Arginine vasopressin prevents amyloid beta protein-induced impairment of long-term potentiation in rat hippocampus in vivo

Therapeutic potential of vasopressin in the treatment of neurological disorders

Vasopressin (VP) is a nonapeptide made of nine amino acids synthesized by the hypothalamus and released by the pituitary gland. VP acts as a neurohormone, neuropeptide and neuromodulator and plays an important role in the regulation of water balance, osmolarity, blood pressure, body temperature, stress response, emotional challenges, etc. Traditionally VP is known to regulate the osmolarity and tonicity. VP and its receptors are widely expressed in the various region of the brain including cortex, hippocampus, basal forebrain, amygdala, etc. VP has been shown to modulate the behavior, stress response, circadian rhythm, cerebral blood flow, learning and memory, etc. The potential role of VP in the regulation of these neurological functions have suggested the therapeutic importance of VP and its analogues in the management of neurological disorders. Further, different VP analogues have been developed across the world with different pharmacotherapeutic potential. In the present work authors highlighted the therapeutic potential of VP and its analogues in the treatment and management of various neurological disorders.

Oxytocin and vasopressin in the hippocampus

Oxytocin (OXT) and vasopressin (AVP) are related neuropeptides that exert a wide range of effects on general health, homeostasis, development, reproduction, adaptability, cognition, social and nonsocial behaviors. The two peptides are mainly of hypothalamic origin and execute their peripheral and central physiological roles via OXT and AVP receptors, which are members of the G protein-coupled receptor family. These receptors, largely distributed in the body, are abundantly expressed in the hippocampus, a brain region particularly vulnerable to stress exposure and various lesions. OXT and AVP have important roles in the hippocampus, by modulating important processes like neuronal excitability, network oscillatory activity, synaptic plasticity, and social recognition memory. This chapter includes an overview regarding OXT and AVP structure, synthesis, receptor distribution, and functions, focusing on their relationship with the hippocampus and mechanisms by which they influence hippocampal activity. Brief information regarding hippocampal structure and susceptibility to lesions is also provided. The roles of OXT and AVP in neurodevelopment and adult central nervous system function and disorders are highlighted, discussing their potential use as targeted therapeutic tools in neuropsychiatric diseases.

Multicomponent Training Prevents Memory Deficit Related to Amyloid-β Protein-Induced Neurotoxicity

BACKGROUND

Alzheimer's disease (AD) is characterized by the accumulation of the amyloid-β peptide in the brain, leading to early oxidative stress and neurotoxicity. It has been suggested that physical exercise could be beneficial in preventing AD, but studies with multicomponent training are scanty.

OBJECTIVE

Verify the effects of multicomponent exercise training to prevent deficits in recognition memory related to Aβ neurotoxicity.

METHODS

We subjected Wistar rats to multicomponent training (including aerobic and anaerobic physical exercise and cognitive exercise) and then infused amyloid-β peptide into their hippocampus.

RESULTS

We show that long-term multicomponent training prevents the amyloid-β-associated neurotoxicity in the hippocampus. It reduces hippocampal lipid peroxidation, restores antioxidant capacity, and increases glutathione levels, finally preventing recognition memory deficits.

CONCLUSION

Multicomponent training avoids memory deficits related to amyloid-β neurotoxicity on an animal model.

Netrin-1 protects the SH-SY5Y cells against amyloid beta neurotoxicity through NF-κB/Nrf2 dependent mechanism

Many evidence confirms that amyloid beta 1-42 fragment (Aβ_1-42) causes neuroinflammation, oxidative stress, and cell death, which are related to progressive memory loss, cognitive impairments and mental disorders that will lead to Alzheimer's disease (AD) progression. Netrin-1, as a member of the laminins, has been proved to inhibit apoptosis and inflammation outside of nervous system, in addition to having a vital role in morphogenesis and neurogenesis of neural system. This study was designed to assess the protective effects of netrin-1 in SH-SY5Y human neuroblastoma cell line exposed to Aβ_1-42 and to explore some mechanisms that underlie netrin-1 effects. Cultured SH-SY5Y neuroblast-like cells were treated with netrin-1 prior to Aβ_1-42 exposure and the effects were assessed by MTT and ELISA assay kits. Netrin- 1 pretreatment of Aβ_1-42-exposed SH-SY5Y human neuroblastoma cells attenuated Aβ_1-42 induced toxic effects, increased cell viability and partially restored levels of 3 inflammatory and oxidative stress biomarkers including: nuclear factor erythroid 2-like 2 (Nrf2), tumor necrosis factor alpha (TNFα) and nuclear factor kappa-light chain-enhancer of activated B cells (NF-κB). Based on the findings of this study, netrin-1 represents a promising therapeutic bio agent to abrogate cellular inflammation and reactive oxygen species (ROS) activation induced by Aβ_1-42 in the SH-SY5Y cell model of AD.

