MPTP-meditated hippocampal dopamine deprivation modulates synaptic transmission and activity-dependent synaptic plasticity

Identifying candidate genes associated with hippocampal dysfunction in a hemiparkinsonian rat model by transcriptomic profiling

Parkinson's disease (PD) often results in hippocampal dysfunction, which leads to cognitive and emotional challenges and synaptic irregularities. This study attempted to assess behavioral anomalies and identify differentially expressed genes (DEGs) within the hippocampus of a hemiparkinsonian rat model to potentially uncover novel genetic candidates linked to hippocampal dysfunction. Striatal 6-hydroxydopamine (6-OHDA) infusions were performed unilaterally in the brains of adult SD rats, while dopaminergic impairments were verified in rats with 6-OHDA-lesioned striata. RNA sequencing and gene expression analysis unveiled 1018 DEGs in the ipsilateral rat hippocampus following 6-OHDA infusion: 631 genes exhibited upregulation, while 387 genes were downregulated (with FDR-adjusted p-value < 0.05 and absolute fold-change > 1.5). Gene ontology analysis of DEGs indicated that alterations in the hippocampi of 6-OHDA-lesioned rats were primarily associated with synaptic signaling, axon development, behavior, postsynaptic membrane, synaptic membrane, neurotransmitter receptor activity, and peptide receptor activity. The Kyoto Encyclopedia of Genes and Genomes analysis of DEGs demonstrated significant enrichment of the neuroactive ligand-receptor interaction, calcium signaling pathway, cAMP signaling pathway, axon guidance, and notch signaling pathway in rat hippocampi that had been subjected to striatal 6-OHDA infusion. STRING analysis confirmed a notable upregulation of eight hub genes (Notch3, Gng4, Itga3, Grin2d, Hgf, Fgf11, Htr3a, and Col6a2), along with a significant downregulation of two hub genes (Itga11 and Plp1), as validated by reverse transcription-quantitative polymerase chain reaction. This study provides a comprehensive transcriptomic profile of the hippocampi in a hemiparkinsonian rat model, thereby offering insights into the signaling pathways underlying hippocampal dysfunction.

NRSF regulates age-dependently cognitive ability and its conditional knockout in APP/PS1 mice moderately alters AD-like pathology

NRSF/REST (neuron-restrictive silencer element, also known as repressor element 1-silencing transcription factor), plays a key role in neuronal homeostasis as a transcriptional repressor of neuronal genes. NRSF/REST relates to cognitive preservation and longevity of humans, but its specific functions in age-dependent and Alzheimer's disease (AD)-related memory deficits remain unclear. Here, we show that conditional NRSF/REST knockout either in the dorsal telencephalon or specially in neurons induced an age-dependently diminished retrieval performance in spatial or fear conditioning memory tasks and altered hippocampal synaptic transmission and activity-dependent synaptic plasticity. The NRSF/REST deficient mice were also characterized by an increase of activated glial cells, complement C3 protein and the transcription factor C/EBPβ in the cortex and hippocampus. Reduction of NRSF/REST by conditional depletion upregulated the activation of astrocytes in APP/PS1 mice, and increased the C3-positive glial cells, but did not alter the Aβ loads and memory retrieval performances of 6- and 12-month-old APP/PS1 mice. Simultaneously, overexpression of NRSF/REST improved cognitive abilities of aged wild type, but not in AD mice. These findings demonstrated that NRSF/REST is essential for the preservation of memory performance and activity-dependent synaptic plasticity during aging and takes potential roles in the onset of age-related memory impairments. However, while altering the glial activation, NRSF/REST deficiency does not interfere with the Aβ deposits and the electrophysiological and cognitive AD-like pathologies.

Updates on the Physiopathology of Group I Metabotropic Glutamate Receptors (mGluRI)-Dependent Long-Term Depression

Group I metabotropic glutamate receptors (mGluRI), including mGluR1 and mGluR5 subtypes, modulate essential brain functions by affecting neuronal excitability, intracellular calcium dynamics, protein synthesis, dendritic spine formation, and synaptic transmission and plasticity. Nowadays, it is well appreciated that the mGluRI-dependent long-term depression (LTD) of glutamatergic synaptic transmission (mGluRI-LTD) is a key mechanism by which mGluRI shapes connectivity in various cerebral circuitries, directing complex brain functions and behaviors, and that it is deranged in several neurological and psychiatric illnesses, including neurodevelopmental disorders, neurodegenerative diseases, and psychopathologies. Here, we will provide an updated overview of the physiopathology of mGluRI-LTD, by describing mechanisms of induction and regulation by endogenous mGluRI interactors, as well as functional physiological implications and pathological deviations.

