Requirements of Postnatal proBDNF in the Hippocampus for Spatial Memory Consolidation and Neural Function

Early-life manipulation of the serotonergic system exacerbates the harmful effects of sleep deprivation on cognitive functions

Serotonin is a monoamine neurotransmitter that plays a main role in regulating physiological and cognitive functions. Serotonergic system dysfunction is involved in the etiology of various psychiatric and neurological disorders. Therefore, the present study was designed to investigate the effects of early-life serotonin depletion on cognitive disorders caused by sleep deprivation. Serotonin was depleted by para-chlorophenylalanine (PCPA, 100 mg/kg, s.c.) at postnatal days 10-20, followed by sleep deprivation-induced through the multiple platform apparatus for 24 h at PND 60. After the examination of the novel object recognition and passive avoidance memories, the hippocampi and prefrontal cortex were dissected to examine the brain-derived neurotrophic factor (BDNF) mRNA expression by PCR. Our findings showed that postnatal serotonin depletion and sleep deprivation impaired the novel object recognition and passive avoidance memories and changed the BDNF levels. In the same way, the serotonin depletion in early life before sleep deprivation exacerbated the harmful effects of sleep deprivation on cognitive function and BDNF levels. It can be claimed that the serotonergic system plays a main role in the modulation of sleep and cognitive functions.

Regulation of Neuronal Chloride Homeostasis by Pro- and Mature Brain-Derived Neurotrophic Factor (BDNF) via KCC2 Cation-Chloride Cotransporters in Rat Cortical Neurons

The strength of inhibitory neurotransmission depends on intracellular neuronal chloride concentration, primarily regulated by the activity of cation-chloride cotransporters NKCC1 (Sodium-Potassium-Chloride Cotransporter 1) and KCC2 (Potassium-Chloride Cotransporter 2). Brain-derived neurotrophic factor (BDNF) influences the functioning of these co-transporters. BDNF is synthesized from precursor proteins (proBDNF), which undergo proteolytic cleavage to yield mature BDNF (mBDNF). While previous studies have indicated the involvement of BDNF signaling in the activity of KCC2, its specific mechanisms are unclear. We investigated the interplay between both forms of BDNF and chloride homeostasis in rat hippocampal neurons and in utero electroporated cortices of rat pups, spanning the behavioral, cellular, and molecular levels. We found that both pro- and mBDNF play a comparable role in immature neurons by inhibiting the capacity of neurons to extrude chloride. Additionally, proBDNF increases the endocytosis of KCC2 while maintaining a depolarizing shift of EGABA in maturing neurons. Behaviorally, proBDNF-electroporated rat pups in the somatosensory cortex exhibit sensory deficits, delayed huddling, and cliff avoidance. These findings emphasize the role of BDNF signaling in regulating chloride transport through the modulation of KCC2. In summary, this study provides valuable insights into the intricate interplay between BDNF, chloride homeostasis, and inhibitory synaptic transmission, shedding light on the underlying cellular mechanisms involved.

Exploring Rosiglitazone's Potential to Treat Alzheimer's Disease through the Modulation of Brain-Derived Neurotrophic Factor

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that debilitates over 55 million individuals worldwide. Currently, treatments manage and alleviate its symptoms; however, there is still a need to find a therapy that prevents or halts disease progression. Since AD has been labeled as "type 3 diabetes" due to its similarity in pathological hallmarks, molecular pathways, and comorbidity with type 2 diabetes mellitus (T2DM), there is growing interest in using anti-diabetic drugs for its treatment. Rosiglitazone (RSG) is a peroxisome proliferator-activated receptor-gamma agonist that reduces hyperglycemia and hyperinsulinemia and improves insulin signaling. In cellular and rodent models of T2DM-associated cognitive decline and AD, RSG has been reported to improve cognitive impairment and reverse AD-like pathology; however, results from human clinical trials remain consistently unsuccessful. RSG has also been reported to modulate the expression of brain-derived neurotrophic factor (BDNF), a protein that regulates neuroplasticity and energy homeostasis and is implicated in both AD and T2DM. The present review investigates RSG's limitations and potential therapeutic benefits in pre-clinical models of AD through its modulation of BDNF expression.