The Reversal of Memory Deficits in an Alzheimer's Disease Model Using Physical and Cognitive Exercise

Alzheimer’s disease (AD) is the leading cause of dementia in the world, accounting for 50–75% of cases. Currently, there is limited treatment for AD. The current pharmacological therapy minimizes symptom progression but does not reverse brain damage. Studies focused on nonpharmacological treatment for AD have been developed to act on brain plasticity and minimize the neurotoxicity caused by the amyloid-beta (Aβ) peptide. Using a neurotoxicity model induced by Aβ in rats, the present study shows that physical (PE) and cognitive exercise (CE) reverse recognition memory deficits (with a prominent effect of long-term object recognition memory), decrease hippocampal lipid peroxidation, restore the acetylcholinesterase activity altered by Aβ neurotoxicity, and seems to reverse, at least partially, hippocampal tissue disorganization.

AVP(4-8) Improves Cognitive Behaviors and Hippocampal Synaptic Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease

Memory deficits with aging are related to the neurodegeneration in the brain, including a reduction in arginine vasopressin (AVP) in the brain of patients with Alzheimer's disease (AD). AVP(4-8), different from its precursor AVP, plays memory enhancement roles in the CNS without peripheral side-effects. However, it is not clear whether AVP(4-8) can improve cognitive behaviors and synaptic plasticity in the APP/PS1 mouse model of AD. Here, we investigated for the first time the neuroprotective effects of AVP(4-8) on memory behaviors and in vivo long-term potentiation (LTP) in APP/PS1-AD mice. The results showed that: (1) APP/PS1-AD mice had lower spontaneous alternation in the Y-maze than wild-type (WT) mice, and this was significantly reversed by AVP(4-8); (2) the prolonged escape latency of APP/PS1-AD mice in the Morris water maze was significantly decreased by AVP(4-8), and the decreased swimming time in target quadrant recovered significantly after AVP(4-8) treatment; (3) in vivo hippocampal LTP induced by high-frequency stimulation had a significant deficit in the AD mice, and this was partly rescued by AVP(4-8); (4) AVP(4-8) significantly up-regulated the expression levels of postsynaptic density 95 (PSD95) and nerve growth factor (NGF) in the hippocampus of AD mice. These results reveal the beneficial effects of AVP(4-8) in APP/PS1-AD mice, showing that the intranasal administration of AVP(4-8) effectively improved the working memory and long-term spatial memory of APP/PS1-AD mice, which may be associated with the elevation of PSD95 and NGF levels in the brain and the maintenance of hippocampal synaptic plasticity.

Activation of arginine vasopressin receptor 1a facilitates the induction of long-term potentiation in the accessory olfactory bulb of male mice

Olfaction plays an important role in social recognition in most mammals. Central arginine vasopressin (AVP) plays a role in this olfaction-based recognition. The high level of expression of AVP receptors in the accessory olfactory bulb (AOB) at the first relay of the vomeronasal system highlights the importance of AVP signaling at this stage. We therefore analyzed the effects of AVP on the synaptic plasticity of glutamatergic transmission from mitral cells to granule cells in AOB slices from male mice. To monitor the strength of the glutamatergic transmission, we measured the maximal initial slope of the lateral olfactory tract-evoked field potential, which represents the granule cell response to mitral cell activation. AVP paired with 100-Hz stimulation that only produced short-term potentiation enhanced the induction of long-term potentiation (LTP) in a dose-dependent manner. AVP-paired LTP was blocked by the selective AVP receptor 1a (AVPR1a) antagonist, d(CH₂)₅[Tyr(Me)²]AVP (Manning compound), but not by the AVPR1b antagonist SSR149415, and it was mimicked by the selective AVPR1a agonist [Phe², Ile³, Orn⁸]-vasopressin. We further examined the effect of AVP on the reciprocal transmission between mitral and granule cells by stimulating a mitral cell and recording the evoked inhibitory postsynaptic currents (IPSCs) from the same cell using conventional whole-cell patch-clamp techniques. AVP reduced the reciprocal IPSCs triggered by endogenous glutamate release from the excited mitral cell. These results suggest that AVP promotes the induction of LTP at the mitral-to-granule cell synapse via the activation of AVPR1a through an as-yet-to-be-determined mechanism in the AOB of male mice.

