Intrahippocampal Administration Research Articles

Adenosine-A2A Receptor Signaling Plays a Crucial Role in Sudden Unexpected Death in Epilepsy.

Adenosinergic activities are suggested to participate in SUDEP pathophysiology; this study aimed to evaluate the adenosine hypothesis of SUDEP and specifically the role of adenosine A2A receptor (A2AR) in the development of a SUDEP mouse model with relevant clinical features. Using a combined paradigm of intrahippocampal and intraperitoneal administration of kainic acid (KA), we developed a boosted-KA model of SUDEP in genetically modified adenosine kinase (ADK) knockdown (Adk+/-) mice, which has reduced ADK in the brain. Seizure activity was monitored using video-EEG methods, and in vivo recording of local field potential (LFP) was used to evaluate neuronal activity within the nucleus tractus solitarius (NTS). Our boosted-KA model of SUDEP was characterized by a delayed, postictal sudden death in epileptic mice. We demonstrated a higher incidence of SUDEP in Adk+/- mice (34.8%) vs. WTs (8.0%), and the ADK inhibitor, 5-Iodotubercidin, further increased SUDEP in Adk+/- mice (46.7%). We revealed that the NTS level of ADK was significantly increased in epileptic WTs, but not in epileptic Adk+/- mutants, while the A2AR level in NTS was increased in epileptic (WT and Adk+/-) mice vs. non-epileptic controls. The A2AR antagonist, SCH58261, significantly reduced SUDEP events in Adk+/- mice. LFP data showed that SCH58261 partially restored KA injection-induced suppression of gamma oscillation in the NTS of epileptic WT mice, whereas SCH58261 increased theta and beta oscillations in Adk+/- mutants after KA injection, albeit with no change in gamma oscillations. These LFP findings suggest that SCH58261 and KA induced changes in local neuronal activities in the NTS of epileptic mice. We revealed a crucial role for NTS A2AR in SUDEP pathophysiology suggesting A2AR as a potential therapeutic target for SUDEP risk prevention.

Plumbagin Alleviates Intracerebroventricular-Quinolinic Acid Induced Depression-like Behavior and Memory Deficits in Wistar Rats.

Plumbagin, a hydroxy-1,4-naphthoquinone, confers neuroprotection via antioxidant and anti-inflammatory properties. The present study aimed to assess the effect of plumbagin on behavioral and memory deficits induced by intrahippocampal administration of Quinolinic acid (QA) in male Wistar rats and reveal the associated mechanisms. QA (300 nM/4 μL in Normal saline) was administered i.c.v. in the hippocampus. QA administration caused depression-like behavior (forced swim test and tail suspension tests), anxiety-like behavior (open field test and elevated plus maze), and elevated anhedonia behavior (sucrose preference test). Furthermore, oxidative–nitrosative stress (increased nitrite content and lipid peroxidation with reduction of GSH), inflammation (increased IL-1β), cholinergic dysfunction, and mitochondrial complex (I, II, and IV) dysfunction were observed in the hippocampus region of QA-treated rats as compared to normal controls. Plumbagin (10 and 20 mg/kg; p.o.) treatment for 21 days significantly ameliorated behavioral and memory deficits in QA-administered rats. Moreover, plumbagin treatment restored the GSH level and reduced the MDA and nitrite level in the hippocampus. Furthermore, QA-induced cholinergic dysfunction and mitochondrial impairment were found to be ameliorated by plumbagin treatment. In conclusion, our results suggested that plumbagin offers a neuroprotective potential that could serve as a promising pharmacological approach to mitigate neurobehavioral changes associated with neurodegeneration.

