Synaptic and transcriptomic features of cortical and amygdala pyramidal neurons predict inefficient fear extinction.

Fear-related disorders arise from inefficient fear extinction and have immeasurable social and economic costs. Here, we characterize mouse phenotypes that spontaneously show fear-independent behavioral traits predicting adaptive or maladaptive fear extinction. We find that, already before fear conditioning, specific morphological, electrophysiological, and transcriptomic patterns of cortical and amygdala pyramidal neurons predispose to fear-related disorders. Finally, by using an optogenetic approach, we show the possibility to rescue inefficient fear extinction by activating infralimbic pyramidal neurons and to impair fear extinction by activating prelimbic pyramidal neurons.

Cerebrospinal fluid from frontotemporal dementia patients is toxic to neurons.

Frontotemporal Lobar Degeneration (FTD) is a neurodegenerative disease characterized by a progressive deterioration of cognitive functions. Currently, no effective treatment exists. We have studied cytotoxicity and neuronal functionality in cortical and spinal cord cultures upon exposure to cerebrospinal fluid (CSF) from 39 FTD patients. FTD-CSF alters the miniature excitatory postsynaptic currents in the cortical cultures and it is toxic to spinal cord cultures, particularly to GABAergic+ and calbindin-D28k + neurons.

Optogenetic Stimulation of Prelimbic Pyramidal Neurons Maintains Fear Memories and Modulates Amygdala Pyramidal Neuron Transcriptome.

Fear extinction requires coordinated neural activity within the amygdala and medial prefrontal cortex (mPFC). Any behavior has a transcriptomic signature that is modified by environmental experiences, and specific genes are involved in functional plasticity and synaptic wiring during fear extinction. Here, we investigated the effects of optogenetic manipulations of prelimbic (PrL) pyramidal neurons and amygdala gene expression to analyze the specific transcriptional pathways associated to adaptive and maladaptive fear extinction. To this aim, transgenic mice were (or not) fear-conditioned and during the extinction phase they received optogenetic (or sham) stimulations over photo-activable PrL pyramidal neurons. At the end of behavioral testing, electrophysiological (neural cellular excitability and Excitatory Post-Synaptic Currents) and morphological (spinogenesis) correlates were evaluated in the PrL pyramidal neurons. Furthermore, transcriptomic cell-specific RNA-analyses (differential gene expression profiling and functional enrichment analyses) were performed in amygdala pyramidal neurons. Our results show that the optogenetic activation of PrL pyramidal neurons in fear-conditioned mice induces fear extinction deficits, reflected in an increase of cellular excitability, excitatory neurotransmission, and spinogenesis of PrL pyramidal neurons, and associated to strong modifications of the transcriptome of amygdala pyramidal neurons. Understanding the electrophysiological, morphological, and transcriptomic architecture of fear extinction may facilitate the comprehension of fear-related disorders.

hNGF Peptides Elicit the NGF-TrkA Signalling Pathway in Cholinergic Neurons and Retain Full Neurotrophic Activity in the DRG Assay.

In the last decade, Nerve Growth Factor (NGF)-based clinical approaches have lacked specific and efficient Tyrosine Kinase A (TrkA) agonists for brain delivery. Nowadays, the characterization of novel small peptidomimetic is taking centre stage in preclinical studies, in order to overcome the main size-related limitation in brain delivery of NGF holoprotein for Central Nervous System (CNS) pathologies. Here we investigated the NGF mimetic properties of the human NGF 1-14 sequence (hNGF1-14) and its derivatives, by resorting to primary cholinergic and dorsal root ganglia (DRG) neurons. Briefly, we observed that: 1) hNGF1-14 peptides engage the NGF pathway through TrkA phosphorylation at tyrosine 490 (Y490), and activation of ShcC/PI3K and Plc-γ/MAPK signalling, promoting AKT-dependent survival and CREB-driven neuronal activity, as seen by levels of the immediate early gene c-Fos, of the cholinergic marker Choline Acetyltransferase (ChAT), and of Brain Derived Neurotrophic Factor (BDNF); 2) their NGF mimetic activity is lost upon selective TrkA inhibition by means of GW441756; 3) hNGF1-14 peptides are able to sustain DRG survival and differentiation in absence of NGF. Furthermore, the acetylated derivative Ac-hNGF1-14 demonstrated an optimal NGF mimetic activity in both neuronal paradigms and an electrophysiological profile similar to NGF in cholinergic neurons. Cumulatively, the findings here reported pinpoint the hNGF1-14 peptide, and in particular its acetylated derivative, as novel, specific and low molecular weight TrkA specific agonists in both CNS and PNS primary neurons.

