Aging-associated weakening of the action potential in fast-spiking interneurons in the human neocortex.

Aging is associated with the slowdown of neuronal processing and cognitive performance in the brain; however, the exact cellular mechanisms behind this deterioration in humans are poorly elucidated. Recordings in human acute brain slices prepared from tissue resected during brain surgery enable the investigation of neuronal changes with age. Although neocortical fast-spiking cells are widely implicated in neuronal network activities underlying cognitive processes, they are vulnerable to neurodegeneration. Herein, we analyzed the electrical properties of 147 fast-spiking interneurons in neocortex samples resected in brain surgery from 106 patients aged 11-84 years. By studying the electrophysiological features of action potentials and passive membrane properties, we report that action potential overshoot significantly decreases and spike half-width increases with age. Moreover, the action potential maximum-rise speed (but not the repolarization speed or the afterhyperpolarization amplitude) significantly changed with age, suggesting a particular weakening of the sodium channel current generated in the soma. Cell passive membrane properties measured as the input resistance, membrane time constant, and cell capacitance remained unaffected by senescence. Thus, we conclude that the action potential in fast-spiking interneurons shows a significant weakening in the human neocortex with age. This may contribute to the deterioration of cortical functions by aging.

HCN channels at the cell soma ensure the rapid electrical reactivity of fast-spiking interneurons in human neocortex.

Accumulating evidence indicates that there are substantial species differences in the properties of mammalian neurons, yet theories on circuit activity and information processing in the human brain are based heavily on results obtained from rodents and other experimental animals. This knowledge gap may be particularly important for understanding the neocortex, the brain area responsible for the most complex neuronal operations and showing the greatest evolutionary divergence. Here, we examined differences in the electrophysiological properties of human and mouse fast-spiking GABAergic basket cells, among the most abundant inhibitory interneurons in cortex. Analyses of membrane potential responses to current input, pharmacologically isolated somatic leak currents, isolated soma outside-out patch recordings, and immunohistochemical staining revealed that human neocortical basket cells abundantly express hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel isoforms HCN1 and HCN2 at the cell soma membrane, whereas these channels are sparse at the rodent basket cell soma membrane. Antagonist experiments showed that HCN channels in human neurons contribute to the resting membrane potential and cell excitability at the cell soma, accelerate somatic membrane potential kinetics, and shorten the lag between excitatory postsynaptic potentials and action potential generation. These effects are important because the soma of human fast-spiking neurons without HCN channels exhibit low persistent ion leak and slow membrane potential kinetics, compared with mouse fast-spiking neurons. HCN channels speed up human cell membrane potential kinetics and help attain an input-output rate close to that of rodent cells. Computational modeling demonstrated that HCN channel activity at the human fast-spiking cell soma membrane is sufficient to accelerate the input-output function as observed in cell recordings. Thus, human and mouse fast-spiking neurons exhibit functionally significant differences in ion channel composition at the cell soma membrane to set the speed and fidelity of their input-output function. These HCN channels ensure fast electrical reactivity of fast-spiking cells in human neocortex.

Alzheimer risk factors age and female sex induce cortical Aß aggregation by raising extracellular zinc.

Aging and female sex are the major risk factors for Alzheimer's disease and its associated brain amyloid-ß (Aß) neuropathology, but the mechanisms mediating these risk factors remain uncertain. Evidence indicates that Aß aggregation by Zn2+ released from glutamatergic neurons contributes to amyloid neuropathology, so we tested whether aging and sex adversely influences this neurophysiology. Using acute hippocampal slices, we found that extracellular Zn2+-elevation induced by high K+ stimulation was significantly greater with older (65 weeks vs 10 weeks old) rats, and was exaggerated in females. This was driven by slower reuptake of extracellular Zn2+, which could be recapitulated by mitochondrial intoxication. Zn2+:Aß aggregates were toxic to the slices, but Aß alone was not. Accordingly, high K+ caused synthetic human Aß added to the slices to form soluble oligomers as detected by bis-ANS, attaching to neurons and inducing toxicity, with older slices being more vulnerable. Age-dependent energy failure impairing Zn2+ reuptake, and a higher maximal capacity for Zn2+ release by females, could contribute to age and sex being major risk factors for Alzheimer's disease.