Effect of Intrahippocampal Administration of α7 Subtype Nicotinic Receptor Agonist PNU-282987 and Its Solvent Dimethyl Sulfoxide on the Efficiency of Hypoxic Preconditioning in Rats

We have previously suggested a key role of the hippocampus in the preconditioning action of moderate hypobaric hypoxia (HBH). The preconditioning efficiency of HBH is associated with acoustic startle prepulse inhibition (PPI). In rats with PPI > 40%, HBH activates the cholinergic projections of hippocampus, and PNU-282987, a selective agonist of α7 nicotinic receptors (α7nAChRs), reduces the HBH efficiency and potentiating effect on HBH of its solvent dimethyl sulfoxide (DMSO, anticholinesterase agent) when administered intraperitoneally. In order to validate the hippocampus as a key structure in the mechanism of hypoxic preconditioning and research a significance of α7nAChR activation in the hypoxic preconditioning, we performed an in vivo pharmacological study of intrahippocampal injections of PNU-282987 into the CA1 area on HBH efficiency in rats with PPI ≥ 40%. We found that PNU-282987 (30 μM) reduced HBH efficiency as with intraperitoneal administration, while DMSO (0.05%) still potentiated this effect. Thus, direct evidence of the key role of the hippocampus in the preconditioning effect of HBH and some details of this mechanism were obtained in rats with PPI ≥ 40%. The activation of α7nAChRs is not involved in the cholinergic signaling initiated by HBH or DMSO via any route of administration. Possible ways of the potentiating action of DMSO on HBH efficiency and its dependence on α7nAChRs are discussed.

The involvement of inflammation in the effect of the administration of donepezil, galantamine, memantine and/or fluoxetine in an animal model of depression and dementia.

Alzheimer's disease (AD) and major depressive disorder (MDD) can share the same inflammatory theory in their pathophysiology, indicating that MDD may not only be a symptom, but a risk factor for AD. Therefore, the present study evaluated the levels of cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL) -1β, IL-6 and IL-10 in the frontal cortex and hippocampus of Wistar rats subjected to chronic mild stress protocol (CMS) for induction of an animal model of depression and administration of intra-hippocampal β-amyloid (βA) oligomers for induction of the dementia model. 60-day-old Wistar rats went subjected to CMS protocol for 40 days. After the CMS, the animals were subjected to stereotaxic surgery for intra-hippocampal administration of βA or artificial cerebrospinal fluid (ACSF). The next day, it was started the treatment with water, memantine, galantamine, donepezil and/or fluoxetine orally for 17 days. On the 59th day of the experimental protocol, euthanasia was performed, and the frontal cortex and hippocampus were dissected for later measurements of the TNF-α, IL-1β, IL-6 and IL-10. The results of this study show that animals subjected to CMS and administration of βA showed increased levels of TNF-α and IL-1β in the frontal cortex and reduced IL-10 level in the hippocampus. Fluoxetine reversed the levels of TNF-α and IL-1β in the frontal cortex. In addition, the fluoxetine + donepezil combination reversed the reduction of IL-10 levels in the hippocampus. Galantamine was also effective in reversing TNF-α levels in the cortex, as well as its association with fluoxetine and the association of donepezil with fluoxetine. The animals treated with memantine, as well as their association with fluoxetine, association of galantamine and fluoxetine and the association of donepezil with fluoxetine had levels of IL-10 significantly increased in the frontal cortex. In the hippocampus, only treatments with donepezil were able to raise the levels of IL-1β and IL-10. The results obtained in the present study indicate that there is a pathophysiological interaction between diseases, and that the association of medications in the future may be a possible therapeutic strategy to reduce the inflammation, especially in association with fluoxetine.

Acute and chronic cardiorespiratory consequences of focal intrahippocampal administration of seizure-inducing agents. Implications for SUDEP

<h2>Abstract</h2> The risk factors for SUDEP are undoubtedly heterogenous but the main factor is the frequency of generalized tonic-clonic seizures with apnoea and/or cardiac abnormalities likely precipitating the lethal event. By its very nature modelling SUDEP experimentally is challenging, yet insights into the nature of the lethal event and precipitating factors are vital in order to understand and prevent fatalities. Acute animal models, which induce status epilepticus (SE), can be used to help understand pathophysiological processes during and following seizures, which sometimes lead to death. The most commonly used method to induce seizures and status epilepticus is systemic administration of an ictogenic agent. Microinjection of such agents into restricted regions within the brain induces a more localised epileptic focus and circumvents the risk of direct actions on cardiorespiratory control centres. Both approaches have revealed substantial cardiovascular and respiratory consequences, including death as a result of apnoea, which may be of central origin, obstructive due to laryngospasm or, at least in genetically modified mice, a result of spreading depolarisation to medullary respiratory control centres. SUDEP is by definition a result of epilepsy, which in turn is diagnosed on the basis of two or more unprovoked seizures. The incidence of tonic-clonic seizures is the main risk factor, raising the possibility that repeated seizures cause cumulative pathological and/or pathophysiological changes that contribute to the risk of SUDEP. Chronic experimental models, which induce repeated seizures that in some cases lead to death, do show progressive development of pathophysiological changes in the myocardium, e.g. prolongation of QT the interval of the ECG or, over longer periods, ventricular hypertrophy. However, the currently available evidence indicates that seizure-related deaths are primarily due to apnoeas, but cardiac factors, particularly cumulative cardiac pathophysiologies due to repeated seizures, are potential contributing factors.