An Imbalance in the Pro/mature BDNF Ratio Occurs in Multiple Brain Regions During Normal Ageing in Wild-Type Mice

The early transition to Alzheimer's disease is characterized by a period of accelerated brain atrophy that exceeds normal ageing. Identifying the molecular basis of this atrophy could facilitate the discovery of novel drug targets. The precursor of brain-derived neurotrophic factor, a well characterized neurotrophin, is increased in the hippocampus of aged rodents, while its mature isoform is relatively stable. This imbalance could increase the risk of Alzheimer's disease by precipitating its pathological hallmarks. However, less is known about how relative levels of these isoforms change in middle-aged mice. In addition, the underlying mechanisms that might cause an imbalance are unknown. The main aim of this study was to determine how precursor brain-derived neurotrophic factor changes relative to its mature isoform with normal brain ageing in wild type mice. A secondary aim was to determine if signaling through the neurotrophin receptor, p75 influences this ratio. An increasing ratio was identified in several brain regions, except the hippocampus, suggesting a neurotrophic imbalance occurs as early as middle age. Some changes in receptors that mediate the isoforms effects were also identified, but these did not correspond with trends in the isoforms. Relative amounts of precursor brain-derived neurotrophic factor were mostly unchanged in mutant p75 mice. The lack of changes suggested that signaling through the receptor had no influence on the ratio.

Prenatal cyanuric acid exposure induced spatial learning impairments associated with alteration of acetylcholine-mediated neural information flow at the hippocampal CA3-CA1 synapses of male rats

Cyanuric acid (CA) is reported to induce nephrotoxicity but its toxic effect is not fully known. Prenatal CA exposure causes neurodevelopmental deficits and abnormal behavior in spatial learning ability. Dysfunction of the acetyl-cholinergic system in neural information processing is correlated with spatial learning impairment and was found in the previous reports of CA structural analogue melamine. To further investigate the neurotoxic effects and the potential mechanism, the acetylcholine (ACh) level was detected in the rats which were exposed to CA during the whole of gestation. Local field potentials (LFPs) were recorded when rats infused with ACh or cholinergic receptor agonist into hippocampal CA3 or CA1 region were trained in the Y-maze task. We found the expression of ACh in the hippocampus was significantly reduced in dose-dependent manners. Intra-hippocampal infusion of ACh into the CA1 but not the CA3 region could effectively mitigate learning deficits induced by CA exposure. However, activation of cholinergic receptors did not rescue the learning impairments. In the LFP recording, we found that the hippocampal ACh infusions could enhance the values of phase synchronization between CA3 and CA1 regions in theta and alpha oscillations. Meanwhile, the reduction in the coupling directional index and the strength of CA3 driving CA1 in the CA-treated groups was also reversed by the ACh infusions. Our findings are consistent with the hypothesis and provide the first evidence that prenatal CA exposure induced spatial learning defect is attributed to the weakened ACh-mediated neuronal coupling and NIF in the CA3-CA1 pathway.

Aluminum Oxide Nanoparticles Impair Working Memory and Neuronal Activity through the GSK3β/BDNF Signaling Pathway of Prefrontal Cortex in Rats

Studies demonstrated that alumina nanoparticles (alumina NPs) impair spatial cognition and hippocampus-dependent synaptic plasticity. Although alumina NPs accumulate in the prefrontal cortex (PFC), their effects on PFC-mediated neuronal and cognitive function have been not yet documented. Here, alumina NPs (10 or 20 μg/kg of body weight) were bilaterally injected into the medial PFC (mPFC) of adult rats, and the levels of glycogen synthase kinase 3β (GSK3β) and the brain-derived neurotrophic factor (BDNF) were detected. The PFC-dependent working memory task with one-minute or three-minute delay time was conducted. Meanwhile, the neuronal correlates of working memory performance were recorded. The specific expression of neuronal BDNF was assessed by colabeled BDNF expression with the neuronal nuclear antigen (NeuN). Whole-cell patch-clamp recordings were employed to detect neuronal excitability. Intra-mPFC alumina NP infusions significantly enhanced the expression of GSK3β but reduced the phosphorylation of GSK3β (pGSK3β) and BDNF levels more severely at a dose of 20 μg/kg. Alumina NPs acted in a dose-dependent manner to impair working memory. The neuronal expression of BDNF in the 20 μg/kg group was markedly declined compared with the 10 μg/kg group. During the delay time, the neuronal frequency of pyramidal cells but not interneurons was significantly weakened. Furthermore, both the frequency and amplitude of the excitatory postsynaptic currents (EPSCs) were descended in the mPFC slices. Additionally, the infusion of GSK3β inhibitor SB216763 or BDNF could effectively attenuate the impairments in neuronal correlate, neuronal activity, and working memory. From the perspective of the identified GSK3β/BDNF pathway, these findings demonstrated for the first time that alumina NPs exposure can be a risk factor for prefrontal neuronal and cognitive functions.

