BDNF induces in vivo long-lasting enhancement of synaptic transmission and structural reorganization at the hippocampal mossy fibers in a transcription and translation-independent manner

Alternating current stimulation promotes neurite outgrowth and plasticity in neurons through activation of the PI3K/AKT signaling pathway

As a commonly used physical intervention, electrical stimulation (ES) has been demonstrated to be effective in the treatment of central nervous system disorders. Currently, researchers are studying the effects of electrical stimulation on individual neurons and neural networks, which are dependent on factors such as stimulation intensity, duration, location, and neuronal properties. However, the exact mechanism of action of electrical stimulation remains unclear. In some cases, repeated or prolonged electrical stimulation can lead to changes in the morphology or function of the neuron. In this study, immunofluorescence staining and Sholl analysis are used to assess changes in the neurite number and axon length to determine the optimal pattern and stimulation parameters of ES for neurons. Neuronal death and plasticity are detected by TUNEL staining and microelectrode array assays, respectively. mRNA sequencing and bioinformatics analysis are applied to predict the key targets of the action of ES on neurons, and the identified targets are validated by western blot analysis and qRT-PCR. The effects of alternating current stimulation (ACS) on neurons are more significant than those of direct current stimulation (DCS), and the optimal parameters are 3 μA and 20 min. ACS stimulation significantly increases the number of neurites, the length of axons and the spontaneous electrical activity of neurons, significantly elevates the expression of growth-associated protein-43 (GAP-43) without significant changes in the expression of neurotrophic factors. Furthermore, application of PI3K/AKT-specific inhibitors significantly abolishes the beneficial effects of ACS on neurons, confirming that the PI3K/AKT pathway is an important potential signaling pathway in the action of ACS.

BDNF and Lactate as Modulators of Hippocampal CA3 Network Physiology

Growing evidence supports the notion that brain-derived neurotrophic factor (BDNF) and lactate are potent modulators of mammalian brain function. The modulatory actions of those biomolecules influence a wide range of neuronal responses, from the shaping of neuronal excitability to the induction and expression of structural and synaptic plasticity. The biological actions of BDNF and lactate are mediated by their cognate receptors and specific transporters located in the neuronal membrane. Canonical functions of BDNF occur via the tropomyosin-related kinase B receptor (TrkB), whereas lactate acts via monocarboxylate transporters or the hydroxycarboxylic acid receptor 1 (HCAR1). Both receptors are highly expressed in the central nervous system, and some of their physiological actions are particularly well characterized in the hippocampus, a brain structure involved in the neurophysiology of learning and memory. The multifarious neuronal circuitry between the axons of the dentate gyrus granule cells, mossy fibers (MF), and pyramidal neurons of area CA3 is of great interest given its role in specific mnemonic processes and involvement in a growing number of brain disorders. Whereas the modulation exerted by BDNF via TrkB has been extensively studied, the influence of lactate via HCAR1 on the properties of the MF-CA3 circuit is an emerging field. In this review, we discuss the role of both systems in the modulation of brain physiology, with emphasis on the hippocampal CA3 network. We complement this review with original data that suggest cross-modulation is exerted by these two independent neuromodulatory systems.

Brief environmental enrichment elicits metaplasticity on the insular cortex in vivo and reduces the strength of conditioned taste aversion

Environmental enrichment (EE) is known to improve memory and cognition and modulate the impact of aversive stimuli in animals, promoting the development of resilience to stressful situations. Likewise, it is known that EE can modulate synaptic plasticity as is the case of long-term potentiation (LTP). These findings have been described initially in ex vivo preparations, suggesting that the effects of EE are the result of an early modification of the synaptic excitability and transmission. In this regard, it is known that metaplasticity refers to the persistent modification, by previous activity, in the ability to induce synaptic plasticity. Our previous studies have shown that prior training in conditioned taste aversion (CTA) prevents the subsequent induction of LTP in the projection from the basolateral nucleus of the amygdala (Bla) to the insular cortex (IC) in vivo. In addition, we have shown that CTA extinction allows the induction but not the maintenance of IC-LTP of the Bla-IC pathway. Recently, we also showed that prior exposure to environmental enrichment for three weeks reduces the strength of CTA, restoring the brain-derived neurotrophic factor (BDNF) levels in the IC. The present study aimed to analyze the effects of brief exposure to an enriched environment on the strength of aversive memory, as well as on the in vivo IC-LTP. To do so, adult rats were exposed for seven days to an EE, either before CTA training or LTP induction in the Bla-IC pathway. Our results demonstrate that a seven-day exposure to an enriched environment attenuates the aversive response to a strong CTA and allows the induction but not the maintenance of LTP in the insular cortex. These findings provide evidence that metaplastic regulation in a neocortical region takes part in the mechanisms through which brief exposure to enriched environments attenuates an aversive response.