Rising of intracellular NAD+ level and oppositely directed changes in CD38 expression in hippocampal cells in experimental Alzheimer’s disease

The aim of the study was to assess the level of NAD+in the brain of mice treated with beta-amyloid (Aβ), as well as to determine the activity of ADP-ribosyl cyclase/CD38 and the number of CD38-immunopositive neurons, astrocytes and endothelial cells.Material and methods.The Alzheimer’s disease model was reproduced by intrahippocampal administration of Aβ to C57BL/6 mice. Determination of the NAD+level in the extracellular fluid of the brain and in the hippocampal tissue was carried out by spectrophotometric analysis. Evaluation of the enzymatic activity of ADP-ribosyl cyclase / CD38 was carried out by the fluorimetric method, determination of the number of CD38-immunopositive cells by the immunohistochemistry method.Results and discussion.The level of NAD+was significantly increased in the hippocampal tissue in mice after administration of Aβ, while the level of extracellular NAD+did not change. The activity of ADP-ribosyl cyclase / CD38 in the hippocampal tissue did not change, but the number of CD38-immunopositive neurons decreased, and the number of CD38+endothelial cells increased in the hippocampus of mice after administration of Aβ.Conclusion.Opposite changes in the expression of ADP-ribosyl cyclase / CD38 in neurons and endotheliocytes correspond to different metabolic states of these types of cells and, along with an increased intracellular pool of NAD+in experimental Alzheimer’s disease, reflect an adaptive stress response to Aβ administration.

Pretreatment with metformin prevents microcystin-LR-induced tau hyperphosphorylation via mTOR-dependent PP2A and GSK-3β activation.

Microcystin-leucine-arginine (MC-LR) is a toxin secreted by freshwater cyanobacteria that is considered a potential environmental risk factor for Alzheimer's disease (AD). A previous study indicated that tau protein hyperphosphorylation via protein phosphatase 2A (PP2A) and GSK-3β inhibition was the mechanism by which MC-LR induces neurotoxicity; however, how MC-LR-induced neurotoxicity can be effectively prevented remains unclear. In this study, the reversal effect of metformin on MC-LR-induced neurotoxicity was investigated. The results showed that metformin effectively prevented tau hyperphosphorylation at Ser202 caused by MC-LR through PP2A and GSK-3b activity. The effect of metformin on PP2A activity was dependent on the inhibition of mTOR in MC-LR-treated SH-SY5Y cells. Metformin prevented spatial memory deficits in rats caused by intrahippocampal MC-LR administration. In sum, the results suggested that metformin can ameliorate the MC-LR-induced AD-like phenotype by preventing tau phosphorylation at Ser202, which was mainly mediated by mTOR-dependent PP2A and GSK-3β activation.

Modulating effect of liposomal miR-101 on the processes of amyloidogenesis, smell, sleep and neuroinflammation in experimental Alzheimer's disease