Treadmill Exercise Alleviates Cognition Disorder by Activating the FNDC5: Dual Role of Integrin αV/β5 in Parkinson's Disease

Parkinson's disease with cognitive impairment (PD-CI) results in several clinical outcomes for which specific treatment is lacking. Although the pathogenesis of PD-CI has not yet been fully elucidated, it is related to neuronal plasticity decline in the hippocampus region. The dopaminergic projections from the substantia nigra to the hippocampus are critical in regulating hippocampal plasticity. Recently, aerobic exercise has been recognized as an effective therapeutic strategy for enhancing plasticity through the secretion of various muscle factors. The exact role of FNDC5-an upregulated, newly identified myokine produced after exercise-in mediating hippocampal plasticity and regional dopaminergic projections in PD-CI remains unclear. In this study, the effect of treadmill exercise on hippocampal synaptic plasticity was evaluated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced chronic PD models. The results showed that treadmill exercise substantially alleviated the motor dysfunction, cognition disorder, and dopaminergic neuron degeneration induced by MPTP. Here, we discovered that the quadriceps, serum, and brain FNDC5 levels were lower in PD mice and that intervention with treadmill exercise restored FNDC5 levels. Moreover, treadmill exercise enhanced the synaptic plasticity of hippocampal pyramidal neurons via increased dopamine levels and BDNF in the PD mice. The direct protective effect of FNDC5 is achieved by promoting the secretion of BDNF in the hippocampal neurons via binding the integrin αVβ5 receptor, thereby improving synaptic plasticity. Regarding the indirect protection effect, FNDC5 promotes the dopaminergic connection from the substantia nigra to the hippocampus by mediating the interaction between the integrin αVβ5 of the hippocampal neurons and the CD90 molecules on the membrane of dopaminergic terminals. Our findings demonstrated that treadmill exercise could effectively alleviate cognitive disorders via the activation of the FNDC5-BDNF pathway and enhance the dopaminergic synaptic connection from SNpc to the hippocampus in the MPTP-induced chronic PD model.

Cordycepin improved the cognitive function through regulating adenosine A2A receptors in MPTP induced Parkinson's disease mice model

BACKGROUND

Parkinson's disease (PD), the most common neurodegenerative disorder, primarily affects dopaminergic neurons in the substantia nigra (SN). In addition to severe motor dysfunction, PD patients appear apparent cognitive impairments in the late stage. Cognitive dysfunction is accompanied by synaptic transmission damage in the hippocampus. Cordycepin has been reported to alleviate cognitive impairments in neurodegenerative diseases.

PURPOSE

The study aimed to estimate the protection roles of cordycepin on cognitive dysfunction in PD model and explore the potential mechanisms.

METHODS

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was used to establish the PD model in vivo and in vitro experiments. In the in vivo experiments, the C57BL / 6 mice were intraperitoneally injected with MPTP and intragastric administration with cordycepin. Open field test (OFT) was used to estimate the exercise ability. Spontaneous alternation behavioral (SAB) and morris water maze (MWM) tests were used to evaluate the learning and memory abilities. The hippocampal slices from C57BL / 6 and Kunming mice in the in vitro experiments were used to record field excitatory postsynaptic potential (fEPSP) by electrophysiological methods. Western blotting was used to examine the level of tyrosine hydroxylase (TH) in the in vivo experiments and the levels of adenosine A₁ and A_2A receptors (A₁R and A_2AR) in the in vitro experiments, respectively. The drugs of MPTP, cordycepin, DPCPX and SCH58261 were perfused through dissolving in artificial cerebrospinal fluid.

RESULTS

Cordycepin could significantly reduce the impairments on motor, exploration, spatial learning and memory induce by MPTP. MPTP reduced the amplitude of LTP in hippocampal CA1 area but cordycepin could improve LTP amplitudes. Cordycepin at dosage of 20 mg/kg also increased the TH level in SN. In the in vitro experiments, MPTP inhibited synaptic transmission in hippocampal Schaffer-CA1 pathway with a dose-dependent relationship, while cordycepin could reverse the inhibition of synaptic transmission. Furthermore, the roles of cordycepin on synaptic transmission could been attenuated in the presence of the antagonists of A₁R and A_2AR, DPCPX and SCH58261, respectively. Interestingly, the level of A_2AR rather than A₁R in hippocampus was significantly decreased in the cordycepin group as compared to the control.

CONCLUSION

The present study has showed that cordycepin could improve cognitive function in the PD model induced by MPTP through regulating the adenosine A_2A receptors. These findings were helpful to provide a new strategy for the dementia caused by Parkinson's disease.

The effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on the cognitive and motor functions in rodents: A systematic review and meta-analysis

Memory and motor deficits are commonly identified in Parkinson's disease (PD). 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is transformed to MPP+ via monoamine oxidase B (MAOB), which causes oxidative stress and destroys dopaminergic (DA) neurons in substantia nigra pars compacta (SNc) and is widely used to create animal models of PD. However, to-date, a comprehensive analysis of the MPTP effects on various aspects of PD does not exist. Here, we provide a systematic review and meta-analysis on the MPTP effects on memory and motor functions by analyzing 51 studies on more than one thousand animals mainly including rats and mice. The results showed that in addition to motor functions such as coordination, balance and locomotor activity, MPTP significantly affects various mnemonic processes including spatial memory, working memory, recognition memory, and associative memory compared with the control group with some differences between systemic and intra-nigral injections on spatial memory, familiar object recognition, and anxiety-like behaviors. Nevertheless, our analysis failed to find systematic relationship between MPTP injection protocol parameters reported and the extent of the induced PD symptoms that can be a cause of concern for replicability of MPTP studies.