Modified age-dependent expression of NaV1.6 in an ALS model correlates with motor cortex excitability alterations.

Cortical hyperexcitability is an early and intrinsic feature of Amyotrophic Lateral Sclerosis (ALS), but the mechanisms underlying this critical neuronal dysfunction are poorly understood. Recently, we have demonstrated that layer V pyramidal neurons (PNs) in the primary motor cortex (M1) of one-month old (P30) G93A ALS mice display an early hyperexcitability status compared to Control mice. In order to investigate the time-dependent evolution of the cortical excitability in the G93A ALS model, here we have performed an electrophysiological and immunohistochemical study at three different mouse ages. M1 PNs from 14-days old (P14) G93A mice have shown no excitability alterations, while M1 PNs from 3-months old (P90) G93A mice have shown a hypoexcitability status, compared to Control mice. These age-dependent cortical excitability dysfunctions correlate with a similar time-dependent trend of the persistent sodium current (INaP) amplitude alterations, suggesting that INaP may play a crucial role in the G93A cortical excitability aberrations. Specifically, immunohistochemistry experiments have indicated that the expression level of the NaV1.6 channel, one of the voltage-gated Na+ channels mainly distributed within the central nervous system, varies in G93A primary motor cortex during disease progression, according to the excitability and INaP alterations, but not in other cortical areas. Microfluorometry experiments, combined with electrophysiological recordings, have verified that P30 G93A PNs hyperexcitability is associated to a greater accumulation of intracellular calcium ([Ca2+]i) compared to Control PNs, and that this difference is still present when G93A and Control PNs fire action potentials at the same frequency. These results suggest that [Ca2+]i de-regulation in G93A PNs may contribute to neuronal demise and that the NaV1.6 channels could be a potential therapeutic target to ameliorate ALS disease progression.

Modelling the pathogenesis of Myotonic Dystrophy type 1 cardiac phenotype through human iPSC-derived cardiomyocytes.

Myotonic Dystrophy type 1 (DM1) is a multisystemic disease, autosomal dominant, caused by a CTG repeat expansion in DMPK gene. We assessed the appropriateness of patient-specific induced pluripotent stem cell-derived cardiomyocytes (CMs) as a model to recapitulate some aspects of the pathogenetic mechanism involving cardiac manifestations in DM1 patients. Once obtained in vitro, CMs have been characterized for their morphology and their functionality. CMs DM1 show intranuclear foci and transcript markers abnormally spliced respect to WT ones, as well as several irregularities in nuclear morphology, probably caused by an unbalanced lamin A/C ratio. Electrophysiological characterization evidences an abnormal profile only in CMs DM1 such that the administration of antiarrythmic drugs to these cells highlights even more the functional defect linked to the disease. Finally, Atomic Force Measurements reveal differences in the biomechanical behaviour of CMs DM1, in terms of frequencies and synchronicity of the beats. Altogether the complex phenotype described in this work, strongly reproduces some aspects of the human DM1 cardiac phenotype. Therefore, the present study provides an in vitro model suggesting novel insights into the mechanisms leading to the development of arrhythmogenesis and dilatative cardiomyopathy to consider when approaching to DM1 patients, especially for the risk assessment of sudden cardiac death (SCD). These data could be also useful in identifying novel biomarkers effective in clinical settings and patient-tailored therapies.