Serum brain injury biomarkers are gestationally and post-natally regulated in non-brain injured neonates

BACKGROUND

To determine the association of gestational age (GA) and day of life (DOL) with the circulating serum concentration of six brain injury-associated biomarkers in non-brain injured neonates born between 23 and 41 weeks' GA.

METHODS

In a multicenter prospective observational cohort study, serum CNS-insult, inflammatory and trophic proteins concentrations were measured daily in the first 7 DOL.

RESULTS

Overall, 3232 serum samples were analyzed from 745 enrollees, median GA 32.3 weeks. BDNF increased 3.7% and IL-8 increased 8.9% each week of gestation. VEGF, IL-6, and IL-10 showed no relationship with GA. VEGF increased 10.8% and IL-8 18.9%, each DOL. IL-6 decreased by 15.8% each DOL. IL-10 decreased by 81.4% each DOL for DOL 0-3. BDNF did not change with DOL. Only 49.67% of samples had detectable GFAP and 33.15% had detectable NRGN. The odds of having detectable GFAP and NRGN increased by 53% and 11%, respectively, each week after 36 weeks' GA. The odds of having detectable GFAP and NRGN decreased by 15% and 8%, respectively, each DOL.

CONCLUSIONS

BDNF and IL-8 serum concentrations vary with GA. VEGF and interleukin concentrations are dynamic in the first week of life, suggesting circulating levels should be adjusted for GA and DOL for clinically relevant assessment of brain injury.

IMPACT

Normative data of six brain injury-related biomarkers is being proposed. When interpreting serum concentrations of brain injury biomarkers, it is key to adjust for gestational age at birth and day of life during the first week to correctly assess for clinical brain injury in neonates. Variation in levels of some biomarkers may be related to gestational and postnatal age and not necessarily pathology.

Behavioral changes and brain epigenetic alterations induced by maternal deficiencies of B vitamins in a mouse model

RATIONALE

B vitamins play essential roles in brain development and functionality; however, the effects of their deficiency during early life on mental health are not thoroughly understood.

OBJECTIVES

The objective of this study is to investigate the effects of a maternal deficiency of vitamin B6, B9 (folate), and B12 on behavioral changes in adult offspring.

METHODS

Female C57BL/6 J mice were put on a diet lacking vitamin B6, B9, B12, or the above three vitamins from pregnancy to weaning. The growth and developmental characteristics of both the pregnant mothers and offspring were collected. In the adult offspring, the serum levels of neuroactive substances were measured using an enzyme-linked immunosorbent assay. The level of BDNF and dimethylated lysine 9 on histone H3 (H3K9me2) was detected by immunohistochemical staining. In addition, their depressive-like behaviors, anxiety-like behaviors, and sociability were recorded using sucrose preference, a forced swim, social interaction, tail suspension, and open field tests.

RESULTS

The maternal deficiency of the three B vitamins delayed offspring development. Compared to the controls, all of the groups showed decreased serum levels of 5-HT and neuropeptide Y. In the groups with deficiency of B9 or the three B vitamins, there were significant changes in sociability and social novelty preference. In groups with deficiencies in B9, B12, or all three B vitamins, the expression levels of BDNF and H3K9me2 in the hippocampus were significantly decreased.

