Influence of SPION Surface Coating on Magnetic Properties and Theranostic Profile.

This study aimed to develop multifunctional nanoplatforms for both cancer imaging and therapy using superparamagnetic iron oxide nanoparticles (SPIONs). Two distinct synthetic methods, reduction-precipitation (MR/P) and co-precipitation at controlled pH (MpH), were explored, including the assessment of the coating's influence, namely dextran and gold, on their magnetic properties. These SPIONs were further functionalized with gadolinium to act as dual T1/T2 contrast agents for magnetic resonance imaging (MRI). Parameters such as size, stability, morphology, and magnetic behavior were evaluated by a detailed characterization analysis. To assess their efficacy in imaging and therapy, relaxivity and hyperthermia experiments were performed, respectively. The results revealed that both synthetic methods lead to SPIONs with similar average size, 9 nm. Mössbauer spectroscopy indicated that samples obtained from MR/P consist of approximately 11-13% of Fe present in magnetite, while samples obtained from MpH have higher contents of 33-45%. Despite coating and functionalization, all samples exhibited superparamagnetic behavior at room temperature. Hyperthermia experiments showed increased SAR values with higher magnetic field intensity and frequency. Moreover, the relaxivity studies suggested potential dual T1/T2 contrast agent capabilities for the coated SPpH-Dx-Au-Gd sample, thus demonstrating its potential in cancer diagnosis.

Peptide-Conjugated MRI Probe Targeted to Netrin-1, a Novel Metastatic Breast Cancer Biomarker.

Despite significant progress in cancer imaging and treatment over the years, early diagnosis and metastasis detection remain a challenge. Molecular magnetic resonance imaging (MRI), with its high resolution, can be well adapted to fulfill this need, requiring the design of contrast agents which target specific tumor biomarkers. Netrin-1 is an extracellular protein overexpressed in metastatic breast cancer and implicated in tumor progression and the appearance of metastasis. This study focuses on the design and preclinical evaluation of a novel Netrin-1-specific peptide-based MRI probe, GdDOTA-KKTHDAVR (Gd-K), to visualize metastatic breast cancer. The targeting peptide sequence was identified based on the X-ray structure of the complex between Netrin-1 and its transmembrane receptor DCC. Molecular docking simulations support the probe design. In vitro studies evidenced submicromolar affinity of Gd-K for Netrin-1 (KD = 0.29 µM) and good MRI efficacy (proton relaxivity, r1 = 4.75 mM-1 s-1 at 9.4 T, 37 °C). In vivo MRI studies in a murine model of triple-negative metastatic breast cancer revealed successful tumor visualization at earlier stages of tumor development (smaller tumor volume). Excellent signal enhancement, 120% at 2 min and 70% up to 35 min post injection, was achieved (0.2 mmol/kg injected dose), representing a reasonable imaging time window and a superior contrast enhancement in the tumor as compared to Dotarem injection.

Zinc-sensitive MRI contrast agents: importance of local probe accumulation in zinc-rich tissues.

We present the in vitro characterisation of a Gd3+-based contrast agent that responds to Zn2+ upon interaction with Human Serum Albumin. We show that the contradictory in vivo behaviour is related to Gd3+-accumulation in Zn-rich tissues. This highlights the importance of the biodistribution of such contrast agents.

Deciphering the Role of Klf10 in the Cerebellum.

Recent studies have demonstrated a new role for Klf10, a Krüppel-like transcription factor, in skeletal muscle, specifically relating to mitochondrial function. Thus, it was of interest to analyze additional tissues that are highly reliant on optimal mitochondrial function such as the cerebellum and to decipher the role of Klf10 in the functional and structural properties of this brain region. In vivo (magnetic resonance imaging and localized spectroscopy, behavior analysis) and in vitro (histology, spectroscopy analysis, enzymatic activity) techniques were applied to comprehensively assess the cerebellum of wild type (WT) and Klf10 knockout (KO) mice. Histology analysis and assessment of locomotion revealed no significant difference in Klf10 KO mice. Diffusion and texture results obtained using MRI revealed structural changes in KO mice characterized as defects in the organization of axons. These modifications may be explained by differences in the levels of specific metabolites (myo-inositol, lactate) within the KO cerebellum. Loss of Klf10 expression also led to changes in mitochondrial activity as reflected by a significant increase in the activity of citrate synthase, complexes I and IV. In summary, this study has provided evidence that Klf10 plays an important role in energy production and mitochondrial function in the cerebellum.