The current therapy for Alzheimer's disease does not give patients a chance of recovery. Therefore, it is relevant to study the novel factors of influence, in particular microRNA, on the pathogenic mechanisms of amyloidosis. The aim of this work was to determine the effect of miR-101 on early predictors of amyloidosis in experimental Alzheimer's disease in animals. The study was carried out on 25 male rats of 14 months of age. A model of Alzheimer's disease was created by intrahippocampal administration of Aβ40 aggregates to animals. Ten days later, a 10-day course of nasal administration of miR-101 in liposomes was launched. The level of endogenous Aβ42 and cytokines (TNFα, IL-6 and IL-10) was determined in the supernatants of the nerve tissues of the target brain structures (hippocampus, olfactory bulbs, and olfactory tubercles). A neuroethological method of presenting smells of isovaleric acid and peanut butter was used to assess the olfactory system functional state in the experimental rats. In the course of polygraphic registration of the sleep-wakefulness cycle, the representation of wakefulness and individual sleep phases, as well as proportion of incomplete and complete sleep cycles were determined. It was shown that injection of Aβ40 aggregates into the hippocampus simulates an amyloidogenic state in the rat’s hippocampus and olfactory tubercles, but not in the olfactory bulbs. Moreover, a pro-inflammatory state was registered in the hippocampus of the animal brain (an increase in the concentration of pro-inflammatory cytokines TNFα and IL-6), while the cytokine level in the olfactory bulbs and tubercles did not change. When studying the functional state of olfactory analyzers in the rats with Alzheimer's disease, we revealed negative changes in behavioral response to the smell of isovaleric acid and peanut butter. In terms of somnograms, the Aβ40 toxicity caused reduction in the deep slow-wave sleep stage combined with deficiency of the paradoxical sleep phase, and predominance of incomplete sleep cycles. Nasal therapy with miR-101 in liposomes normalized the level of Aβ42 in the hippocampus and olfactory tubercles and decreased the level of proinflammatory cytokines in the hippocampus. MiR-101 prevented olfactory disfunctions in assessing smells of isovaleric acid and peanut butter, increased the ratio of deep slow-wave sleep and paradoxical sleep in the cycle structure and restored proportion of complete sleep cycles in animals. Thus, liposomal miR-101 has an anti-amyloidogenic and anti-inflammatory effect in rats with a model of Alzheimer's disease. It helps to restore the functional state of olfactory analyzer and optimize structural organization of the sleep-wakefulness cycle in sick animals.

Brain-wide Cas9-mediated cleavage of a gene causing familial Alzheimer's disease alleviates amyloid-related pathologies in mice.

The pathology of familial Alzheimer's disease, which is caused by dominant mutations in the gene that encodes amyloid-beta precursor protein (APP) and in those that encode presenilin 1 and presenilin 2, is characterized by extracellular amyloid plaques and intracellular neurofibrillary tangles in multiple brain regions. Here we show that the brain-wide selective disruption of a mutated APP allele in transgenic mouse models carrying the human APP Swedish mutation alleviates amyloid-beta-associated pathologies for at least six months after a single intrahippocampal administration of an adeno-associated virus that encodes both Cas9 and a single-guide RNA that targets the mutation. We also show that the deposition of amyloid-beta, as well as microgliosis, neurite dystrophy and the impairment of cognitive performance, can all be ameliorated when the CRISPR-Cas9 construct is delivered intravenously via a modified adeno-associated virus that can cross the blood-brain barrier. Brain-wide disease-modifying genome editing could represent a viable strategy for the treatment of familial Alzheimer's disease and other monogenic diseases that affect multiple brain regions.

Intrahippocampal co-administration of nicotine and O-acetyl-L-carnitine prevents the H-89-induced spatial learning deficits in Morris water maze.

H-89 (a protein kinase AII [PKA II] inhibitor) impairs the spatial memory in the Morris water maze task in rats. In the present study, we aimed to study the protective effects of nicotine and O-acetyl-L-carnitine against H-89-induced spatial memory deficits. Spatial memory impairment was induced by the bilateral intrahippocampal administration of 10µM H-89 (dissolved in dimethyl sulfoxide, DMSO) to rats. The rats then received bilateral administrations of either nicotine (1μg/μL, dissolved in saline) or O-acetyl-L-carnitine (100μM/side, dissolved in deionized water) alone and in combination. Control groups received either saline, deionized water, or DMSO. The H-89-treated animals showed significant increases in the time and distance travelled to find hidden platforms, and there was also a significant decrease in the time spent in the target quadrant compared to DMSO-treated animals. Nicotine and O-acetyl-L-carnitine had no significant effects on H-89-induced spatial learning impairments alone, but the bilateral intrahippocampal co-administration of nicotine and O-acetyl-L-carnitine prevented H-89-induced spatial learning deficits and increased the time spent in the target quadrant in comparison with H-89-treated animals. Our results indicated the potential synergistic effects of nicotine and O-acetyl-L-carnitine in preventing protein kinase AII inhibitor (H-89)-induced spatial learning impairments.