Probing the Neural Circuitry Targets of Neurotoxicants In Vivo Through High Density Silicon Probe Brain Implants

Adverse effects of drugs on the human nervous system are rarely possible to anticipate based on preclinical neurotoxicity data, thus propagating the centuries long single most important obstacle to drug discovery and development for disorders of the nervous system. An emerging body of evidence indicates that in vivo electrophysiology using chronically implanted high-density electrodes (ciHDE) in freely moving animals is a rigorous method with enhanced potential for use in translational research. In particular, the structure and function of the hippocampal trisynaptic circuit (HTC) is conserved from rodents to primates, including Homo sapiens, suggesting that the effects of therapeutic agents and other potential neurologically active agents, whether beneficial or adverse, are likely to translate across species when interrogated using a conserved neural circuitry platform. This review explores science advances in the rapidly moving field of in vivo ciHDE in animal models of learning and memory. For this reason we focus on the HTC, where substantial research has investigated neural circuitry level responses and specific behaviors that reflect memory permitting a test of the ground truth validity of the findings. Examples of changes in neural network activity induced by endogenous neurotoxicants associated with neurodegenerative diseases, as well as exogenous therapeutics, drugs, and neurotoxicants are presented. Several illustrative examples of relevant findings that involve longer range neural circuitry outside of the HTC are discussed. Lastly, the limitations of in vivo ciHDE as applied to preclinical neurotoxicology are discussed with a view toward leveraging circuitry level actions to enhance our ability to project the specificity of in vitro target engagement with the desired psychopharmacological or neurological outcome. At the same time, the goal of reducing or eliminating significant neurotoxic adverse events in human is the desired endpoint. We believe that this approach will lead to enhanced discovery of high value neuroactive therapeutics that target neural circuitry domains as their primary mechanism of action, thus enhancing their ultimate contribution toward discovery of precision therapeutics.

Acute MPTP Treatment Impairs Dendritic Spine Density in the Mouse Hippocampus

Among the animal models of Parkinson’s disease (PD), the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mouse model has shown both dopaminergic (DA) damage and related motor control defects, as observed in patients with PD. Recent studies have suggested that the DA system interacts with the synaptic plasticity of the hippocampus in PD. However, little is known about how alterations in the hippocampal structural plasticity are affected by the DA damage in MPTP-lesioned models. In the present study, we investigated alterations in dendritic complexity and spine density in the mouse hippocampus following acute MPTP treatment (22 mg/kg, intraperitoneally, four times/day, 2-h intervals). We confirmed that acute MPTP treatment significantly decreased initial motor function and persistently reduced the number of tyrosine hydroxylase-positive DA neurons in the substantia nigra. Golgi staining showed that acute MPTP treatment significantly reduced the spine density of neuronal dendrites in the cornu ammonis 1 (CA1) apical/basal and dentate gyrus (DG) subregions of the mouse hippocampus at 8 and 16 days after treatment, although it did not affect dendritic complexity (e.g., number of crossing dendrites, total dendritic length, and branch points per neuron) in both CA1 and DG subregions at all time points after treatment. Therefore, the present study provides anatomical evidence that acute MPTP treatment affects synaptic structure in the hippocampus during the late phase after acute MPTP treatment in mice, independent of any changes in the dendritic arborization of hippocampal neurons. These findings offer data for the ability of the acute MPTP-lesioned mouse model to replicate the non-nigrostriatal lesions of clinical PD.

Transcranial Magneto-Acoustic Stimulation Improves Neuroplasticity in Hippocampus of Parkinson's Disease Model Mice

In this study, we have, for the first time, demonstrated the beneficial effects of transcranial magneto-acoustic stimulation (TMAS), a technique based on focused ultrasound stimulation within static magnetic field, on the learning and memory abilities and neuroplasticity of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). Our results showed that chronic TMAS treatment (2 weeks) improved the outcome of Morris water maze, long-term potentiation (LTP), and dendritic spine densities in the dentate gyrus (DG) region of the hippocampus of PD model mice. To further investigate into the underlying mechanisms of these beneficial effects by TMAS, we quantified the proteins in the hippocampus that regulated neuroplasticity. Results showed that the level of postsynaptic density protein 95 was elevated in the brain of TMAS-treated PD model mice while the level of synaptophysin (SYP) did not show any change. We further quantified proteins that mediated neuroplasticity mechanisms, such as brain-derived neurotrophic factor (BDNF) and other important proteins that mediated neuroplasticity. Results showed that TMAS treatment elevated the levels of BDNF, cAMP response element-binding protein (CREB), and protein kinase B (p-Akt) in the PD model mouse hippocampus, but not in the non-PD mouse hippocampus. These results suggest that the beneficial effects on the neuroplasticity of PD model mice treated with TMAS could possibly be conducted through postsynaptic regulations and mediated by BDNF.