Mn2+ Bispidine Complex Combining Exceptional Stability, Inertness, and MRI Efficiency.

As an essential metal ion and an efficient relaxation agent, Mn2+ holds a great promise to replace Gd3+ in magnetic resonance imaging (MRI) contrast agent applications, if its stable and inert complexation can be achieved. Toward this goal, four pyridine and one carboxylate pendants have been introduced in coordinating positions on the bispidine platform to yield ligand L3. Thanks to its rigid and preorganized structure and perfect size match for Mn2+, L3 provides remarkably high thermodynamic stability (log KMnL = 19.47), selectivity over the major biological competitor Zn2+ (log(KMnL/KZnL) = 4.4), and kinetic inertness. Solid-state X-ray data show that [MnL3(MeOH)](OTf)2 has an unusual eight-coordinate structure with a coordinated solvent molecule, in contrast to the six-coordinate structure of [ZnL3](OTf), underlining that the coordination cavity is perfectly adapted for Mn2+, while it is too large for Zn2+. In aqueous solution, 17O NMR data evidence one inner sphere water and dissociatively activated water exchange (kex298 = 13.5 × 107 s-1) for MnL3. Its water proton relaxivity (r1 = 4.44 mM-1 s-1 at 25 °C, 20 MHz) is about 30% higher than values for typical monohydrated Mn2+ complexes, which is related to its larger molecular size; its relaxation efficiency is similar to that of clinically used Gd3+-based agents. In vivo MRI experiments realized in control mice at 0.02 mmol/kg injected dose indicate good signal enhancement in the kidneys and fast renal clearance. Taken together, MnL3 is the first chelate that combines such excellent stability, selectivity, inertness and relaxation properties, all of primary importance for MRI use.

Doxorubicin-Sensitized Luminescence of NIR-Emitting Ytterbium Liposomes: Towards Direct Monitoring of Drug Release.

Drug-loaded liposomes are typical examples of nanomedicines. We show here that doxorubicin, the anti-cancer agent in the liposomal drug Doxil, can sensitize Ytterbium (Yb3+ ) and generate its near-infrared (NIR) emission. When doxorubicin and amphiphilic Yb3+ chelates are incorporated into liposomes, the sensitized emission of Yb3+ is dependent on the integrity of the particles, which can be used to monitor drug release. We also established the first demonstration that the NIR Yb3+ emission signal is observable in living mice following intratumoral injection of the Yb3+ -doxorubicin-liposomes, using a commercial macroscopic setup equipped with a NIR camera.

Brain orchestration of pregnancy and maternal behavior in mice: A longitudinal morphometric study.

Reproduction induces changes within the brain to prepare for gestation and motherhood. However, the dynamic of these central changes and their relationships with the development of maternal behavior remain poorly understood. Here, we describe a longitudinal morphometric neuroimaging study in female mice between pre-gestation and weaning, using new magnetic resonance imaging (MRI) resources comprising a high-resolution brain template, its associated tissue priors (60-µm isotropic resolution) and a corresponding mouse brain atlas (1320 regions of interest). Using these tools, we observed transient hypertrophies not only within key regions controlling gestation and maternal behavior (medial preoptic area, bed nucleus of the stria terminalis), but also in the amygdala, caudate nucleus and hippocampus. Additionally, unlike females exhibiting lower levels of maternal care, highly maternal females developed transient hypertrophies in somatosensory, entorhinal and retrosplenial cortices among other regions. Therefore, coordinated and transient brain modifications associated with maternal performance occurred during gestation and lactation.

Mn(II)-Based MRI Contrast Agent Candidate for Vascular Imaging.

Toxicity concerns related to Gd(III)-based magnetic resonance imaging (MRI) agents prompted an intensive research toward their replacement by complexes of essential metal ions, like Mn(II). Here, we report a macrocyclic chelate, [Mn(PC2A-BP)], which possesses high thermodynamic stability (log KMnL = 14.86 and pMn=8.35) and kinetic inertness (t1/2pH=7.4 = 286.2 h) as well as as remarkable relaxivity (r1p = 23.5 mM-1 s-1, 0.49 T, 37 °C) in the presence of human serum albumin, allowing a significant MRI signal intensity increase in the vasculature even at low dose (25 µmol/kg) of the complex.