NGF-Dependent Changes in Ubiquitin Homeostasis Trigger Early Cholinergic Degeneration in Cellular and Animal AD-Model.

Basal forebrain cholinergic neurons (BFCNs) depend on nerve growth factor (NGF) for their survival/differentiation and innervate cortical and hippocampal regions involved in memory/learning processes. Cholinergic hypofunction and/or degeneration early occurs at prodromal stages of Alzheimer's disease (AD) neuropathology in correlation with synaptic damages, cognitive decline and behavioral disability. Alteration(s) in ubiquitin-proteasome system (UPS) is also a pivotal AD hallmark but whether it plays a causative, or only a secondary role, in early synaptic failure associated with disease onset remains unclear. We previously reported that impairment of NGF/TrkA signaling pathway in cholinergic-enriched septo-hippocampal primary neurons triggers "dying-back" degenerative processes which occur prior to cell death in concomitance with loss of specific vesicle trafficking proteins, including synapsin I, SNAP-25 and α-synuclein, and with deficit in presynaptic excitatory neurotransmission. Here, we show that in this in vitro neuronal model: (i) UPS stimulation early occurs following neurotrophin starvation (-1 h up to -6 h); (ii) NGF controls the steady-state levels of these three presynaptic proteins by acting on coordinate mechanism(s) of dynamic ubiquitin-C-terminal hydrolase 1 (UCHL-1)-dependent (mono)ubiquitin turnover and UPS-mediated protein degradation. Importantly, changes in miniature excitatory post-synaptic currents (mEPSCs) frequency detected in -6 h NGF-deprived primary neurons are strongly reverted by acute inhibition of UPS and UCHL-1, indicating that NGF tightly controls in vitro the presynaptic efficacy via ubiquitination-mediated pathway(s). Finally, changes in synaptic ubiquitin and selective reduction of presynaptic markers are also found in vivo in cholinergic nerve terminals from hippocampi of transgenic Tg2576 AD mice, even from presymptomatic stages of neuropathology (1-month-old). By demonstrating a crucial role of UPS in the dysregulation of NGF/TrkA signaling on properties of cholinergic synapses, these findings from two well-established cellular and animal AD models provide novel therapeutic targets to contrast early cognitive and synaptic dysfunction associated to selective degeneration of BFCNs occurring in incipient early/middle-stage of disease.

miR-135a Regulates Synaptic Transmission and Anxiety-Like Behavior in Amygdala.

MicroRNAs are a class of non-coding RNAs with a growing relevance in the regulation of gene expression related to brain function and plasticity. They have the potential to orchestrate complex phenomena, such as the neuronal response to homeostatic challenges. We previously demonstrated the involvement of miR-135a in the regulation of early stress response. In the present study, we examine the role of miR-135a in stress-related behavior. We show that the knockdown (KD) of miR-135a in the mouse amygdala induces an increase in anxiety-like behavior. Consistently with behavioral studies, electrophysiological experiments in acute brain slices indicate an increase of amygdala spontaneous excitatory postsynaptic currents, as a result of miR-135a KD. Furthermore, we presented direct evidences, by in vitro assays and in vivo miRNA overexpression in the amygdala, that two key regulators of synaptic vesicle fusion, complexin-1 and complexin-2, are direct targets of miR-135a. In vitro analysis of miniature excitatory postsynaptic currents on miR-135a KD primary neurons indicates unpaired quantal excitatory neurotransmission. Finally, increased levels of complexin-1 and complexin-2 proteins were detected in the mouse amygdala after acute stress, accordingly to the previously observed stress-induced miR-135a downregulation. Overall, our results unravel a previously unknown miRNA-dependent mechanism in the amygdala for regulating anxiety-like behavior, providing evidences of a physiological role of miR-135a in the modulation of presynaptic mechanisms of glutamatergic neurotransmission.