The piperine derivative HJ105 inhibits Aβ1–42-induced neuroinflammation and oxidative damage via the Keap1-Nrf2-TXNIP axis

BackgroundPiperine is a great lead compound, as a phytopharmaceutical with reported neuroprotective effects in neurodegenerative diseases. HJ105, a piperine derivative with high affinity to Keap1 receptor, attracts increasing attention in Alzheimer's disease (AD) treatment. PurposeThis work mainly aimed to study HJ105’s therapeutic effects on Aβ1–42-associated AD and the underpinning mechanisms. MethodsIn the in vivo part, a rat model of AD was established by bilateral intra-hippocampal administration of aggregated Aβ1–42, followed by a month of intragastric HJ105 or donepezil administration. Spatial and learning memories were detected by the Morris water maze assay, passive avoidance learning as well as Y-maze test. The morphology of hippocampal neurons was assessed by hematoxylin-eosin (H&E) staining. In addition, the amounts of the IL-1β and TNF-α were obtained with specific ELISA kits. More importantly, apoptosis-related proteins and factors involved in Nrf2/TXNIP/NLPR3 pathways were detected by Western blot, while the interaction between Keap1 and Nrf2 was assessed by co-immunoprecipitation. In the in vitro part, human neuroblastoma (SH-SY5Y) cells were applied to evaluate the role of HJ105 on Aβ1–42-induced neuronal damage. ResultsTreatment of HJ105 not only reversed memory impairment, but also protected neurons in the hippocampus by inhibiting Bax/Bcl2 ratio increase. HJ105 decreased TXNIP expression, suppressing NLRP3 inflammasome activation in the hippocampus, which in turn counteracted the upregulation of IL-1β and TNF-α. Notably, HJ105 exerted an inhibitory effect on Keap1-Nrf2 interaction and upregulated nuclear Nrf2, which conversely increased the expression levels of superoxide dismutase, catalase and glutathione peroxidase and downregulated malondialdehyde. Additionally, neurotoxicity induced by Aβ1–42 in SH-SY5Y cells was alleviated by HJ105. ConclusionOverall, HJ105 exerts neuroprotective effects in SH-SY5Y cells induced by Aβ1–42 as well as in experimental rats with AD by decreasing apoptosis, oxidative stress and neuroinflammation, partly via suppression of Keap1-Nrf2 complex generation. HJ105 might represent a promising compound for AD treatment.

The Effect of Omega-lycotoxin on the Cognitive Impairment Induced by Kainic Acid in Rats

Background: Excitotoxicity is a common pathological process in neurodegenerative diseases associated with overactivity of N-methyl-D-aspartate (NMDA) and P/Q type voltage-gated calcium (Cav2.1) channels. Omega-lycotoxin-Gsp2671g is a therapeutic tool to modulate overactive Cav2.1 (P/Q type) channels. Omega-lycotoxin binds to Cav2.1 channels with high affinity and selectivity. This study aimed to investigate the effects of Omega-lycotoxin on the cognitive impairment induced by kainic acid in rats. Methods: The effect of pre-treatment and post-treatment trials of intra-hippocampal Cornu Ammonis-3 administration of omega-lycotoxin (0.5, 1 or 2µg) was studied on the cognitive impairment induced by kainic acid in rats. The rats’ learning and memory were assessed by the passive avoidance and a single-day testing version of the Morris water maze method. Results: Omega-lycotoxin caused a significant increase in the latency of the passive avoidance test and the duration of their presence in the target area of the Morris water maze test compared to the groups treated with kainic acid (P&lt;0.0001). There were statistically significant differences for the effects of various doses of omega-lycotoxin. The post-treatment groups showed a greater improvement than those in the pretreatment groups. Conclusion: The findings demonstrated that a single dose of omega-lycotoxin can prevent or revert the memory impairment caused by kainic acid in rats.

The Interplay Between Beta-Amyloid 1-42 (Aβ1-42)-Induced Hippocampal Inflammatory Response, p-tau, Vascular Pathology, and Their Synergistic Contributions to Neuronal Death and Behavioral Deficits.