Vitamin D interacts with Esr1 and Igf1 to regulate molecular pathways relevant to Alzheimer's disease

Background

Increasing evidence suggests a potential therapeutic benefit of vitamin D supplementation against Alzheimer’s disease (AD). Although studies have shown improvements in cognitive performance and decreases in markers of the pathology after chronic treatment, the mechanisms by which vitamin D acts on brain cells are multiple and remain to be thoroughly studied. We analyzed the molecular changes observed after 5 months of vitamin D3 supplementation in the brains of transgenic 5xFAD (Tg) mice, a recognized mouse model of AD, and their wild type (Wt) littermates. We first performed a kinematic behavioural examination at 4, 6 and 8 months of age (M4, M6 and M8) followed by a histologic assessment of AD markers. We then performed a comparative transcriptomic analysis of mRNA regulation in the neocortex and hippocampus of 9 months old (M9) female mice.

Results

Transcriptomic analysis of the hippocampus and neocortex of both Wt and Tg mice at M9, following 5 months of vitamin D3 treatment, reveals a large panel of dysregulated pathways related to i) immune and inflammatory response, ii) neurotransmitter activity, iii) endothelial and vascular processes and iv) hormonal alterations. The differentially expressed genes are not all direct targets of the vitamin D-VDR pathway and it appears that vitamin D action engages in the crosstalk with estrogen and insulin signaling. The misexpression of the large number of genes observed in this study translates into improved learning and memory performance and a decrease in amyloid plaques and astrogliosis in Tg animals.

Conclusions

This study underlies the multiplicity of action of this potent neurosteroid in an aging and AD-like brain. The classical and non-classical actions of vitamin D3 can act in an additive and possibly synergistic manner to induce neuroprotective activities in a context-specific way.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0087-2) contains supplementary material, which is available to authorized users.

Osthole improves synaptic plasticity in the hippocampus and cognitive function of Alzheimer's disease rats via regulating glutamate

Osthole, an effective monomer in Chinese medicinal herbs, can cross the blood-brain barrier and protect against brain injury, with few toxic effects. In this study, a rat model of Alzheimer's disease was established after intracerebroventricular injection of β-amyloid peptide (25-35). Subsequently, the rats were intraperitoneally treated with osthole (12.5 or 25.0 mg/kg) for 14 successive days. Results showed that osthole treatment significantly improved cognitive impairment and protected hippocampal neurons of Alzheimer's disease rats. Also, osthole treatment alleviated suppressed long-term potentiation in the hippocampus of Alzheimer's disease rats. In these osthole-treated Alzheimer's disease rats, the level of glutamate decreased, but there was no significant change in γ-amino-butyric acid. These experimental findings suggest that osthole can improve learning and memory impairment, and increase synaptic plasticity in Alzheimer's disease rats. These effects of osthole may be because of its regulation of central glutamate and γ-amino-butyric acid levels.

Targeting synaptic dysfunction in Alzheimer's disease therapy

In the past years, major efforts have been made to understand the genetics and molecular pathogenesis of Alzheimer's disease (AD), which has been translated into extensive experimental approaches aimed at slowing down or halting disease progression. Advances in transgenic (Tg) technologies allowed the engineering of different mouse models of AD recapitulating a range of AD-like features. These Tg models provided excellent opportunities to analyze the bases for the temporal evolution of the disease. Several lines of evidence point to synaptic dysfunction as a cause of AD and that synapse loss is a pathological correlate associated with cognitive decline. Therefore, the phenotypic characterization of these animals has included electrophysiological studies to analyze hippocampal synaptic transmission and long-term potentiation, a widely recognized cellular model for learning and memory. Transgenic mice, along with non-Tg models derived mainly from exogenous application of Aβ, have also been useful experimental tools to test the various therapeutic approaches. As a result, numerous pharmacological interventions have been reported to attenuate synaptic dysfunction and improve behavior in the different AD models. To date, however, very few of these findings have resulted in target validation or successful translation into disease-modifying compounds in humans. Here, we will briefly review the synaptic alterations across the different animal models and we will recapitulate the pharmacological strategies aimed at rescuing hippocampal plasticity phenotypes. Finally, we will highlight intrinsic limitations in the use of experimental systems and related challenges in translating preclinical studies into human clinical trials.