Membrane cholesterol depletion in cortical neurons highlights altered NMDA receptor functionality in a mouse model of amyotrophic lateral sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a chronic neurodegenerative disease affecting upper and lower motor neurons, with unknown aetiology. Lipid rafts, cholesterol enriched microdomains of the plasma membrane, have been linked to neurodegenerative disorders like ALS. The NMDA-receptor subcellular localization in lipid rafts is known to play many roles, from modulating memory strength to neurotoxicity. In this study, performed on the widely used G93A mouse model of ALS, we have shown an equal content of total membrane cholesterol in Control and G93A cortical cultures. Moreover, by electrophysiological studies, we have recorded NMDA- and AMPA-evoked currents which were not significantly different between the two neuronal populations. To study the role of membrane cholesterol on glutamate receptor functionality, we have analysed NMDA and AMPA receptors following cholesterol membrane depletion by methyl-ß-cyclodextrin (MßCD). Interestingly, MßCD chronic treatment has provoked a significant reduction of NMDA-evoked currents in both cellular populations which was dose- and time-dependent but significantly higher in ALS neurons compared to Control. The different MßCD effect on NMDA-evoked currents was not due to a different membrane receptor subunit composition but seemed to cause in both neuronal populations a NMDA receptor membrane redistribution. MßCD treatment effect was receptor-specific since no alterations in the two neuronal populations were detected on AMPA receptors. These results lead us to speculate for an altered proteomic composition of lipid rafts in cortical mutated neurons and suggest the need for further studies on the lipid rafts composition and on their interaction with membrane receptors in ALS cortices.

Impaired NGF/TrkA Signaling Causes Early AD-Linked Presynaptic Dysfunction in Cholinergic Primary Neurons.

Alterations in NGF/TrkA signaling have been suggested to underlie the selective degeneration of the cholinergic basal forebrain neurons occurring in vivo in AD (Counts and Mufson, 2005; Mufson et al., 2008; Niewiadomska et al., 2011) and significant reduction of cognitive decline along with an improvement of cholinergic hypofunction have been found in phase I clinical trial in humans affected from mild AD following therapeutic NGF gene therapy (Tuszynski et al., 2005, 2015). Here, we show that the chronic (10-12 D.I.V.) in vitro treatment with NGF (100 ng/ml) under conditions of low supplementation (0.2%) with the culturing serum-substitute B27 selectively enriches the basal forebrain cholinergic neurons (+36.36%) at the expense of other non-cholinergic, mainly GABAergic (-38.45%) and glutamatergic (-56.25%), populations. By taking advantage of this newly-developed septo-hippocampal neuronal cultures, our biochemical and electrophysiological investigations demonstrate that the early failure in excitatory neurotransmission following NGF withdrawal is paralleled by concomitant and progressive loss in selected presynaptic and vesicles trafficking proteins including synapsin I, SNAP-25 and α-synuclein. This rapid presynaptic dysfunction: (i) precedes the commitment to cell death and is reversible in a time-dependent manner, being suppressed by de novo external administration of NGF within 6 hr from its initial withdrawal; (ii) is specific because it is not accompanied by contextual changes in expression levels of non-synaptic proteins from other subcellular compartments; (ii) is not secondary to axonal degeneration because it is insensible to pharmacological treatment with known microtubule-stabilizing drug such paclitaxel; (iv) involves TrkA-dependent mechanisms because the effects of NGF reapplication are blocked by acute exposure to specific and cell-permeable inhibitor of its high-affinity receptor. Taken together, this study may have important clinical implications in the field of AD neurodegeneration because it: (i) provides new insights on the earliest molecular mechanisms underlying the loss of synaptic/trafficking proteins and, then, of synapes integrity which occurs in vulnerable basal forebrain population at preclinical stages of neuropathology; (ii) offers prime presynaptic-based molecular target to extend the therapeutic time-window of NGF action in the strategy of improving its neuroprotective in vivo intervention in affected patients.

Prokineticin system modulation as a new target to counteract the amyloid beta toxicity induced by glutamatergic alterations in an in vitro model of Alzheimer's disease.