CONCLUSIONS

Maternal deficiencies of the major B vitamins caused changes in social behaviors in adult mice accompanied with epigenetic alterations in the brain and changes in the serum levels of neuroactive substances.

Sulfated Polysaccharide Isolated from the Nacre of Pearl Oyster Improves Scopolamine-Induced Memory Impairment

Pearl and nacre have been used in traditional medicines for treating brain dysfunctions, such as epilepsy, myopia, palpitations and convulsions. We previously showed that a pearl oyster nacre extract improves scopolamine-induced memory impairments using the Y-maze, Banes maze and object recognition tests. In this study, we aimed to isolate the memory-improving substance using ion-exchange column chromatography and reverse-phase column chromatography and elucidate the molecular mechanism underlying its memory-improving activity. The isolated substance was found to be a sulfated polysaccharide with a molecular weight of approximately 750 kDa. Monosaccharide composition analysis showed that it was rich in galactose, glucose, mannose and uronic acid. Furthermore, the mRNA expression levels of oxidative stress, inflammatory response and neuroprotective factors in the cerebral cortex were investigated. Treatment with the polysaccharide increased the expression levels of the antioxidant enzymes Cu, Zn -superoxide dismutase (SOD) and catalase and attenuated the scopolamine-mediated upregulation of the inflammatory cytokines interleukin-1 and interleukin-6. In addition, the polysaccharide suppressed the decrease in the expression levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). These findings strongly suggest that the polysaccharide in the nacre extract mediated its antiamnesic effects by preventing oxidative stress and inflammation and increasing the expression levels of BDNF and NGF.

mTOR inhibition impairs extinction memory reconsolidation

Fear-motivated avoidance extinction memory is prone to hippocampal brain-derived neurotrophic factor (BDNF)-dependent reconsolidation upon recall. Here, we show that extinction memory recall activates mammalian target of rapamycin (mTOR) in dorsal CA1, and that post-recall inhibition of this kinase hinders avoidance extinction memory persistence and recovers the learned aversive response. Importantly, coadministration of recombinant BDNF impedes the behavioral effect of hippocampal mTOR inhibition. Our results demonstrate that mTOR signaling is necessary for fear-motivated avoidance extinction memory reconsolidation and suggests that BDNF acts downstream mTOR in a protein synthesis-independent manner to maintain the reactivated extinction memory trace.

Hippocampal neural cell degeneration and memory deficit in high-fat diet-induced postnatal obese rats- exploring the comparable benefits of choline and DHA or environmental enrichment

Purpose: Childhood obesity increases risk for neural dysfunctions causing learning and memory deficits. The objective of the study is to identify the effects of high fat diet-induced obesity in postnatal period on serum lipids, memory and neural cell survival in hippocampus and compare the role of choline and DHA or environmental enrichment in attenuating the alterationsMaterials and methods: 21 day postnatal male Sprague Dawley rats were assigned as Normal control [NC] fed normal chow diet, Obesity-induced [OB] fed high fat diet, Obesity-induced fed choline & DHA [OB + CHO + DHA], Obesity-induced environmental enrichment [OB + EE] [n = 8/group]. Memory was assessed using radial arm maze. Subsequently blood was collected for serum lipid analysis and rats were euthanized. 5 µm hippocampal sections were processed for cresyl-violet stain. Surviving neural cells were counted using 100 µm scale.Results: Memory errors were significantly higher [p < 0.001, 0.01] in OB compared to same in NC rats. Mean number of surviving neural cells in hippocampus of OB was significantly lesser [p < 0.01] compared to same in NC. Interventions in OB + CHO + DHA and OB + EE significantly attenuated [p < 0.01] memory errors and number of surviving neural cells in hippocampus [CA1, CA3 and DG] compared to same in OB. Moreover, hippocampal neural cell survival was found to be inversely related to serum lipid profile in OB group and was attenuated in OB + CHO + DHA and OB + EE rats.Conclusions: High fat diet-induced postnatal obesity in rats causes CA1/CA3 hippocampal neuro-degeneration and memory deficits. Supplementation of choline and DHA in obese rats attenuates these deficits.