Inhibition of MPTP-induced α-synuclein oligomerization by fatty acid-binding protein 3 ligand in MPTP-treated mice

Accumulation and aggregation of α-synuclein (αSyn) triggers dopaminergic (DAergic) neuronal loss in Parkinson's disease (PD). This pathological event is partly facilitated by the presence of long-chain polyunsaturated fatty acids (LC-PUFAs), including arachidonic acid. The intracellular transport and metabolism of LC-PUFAs are mediated by fatty acid-binding proteins (FABPs). We previously reported that heart-type FABP (FABP3) interacts with αSyn, thereby promoting αSyn oligomerization in DAergic neurons in the substantia nigra pars compacta (SNpc) following 1-methyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. This αSyn oligomerization is prevented in Fabp3 gene knock out mice. We document a novel FABP3 ligand, MF1 (4-(2-(1-(2-chlorophenyl)-5-phenyl-1H-pyrazol-3-yl)phenoxy)butanoic acid), that inhibits αSyn accumulation in DA neurons, thereby inhibiting the oligomerization of αSyn, loss of DAergic neurons, and PD-like motor deficits in MPTP-treated mice. Chronic oral administration of MF1 (0.3 or 1.0 mg/kg/day) significantly improved motor impairments and inhibited MPTP-induced accumulation and oligomerization of αSyn in the SNpc, and in turn prevented loss of tyrosine hydroxylase (TH)-positive cells in the SNpc. MF1 administration (0.1, 0.3, or 1.0 mg/kg/day) also restored MPTP-induced cognitive impairments. Although chronic administration of l-DOPA (3,4-dihydroxl-l-phenylalanine; 25 mg/kg/day, i.p.) also improved motor deficits, it failed to improve the cognitive impairments. In addition, l-DOPA failed to inhibit DAergic neuronal loss and αSyn pathologies in the SNpc. In summary, the novel FABP3 ligand MF1 rescues MPTP-induced behavioural and neuropathological features, suggesting that MF1 may be a disease-modifying drug candidate for synucleinopathies.

Mechanisms by which fibroblast growth factor 20 improves motor performance in a mouse model of Parkinson's disease

Genome-wide studies have reported that Parkinson’s disease is associated with abnormal expression of various growth factors. In this study, male C57BL/6 mice aged 10 weeks were used to establish Parkinson’s disease models using an intraperitoneal injection of 60 mg/kg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 28 days later, 10 or 100 ng fibroblast growth factor 20 was injected intracerebroventricularly. The electrophysiological changes in the mouse hippocampus were recorded using a full-cell patch clamp. Expression of Kv4.2 in the substantia nigra was analyzed using a western blot assay. Serum malondialdehyde levels were analyzed by enzyme-linked immunosorbent assay. The motor coordination of mice was evaluated using the rotarod test. The results showed that fibroblast growth factor 20 decreased A-type potassium current in neurons of the substantia nigra, increased long-term potentiation amplitude in the hippocampus, and downregulated Kv4.2 expression. A high dose of fibroblast growth factor 20 reduced serum malondialdehyde levels and enhanced the motor coordination of mice. These findings confirm that fibroblast growth factor 20 has a therapeutic effect on the toxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and its mechanism of action is associated with the inhibition of A-type K⁺ currents and Kv4.2 expression. All animal procedures were approved by the Animal Care and Use Committee of Qilu Hospital of Shandong University, China in 2017 (approval No. KYLL-2017-0012).

Intracerebroventricularly-administered 1-methyl-4-phenylpyridinium ion and brain-derived neurotrophic factor affect catecholaminergic nerve terminals and neurogenesis in the hippocampus, striatum and substantia nigra

Parkinson's disease is a progressive neurological disease characterized by the degeneration of dopaminergic neurons in the substantia nigra. A highly similar pattern of neurodegeneration can be induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 1-methyl-4-phenylpyridinium ion (MPP⁺), which cause the death of dopaminergic neurons. Administration of MPTP or MPP⁺ results in Parkinson's disease-like symptoms in rodents. However, it remains unclear whether intracerebroventricular MPP⁺ administration affects neurogenesis in the substantia nigra and subgranular zone or whether brain-derived neurotrophic factor alters the effects of MPP⁺. In this study, MPP⁺ (100 nmol) was intracerebroventricularly injected into mice to model Parkinson's disease. At 7 days after administration, the number of bromodeoxyuridine (BrdU)-positive cells in the subgranular zone of the hippocampal dentate gyrus increased, indicating enhanced neurogenesis. In contrast, a reduction in BrdU-positive cells was detected in the substantia nigra. Administration of brain-derived neurotrophic factor (100 ng) 1 day after MPP⁺ administration attenuated the effect of MPP⁺ in the subgranular zone and the substantia nigra. These findings reveal the complex interaction between neurotrophic factors and neurotoxins in the Parkinsonian model that result in distinct effects on the catecholaminergic system and on neurogenesis in different brain regions.