Maternal immune activation-induced proBDNF-mediated neural information processing dysfunction at hippocampal CA3-CA1 synapses associated with memory deficits in offspring

Prenatal exposure to maternal infection increases the risk of offspring developing schizophrenia in adulthood. Current theories suggest that the consequences of MIA on mBDNF secretion may underlie the increased risk of cognitive disorder. There is little evidence for whether the expression of its precursor, proBDNF, is changed and how proBDNF-mediated signaling may involve in learning and memory. In this study, proBDNF levels were detected in the hippocampal CA1 and CA3 regions of male adult rats following MIA by prenatal polyI:C exposure. Behaviorally, learning and memory were assessed in contextual fear conditioning tasks. Local field potentials were recorded in the hippocampal CA3-CA1 pathway. The General Partial Directed Coherence approach was utilized to identify the directional alternation of neural information flow between CA3 and CA1 regions. EPSCs were recorded in CA1 pyramidal neurons to explore a possible mechanism involving the proBDNF-p75NTR signaling pathway. Results showed that the expression of proBDNF in the polyI:C-treated offspring was abnormally enhanced in both CA3 and CA1 regions. Meanwhile, the mBDNF expression was reduced in both hippocampal regions. Intra-hippocampal CA1 but not CA3 injection with anti-proBDNF antibody and p75NTR inhibitor TAT-Pep5 effectively mitigated the contextual memory deficits. Meanwhile, reductions in the phase synchronization between CA3 and CA1 and the coupling directional indexes from CA3 to CA1 were enhanced by the intra-CA1 infusions. Moreover, blocking proBDNF/p75NTR signaling could reverse the declined amplitude of EPSCs in CA1 pyramidal neurons, indicating the changes in postsynaptic information processing in the polyI:C-treated offspring. Therefore, the changes in hippocampal proBDNF activity in prenatal polyI:C exposure represent a potential mechanism involved in NIF disruption leading to contextual memory impairments.

BDNF, proBDNF and IGF-1 serum levels in naïve and medicated subjects with autism

Brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) promote the development and maintenance of neural circuits. Alterations in these factors might contribute to autism spectrum disorder (ASD). We asked whether serum BDNF, proBDNF, and IGF-1 levels are altered in an ASD population compared to controls. We measured serum BDNF, proBDNF, and IGF-1 immunoreactive protein in boys and girls aged 5–15 years old with mild to moderate ASD and non-autistic controls by ELISA. IGF-1 was increased in ASD serum compared to controls and was correlated with age and with CARS scores. Serum BDNF levels did not differ between groups, however, proBDNF serum levels were decreased in subjects with ASD compared to non-autistic controls. Medicated, but not unmedicated, ASD subjects exhibited lower serum proBDNF levels compared to controls, while neither IGF-1 nor BDNF levels differed between treatment groups. These data support the involvement of proBDNF and IGF-1 in the pathogenesis and treatment of autism.

Aluminium oxide nanoparticles compromise spatial memory performance and proBDNF-mediated neuronal function in the hippocampus of rats

Background

Alumina nanoparticles (aluminaNPs), which are widely used in a range of daily and medical fields, have been shown to penetrate blood-brain barrier, and distribute and accumulate in different brain areas. Although oral treatment of aluminaNPs induces hippocampus-dependent learning and memory impairments, characteristic effects and exact mechanisms have not been fully elucidated. Here, male adult rats received a single bilateral infusion of aluminaNPs (10 or 20 µg/kg of body weight) into the hippocampal region, and their behavioral performance and neural function were assessed.

Results

The results indicated that the intra-hippocampus infusions at both doses of aluminaNPs did not cause spatial learning inability but memory deficit in the water maze task. This impairment was attributed to the effects of aluminaNP on memory consolidation phase through activation of proBDNF/RhoA pathway. Inhibition of the increased proBDNF by hippocampal infusions of p75^NTR antagonist could effectively rescue the memory impairment. Incubation of aluminaNPs exaggerated GluN2B-dependent LTD induction with no effects on LTD expression in hippocampal slices. AluminaNP could also depress the amplitude of NMDA-GluN2B EPSCs. Meanwhile, increased reactive oxygen specie production was reduced by blocking proBDNF-p75^NTR pathway in the hippocampal homogenates. Furthermore, the neuronal correlate of memory behavior was drastically weakened in the aluminaNP-infused groups. The dysfunction of synaptic and neuronal could be obviously mitigated by blocking proBDNF receptor p75^NTR, implying the involvement of proBDNF signaling in aluminaNP-impaired memory process.

Conclusions

Taken together, our findings provide the first evidence that the accumulation of aluminaNPs in the hippocampus exaggeratedly activates proBDNF signaling, which leads to neural and memory impairments.