Robust perisomatic GABAergic self-innervation inhibits basket cells in the human and mouse supragranular neocortex.

Inhibitory autapses are self-innervating synaptic connections in GABAergic interneurons in the brain. Autapses in neocortical layers have not been systematically investigated, and their function in different mammalian species and specific interneuron types is poorly known. We investigated GABAergic parvalbumin-expressing basket cells (pvBCs) in layer 2/3 (L2/3) in human neocortical tissue resected in deep-brain surgery, and in mice as control. Most pvBCs showed robust GABAAR-mediated self-innervation in both species, but autapses were rare in nonfast-spiking GABAergic interneurons. Light- and electron microscopy analyses revealed pvBC axons innervating their own soma and proximal dendrites. GABAergic self-inhibition conductance was similar in human and mouse pvBCs and comparable to that of synapses from pvBCs to other L2/3 neurons. Autaptic conductance prolonged somatic inhibition in pvBCs after a spike and inhibited repetitive firing. Perisomatic autaptic inhibition is common in both human and mouse pvBCs of supragranular neocortex, where they efficiently control discharge of the pvBCs.

Plasma phospholipid profiling of a mouse model of anxiety disorder by hydrophilic interaction liquid chromatography coupled to high-resolution mass spectrometry.

Glycerophospholipids (PLs), as amphipathic small molecules and the main constituents of biological membranes, play an important role in several cellular processes, even though their accurate identification from complex biological samples remains a challenge. In this paper, we report a fast and comprehensive HILIC-ESI-MS method for the analysis of glycerophospholipid classes using high-resolution mass spectrometry in negative mode. The final method enabled the quantitative analysis of 130 endogenous PL species in mouse plasma. The application of the method developed was to find differences of plasma PL composition in a mouse model of anxiety disorder. In the case of four PL classes and 35 PL species, significant differences were observed comparing low anxiety-related behavior with high anxiety-related behavior groups. The most characteristic trend was up-regulation in both the PL classes and PL species, and decreases were only detected in two phosphatidylcholines among 35 species in mice having elevated anxiety.

Comprehensive phospholipid and sphingomyelin profiling of different brain regions in mouse model of anxiety disorder using online two-dimensional (HILIC/RP)-LC/MS method.

A novel online system including two-dimensional liquid chromatography coupled to high-resolution mass spectrometry (2D-LC/MS) was developed and applied for comprehensive phospholipid (PL) and sphingomyelin (SM) profiling of dorsal hippocampus (DHPC), ventral (VHPC) and prefrontal cortex (PFC) brain regions in a mouse model of anxiety disorder. In the first dimension, lipid classes were distinguished by hydrophilic interaction liquid chromatography (HILIC), while the second dimensional separation of individual PL and SM species was achieved by reversed-phase (RP) chromatography. For the enrichment of lipid species in diluted HILIC effluent, two RP trapping columns were used separately. The developed fully-automated 2D method allowed the quantitative analysis of over 150 endogenous PL and SM species in mouse brain regions within 40min. The developed method was applied in a pilot study, which aimed to find alteration of PL and SM composition in a mouse model of anxiety disorder. In the case of 37 PL and SM species, significant differences were observed between high anxiety-related behavior (AX) and low anxiety-related behavior (nAX) mice. In mice having elevated anxiety, the most typical trend was the downregulation of PL species, in particular, in VHPC.

Studies for Improving a Rat Model of Alzheimer's Disease: Icv Administration of Well-Characterized ß-Amyloid 1-42 Oligomers Induce Dysfunction in Spatial Memory.