Pramipexole restores depressed transmission in the ventral hippocampus following MPTP-lesion

The hippocampus has a significant association with memory, cognition and emotions. The dopaminergic projections from both the ventral tegmental area and substantia nigra are thought to be involved in hippocampal activity. To date, however, few studies have investigated dopaminergic innervation in the hippocampus or the functional consequences of reduced dopamine in disease models. Further complicating this, the hippocampus exhibits anatomical and functional differentiation along its dorso-ventral axis. In this work we investigated the role of dopamine on hippocampal long term potentiation using D-amphetamine, which stimulates dopamine release, and also examined how a dopaminergic lesion affects the synaptic transmission across the anatomic subdivisions of the hippocampus. Our findings indicate that a 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine induced dopaminergic lesion has time-dependent effects and impacts mainly on the ventral region of the hippocampus, consistent with the density of dopaminergic innervation. Treatment with a preferential D₃ receptor agonist pramipexole partly restored normal synaptic transmission and Long-Term Potentiation. These data suggest a new mechanism to explain some of the actions of pramipexole in Parkinson´s disease.

Impairment in the mesohippocampal dopamine circuit following exposure to the brominated flame retardant, HBCDD

Many chemicals have been used to increase the safety of consumer products by reducing their flammability and risk for ignition. Recent focus on brominated flame retardants, such as polybrominated diphenyl ethers (PBDEs) has shown them to contribute to neurobehavioral deficits in children, including learning and memory. As the manufacture and use of PBDEs have been reduced, replacement chemicals, such as hexabromocyclododecane (HBCDD) have been substituted. Our current study evaluated the neurotoxicity of HBCDD, concentrating on dopaminergic innervation to the hippocampus. Using an in vivo model, we exposed male mice to HBCDD and then assessed alterations to the dopamine synapse 6 weeks later. These exposures elicited significant reductions in presynaptic dopaminergic proteins, including TH, COMT, MAO-B, DAT, VMAT2, and alpha-synuclein. In contrast, postsynaptic dopamine receptors were not impaired. These findings suggest that the mesohippocampal dopamine circuit is vulnerable to HBCDD and the dopamine terminal may be a selective target for alteration.

MPP+ inhibits mGluR1/5-mediated long-term depression in mouse hippocampus by calpain activation

Neurotoxins are harmful to nervous system and cause either neuronal cell death or impairment of synaptic activity, which contributes to Parkinson's disease or other neuronal disorders. Hippocampal synaptic plasticity was proposed as a cellular model for memory processing. In this study, we reported a novel effect of neurotoxin, 1-methyl-4-phenylpyridinium (MPP⁺), on metabotropic glutamate receptor 1/5 agonist, 3,5-dihydroxyphenylglycine (DHPG)-induced hippocampal synaptic plasticity, and MPP⁺ incubation blocked DHPG-induced hippocampal long-term depression (LTD) in Schaffer collateral-CA1 synapses. Our further findings indicated that, this blockage was reversed by pre-application of calpain inhibitor III, but not by cathepsin inhibitors. Biochemical analysis showed that MPP⁺ treatment stimulated calpain activation, displayed by spectrin breakdown. Interestingly, the level and activity of protein tyrosine phosphatase 1B (PTP1B) were reduced after MPP⁺ incubation and the decrease of PTP1B was prohibited by calpain inhibitor III. In addition, PTP1B inhibitor also blocked DHPG-induced LTD, mimicking the effect of MPP⁺. In summary, our data implicated that MPP⁺ activated calpain-dependent PTP1B degradation, which subsequently impaired hippocampal LTD. This novel effect of MPP⁺ might partially explain the impairment of memory processing in the pathogenesis of PD.

A drug delivery hydrogel system based on activin B for Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Activins are members of the superfamily of transforming growth factors and have many potential neuroprotective effects. Herein, at the first place, we verified activin B's neuroprotective role in a PD model, and revealed that activin B's fast release has limited function in the PD therapy. To this end, we developed a multi-functional crosslinker based thermosensitive injectable hydrogels to deliver activin B, and stereotactically injected the activin B-loaded hydrogel into the striatum of a mouse model of PD. The histological evaluation showed that activin B can be detected even 5 weeks post-surgery in PD mice implanted with activin B-loaded hydrogels, and activin B-loaded hydrogels can significantly increase the density of tyrosine hydroxylase positive (TH(+)) nerve fibers and reduce inflammatory responses. The behavioral evaluation demonstrated that activin B-loaded hydrogels significantly improved the performance of the mice in the PD model. Meanwhile, we found that hydrogels can slightly induce the activation of microglia cells and astrocytes, while cannot induce apoptosis in the striatum. Overall, our data demonstrated that the developed activin B-loaded hydrogels provide sustained release of activin B for over 5 weeks and contribute to substantial cellular protection and behavioral improvement, suggesting their potential as a therapeutic strategy for PD.