Prelimbic proBDNF Facilitates Retrieval-Dependent Fear Memory Destabilization by Regulation of Synaptic and Neural Functions in Juvenile Rats

Fear regulation changes as a function of the early life is a key developmental period for the continued maturation of fear neural circuitry. The mechanisms of fear retrieval-induced reconsolidation have been investigated but remain poorly understood. The involvement of prelimbic proBDNF in fear memory extinction and its mediated signaling have been reported previously. Specifically, blocking the proBDNF/p75^NTR pathway during the postnatal stage disrupts synaptic development and neuronal activity in adulthood. Given the inherent high expression of proBDNF during the juvenile period, we tested whether the prelimbic proBDNF regulated synaptic and neuronal functions allowing to influencing retrieval-dependent memory processing. By examining the freezing behavior of auditory fear-conditioned rats, we found the high level of the prelimbic proBDNF in juvenile rats enhanced the destabilization of the retrieval-dependent weak but not strong fear memory through activating p75^NTR-GluN2B signaling. This modification of fear memory traces was attributed to the increment in the proportion of thin-type spine and promotion in synaptic function, as evidenced by the facilitation of NMDA-mediated EPSCs and GluN2B-dependent synaptic depression at the prelimbic projection. Furthermore, the strong prelimbic theta- and gamma-oscillation coupling predicted the suppressive effect of juvenile proBDNF on the recall of postretrieval memory. Our results critically emphasize the importance of developmental proBDNF for modification of retrieval-dependent memory and provide a potential critical targeting to inhibit threaten memories associated with neurodevelopment disorders.

The cAMP Response Element- Binding Protein/Brain-Derived Neurotrophic Factor Pathway in Anterior Cingulate Cortex Regulates Neuropathic Pain and Anxiodepression Like Behaviors in Rats

Neuropathic pain is often accompanied by anxiety and depression-like manifestations. Many studies have shown that alterations in synaptic plasticity in the anterior cingulate cortex (ACC) play a critical role, but the specific underlying mechanisms remain unclear. Previously, we showed that cAMP response element-binding protein (CREB) in the dorsal root ganglion (DRG) acts as a transcription factor contributing to neuropathic pain development. At the same time, brain-derived neurotrophic factor (BDNF), as important targets of CREB, is intricate in neuronal growth, differentiation, as well as the establishment of synaptic plasticity. Here, we found that peripheral nerve injury activated the spinal cord and ACC, and silencing the ACC resulted in significant relief of pain sensitivity, anxiety, and depression in SNI rats. In parallel, the CREB/BDNF pathway was activated in the spinal cord and ACC. Central specific knockdown and peripheral non-specific inhibition of CREB reversed pain sensitivity and anxiodepression induced by peripheral nerve injury. Consequently, we identified cingulate CREB/BDNF as an assuring therapeutic method for treating neuropathic pain as well as related anxiodepression.

Regulation of AMPAR trafficking in synaptic plasticity by BDNF and the impact of neurodegenerative disease

Research demonstrates that the neural mechanisms underlying synaptic plasticity and learning and memory involve mobilization of AMPA-type neurotransmitter receptors at glutamatergic synaptic contacts, and that these mechanisms are targeted during neurodegenerative disease. Strengthening neural transmission occurs with insertion of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) into synapses while weakening results from receptor withdrawal. A key player in the trafficking of AMPARs during plasticity and learning is the brain-derived neurotrophic factor (BDNF) signaling system. BDNF is a neurotrophic factor that supports neuronal growth and is required for learning and memory. Significantly, a primary feature of many neurodegenerative diseases is a reduction in BDNF protein as well as disrupted neuronal surface expression of synaptic AMPARs. The resulting weakening of synaptic contacts leads to synapse loss and neuronal degeneration that underlies the cognitive impairment and dementia observed in patients with progressive neurodegenerative disease such as Alzheimer's. In the face of these data, one therapeutic approach is to increase BDNF bioavailability in brain. While this has been met with significant challenges, the results of the research have been promising. In spite of this, there are currently no clinical trials to test many of these findings on patients. Here, research showing that BDNF drives AMPARs to synapses, AMPAR trafficking is essential for synaptic plasticity and learning, and that neurodegenerative disease results in a significant decline in BDNF will be reviewed. The aim is to draw attention to the need for increasing patient-directed clinical studies to test the possible benefits of increasing levels of neurotrophins, specifically BDNF, to treat brain disorders. Much is known about the cellular mechanisms that underlie learning and memory in brain. It can be concluded that signaling by neurotrophins like BDNF and AMPA-type glutamate receptor synaptic trafficking are fundamental to these processes. Data from animal models and patients reveal that these mechanisms are adversely targeted during neurodegenerative disease and results in memory loss and cognitive decline. A brief summary of our understanding of these mechanisms indicates that it is time to apply this knowledge base directly to development of therapeutic treatments that enhance neurotrophins for brain disorders in patient populations.