Effect of Aggregated β-Amyloid (1-42) on Synaptic Plasticity of Hippocampal Dentate Gyrus Granule Cells in Vivo

INTRODUCTION

Alzheimer's disease (AD) is a common neurodegenerative disorder in elderly people with an impairment of cognitive decline and memory loss. β-amyloid (Aβ) as a potent neurotoxic peptide has a pivotal role in the pathogenesis of AD. This disease begins with impairment in synaptic functions before developing into later neuro¬degeneration and neuronal loss. The aim of this study was to evaluate the synaptic plasticity and electrophysiological function of granule cells in hippocampal dentate gyrus (DG) after intracerebroventricular (i.c.v.) administration of aggregated Aβ (1-42) peptide in vivo.

METHODS

Animals were divided to control and Aβ (1-42) groups. Long-term potentia¬tion (LTP) in perforant path-DG synapses was assessed in order to investigate the effect of aggregated Aβ (1-42) on synaptic plasticity. Field excitatory post-synaptic potential (fEPSP) slope and population spike (PS) amplitude were measured.

RESULTS

Administration of Aβ (1-42) significantly decreased fEPSP slope and PS amplitude in Aβ (1-42) group comparing with the control group and had no effect on baseline activity of neurons.

CONCLUSION

The present study indicates that administration of aggregated form of Aβ (1-42) into the lateral ventricle effectively inhibits LTP in granular cells of the DG in hippocampus in vivo.

Arginine vasopressin prevents against Abeta(25-35)-induced impairment of spatial learning and memory in rats

Amyloid beta protein (Abeta) is thought to be responsible for loss of memory in Alzheimer's disease (AD). A significant decrease in [Arg(8)]-vasopressin (AVP) has been found in the AD brain and in plasma; however, it is unclear whether this decrease in AVP is involved in Abeta-induced impairment of spatial cognition and whether AVP can protect against Abeta-induced deficits in cognitive function. The present study examined the effects of intracerebroventricular (i.c.v.) injection of AVP on spatial learning and memory in the Morris water maze test and investigated the potential protective function of AVP against Abeta-induced impairment in spatial cognition. The results were as follows: (1) i.c.v. injection of 25 nmol Abeta(25-35) resulted in a significant decline in spatial learning and memory; (2) 1 nmol and 10 nmol, but not 0.1 nmol, AVP injections markedly improved learning and memory; (3) pretreatment with 1 nmol or 10 nmol, but not 0.1 nmol, AVP effectively reversed the impairment in spatial learning and memory induced by Abeta(25-35); and (4) none of the drugs, including Abeta(25-35) and different concentrations of AVP, affected the vision or swimming speed of the rats. These results indicate that Abeta(25-35) could significantly impair spatial learning and memory in rats, and pretreatment with AVP centrally can enhance spatial learning and effectively prevent the behavioral impairment induced by neurotoxic Abeta(25-35). Thus, the present study provides further insight into the mechanisms by which Abeta impairs spatial learning and memory, suggesting that up-regulation of central AVP might be beneficial in the prevention and treatment of AD.

Secretin as a neurohypophysial factor regulating body water homeostasis

Hypothalamic magnocellular neurons express either one of the neurohypophysial hormones, vasopressin or oxytocin, along with different neuropeptides or neuromodulators. Axonal terminals of these neurons are generally accepted to release solely the two hormones but not others into the circulation. Here, we show that secretin, originally isolated from upper intestinal mucosal extract, is present throughout the hypothalamo-neurohypophysial axis and that it is released from the posterior pituitary under plasma hyperosmolality conditions. In the hypothalamus, it stimulates vasopressin expression and release. Considering these findings together with our previous findings that show a direct effect of secretin on renal water reabsorption, we propose here that secretin works at multiple levels in the hypothalamus, pituitary, and kidney to regulate water homeostasis. Findings presented here challenge previous understanding regarding the neurohypophysis and could provide new concepts in treating disorders related to osmoregulation.