The accumulation of ß-amyloid (Aß) is one of the hallmarks of Alzheimer disease (AD). Beyond the inflammatory reactions promoted by Aß, it has been demonstrated that the prokineticin (PK) system, composed of the chemokine prokineticin 2 (PK2) and its receptors, is involved in Aß toxicity. In this study we have analyzed how the Aß chronic treatment affects the glutamatergic transmission on neurons from primary cortical cultures, clearly demonstrating the PK system involvement on its action mechanism. In fact, we have observed a significant increase of the ionic current through the AMPA receptors in primary cortical neurons and an up-regulation of the PK system in cultures chronically treated with Aß. All effects were nullified by the prokineticin antagonist PC-1. Moreover, we have herein firstly demonstrated that the incubation of primary cortical culture with Bv8, the amphibian homologue of PK2, was able to increase in neurons the AMPA currents at specific doses and exposure times, measured both as evoked and as spontaneous currents. This effect was not due to a modification of the AMPA receptor subunit expression. In contrast, the up-modulation of AMPA currents were blocked by PC-1 and were mediated by the activation of the intracellular protein kinase C (PKC) transduction pathways because Gö6983, the PKC inhibitor added in the medium, nullified the effect. Finally, cellular death induced by kainate was also reduced following treatment with PC1. In conclusion, our results show that the prokineticin system may be a key mediator in the Aß-induced neuronal damage, suggesting PK antagonists as new therapeutic compounds to ameliorate the AD progression.

Maintenance of aversive memories shown by fear extinction-impaired phenotypes is associated with increased activity in the amygdaloid-prefrontal circuit.

Although aversive memory has been mainly addressed by analysing the changes occurring in average populations, the study of neuronal mechanisms of outliers allows understanding the involvement of individual differences in fear conditioning and extinction. We recently developed an innovative experimental model of individual differences in approach and avoidance behaviors, classifying the mice as Approaching, Balancing or Avoiding animals according to their responses to conflicting stimuli. The approach and avoidance behaviors appear to be the primary reactions to rewarding and threatening stimuli and may represent predictors of vulnerability (or resilience) to fear. We submitted the three mice phenotypes to Contextual Fear Conditioning. In comparison to Balancing animals, Approaching and Avoiding mice exhibited no middle- or long-term fear extinction. The two non-extinguishing phenotypes exhibited potentiated glutamatergic neurotransmission (spontaneous excitatory postsynaptic currents/spinogenesis) of pyramidal neurons of medial prefrontal cortex and basolateral amygdala. Basing on the a priori individuation of outliers, we demonstrated that the maintenance of aversive memories is linked to increased spinogenesis and excitatory signaling in the amygdala-prefrontal cortex fear matrix.

Baicalein reverts L-valine-induced persistent sodium current up-modulation in primary cortical neurons.

L-valine is a branched-chain amino acid (BCAA) largely used as dietary integrator by athletes and involved in some inherited rare diseases such as maple syrup urine disease. This pathology is caused by an altered BCAA metabolism with the accumulation of toxic keto acids in tissues and body fluids with consequent severe neurological symptoms. In animal models of BCAA accumulation, increased oxidative stress levels and lipid peroxidation have been reported. The aim of this study was to analyze both whether high BCAA concentrations in neurons induce reactive oxygen species (ROS) production and whether, by performing electrophysiological recordings, the neuronal functional properties are modified. Our results demonstrate that in primary cortical cultures, a high dose of valine increases ROS production and provokes neuronal hyperexcitability because the action potential frequencies and the persistent sodium current amplitudes increase significantly compared to non-treated neurons. Since Baicalein, a flavone obtained from the Scutellaria root, has been shown to act as a strong antioxidant with neuroprotective effects, we evaluated its possible antioxidant activity in primary cortical neurons chronically exposed to L-valine. The preincubation of cortical neurons with Baicalein prevents the ROS production and is able to revert both the neuronal hyperexcitability and the increase of the persistent sodium current, indicating a direct correlation between the ROS production and the altered physiological parameters. In conclusion, our data show that the electrophysiological alterations of cortical neurons elicited by high valine concentration are due to the increase in ROS production, suggesting much caution in the intake of BCAA dietary integrators.