Alzheimer’s disease (AD), the most common chronic neurodegenerative disorder, has complex neuropathology. The principal neuropathological hallmarks of the disease are the deposition of extracellular β-amyloid (Aβ) plaques and neurofibrillary tangles (NFTs) comprised of hyperphosphorylated tau (p-tau) protein. These changes occur with neuroinflammation, a compromised blood-brain barrier (BBB) integrity, and neuronal synaptic dysfunction, all of which ultimately lead to neuronal cell loss and cognitive deficits in AD. Aβ1–42 was stereotaxically administered bilaterally into the CA1 region of the hippocampi of 18-month-old male C57BL/6 mice. This study aimed to characterize, utilizing immunohistochemistry and behavioral testing, the spatial and temporal effects of Aβ1–42 on a broad set of parameters characteristic of AD: p-tau, neuroinflammation, vascular pathology, pyramidal cell survival, and behavior. Three days after Aβ1–42 injection and before significant neuronal cell loss was detected, acute neuroinflammatory and vascular responses were observed. These responses included the up-regulation of glial fibrillary acidic protein (GFAP), cell adhesion molecule-1 (PECAM-1, also known as CD31), fibrinogen labeling, and an increased number of activated astrocytes and microglia in the CA1 region of the hippocampus. From day 7, there was significant pyramidal cell loss in the CA1 region of the hippocampus, and by 30 days, significant localized up-regulation of p-tau, GFAP, Iba-1, CD31, and alpha-smooth muscle actin (α-SMA) in the Aβ1–42-injected mice compared with controls. These molecular changes in Aβ1–42-injected mice were accompanied by cognitive deterioration, as demonstrated by long-term spatial memory impairment. This study is reporting a comprehensive examination of a complex set of parameters associated with intrahippocampal administration of Aβ1–42 in mice, their spatiotemporal interactions and combined contribution to the disease progression. We show that a single Aβ injection can reproduce aspects of the inflammatory, vascular, and p-tau induced pathology occurring in the AD human brain that lead to cognitive deficits.

Evidence of Progenitor Cell Lineage Rerouting in the Adult Mouse Hippocampus After Status Epilepticus

Cell lineage in the adult hippocampus comprises multipotent and neuron-committed progenitors. In the present work, we fate-mapped neuronal progenitors using Dcx-CreERT2 and CAG-CAT-EGFP double-transgenic mice (cDCX/EGFP). We show that 3 days after tamoxifen-mediated recombination in cDCX/EGFP adult mice, GFP+ cells in the dentate gyrus (DG) co-expresses DCX and about 6% of these cells are proliferative neuronal progenitors. After 30 days, 20% of GFP+ generated from these progenitors differentiate into GFAP+ astrocytes. Unilateral intrahippocampal administration of the chemoconvulsants kainic acid (KA) or pilocarpine (PL) triggered epileptiform discharges and led to a significant increase in the number of GFP+ cells in both ipsi and contralateral DG. However, while PL favored the differentiation of neurons in both ipsi- and contralateral sides, KA stimulated neurogenesis only in the contralateral side. In the ipsilateral side, KA injection led to an unexpected increase of astrogliogenesis in the Dcx-lineage. We also observed a small number of GFP+/GFAP+ cells displaying radial-glia morphology ipsilaterally 3 days after KA administration, suggesting that some Dcx-progenitors could regress to a multipotent stage. The boosted neurogenesis and astrogliogenesis observed in the Dcx-lineage following chemoconvulsants administration correlated, respectively, with preservation or degeneration of the parvalbuminergic plexus in the DG. Increased inflammatory response, by contrast, was observed both in the DG showing increased neurogenesis or astrogliogenesis. Altogether, our data support the view that cell lineage progression in the adult hippocampus is not unidirectional and could be modulated by local network activity and GABA-mediated signaling.

Cross-Frequency Phase-Amplitude Coupling between Hippocampal Theta and Gamma Oscillations during Recall Destabilizes Memory and Renders It Susceptible to Reconsolidation Disruption.