Unprecedented Kinetic Inertness for a Mn2+ -Bispidine Chelate: A Novel Structural Entry for Mn2+ -Based Imaging Agents.

The search for more biocompatible alternatives to Gd3+ -based MRI agents, and the interest in 52 Mn for PET imaging call for ligands that form inert Mn2+ chelates. Given the labile nature of Mn2+ , high inertness is challenging to achieve. The strongly preorganized structure of the 2,4-pyridyl-disubstituted bispidol ligand L1 endows its Mn2+ complex with exceptional kinetic inertness. Indeed, MnL1 did not show any dissociation for 140 days in the presence of 50 equiv. of Zn2+ (37 °C, pH 6), while recently reported potential MRI agents MnPyC3A and MnPC2A-EA have dissociation half-lives of 0.285 h and 54.4 h under similar conditions. In addition, the relaxivity of MnL1 (4.28 mm-1 s-1 at 25 °C, 20 MHz) is remarkable for a monohydrated, small Mn2+ chelate. In vivo MRI experiments in mice and determination of the tissue Mn content evidence rapid renal clearance of MnL1 . Additionally, L1 could be radiolabeled with 52 Mn and the complex revealed good stability in biological media.

Dual Imaging Gold Nanoplatforms for Targeted Radiotheranostics.

Gold nanoparticles (AuNPs) are interesting for the design of new cancer theranostic tools, mainly due to their biocompatibility, easy molecular vectorization, and good biological half-life. Herein, we report a gold nanoparticle platform as a bimodal imaging probe, capable of coordinating Gd3+ for Magnetic Resonance Imaging (MRI) and 67Ga3+ for Single Photon Emission Computed Tomography (SPECT) imaging. Our AuNPs carry a bombesin analogue with affinity towards the gastrin releasing peptide receptor (GRPr), overexpressed in a variety of human cancer cells, namely PC3 prostate cancer cells. The potential of these multimodal imaging nanoconstructs was thoroughly investigated by the assessment of their magnetic properties, in vitro cellular uptake, biodistribution, and radiosensitisation assays. The relaxometric properties predict a potential T1- and T2- MRI application. The promising in vitro cellular uptake of 67Ga/Gd-based bombesin containing particles was confirmed through biodistribution studies in tumor bearing mice, indicating their integrity and ability to target the GRPr. Radiosensitization studies revealed the therapeutic potential of the nanoparticles. Moreover, the DOTA chelating unit moiety versatility gives a high theranostic potential through the coordination of other therapeutically interesting radiometals. Altogether, our nanoparticles are interesting nanomaterial for theranostic application and as bimodal T1- and T2- MRI / SPECT imaging probes.

Aza-BODIPY Platform: Toward an Efficient Water-Soluble Bimodal Imaging Probe for MRI and Near-Infrared Fluorescence.

In this study, an original aza-BODIPY system comprising two Gd3+ complexes has been designed and synthesized for magnetic resonance imaging/optical imaging applications, by functionalization of the boron center. This strategy enabled the obtainment of a positively charged bimodal probe, which displays an increased water solubility, optimized photophysical properties in the near-infrared region, and very promising relaxometric properties. The absorption and emission wavelengths are 705 and 741 nm, respectively, with a quantum yield of around 10% in aqueous media. Moreover, the system does not produce singlet oxygen upon excitation, which would be toxic for tissues. The relaxivity obtained is high at intermediate fields (16.1 mM-1 s-1 at 20 MHz and 310 K) and competes with that of bigger or more rigid systems. A full relaxometric and 17O NMR study and fitting of the data using the Lipari-Szabo approach showed that this high relaxivity can be explained by the size of the system and the presence of some small aggregates. These optimized photophysical and relaxometric properties highlight the potential use of such systems for future bimodal imaging studies.

Novel role of Tieg1 in muscle metabolism and mitochondrial oxidative capacities.