Bv8/prokineticin 2 is involved in Aß-induced neurotoxicity.

Bv8/Prokineticin 2 (PROK2) is a bioactive peptide initially discovered as a regulator of gastrointestinal motility. Among multiple biological roles demonstrated for PROK2, it was recently established that PROK2 is an insult-inducible endangering mediator for cerebral damage. Aim of the present study was to evaluate the PROK2 and its receptors' potential involvement in amyloid beta (Aß) neurotoxicity, a hallmark of Alzheimer's disease (AD) and various forms of traumatic brain injury (TBI). Analyzing primary cortical cultures (CNs) and cortex and hippocampus from Aß treated rats, we found that PROK2 and its receptors PKR1 and PKR2 mRNA are up-regulated by Aß, suggesting their potential involvement in AD. Hence we evaluated if impairing the prokineticin system activation might have protective effect against neuronal death induced by Aß. We found that a PKR antagonist concentration-dependently protects CNs against Aß(1-42)-induced neurotoxicity, by reducing the Aß-induced PROK2 neuronal up-regulation. Moreover, the antagonist completely rescued LTP impairment in hippocampal slices from 6 month-old Tg2576 AD mice without affecting basal synaptic transmission and paired pulse-facilitation paradigms. These results indicate that PROK2 plays a role in cerebral amyloidosis and that PROK2 antagonists may represent a new approach for ameliorating the defining pathology of AD.

Bindarit, inhibitor of CCL2 synthesis, protects neurons against amyloid-ß-induced toxicity.

One of the hallmarks of Alzheimer's disease (AD), the most common age-related neurodegenerative pathology, is the abnormal extracellular deposition of neurotoxic amyloid-ß (Aß) peptides that accumulate in senile plaques. Aß aggregates are toxic to neurons and are thought to contribute to neuronal loss. Evidence indicates that inflammation is involved in the pathophysiology of AD, and activation of glial cells by a variety of factors, including Aß, appears to be a central event. Among molecules produced during inflammation associated with neuronal death, CCL2, also known as monocyte chemotactic protein-1 (MCP-1), seems to be particularly important. Indeed, CCL2 levels are higher in the cerebrospinal fluid of patients with AD than in controls. In the present study, we demonstrated the protective effect of bindarit (which inhibits CCL2 synthesis) against both Aß25-35 and Aß1-42-induced toxicity in primary mixed neural cultures. Bindarit (30-500 µM) reversed cell death induced by Aß in a dose-dependent manner and reduced the transcription and release of CCL2 by astrocytes after Aß treatment, as revealed by qRT-PCR, ELISA, and immunofluorescence staining. Astroglial activation and CCL2 release was induced by ATP released by damaged neurons through interaction with P2X7 receptors present on astrocyte surface. CCL2, interacting with its cognate receptor CCR2, present on neuron surface, strongly contributes to the toxic activity of Aß. Bindarit was able to disconnect this neuro-glial interaction. Our results demonstrate the ability of bindarit to inhibit Aß-induced neuronal death and suggest the potential role of CCL2 inhibitors in the treatment of neuroinflammatory/neurodegenerative diseases.

Systemic administration of substance P recovers beta amyloid-induced cognitive deficits in rat: involvement of Kv potassium channels.