During the past 15 years, several genetically altered mouse models of human Alzheimer's disease (AD) have been developed. These costly models have greatly facilitated the evaluation of novel therapeutic approaches. Injecting synthetic ß-amyloid (Aß) 1-42 species into different parts of the brain of non-transgenic rodents frequently provided unreliable results, owing to a lack of a genuine characterization of the administered Aß aggregates. Previously, we have published a new rat AD-model in which protofibrillar-fibrillar Aß1-42 was administered into rat entorhinal cortex (Sipos 2007). In order to develop a more reliable model, we have injected well-characterized toxic soluble Aß1-42 species (oligomers, protofibrils and fibrils) intracerebroventricularly (icv) into rat brain. Studies of the distribution of fluorescent-labeled Aß1-42 in the brain showed that soluble Aß-species diffused into all parts of the rat brain. After seven days, the Aß-treated animals showed a significant decrease of spatial memory in Morris water maze test and impairment of synaptic plasticity (LTP) measured in acute hippocampal slices. The results of histological studies (decreased number of viable neurons, increased tau levels and decreased number of dendritic spines) also supported that icv administration of well-characterized toxic soluble Aß species into rat brain provides a reliable rat AD-model.

High-Precision Fast-Spiking Basket Cell Discharges during Complex Events in the Human Neocortex.

In the human neocortex, solitary action potentials in some layer 2-3 pyramidal cells (PCs) trigger brief episodes of network activity known as complex events through strong excitatory synapses that specifically innervate GABAergic interneurons. Yet, how these "master PCs" configure the local network activity is not well understood. We report that single spikes in the PCs, studied here in synaptically connected cell pairs in frontal or temporal neocortical areas of both males and females, elicit firing of fast-spiking basket cells (FSBCs) with a short delay (on average 2.7 ms). The FSBC discharge is triggered by 13 mV (on average) monosynaptic EPSPs, and the action potential is time locked to the master PC spike with high temporal precision, showing little jitter in delay. In the complex events, the FSBC discharge occurs in the beginning of the activity episode, forming the first wave of the complex event activity. Firing of FSBCs generates GABAergic IPSCs with fast kinetics in layer 2-3 PCs, and similar IPSCs regularly occur time locked to master PC spikes in the beginning of the complex events with high probability and short (median 4.1 ms) delay with little jitter. In comparison, discharge of nonfast spiking interneurons (non-FSINs) investigated here appears inconsistently in the complex events and shows low probability. Thus, firing of layer 2-3 FSBCs with high temporal fidelity characterizes early phase of the complex events in the human neocortex.

Plasticity in Single Axon Glutamatergic Connection to GABAergic Interneurons Regulates Complex Events in the Human Neocortex.

In the human neocortex, single excitatory pyramidal cells can elicit very large glutamatergic EPSPs (VLEs) in inhibitory GABAergic interneurons capable of triggering their firing with short (3-5 ms) delay. Similar strong excitatory connections between two individual neurons have not been found in nonhuman cortices, suggesting that these synapses are specific to human interneurons. The VLEs are crucial for generating neocortical complex events, observed as single pyramidal cell spike-evoked discharge of cell assemblies in the frontal and temporal cortices. However, long-term plasticity of the VLE connections and how the plasticity modulates neocortical complex events has not been studied. Using triple and dual whole-cell recordings from synaptically connected human neocortical layers 2-3 neurons, we show that VLEs in fast-spiking GABAergic interneurons exhibit robust activity-induced long-term depression (LTD). The LTD by single pyramidal cell 40 Hz spike bursts is specific to connections with VLEs, requires group I metabotropic glutamate receptors, and has a presynaptic mechanism. The LTD of VLE connections alters suprathreshold activation of interneurons in the complex events suppressing the discharge of fast-spiking GABAergic cells. The VLEs triggering the complex events may contribute to cognitive processes in the human neocortex, and their long-term plasticity can alter the discharging cortical cell assemblies by learning.

Possible contribution of epigenetic changes in the development of schizophrenia-like behavior in vasopressin-deficient Brattleboro rats.