AIM: Tieg1 is involved in multiple signalling pathways, human diseases, and is highly expressed in muscle where its functions are poorly understood. METHODS: We have utilized Tieg1 knockout (KO) mice to identify novel and important roles for this transcription factor in regulating muscle ultrastructure, metabolism and mitochondrial functions in the soleus and extensor digitorum longus (EDL) muscles. RNA sequencing, immunoblotting, transmission electron microscopy, MRI, NMR, histochemical and mitochondrial function assays were performed. RESULTS: Loss of Tieg1 expression resulted in altered sarcomere organization and a significant decrease in mitochondrial number. Histochemical analyses demonstrated an absence of succinate dehydrogenase staining and a decrease in cytochrome c oxidase (COX) enzyme activity in KO soleus with similar, but diminished, effects in the EDL. Decreased complex I, COX and citrate synthase (CS) activities were detected in the soleus muscle of KO mice indicating altered mitochondrial function. Complex I activity was also diminished in KO EDL. Significant decreases in CS and respiratory chain complex activities were identified in KO soleus. 1 H-NMR spectra revealed no significant metabolic difference between wild-type and KO muscles. However, 31 P spectra revealed a significant decrease in phosphocreatine and ATPγ. Altered expression of 279 genes, many of which play roles in mitochondrial and muscle function, were identified in KO soleus muscle. Ultimately, all of these changes resulted in an exercise intolerance phenotype in Tieg1 KO mice. CONCLUSION: Our findings have implicated novel roles for Tieg1 in muscle including regulation of gene expression, metabolic activity and organization of tissue ultrastructure. This muscle phenotype resembles diseases associated with exercise intolerance and myopathies of unknown consequence.

Effect of Long-Term Retention of Gadolinium on Metabolism of Deep Cerebellar Nuclei After Repeated Injections of Gadodiamide in Rats.

OBJECTIVES: The aim of this study was to determine potential metabolism and histological modifications due to gadolinium retention within deep cerebellar nuclei (DCN) after linear gadolinium-based contrast agent injection (gadodiamide) in rats at 1 year after the last injection. MATERIALS AND METHODS: Twenty female rats received 20 doses of gadodiamide (0.6 mmol of gadolinium per kilogram each) over 5 weeks. They were followed at 1 week (M0), 6 weeks (M1), and 54 to 55 weeks (M13) postinjections to evaluate hypersignal on unenhanced T1-weighted magnetic resonance imaging and metabolic alterations by H magnetic resonance spectroscopy (H-MRS). At 1 year postinjections, brains were sampled to determine the localization of gadolinium within cerebellum by laser ablation inductively coupled mass spectroscopy and to evaluate morphological changes by semiquantitative immunofluorescence analysis. RESULTS: There is a significant increase of the ratio DCN/brainstem for the gadodiamide group at M0 (+7.2% vs control group = 0.989 ± 0.01), M1 (+7.6% vs control group = 1.002 ± 0.018), and it lasted up to M13 (+4.7% vs control group = 0.9862 ± 0.008). No variation among metabolic markers (cellular homeostasis [creatine, choline, taurine], excitatory neurotransmitter [glutamate], and metabolites specific to a cellular compartment [N-acetyl aspartate for neurons and myo-inositol for glial cells]) were detected by H-MRS between gadodiamide and saline groups at M0, M1, and M13. At M13, laser ablation inductively coupled mass spectroscopy demonstrated that long-term gadolinium retention occurred preferentially in DCN. No histological abnormalities (including analysis of astrocytes, neurons, and microglial cells) were found in the rostral part of DCN. CONCLUSIONS: Repeated administration of gadodiamide lead to a retention of gadolinium preferentially within DCN at 1 year postinjections. This retention did not lead to any detectable changes of the measured metabolic biomarkers nor histological alterations.

Development of a novel multiphysical approach for the characterization of mechanical properties of musculotendinous tissues.

At present, there is a lack of well-validated protocols that allow for the analysis of the mechanical properties of muscle and tendon tissues. Further, there are no reports regarding characterization of mouse skeletal muscle and tendon mechanical properties in vivo using elastography thereby limiting the ability to monitor changes in these tissues during disease progression or response to therapy. Therefore, we sought to develop novel protocols for the characterization of mechanical properties in musculotendinous tissues using atomic force microscopy (AFM) and ultrasound elastography. Given that TIEG1 knockout (KO) mice exhibit well characterized defects in the mechanical properties of skeletal muscle and tendon tissue, we have chosen to use this model system in the present study. Using TIEG1 knockout and wild-type mice, we have devised an AFM protocol that does not rely on the use of glue or chemical agents for muscle and tendon fiber immobilization during acquisition of transversal cartographies of elasticity and topography. Additionally, since AFM cannot be employed on live animals, we have also developed an ultrasound elastography protocol using a new linear transducer, SLH20-6 (resolution: 38 µm, footprint: 2.38 cm), to characterize the musculotendinous system in vivo. This protocol allows for the identification of changes in muscle and tendon elasticities. Such innovative technological approaches have no equivalent to date, promise to accelerate our understanding of musculotendinous mechanical properties and have numerous research and clinical applications.