Reduced levels of Substance P (SP), an endogenous neuropeptide endowed with neuroprotective and anti-apoptotic properties, have been found in brain and spinal fluid of Alzheimer's disease (AD) patients. Potassium (K(+)) channel dysfunction is implicated in AD development and the amyloid-ß (Aß)-induced up-regulation of voltage-gated potassium channel subunits could be considered a significant step in Aß brain toxicity. The aim of this study was to evaluate whether SP could reduce, in vivo, Aß-induced overexpression of Kv subunits. Rats were intracerebroventricularly infused with amyloid-ß 25-35 (Aß25-35, 20 µg) peptide. SP (50 µg/Kg, i.p.) was daily administered, for 7 days starting from the day of the surgery. Here we demonstrate that the Aß infused rats showed impairment in cognitive performances in the Morris water maze task 4 weeks after Aß25-35 infusion and that this impairing effect was prevented by SP administration. Kv1.4, Kv2.1 and Kv4.2 subunit levels were quantified in hippocampus and in cerebral cortex by Western blot analysis and immunofluorescence. Interestingly, SP reduced Kv1.4 levels overexpressed by Aß, both in hippocampus and cerebral cortex. Our findings provide in vivo evidence for a neuroprotective activity of systemic administration of SP in a rat model of AD and suggest a possible mechanism underlying this effect.

Monocyte Chemoattractant Protein-1 upregulates GABA-induced current: evidence of modified GABAA subunit composition in cortical neurons from the G93A mouse model of Amyotrophic Lateral Sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disorder that affects upper and lower motor neurons. Previous evidence has indicated that excitotoxic cell death in ALS may remarkably depend on Cl(-) ion influx through the GABA(A) receptors. In this study we have analysed the effect of Monocyte Chemoattractant Protein-1 (MCP-1), a chemokine expressed to a higher level in ALS patients, on GABAA receptors in cultured cortical neurons from a genetic model of ALS (G93A) and compared with wild type SOD1 (SOD1) and their corresponding non transgenic littermates (Control). By performing electrophysiological experiments we have observed that, in cortical neurons MCP-1 (2-150 ng/ml) induced an enhancement of GABA-evoked currents that was significantly higher in G93A neurons compared to controls. The effect of MCP-1 was not dependent on the activation of its receptor CCR2, while it was blocked by flumazenil, the antagonist of benzodiazepine sites. Analysis of GABAA receptor subunit composition has indicated an altered subunit expression level in G93A cortical neurons compared to controls. Instead, in cultured spinal neurons MCP-1 induced a significant reduction of GABA-evoked currents, also through the benzodiazepine sites, indicating a region-specific mechanism of action. However, no differences were observed in the current reduction between the three neuronal populations. These findings provide the first evidence that MCP-1, acting on benzodiazepine sites, can modulate the GABA-evoked currents, depending on the subunit composition of GABA(A) receptor. In cortical neurons MCP-1 upmodulates the GABA-evoked current and this effect is exacerbated in the mutated neurons. It is reasonable to assume that the higher Cl(-) influx through GABA(A) receptors in the presence of MCP-1 in mutated cortical neurons may induce an excitotoxicity acceleration. Agents able to block the MCP-1 production may then prove useful for ALS treatment.

Over-expression of N-type calcium channels in cortical neurons from a mouse model of Amyotrophic Lateral Sclerosis.

Voltage-gated Ca(2+) channels (VGCCs) mediate calcium entry into neuronal cells in response to membrane depolarisation and play an essential role in a variety of physiological processes. In Amyotrophic Lateral Sclerosis (ALS), a fatal neurodegenerative disease caused by motor neuron degeneration in the brain and spinal cord, intracellular calcium dysregulation has been shown, while no studies have been carried out on VGCCs. Here we show that the subtype N-type Ca(2+) channels are over expressed in G93A cultured cortical neurons and in motor cortex of G93A mice compared to Controls. In fact, by western blotting, immunocytochemical and electrophysiological experiments, we observe higher membrane expression of N-type Ca(2+) channels in G93A neurons compared to Controls. G93A cortical neurons filled with calcium-sensitive dye Fura-2, show a net calcium entry during membrane depolarization that is significantly higher compared to Control. Analysis of neuronal vitality following the exposure of neurons to a high K(+) concentration (25 mM, 5h), shows a significant reduction of G93A cellular survival compared to Controls. N-type channels are involved in the G93A higher mortality because ω-conotoxin GVIA (1 µM), which selectively blocks these channels, is able to abolish the higher G93A mortality when added to the external medium. These data provide robust evidence for an excess of N-type Ca(2+) expression in G93A cortical neurons which induces a higher mortality following membrane depolarization. These results may be central to the understanding of pathogenic pathways in ALS and provide novel molecular targets for the design of rational therapies for the ALS disorder.

