioral changes as a consequence of a complex centrally coordinated response. To understand the molecular mechanisms of action of aromatic compounds on emotional responses, we evaluated the stress-induced changes in mouse brain and the efficacy of inhaled essential oil from Lavandula officinalis (LvEO) using two approaches: a behavioral test, and examining the expression levels of selected genes {fast nerve growth factor receptor (NGFR) mRNA, activity regulated cytoskeletal-associated protein (Arc) mRNA} and proteins {galactokinase 1 (GLK1) and brain-derived neurotrophic factor (BDNF)}. Animals were randomly divided into 4 groups depending on the treatment given: stress (-)/H2O, stress (-)/LvEO, stress (+)/H2O, and stress (+)/LvEO group. For behavioral testing, using an elevated plus-maze test, significant anxiolytic-like effects were seen in both the stress (-)/LvEO and stress (+)/LvEO groups, indicating that LvEO exerts anxiolytic-like effects regardless of the administration of water immersion stress. On expression analysis, the levels of NGFR and Arc mRNA were significantly lower in animals subjected to stress. Inhalation of LvEO, however, reversed this change, thus suggesting that LvEO negates the impact of stress on gene expression levels. Meanwhile, significant decreases in expression levels were also observed in the stress (-)/LvEO group, which implies that LvEO, when given in a stress-free situation, may act as a stress stimulus. Taken together, our data suggest that inhalation of LvEO exerts bidirectional influences in the central nervous system (CNS) of animals, either attenuating the effects of stress or acting as a stressor, depending on the subject state.

Antidepressant-like effects of young green barley leaf (Hordeum vulgare L.) in the mouse forced swimming test

BACKGROUND

Young green barley leaf is one of the richest sources of antioxidants and has been widely consumed for health management in Japan. In this study, we examined whether oral administration of young green barley leaf has an antidepressant effect on the forced swimming test in mice.

MATERIALS AND METHODS

Mice were individually forced to swim in an open cylindrical container, one hour after oral administration of young green barley leaf (400 or 1000 mg / kg) or imipramine (100 mg / kg). Expression of mRNA for nerve growth factor (NGF), brain-derived neurotrophic factor, and glucocorticoid receptor in the brain was analyzed using real-time quantitative polymerase chain reaction (PCR).

RESULTS

There was a significant antidepressant-like effect in the forced swimming test; both 400 and 1000 mg / kg young green barley leaves, as well as the positive control imipramine (100 mg / kg), reduced the immobility duration compared to the vehicle group. The expression of mRNA for NGF detected in the hippocampus immediately after the last swimming test was higher than that in the non-swimming group (Nil). Oral administration of imipramine suppressed this increase to the level of the Nil group. Young green barley leaf (400 and 1000 mg / kg) also showed a moderate decrease in the expression of mRNA for NGF, in a dose-dependent manner.

CONCLUSION

Oral administration of young green barley leaf is able to produce an antidepressant-like effect in the forced swimming test. Consequently it is possible that the antidepressant-like effects of the young green barley leaf are, at least in part, mediated by an inhibition of the increase in the hippocampus levels of NGF.

Beneficial effects of benzodiazepine diazepam on chronic stress-induced impairment of hippocampal structural plasticity and depression-like behavior in mice

Whether benzodiazepines (BZDs) have beneficial effects on the progress of chronic stress-induced impairment of hippocampal structural plasticity and major depression is uncertain. The present study designed four preclinical experiments to determine the effects of BZDs using chronic unpredictable stress model. In Experiment 1, several time course studies on behavior and hippocampus response to stress were conducted using the forced swim and tail suspension tests (FST and TST) as well as hippocampal structural plasticity markers. Chronic stress induced depression-like behavior in the FST and TST as well as decreased hippocampal structural plasticity that returned to normal within 3 wk. In Experiment 2, mice received p.o. administration of three diazepam dosages prior to each variate stress session for 4 wk. This treatment significantly antagonized the elevation of stress-induced corticosterone levels. Only low- (0.5mg/kg) and medium-dose (1mg/kg) diazepam blocked the detrimental effects of chronic stress. In Experiment 3, after 7 wk of stress sessions, daily p.o. diazepam administration during 1 wk recovery phase dose-dependently accelerated the recovery of stressed mice. In Experiment 4, 1 wk diazepam administration to control mice enhanced significantly hippocampal structural plasticity and induced an antidepressant-like behavioral effect, whereas 4 wk diazepam administration produced opposite effects. Hence, diazepam can slow the progress of chronic stress-induced detrimental consequences by normalizing glucocorticoid hormones. Considering the adverse effect of long-term diazepam administration on hippocampal plasticity, the preventive effects of diazepam may depend on the proper dose. Short-term diazepam treatment enhances hippocampal structural plasticity and is beneficial to recovery following chronic stress.

Nerve growth factor (NGF) immunoreactive neurons in the juvenile rat hippocampus: response to acute and long-term high-light open-field (HL-OF) or forced swim (FS) stress stimulation

This study aimed at examining and comparing the influence of two different stress stimuli on the density (number of cells/mm²) of nerve growth factor (NGF) containing neurons in the hippocampal CA1 and CA3 pyramidal cell layers and the dentate gyrus (DG) granule cell layer in juvenile rats (P28; P-postnatal day). The high-light open-field (HL-OF) test and forced swim (FS) test were employed to investigate the effects of a single, 15-min acute exposure and repeated (15 min daily for 21 days) long-term exposure to stress. In order to detect NGF-ir neurons, immunohistochemical (-ir) techniques were used. In comparison with nonstressed animals, acute and long-term HL-OF or FS stimulation resulted in a marked increase (P<0.001) in the density of NGF-ir containing cells in all the hippocampal structures. The frequency of stress application (acute vs. long-term), however, did not have a substantial impact on the studied parameter, with the exception of the CA3 sector, where a decreased density (P<0.001) of NGF-ir neurons was observed after long-term exposure to FS. It may be concluded that a rise in the density of NGF-ir neurons in the juvenile rat hippocampus after exposure to HL-OF or FS stressors could have affected the activity of the hypothalamic-pituitary-adrenocortical (HPA) stress axis. Prolonged HL-OF or FS stress was probably aggravating enough not to trigger the habituation process. The type of stressor applied (HL-OF vs. FS) was not essentially a factor determining the density of NGF-ir cells in the hippocampus.

Synergistic NGF/B27 gradients position synapses heterogeneously in 3D micropatterned neural cultures

Native functional brain circuits show different numbers of synapses (synaptic densities) in the cerebral cortex. Until now, different synaptic densities could not be studied in vitro using current cell culture methods for primary neurons. Herein, we present a novel microfluidic based cell culture method that combines 3D micropatterning of hydrogel layers with linear chemical gradient formation. Micropatterned hydrogels were used to encapsulate dissociated cortical neurons in laminar cell layers and neurotrophic factors NGF and B27 were added to influence the formation of synapses. Neurotrophic gradients allowed for the positioning of distinguishable synaptic densities throughout a 3D micropatterned neural culture. NGF and B27 gradients were maintained in the microfluidic device for over two weeks without perfusion pumps by utilizing a refilling procedure. Spatial distribution of synapses was examined with a pre-synaptic marker to determine synaptic densities. From our experiments, we observed that (1) cortical neurons responded only to synergistic NGF/B27 gradients, (2) synaptic density increased proportionally to synergistic NGF/B27 gradients; (3) homogeneous distribution of B27 disturbed cortical neurons in sensing NGF gradients and (4) the cell layer position significantly impacted spatial distribution of synapses.