Avoidance memory reactivation at recall triggers theta-gamma hippocampal phase amplitude coupling (hPAC) only when it elicits hippocampus-dependent reconsolidation. However, it is not known whether there is a causal relationship between these phenomena. We found that in adult male Wistar rats, silencing the medial septum during recall did not affect avoidance memory expression or maintenance but abolished hPAC and the amnesia caused by the intrahippocampal administration of reconsolidation blockers, both of which were restored by concomitant theta burst stimulation of the fimbria-fornix pathway. Remarkably, artificial hPAC generated by fimbria-fornix stimulation during recall of a learned avoidance response naturally resistant to hippocampus-dependent reconsolidation made it susceptible to reactivation-dependent amnesia. Our results indicate that hPAC mediates the destabilization required for avoidance memory reconsolidation and suggest that the generation of artificial hPAC at recall overcomes the boundary conditions of this process.SIGNIFICANCE STATEMENT Theta-gamma hippocampal phase-amplitude coupling (hPAC) increases during the induction of hippocampus-dependent avoidance memory reconsolidation. However, whether hPAC plays a causal role in this process remains unknown. Using behavioral, electrophysiological, optogenetic, and biochemical tools in adult male Wistar rats, we demonstrate that reactivation-induced hPAC is necessary for avoidance memory destabilization, and that artificial induction of this patterned activity during recall of reconsolidation-resistant aversive memories renders them liable to the amnesic effect of reconsolidation inhibitors.

Involvement of hippocampal agmatine in β1-42 amyloid induced memory impairment, neuroinflammation and BDNF signaling disruption in mice

Alzheimer's disease (AD) is a chronic and progressive neurodegenerative disorder characterized by abnormal accumulation of extracellular β-amyloid (Aβ) plaques and neuronal damage. The present study investigated the effect of chronic intra-hippocampal agmatine administration on β-Amyloid (Aβ) induced memory impairment in mice. Aβ1-42 peptide injected mice demonstrated impairment of cognitive abilities evaluated as reference memory error and working memory error in radial arm maze (RAM) and decreased exploration time for novel object as well as recognition index in novel object recognition (NOR) test along with elevation in Aβ1-42 peptide, β-Site APP cleaving enzyme 1 (BACE 1), microtubule-associated protein tau (MAPt), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and reduction in neprilysin and brain derived neurotrophic factor (BDNF) immunocontent within hippocampus and prefrontal cortex. Importantly, this was associated with a reduction in the agmatine levels following Aβ1-42 peptide administration. Chronic administration of agmatine from day 8–27, prevented the memory impairment in mice and normalized the neurochemical alteration within prefrontal cortex and hippocampus induced by Aβ1-42 peptide administration. However, it did not modulate the amyloid precursor protein and BACE expression. This study suggests that agmatine improves learning and memory impairment possibly through the down regulation of neuroinflammatory pathways in AD.

The facilitating effect of MK-801 on inhibitory avoidance memory via mTOR signaling in the mouse hippocampus

Despite the widespread belief that MK-801 induces memory deficits associated with dementia and schizophrenia in animal models, data regarding the impairing effect of MK-801 on aversive memory have been inconclusive. In this study, we investigated the effect of MK-801 on multiple memory stages of the inhibitory avoidance task, as well as its underlying signaling mechanism in the mouse hippocampus. We successfully replicated a previous finding suggesting that systemic injection of MK-801 impaired memory acquisition, but we observed that an intrahippocampal infusion of MK-801 facilitated the same memory process. We also found that both systemic and intrahippocampal administration of MK-801 facilitated memory consolidation and memory retrieval of the inhibitory avoidance task. We demonstrated that MK-801-induced increases in shock sensitivity and locomotor activity in the pre-training regimen confounded the detrimental effect of MK-801 on memory acquisition, thereby reconciling the inconsistent results in previous studies. In addition, the memory-facilitating effect of MK-801 was found to be dependent on drug dose and shock intensity. We next showed that MK-801 induced a fast-onset increase in the extent of mammalian target of rapamycin (mTOR) phosphorylation in the hippocampus. Finally, we observed that rapamycin, an mTOR inhibitor, blocked both the MK-801-induced increases in phosphorylated mTOR and the facilitating effect of MK-801 on memory consolidation. These results indicate that hippocampal mTOR signaling mediates the facilitating effect of MK-801 on memory consolidation of the inhibitory avoidance task. These findings further imply that MK-801 indeed functions as a memory enhancer and that mTOR signaling serves as a therapeutic target for memory disorders.