Substance P receptor activation induces downregulation of the AMPA receptor functionality in cortical neurons from a genetic model of Amyotrophic Lateral Sclerosis.

Substance P (SP), a neuropeptide member of the tachykinin (TK) family, has a functional role both in physiological and pathological conditions, including Amyotrophic Lateral Sclerosis disease. One hypothesis of the selective motor neuron death in ALS involves the excitatory neurotransmitter glutamate, because these neurons are extremely susceptible to excessive stimulation of AMPA receptors. It has been reported that SP exerts its action against a variety of insults including excitotoxicity, and that altered levels of SP have been observed in the cerebrospinal fluid (CSF) of patients with ALS. Here we have analyzed the interaction between SP and AMPA receptor functionality, both in Control cortical neurons in culture and in those obtained from a genetic mouse model of ALS (G93A). Our studies demonstrate that SP reduces the kainate-activated currents in Control and G93A neurons and that this reduction is significantly higher in the mutated neurons. SP effect is mediated by its receptor NK1 because GR 82334 (5 µM), a NK1 competitive antagonist, is able to suppress the current reduction. Analysis of miniature excitatory postsynaptic currents (mEPSCs) in Control and G93A neurons indicates that SP (200 nM) is able to significantly decrease the mEPSC amplitudes in G93A neurons, whereas it is ineffective on Control mEPSCs. Western blotting experiments in cultures and cortical tissues show a higher NK1 expression level in G93A mice compared to that of Control. This is also confirmed by immunocytochemistry experiments in cultured neurons. In addition, the amount of GluR1 subunit AMPA receptors is not modified following SP exposure, indicating a non internalization of the AMPA receptors. Finally, toxicity experiments have revealed that SP is able to rescue G93A cortical cells whereas it is ineffective on those of Control. These findings provide the first evidence of SP having a physiological and protective role in the G93A mouse model of ALS, and may suggest the possible use of SP as a clinical therapeutic treatment.

Complex behavioral and synaptic effects of dietary branched chain amino acids in a mouse model of amyotrophic lateral sclerosis.

SCOPE: We hypothesized that chronic supplementation with branched chain amino acids (BCAAs) affects neurobehavioral development in vulnerable gene backgrounds. METHODS AND RESULTS: A murine model of amyotrophic lateral sclerosis (ALS), G93A mice bearing the mutated human superoxide dismutase 1 (SOD1) gene, and control mice received from 4 to 16 wk of age dietary supplementation with BCAAs at doses comparable to human usage. Motor coordination, exploratory behaviors, pain threshold, synaptic activity and response to glutamatergic stimulation in primary motor cortex slices were evaluated between the 8th and 16th week. The glial glutamate transporter 1 (GLT-1) and metabotropic glutamate 5 receptor (mGlu5R) were analyzed by immunoblotting in cortex, hippocampus and striatum. BCAAs induced hyperactivity, decreased pain threshold in wild-type mice and exacerbated the motor deficits of G93A mice while counteracting their abnormal pain response. Electrophysiology on G93A brain slices showed impaired synaptic function, reduced toxicity of GLT-1 blocking and increased glutamate toxicity prevented by BCAAs. Immunoblotting indicated down-regulation of GLT-1 and mGlu5R in G93A, both effects counteracted by BCAAs. CONCLUSION: These results, though not fully confirming a role of BCAAs in ALS-like etiology in the genetic model, clearly indicate that BCAAs' complex effects on central nervous system depend on gene background and raise alert over their spread use.