Schizophrenia-like symptoms were detected in vasopressin-deficient (di/di) Brattleboro rats, and it was also suggested that schizophrenia might have an epigenetic component. We aimed to clarify if epigenetic changes contribute to schizophrenia-like behavior of this strain. Behavioral (locomotion by telemetry, cognition by novel object recognition, social recognition and social avoidance test, attention by pre-pulse inhibition) and epigenetic differences were compared between wild type and di/di animals. DNA methyltransferase1 (DNMT1), DNMT3a, as well as COMT, GAD, VGLUT1, 5HT2A, BDNF mRNA levels in prefrontal brain region and hippocampus were studied by qRT-PCR. Histone3 (H3) and H4 acetylation (Ac) were studied by western-blot followed by region specific examination of H3 lysine9 (K9) acetylation by immunohistochemistry. Impaired cognitive, social and attention behavior of di/di rats confirmed schizophrenia-like symptoms in our local colony. The pan-AcH3 immunoreactivity was lower in prefrontal region and elevated in the hippocampus of di/di animals. We found lower immunopositive cell number in the dorsal peduncular prefrontal cortex and the ventral lateral septum and increased AcH3K9 immunoreactivity in CA1 region of di/di animals. There were no major significant alterations in the studied mRNA levels. We confirmed that Brattleboro rat is a good preclinical model of schizophrenia. Its schizophrenia-like behavioral alteration was accompanied by changes in H3 acetylation in the prefrontal region and hippocampus. This may contribute to disturbances of many schizophrenia-related substances leading to development of schizophrenia-like symptoms. Our studies confirmed that not a single gene, rather fine changes in an array of molecules are responsible for the majority of schizophrenia cases.

Anxious and nonanxious mice show similar hippocampal sensory evoked oscillations under urethane anesthesia: difference in the effect of buspirone.

Hippocampal oscillations recorded under urethane anesthesia are proposed to be modulated by anxiolytics. All classes of clinically effective anxiolytics were reported to decrease the frequency of urethane theta; however, recent findings raise concerns about the direct correlation of anxiolysis and the frequency of hippocampal theta. Here, we took advantage of our two inbred mouse strains displaying extremes of anxiety (anxious (AX) and nonanxious (nAX)) to compare the properties of hippocampal activity and to test the effect of an anxiolytic drugs. No difference was observed in the peak frequency or in the peak power between AX and nAX strains. Buspirone (Bus) applied in 2.5 mg/kg decreased anxiety of AX but did not have any effect on nAX as was tested by elevated plus maze and open field. Interestingly, Bus treatment increased hippocampal oscillatory frequency in the AX but left it unaltered in nAX mice. Saline injection did not have any effect on the oscillation. Paired-pulse facilitation was enhanced by Bus in the nAX, but not in the AX strain. Collectively, these results do not support the hypothesis that hippocampal activity under urethane may serve as a marker for potential anxiolytic drugs. Moreover, we could not confirm the decrease of frequency after anxiolytic treatment.

Amyloid-ß1-42 Disrupts Synaptic Plasticity by Altering Glutamate Recycling at the Synapse.

Alzheimer's disease (AD) is the most prevalent form of neurodegenerative disorders characterized by neuritic plaques containing amyloid-ß peptide (Aß) and neurofibrillary tangles. Evidence has been reported that Aß(1-42) plays an essential pathogenic role in decreased spine density, impairment of synaptic plasticity, and neuronal loss with disruption of memory-related synapse function, all associated with AD. Experimentally, Aß(1-42) oligomers perturb hippocampal long-term potentiation (LTP), an electrophysiological correlate of learning and memory. Aß was also reported to perturb synaptic glutamate (Glu)-recycling by inhibiting excitatory-amino-acid-transporters. Elevated level of extracellular Glu leads to activation of perisynaptic receptors, including NR2B subunit containing NMDARs. These receptors were shown to induce impaired LTP and enhanced long-term depression and proapoptotic pathways, all central features of AD. In the present study, we investigated the role of Glu-recycling on Aß(1-42)-induced LTP deficit in the CA1. We found that Aß-induced LTP damage, which was mimicked by the Glu-reuptake inhibitor TBOA, could be rescued by blocking the NR2B subunit of NMDA receptors. Furthermore, decreasing the level of extracellular Glu using a Glu scavenger also restores TBOA or Aß induces LTP damage. Overall, these results suggest that reducing ambient Glu in the brain can be protective against Aß-induced synaptic disruption.