Neuroprotective effects of 3-O-demethylswertipunicoside against MPTP-induced Parkinson's disease in vivo and its antioxidant properties in vitro

3-O-demethylswertipunicoside (3-ODS) has been reported to protect dopaminergic neurons against neurotoxicity induced by 1-methyl-4-phenylpyridinium (MPP(+)) in PC12 cells. Here, we investigate the neuroprotective effects in vivo and antioxidant activities in vitro of 3-ODS. In the 1-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP)-treated mouse model of Parkinson's disease (PD), 3-ODS dose-dependently improved motor coordination (as shown by rotarod test), increased the contents of dopamine (DA) and its metabolites in the striatum, and increased the number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra (SN). In addition, 3-ODS also increased the spine density in hippocampal CA1 neurons. In antioxidant assays, 3-ODS showed a strong capacity in scavenging hydroxyl radical, superoxide anion and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical in a concentration-dependent manner. Taken together, we conclude that 3-ODS attenuates the PD-related motor deficits mainly through its neuroprotective effects, growth-promoting effects on spine density, and its antioxidant activities.

The neurotoxin 1-methyl-4-phenylpyridinium (MPP(+)) alters hippocampal excitatory synaptic transmission by modulation of the GABAergic system

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces Parkinson's disease-like symptoms following administration to mice, monkeys, and humans. A common view is that MPTP is metabolized to 1-methyl-4-phenylpyridinium ion (MPP(+)) to induce its neurodegenerative effects on dopaminergic neurons in the substantia nigra (SN). Moreover, the hippocampus contains dopaminergic fibers, which are projecting from the ventral tegmental area, SN and pars compacta and contain the whole machinery required for dopamine synthesis making them sensitive to MPTP and MPP(+). Here, we present data showing that acute bath-application of MPP(+) elicited a dose-dependent facilitation followed by a depression of synaptic transmission of hippocampal Schaffer collaterals-CA1 synapses in mice. The effects of MPP(+) were not mediated by D1/D5- and D2-like receptor activation. Inhibition of the dopamine transporters did not prevent but increased the depression of excitatory post-synaptic field potentials. In the search for a possible mechanism, we observed that MPP(+) reduced the appearance of polyspikes in population spikes recorded in str. pyramidale and increased the frequency of miniature inhibitory post-synaptic currents. The acute effect of MPP(+) on synaptic transmission was attenuated by co-application of a GABAA receptor antagonist. Taking these data together, we suggest that MPP(+) affects hippocampal synaptic transmission by enhancing some aspects of the hippocampal GABAergic system.

MPTP-induced changes in hippocampal synaptic plasticity and memory are prevented by memantine through the BDNF-TrkB pathway

BACKGROUND AND PURPOSE

Mild cognitive deficit in early Parkinson's disease (PD) has been widely studied. Here we have examined the effects of memantine in preventing memory deficit in experimental PD models and elucidated some of the underlying mechanisms.

EXPERIMENTAL APPROACHES

I.p. injection of 1-methyl-4- phenyl-1,2,3,6-tetrahydro pyridine (MPTP) in C57BL/6 mice was used to produce models of PD. We used behavioural tasks to test memory. In vitro, we used slices of hippocampus, with electrophysiological, Western blotting, real time PCR, elisa and immunochemical techniques.

KEY RESULTS

Following MPTP injection, long-term memory was impaired and these changes were prevented by pre-treatment with memantine. In hippocampal slices from MPTP treated mice, long-term potentiation (LTP) -induced by θ burst stimulation (10 bursts, 4 pulses) was decreased, while long-term depression (LTD) induced by low-frequency stimulation (1 Hz, 900 pulses) was enhanced, compared with control values. A single dose of memantine (i.p., 10 mg·kg(-1) ) reversed the decreased LTP and the increased LTD in this PD model. Activity-dependent changes in tyrosine kinase receptor B (TrkB), ERK and brain-derived neurotrophic factor (BDNF) expression were decreased in slices from mice after MPTP treatment. These effects were reversed by pretreatment with memantine. Incubation of slices in vitro with 1-methyl-4-phenylpyridinium (MPP(+) ) decreased depolarization-induced expression of BDNF. This effect was prevented by pretreatment of slices with memantine or with calpain inhibitor III, suggesting the involvement of an overactivated calcium signalling pathway.

CONCLUSIONS AND IMPLICATIONS

Memantine should be useful in preventing loss of memory and hippocampal synaptic plasticity in PD models.