Effect of β-asarone in normal and β-amyloid-induced Alzheimeric rats.

Introductionβ-Asarone is a major component of Acorus tatarinowii Schott. It has pharmacological effects that include antihyperlipidemic, anti-inflammatory, and antioxidant activity. In the present study, the effect of β-asarone on neurodegeneration induced by intrahippocampal administration of β-amyloid was investigated in adult male Wistar rats.Material and methodsThe rats were randomly divided into 9 groups: normal control, sham-operated control, β-asarone (12.5, 25, and 50 mg/kg intragastrically, daily) alone, Alzheimeric control rats (β-amyloid, intrahippocampal), β-asarone (12.5, 25, and 50 mg/kg intragastrically, daily) together with β-amyloid, and treatment was performed accordingly. Animals were injected with β-amyloid bilaterally. Animals received β-asarone daily using an intragastric tube for 50 days, starting from 30 days before administration of the β-amyloid. The rats were sacrificed and parameters of oxidative stress, superoxide dismutase (SOD) and glutathione peroxidase (GPX) activity were measured in hippocampus homogenate. Histopathological changes were examined by Bielschowsky staining.ResultsOur results showed that administration of β-asarone (25 and 50 mg/kg) significantly increased the levels of antioxidant enzymes, including SOD (1.09 ±0.02, 1.21 ±0.02, p < 0.001, respectively) and GPX (58.94 ±0.78, 68.92 ±3.64, p < 0.001, respectively) in comparison with Alzheimeric control rats (SOD and GPX level for Alzheimeric control group: 0.44 ±0.01, 35.09 ±1.15, respectively). Histopathological examination showed that β-asarone decreased cell loss in the cerebral cortex and hippocampus in Alzheimeric rats.ConclusionsThese results indicate that β-asarone is effective in providing protection against oxidative stress and neuronal damage induced by β-amyloid.

Ultrastructural Evidence for a Role of Astrocytes and Glycogen-Derived Lactate in Learning-Dependent Synaptic Stabilization.

Long-term memory formation (LTM) is a process accompanied by energy-demanding structural changes at synapses and increased spine density. Concomitant increases in both spine volume and postsynaptic density (PSD) surface area have been suggested but never quantified in vivo by clear-cut experimental evidence. Using novel object recognition in mice as a learning task followed by 3D electron microscopy analysis, we demonstrate that LTM induced all aforementioned synaptic changes, together with an increase in the size of astrocytic glycogen granules, which are a source of lactate for neurons. The selective inhibition of glycogen metabolism in astrocytes impaired learning, affecting all the related synaptic changes. Intrahippocampal administration of l-lactate rescued the behavioral phenotype, along with spine density within 24 hours. Spine dynamics in hippocampal organotypic slices undergoing theta burst-induced long-term potentiation was similarly affected by inhibition of glycogen metabolism and rescued by l-lactate. These results suggest that learning primes astrocytic energy stores and signaling to sustain synaptic plasticity via l-lactate.

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.

Brain-derived neurotrophic factor (BDNF) is an essential product of protein synthesis with a prominent impact on brain signaling and synaptic plasticity. Exogenous application of this neurotrophin is able to induce long-term potentiation (LTP) in several brain structures such as the hippocampus along with increases in gene transcription and translation of proteins involved in functional and structural plasticity. In this regard, our previous studies have demonstrated that acute intrahippocampal administration of BDNF induces long-lasting enhancement of synaptic transmission at the mossy fibers projection (MF) accompanied by a structural reorganization at the CA3 hippocampus area. Thus, considering the non-canonical molecular mechanisms underlying MF-CA3-LTP and the high expression of this neurotrophin in the CA3 area, we wonder whether transcriptional and translational inhibition interferes with the persistence of the MF functional and structural synaptic plasticity elicited by BDNF in adult rats in vivo. Our results show that BDNF is able to induce a lasting potentiation of synaptic efficacy at the MF projection accompanied by a structural reorganization at the CA3 area in an mRNA synthesis and protein translation-independent manner. The present findings support the idea that BDNF is an essential plasticity related product, which is necessary and sufficient to induce and maintain functional and structural synaptic plasticity at the MF-CA3 pathway.