Abeta(1-42) enhances neuronal excitability in the CA1 via NR2B subunit-containing NMDA receptors.

Neuronal hyperexcitability is a phenomenon associated with early Alzheimer's disease. The underlying mechanism is considered to involve excessive activation of glutamate receptors; however, the exact molecular pathway remains to be determined. Extracellular recording from the CA1 of hippocampal slices is a long-standing standard for a range of studies both in basic research and in neuropharmacology. Evoked field potentials (fEPSPs) are regarded as the input, while spiking rate is regarded as the output of the neuronal network; however, the relationship between these two phenomena is not fully clear. We investigated the relationship between spontaneous spiking and evoked fEPSPs using mouse hippocampal slices. Blocking AMPA receptors (AMPARs) with CNQX abolished fEPSPs, but left firing rate unchanged. NMDA receptor (NMDAR) blockade with MK801 decreased neuronal spiking dose dependently without altering fEPSPs. Activating NMDARs by small concentration of NMDA induced a trend of increased firing. These results suggest that fEPSPs are mediated by synaptic activation of AMPARs, while spontaneous firing is regulated by the activation of extrasynaptic NMDARs. Synaptotoxic Abeta(1-42) increased firing activity without modifying evoked fEPSPs. This hyperexcitation was prevented by ifenprodil, an antagonist of the NR2B NMDARs. Overall, these results suggest that Abeta(1-42) induced neuronal overactivity is not dependent on AMPARs but requires NR2B.

Overexpression of Hsp27 ameliorates symptoms of Alzheimer's disease in APP/PS1 mice.

Hsp27 belongs to the small heat shock protein family, which are ATP-independent chaperones. The most important function of Hsp27 is based on its ability to bind non-native proteins and inhibit the aggregation of incorrectly folded proteins maintaining them in a refolding-competent state. Additionally, it has anti-apoptotic and antioxidant activities. To study the effect of Hsp27 on memory and synaptic functions, amyloid-ß (Aß) accumulation, and neurodegeneration, we generated transgenic mice overexpressing human Hsp27 protein and crossed with APPswe/PS1dE9 mouse strain, a mouse model of Alzheimer's disease (AD). Using different behavioral tests, we found that spatial learning was impaired in AD model mice and was rescued by Hsp27 overexpression. Electrophysiological recordings have revealed that excitability of neurons was significantly increased, and long-term potentiation (LTP) was impaired in AD model mice, whereas they were normalized in Hsp27 overexpressing AD model mice. Using anti-amyloid antibody, we counted significantly less amyloid plaques in the brain of APPswe/PS1dE9/Hsp27 animals compared to AD model mice. These results suggest that overexpression of Hsp27 protein might ameliorate certain symptoms of AD.

The anxiolytic buspirone shifts coping strategy in novel environmental context of mice with different anxious phenotype.

Patients suffering from anxiety disorders show increased fear when encounter a novel environment. Rodents, placed in new environmental context may respond either with increased novelty seeking (active), or enhanced anxiety (passive coping style), which may depend on the trait anxiety of the animal. Here, the connection between the initial level of anxiety and the behavioral responses in a novel environment was investigated. Two inbred mouse strains having either high- or low-anxiety related behavior (AX and nAX) were exposed to elevated plus maze (EPM), a standard test for assessing anxiety level, for 8 consecutive days. The initial anxiety level was modulated by chronic treatment with buspirone (bus) treatment, a clinically effective anxiolytic, using 2.5mg/kg and 5.0mg/kg doses. Both strains showed a gradual decrease of open-arm exploration, which was not prevented by bus treatment. Another cohort of animals was exposed to EPM for 2 days, and then we changed to blue light illumination and used a different cleaning substance with citrus odor (context change, CC). It was found that upon CC AX mice exhibited increased, while nAX mice showed decreased anxiety. Bus in 2.5mg/kg changed the coping strategy from passive to active exploration after CC in the AX mice; however, the same treatment rendered nAX mice passive upon CC. Bus in 5.0mg/kg failed to alter the overall coping style in the novel environment of both strains. These results suggest that these mouse lines use different coping strategy in novel context, which can be changed with bus treatment.