Alterations of NMDA receptor binding in various brain regions among 6-hydroxydopamine-induced Parkinsonian rats

The N-methyl-d-aspartate (NMDA) system closely interacts with the dopaminergic system and is strongly implicated in the pathophysiological mechanisms and therapeutic paradigms of Parkinson's disease. This study aims to systematically investigate the changes of NMDA receptors in a wide range of brain structures 3 weeks after unilateral medial forebrain bundle lesion by 6-hydroxydopamine (6-OHDA). NMDA receptor distributions and alterations in the post-mortem rat brain were detected by [(3)H] MK-801 binding autoradiography. In the 6-OHDA-induced Parkinsonian rat model, nigrostriatal dopaminergic neuron loss significantly mediated the decreased [(3)H] MK-801 binding, predominantly in the hippocampus (-22.4%, p < 0.001), caudate putamen (-14.1%, p < 0.01), accumbens nucleus (-13.8%, p < 0.05), cingulate cortex (-13.4%, p < 0.001), posteromedial cortical amygdala (-14.5%, p < 0.01) and piriform cortex (-9%, p < 0.05) compared to the controls, while there was a profound reduction of tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compacta. Alterations in [(3)H] MK-801 in the specific brain regions related to cognitive functions may indicate that cognitive dysfunctions caused by 6-OHDA lesion were via the NMDA system. The downregulation of NMDA receptor binding in the present study provides indirect evidence for plasticity in the NMDA system in the rat brain. The present study improves our understanding of the critical roles of the NMDA receptors in treating neurodegenerative disorders, and implicates NMDA receptors as a novel therapeutic target in the treatment of Parkinson's disease.

Parkin overexpression ameliorates hippocampal long-term potentiation and β-amyloid load in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by a severe decline of memory performance. A widely studied AD mouse model is the APPswe/PSEN1ΔE9 (APP/PS1) strain, as mice exhibit amyloid plaques as well as impaired memory capacities. To test whether restoring synaptic plasticity and decreasing β-amyloid load by Parkin could represent a potential therapeutic target for AD, we crossed APP/PS1 transgenic mice with transgenic mice overexpressing the ubiquitin ligase Parkin and analyzed offspring properties. Overexpression of Parkin in APP/PS1 transgenic mice restored activity-dependent synaptic plasticity and rescued behavioral abnormalities. Moreover, overexpression of Parkin was associated with down-regulation of APP protein expression, decreased β-amyloid load and reduced inflammation. Our data suggest that Parkin could be a promising target for AD therapy.

Effect of oestrogen receptors on brain NMDA receptors of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice

Parkinson's disease (PD) is characterised by the loss of nigrostriatal dopamine (DA) neurones and glutamate overactivity. There is substantial evidence to suggest that oestrogens prevent or delay the disease. 17β-oestradiol has neuroprotective effects in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD and modulates brain NMDA receptors. In MPTP-lesioned mice, oestrogen receptor (ER)α and ERβ are important in 17β-oestradiol-induced neuroprotection. To evaluate the role of ERs in the response of NMDA receptors to lesion, we compared wild-type (WT) with ER knockout (KO) C57Bl/6 male mice that received 7, 9 or 11 mg/kg of MPTP. These mice were also treated with MPTP (9 mg/kg) and 17β-oestradiol. [(3) H]Ro 25-6981 specific binding autoradiography was used to label NMDA receptors containing NR2B subunits. In the frontal and cingulate cortex and striatum, vehicle-treated WT mice had higher [(3) H]Ro 25-6981 specific binding compared to ERKO mice. Cortical [(3) H]Ro 25-6981 specific binding decreased with increasing doses of MPTP in WT and ERKOα but not ERKOβ mice, whereas a dose-related decrease was only observed in the striatum of WT mice remaining low in ERKOα and ERKOβ mice. No effect of 17β-oestradiol treatment in intact or MPTP-lesioned mice of all three genotypes was observed in the cortex, whereas it increased striatal specific binding of intact ERKOβ and MPTP-lesioned WT mice. Striatal [(3) H]Ro 25-6981 specific binding positively correlated with striatal DA concentrations only in WT mice. MPTP and 17β-oestradiol treatments had more limited effects in the hippocampus. Only in the CA3 and dentate gyrus did vehicle and 17β-oestradiol-treated ERKOα mice have higher [(3) H]Ro 25-6981 specific binding than WT and ERKOβ mice, whereas MPTP decreased this specific binding only in the CA1, CA2 and CA3 of ERKOα mice. Hence, brain NMDA receptors were affected by the deletion of ERs, which affect the response to MPTP and 17β-oestradiol treatments with brain region specificity.

Curcumin rescues aging-related loss of hippocampal synapse input specificity of long term potentiation in mice

Curcumin has neuroprotective effect and could enhance memory. However, the mechanisms underlying the protection of curcumin on aging-related memory decline are not well understood. In this study, high frequency stimulation (HFS)-induced long term potentiation (LTP) was evaluated by a cellular model of memory formation. A two-input stimulation paradigm was used to record the potentiation as well as synapse input specificity. The data suggested that an N-Methyl-D-aspartate receptors (NMDAR) -dependent LTP was inducible in adult hippocampal slices with a characteristic of synapse input specificity. It also indicated that aging resulted in a reduction in LTP but more importantly a loss of synaptic input specificity. The reason behind the above conclusions is that LTP induction is more dependent on the calcium channel. This is due to a switch of the dependence of LTP induction to voltage-dependent calcium channel (VDCC) compared to NMDA receptors. Curcumin administration recovers input specificity by re-establishing NMDA receptor dependence of induction. In addition, curcumin administration ameliorated aging-related increase of brain thiobarbituric acid-reactive substances and elevated aging-related decrease of glutathione in hippocampus. It is then concluded that curcumin modulates hippocampal redox status and restores aging-related loss of synapse input specificity of HFS-induced LTP by switching VDCC calcium source into NMDA receptor-dependent one.