The IL-33 Receptor ST2 Regulates Pulmonary Inflammation and Fibrosis to Bleomycin.

Idiopathic pulmonary fibrosis is a progressive, devastating, and yet untreatable fibrotic disease of unknown origin. Interleukin-33 (IL-33), an IL-1 family member acts as an alarmin with pro-inflammatory properties when released after stress or cell death. Here, we investigated the role of IL-33 in the bleomycin (BLM)-induced inflammation and fibrosis model using mice IL-33 receptor [chain suppression of tumorigenicity 2 (ST2)] mice compared with C57BL/6 wild-type mice. Unexpectedly, 24 h post-BLM treatment ST2-deficient mice displayed augmented inflammatory cell recruitment, in particular by neutrophils, together with enhanced levels of chemokines and remodeling factors in the bronchoalveolar space and/or the lungs. At 11 days, lung remodeling and fibrosis were decreased with reduced M2 macrophages in the lung associated with M2-like cytokine profile in ST2-deficient mice, while lung cellular inflammation was decreased but with fluid retention (edema) increased. In vivo magnetic resonance imaging (MRI) analysis demonstrates a rapid development of edema detectable at day 7, which was increased in the absence of ST2. Our results demonstrate that acute neutrophilic pulmonary inflammation leads to the development of an IL-33/ST2-dependent lung fibrosis associated with the production of M2-like polarization. In addition, non-invasive MRI revealed enhanced inflammation with lung edema during the development of pulmonary inflammation and fibrosis in absence of ST2.

Gestational and lactational exposure to dichlorinated bisphenol A induces early alterations of hepatic lipid composition in mice.

OBJECTIVE: Using non-invasive magnetic resonance (MR) techniques and a histological approach, we assessed the outcomes of perinatal exposure at a low dose of 3,3'-DCBPA (2-chloro-4-[1-(3-chloro-4-hydroxyphenyl)-1-methylethyl]phenol) and/or 3,5-DCBPA (2,6-dichloro-4-[1-(4-hydroxyphenyl)-1-methylethyl]phenol) on mice livers. MATERIALS AND METHODS: Fertilized female Swiss mice were injected intraperitoneally during gestation and lactation with either vehicle control, 20 µg/kg/day of BPA, 3,5-DCBPA, 3,3'-DCBPA or a mixture (mix-DCBPA). Complementary methods were used to evaluate, in male and female pups, (1) liver structure by texture analysis of images obtained through MR imaging (MRI) and histology, (2) hepatic lipid composition through in vivo 1H MR spectroscopy (1H MRS). RESULTS: Principal component analysis of texture parameters showed no structural modification of the liver with BPA and DCBPA treatments. Accordingly, no hepatic microvesicular steatosis was observed through hematoxylin-eosin staining. Compared to control, MRS revealed no difference in lipid composition for BPA, 3,5-DCBPA or 3,3'-DCBPA groups. However, MRS detected a significant increase in the mix-DCBPA groups for the saturated component of fatty acids (FA), total unsaturated FA bond index and polyunsaturated FA bond index. CONCLUSION: Prior to any structural changes, polyunsaturated fatty acids significantly increased in young male and female mice exposed perinatally at a low dose to a mixture of dichlorinated BPA.

Targeting HER2-breast tumors with scFv-decorated bimodal nanoprobes.