Increased tau phosphorylation and impaired presynaptic function in hypertriglyceridemic ApoB-100 transgenic mice.

AIMS: ApoB-100 is the major protein component of cholesterol- and triglyceride-rich LDL and VLDL lipoproteins in the serum. Previously, we generated and partially described transgenic mice overexpressing the human ApoB-100 protein. Here, we further characterize this transgenic strain in order to reveal a possible link between hypeprlipidemia and neurodegeneration. METHODS AND RESULTS: We analyzed the serum and cerebral lipid profiles, tau phosphorylation patterns, amyloid plaque-formation, neuronal apoptosis and synaptic plasticity of young (3 month old), adult (6 month old) and aging (10-11 month old) transgenic mice. We show that ApoB-100 transgenic animals present i) elevated serum and cerebral levels of triglycerides and ApoB-100, ii) increased cerebral tau phosphorylation at phosphosites Ser(199), Ser(199/202), Ser(396) and Ser(404). Furthermore, we demonstrate, that tau hyperphosphorylation is accompanied by impaired presynaptic function, long-term potentiation and widespread hippocampal neuronal apoptosis. CONCLUSIONS: The results presented here indicate that elevated ApoB-100 level and the consequent chronic hypertriglyceridemia may lead to impaired neuronal function and neurodegeneration, possibly via hyperphosphorylation of tau protein. On account of their specific phenotype, ApoB-100 transgenic mice may be considered a versatile model of hyperlipidemia-induced age-related neurodegeneration.

A foldamer-dendrimer conjugate neutralizes synaptotoxic ß-amyloid oligomers.

BACKGROUND AND AIMS: Unnatural self-organizing biomimetic polymers (foldamers) emerged as promising materials for biomolecule recognition and inhibition. Our goal was to construct multivalent foldamer-dendrimer conjugates which wrap the synaptotoxic ß-amyloid (Aß) oligomers with high affinity through their helical foldamer tentacles. Oligomeric Aß species play pivotal role in Alzheimer's disease, therefore recognition and direct inhibition of this undruggable target is a great current challenge. METHODS AND RESULTS: Short helical ß-peptide foldamers with designed secondary structures and side chain chemistry patterns were applied as potential recognition segments and their binding to the target was tested with NMR methods (saturation transfer difference and transferred-nuclear Overhauser effect). Helices exhibiting binding in the µM region were coupled to a tetravalent G0-PAMAM dendrimer. In vitro biophysical (isothermal titration calorimetry, dynamic light scattering, transmission electron microscopy and size-exclusion chromatography) and biochemical tests (ELISA and dot blot) indicated the tight binding between the foldamer conjugates and the Aß oligomers. Moreover, a selective low nM interaction with the low molecular weight fraction of the Aß oligomers was found. Ex vivo electrophysiological experiments revealed that the new material rescues the long-term potentiation from the toxic Aß oligomers in mouse hippocampal slices at submicromolar concentration. CONCLUSIONS: The combination of the foldamer methodology, the fragment-based approach and the multivalent design offers a pathway to unnatural protein mimetics that are capable of specific molecular recognition, and has already resulted in an inhibitor for an extremely difficult target.

GluA1 phosphorylation alters evoked firing pattern in vivo.