MPTP modulates hippocampal synaptic transmission and activity-dependent synaptic plasticity via dopamine receptors

Parkinson's disease (PD)-like symptoms and cognitive deficits are inducible by 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Since cognitive abilities, including memory formations rely also on hippocampus, we set out to clarify the effects of MPTP on hippocampal physiology. We show that bath-application of MPTP (25 μM) to acute hippocampal slices enhanced AMPA receptor-mediated field excitatory postsynaptic potentials (AMPAr-fEPSPs) transiently, whereas N-methyl-D-aspartate (NMDA) receptor-mediated fEPSPs (NMDAr-fEPSPs) were facilitated persistently. The MPTP-mediated transient AMPAr-fEPSP facilitation was antagonized by the dopamine D2-like receptor antagonists, eticlopride (1 μM) and sulpiride (1 and 40 μM). In contrast, the persistent enhancement of NMDAr-fEPSPs was prevented by the dopamine D1-like receptor antagonist SCH23390 (10 μM). In addition, we show that MPTP decreased paired-pulse facilitation of fEPSPs and mEPSCs frequency. Regarding activity-dependent synaptic plasticity, 25 μM MPTP transformed short-term potentiation (STP) into a long-term potentiation (LTP) and caused a slow onset potentiation of a non-tetanized synaptic input after induction of LTP in a second synaptic input. This heterosynaptic slow onset potentiation required activation of dopamine D1-like and NMDA-receptors. We conclude that acute MPTP application affects basal synaptic transmission by modulation of presynaptic vesicle release and facilitates NMDAr-fEPSPs as well as activity-dependent homo- and heterosynaptic plasticity under participation of dopamine receptors.

Reduced calcium/calmodulin-dependent protein kinase II activity in the hippocampus is associated with impaired cognitive function in MPTP-treated mice

Parkinson's disease (PD) patients frequently reveal deficit in cognitive functions during the early stage in PD. The dopaminergic neurotoxin, MPTP-induced neurodegeneration causes an injury of the basal ganglia and is associated with PD-like behaviors. In this study, we demonstrated that deficits in cognitive functions in MPTP-treated mice were associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and impaired long-term potentiation (LTP) induction in the hippocampal CA1 region. Mice were injected once a day for 5days with MPTP (25mg/kg i.p.). The impaired motor coordination was observed 1 or 2week after MPTP treatment as assessed by rota-rod and beam-walking tasks. In immunoblotting analyses, the levels of tyrosine hydroxylase protein and CaMKII autophosphorylation in the striatum were significantly decreased 1week after MPTP treatment. By contrast, deficits of cognitive functions were observed 3-4weeks after MPTP treatment as assessed by novel object recognition and passive avoidance tasks but not Y-maze task. Impaired LTP in the hippocampal CA1 region was also observed in MPTP-treated mice. Concomitant with impaired LTP induction, CaMKII autophosphorylation was significantly decreased 3weeks after MPTP treatment in the hippocampal CA1 region. Finally, the reduced CaMKII autophosphorylation was closely associated with reduced AMPA-type glutamate receptor subunit 1 (GluR1; Ser-831) phosphorylation in the hippocampal CA1 region of MPTP-treated mice. Taken together, decreased CaMKII activity with concomitant impaired LTP induction in the hippocampus likely account for the learning disability observed in MPTP-treated mice.

Increased mesohippocampal dopaminergic activity and improved depression-like behaviors in maternally separated rats following repeated fasting/refeeding cycles

We have previously reported that rats that experienced 3 h of daily maternal separation during the first 2 weeks of birth (MS) showed binge-like eating behaviors with increased activity of the hypothalamic-pituitary-adrenal axis when they were subjected to fasting/refeeding cycles repeatedly. In this study, we have examined the psychoemotional behaviors of MS rats on the fasting/refeeding cycles, together with their brain dopamine levels. Fasting/refeeding cycles normalized the ambulatory activity of MS rats, which was decreased by MS experience. Depression-like behaviors, but not anxiety, by MS experience were improved after fasting/refeeding cycles. Fasting/refeeding cycles did not significantly affect the behavioral scores of nonhandled (NH) control rats. Fasting/refeeding cycles increased dopamine levels not only in the hippocampus but also in the midbrain dopaminergic neurons in MS rats, but not in NH controls. Results demonstrate that fasting/refeeding cycles increase the mesohippocampal dopaminergic activity and improve depression-like behaviors in rats that experienced MS. Together with our previous paper, it is suggested that increased dopamine neurotransmission in the hippocampus may be implicated in the underlying mechanisms by which the fasting/refeeding cycles induce binge-like eating and improve depression-like behaviors in MS rats.