BACKGROUND: Recent advances in nanomedicine have shown the great interest of active targeting associated to nanoparticles. Single chain variable fragments (scFv) of disease-specific antibodies are very promising targeting entities because they are small, not immunogenic and able to bind their specific antigens. The present paper is devoted to biological properties in vitro and in vivo of fluorescent and pegylated iron oxide nanoparticles (SPIONs-Cy-PEG-scFv) functionalized with scFv targeting Human Epithelial growth Receptor 2 (HER2). RESULTS: Thanks to a site-selective scFv conjugation, the resultant nanoprobes demonstrated high affinity and specific binding to HER2 breast cancer cells. The cellular uptake of SPIONs-Cy-PEG-scFv was threefold higher than that for untargeted PEGylated iron oxide nanoparticles (SPIONs-Cy-PEG) and is correlated to the expression of HER2 on cells. In vivo, the decrease of MR signals in HER2+ xenograft tumor is about 30% at 24 h after the injection. CONCLUSIONS: These results all indicate that SPIONs-Cy-PEG-scFv are relevant tumor-targeting magnetic resonance imaging agents, suitable for diagnosis of HER2 overexpressing breast tumor.

IL-33 receptor ST2 regulates the cognitive impairments associated with experimental cerebral malaria.

Cerebral malaria (CM) is associated with a high mortality rate and long-term neurocognitive impairment in survivors. The murine model of experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA (PbA)-infection reproduces several of these features. We reported recently increased levels of IL-33 protein in brain undergoing ECM and the involvement of IL-33/ST2 pathway in ECM development. Here we show that PbA-infection induced early short term and spatial memory defects, prior to blood brain barrier (BBB) disruption, in wild-type mice, while ST2-deficient mice did not develop cognitive defects. PbA-induced neuroinflammation was reduced in ST2-deficient mice with low Ifng, Tnfa, Il1b, Il6, CXCL9, CXCL10 and Cd8a expression, associated with an absence of neurogenesis defects in hippocampus. PbA-infection triggered a dramatic increase of IL-33 expression by oligodendrocytes, through ST2 pathway. In vitro, IL-33/ST2 pathway induced microglia expression of IL-1ß which in turn stimulated IL-33 expression by oligodendrocytes. These results highlight the IL-33/ST2 pathway ability to orchestrate microglia and oligodendrocytes responses at an early stage of PbA-infection, with an amplification loop between IL-1ß and IL-33, responsible for an exacerbated neuroinflammation context and associated neurological and cognitive defects.

Impact of TIEG1 on the structural properties of fast- and slow-twitch skeletal muscle.

INTRODUCTION: Transforming growth factor-beta (TGF-ß)-inducible early gene-1 (TIEG1) is a transcription factor that is highly expressed in skeletal muscle. The purpose of this study was to characterize the structural properties of both fast-twitch (EDL) and slow-twitch (soleus) muscles in the hindlimb of TIEG1-deficient (TIEG1-/- ) mice. METHODS: Ten slow and 10 fast muscles were analyzed from TIEG1-/- and wild-type (WT) mice using MRI texture (MRI-TA) and histological analyses. RESULTS: MRI-TA could discriminate between WT slow and fast muscles. Deletion of the TIEG1 gene led to changes in the texture profile within both muscle types. Specifically, muscle isolated from TIEG1-/- mice displayed hypertrophy, hyperplasia, and a modification of fiber area distribution. CONCLUSIONS: We demonstrated that TIEG1 plays an important role in the structural properties of skeletal muscle. This study further implicates important roles for TIEG1 in the development of skeletal muscle and suggests that defects in TIEG1 expression and/or function may be associated with muscle disease. Muscle Nerve 55: 410-416, 2017.

L-Phosphinothricin modulation of inwardly rectifying K(+) channels increased excitability in striatal medium-sized spiny neurons.

Phosphinotricin (L-PPT) is the active compound of a broad-spectrum herbicide. Acute poisoning with L-PPT has various clinical manifestations, including seizures and convulsions. However, the exact mechanism of L-PPT toxicity remains unclear. The present study addressed the role of L-PPT, in the excitability of striatal medium-sized spiny neurons (MSNs). In whole-cell current-clamp experiments, L-PPT increased the input resistance (Ri), decreased the rheobase and increased the firing frequency of action potentials. In voltage-clamp experiments, L-PPT inhibited the inward-rectifying potassium (Kir) currents. Finally, the effects of L-PPT mimicked the inhibition of Kir channels with Ba(2+) on neuronal excitability. Altogether, these results suggest that the herbicide L-PPT is a modulator of Kir channels in MSNs. Thereby, Kir channels are potent regulators of the excitability of MSNs and reduced open probability of these channels would generate a powerful upregulation of neuronal output. This effect may represent a possible mechanism for L-PPT dependent neuronal toxicity.