AMPA and NMDA receptors convey fast synaptic transmission in the CNS. Their relative contribution to synaptic output and phosphorylation state regulate synaptic plasticity. The AMPA receptor subunit GluA1 is central in synaptic plasticity. Phosphorylation of GluA1 regulates channel properties and trafficking. The firing rate averaged over several hundred ms is used to monitor cellular input. However, plasticity requires the timing of spiking within a few ms; therefore, it is important to understand how phosphorylation governs these events. Here, we investigate whether the GluA1 phosphorylation (p-GluA1) alters the spiking patterns of CA1 cells in vivo. The antidepressant Tianeptine was used for inducing p-GluA1, which resulted in enhanced AMPA-evoked spiking. By comparing the spiking patterns of AMPA-evoked activity with matched firing rates, we show that the spike-trains after Tianeptine application show characteristic features, distinguishing from spike-trains triggered by strong AMPA stimulation. The interspike-interval distributions are different between the two groups, suggesting that neuronal output may differ when new inputs are activated compared to increasing the gain of previously activated receptors. Furthermore, we also show that NMDA evokes spiking with different patterns to AMPA spike-trains. These results support the role of the modulation of NMDAR/AMPAR ratio and p-GluA1 in plasticity and temporal coding.

Tianeptine potentiates AMPA receptors by activating CaMKII and PKA via the p38, p42/44 MAPK and JNK pathways.

Impairments of cellular plasticity appear to underlie the pathophysiology of major depression. Recently, elevated levels of phosphorylated AMPA receptor were implicated in the antidepressant effect of various drugs. Here, we investigated the effects of an antidepressant, Tianeptine, on synaptic function and GluA1 phosphorylation using murine hippocampal slices and in vivo single-unit recordings. Tianeptine, but not imipramine, increased AMPA receptor-mediated neuronal responses both in vitro and in vivo, in a staurosporine-sensitive manner. Paired-pulse ratio was unaltered by Tianeptine, suggesting a postsynaptic site of action. Tianeptine, 10 µM, enhanced the GluA1-dependent initial phase of LTP, whereas 100 µM impaired the latter phases, indicating a critical role of GluA1 subunit phosphorylation in the excitation. Tianeptine rapidly increased the phosphorylation level of Ser(831)-GluA1 and Ser(845)-GluA1. Using H-89 and KN-93, we show that the activation of both PKA and CaMKII is critical in the effect of Tianeptine on AMPA responses. Moreover, the phosphorylation states of Ser(217/221)-MEK and Thr(183)/Tyr(185)-p42MAPK were increased by Tianeptine and specific kinase blockers of the MAPK pathways (PD 98095, SB 203580 and SP600125) prevented the effects of Tianeptine. Overall these data suggest that Tianeptine potentiates several signaling cascades associated with synaptic plasticity and provide further evidence that a major mechanism of action for Tianeptine is to act as an enhancer of glutamate neurotransmission via AMPA receptors.

Functional changes in transcriptomes of the prefrontal cortex and hippocampus in a mouse model of anxiety.

Anxiety is a multi-etiology disorder influenced by both genetic background and environment. To study the impact of a genetic predisposition, we developed a novel mouse model of anxiety using a combination of crossbreeding and behavioral selection. Comparison of the transcriptomes from the prefrontal cortex and hippocampus of anxious and control mice revealed that the numbers of significantly up- and down-regulated genes were modest, comprising approximately 2% of the tested genes. Functional analysis of the significantly altered gene sets showed that functional groups such as nervous system development, behavior, glial cell differentiation and synaptic transmission were significantly enriched among the up-regulated genes, whereas functional groups such as potassium ion transport, Wnt signaling and neuropeptidergic signaling were significantly enriched among the down-regulated genes. Many of the identified genes and functional groups have been previously linked to the molecular biology of anxiety, while several others, such as transthyretin, vasoactive intestinal polypeptide and various potassium ion channels, are novel or not as well described in this context. Supporting the gene expression data, we also found increased excitability in the hippocampi of anxious mice, which can be a phenotypic result of decreased potassium channel density. Our transcriptome screen showed that the initiation and/or effect of anxiety involve multiple pathways and cellular processes. The identified novel genes and pathways could be involved in the molecular pathogenesis of anxiety and provide potential targets for further drug development.