Monoamines block kainate‐ and carbachol‐induced γ‐oscillations but augment stimulus‐induced γ‐oscillations in rat hippocampus in vitro

Monoamines are implicated in a cognitive processes in a variety of brain regions, including the hippocampal formation, where storage and retrieval of information are facilitated by synchronous network activities. We have investigated the effects of norepinephrine, serotonin, and dopamine on carbachol‐, kainate‐, and stimulus‐induced hippocampal γ‐oscillations employing combined extra‐ and intracellular recordings. Monoamines dose‐dependently and reversibly suppressed kainate‐ and carbachol‐induced γ‐oscillations while increasing the frequency. The effect of serotonin was mimicked by fenfluramine, which releases serotonin from presynaptic terminals. Forskolin also suppressed kainate‐ and carbachol‐induced γ‐oscillations. This effect was mimicked by 8‐Br‐cAMP and isoproterenol, an agonist of noradrenergic β‐receptor suggesting that the monoamines‐mediated suppression of these oscillations could involve intracellular cyclic adenosine 3′,5′‐cyclic monophosphate (AMP). By contrast, stimulus‐induced γ‐oscillations were dose‐dependently augmented in power and duration after monoamines application. Intracellular recordings from pyramidal cells revealed that monoamines prolonged the stimulus‐induced depolarization and membrane potential oscillations. Stimulus‐induced γ‐oscillations were also suppressed by isoproterenol, the D1 agonist SKF‐38393 forskolin, and 8‐Br‐cAMP. This suggests that the augmentation of stimulus‐induced γ‐oscillations by monoamines involves—at least in part—different classes of cells than in case of carbachol‐ and kainate‐induced γ‐oscillations. © 2009 Wiley‐Liss, Inc.     

TGF‐β2 and TGF‐β3 from cultured β‐amyloid‐treated or 3xTg‐AD‐derived astrocytes may mediate astrocyte–neuron communication

Astrocytes participate in the development and resolution of neuroinflammation in numerous ways, including the release of cytokines and growth factors. Among many, astrocytes release transforming growth factors beta (TGF‐β) TGF‐β1, TGF‐β2 and TGF‐β3. TGF‐β1 is the most studied isoform, while production and release of TGF‐β2 and TGF‐β3 by astrocytes have been poorly characterized. Here, we report that purified cultures of hippocampal astrocytes produce mainly TGF‐β3 followed by TGF‐β2 and TGF‐β1. Furthermore, astrocytes release principally the active form of TGF‐β3 over the other two. Changes in release of TGF‐β were sensitive to the calcineurin (CaN) inhibitor FK506. Starvation had no effect on TGF‐β1 and TGF‐β3 while TGF‐β2 mRNA was significantly up‐regulated in a CaN‐dependent manner. We further investigated production and release of astroglial TGF‐β in Alzheimer's disease‐related conditions. Oligomeric β‐amyloid (Aβ) down‐regulated TGF‐β1, while up‐regulating TGF‐β2 and TGF‐β3, in a CaN‐dependent manner. In cultured hippocampal astrocytes from 3xTg‐AD mice, TGF‐β2 and TGF‐β3, but not TGF‐β1, were up‐regulated, and this was CaN‐independent. In hippocampal tissues from symptomatic 3xTg‐AD mice, TGF‐β2 was up‐regulated with respect to control mice. Finally, treatment with recombinant TGF‐βs showed that TGF‐β2 and TGF‐β3 significantly reduced PSD95 protein in cultured hippocampal neurons, and this effect was paralleled by conditioned media from Aβ‐treated astrocytes or from astrocytes from 3xTg‐AD mice. Taken together, our data suggest that TGF‐β2 and TGF‐β3 are produced by astrocytes in a CaN‐dependent manner and should be investigated further in the context of astrocyte‐mediated neurodegeneration.     

α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionic acid receptor activation protects against phencyclidine‐induced caspase‐3 activity by activating voltage‐gated calcium channels

Phencyclidine (PCP) is a noncompetitive, open channel blocker of the N‐methyl‐D‐aspartate (NMDA) receptor–ion channel complex. When administered to immature animals, it is known to cause apoptotic neurodegeneration in several regions, and this is followed by olanzapine‐sensitive, schizophrenia‐like behaviors in late adolescence and adulthood. Clarification of its mechanism of action could yield data that would help to inform the treatment of schizophrenia. In our initial experiments, we found that α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionic acid (AMPA) inhibited PCP‐induced apoptosis in organotypic neonatal rat brain slices in a concentration‐dependent and 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione‐sensitive manner. Calcium signaling pathways are widely implicated in apoptosis, and PCP prevents calcium influx through NMDA receptor channels. We therefore hypothesized that AMPA could protect against this effect by activation of voltage‐dependent calcium channels (VDCCs). In support of this hypothesis, pretreatment with the calcium channel blocker cadmium chloride eliminated AMPA‐mediated protection against PCP. Furthermore, the L‐type VDCC inhibitor nifedipine (10 µM) fully abrogated the effects of AMPA, suggesting that L‐type VDCCs are required for AMPA‐mediated protection against PCP‐induced neurotoxicity. Whereas the P/Q‐type inhibitor ω‐agatoxin TK (200 nM) reduced AMPA protection by 51.7%, the N‐type VDCC inhibitor ω‐conotoxin (2 µM) had no effect. Decreased AMPA‐mediated protection following cotreatment with K252a, a TrkB inhibitor, suggests that brain‐derived neurotrophic factor signaling plays an important role. By analogy, these results suggest that activation of L‐type, and to a lesser extent P/Q‐type, VDCCs might be advantageous in treating conditions associated with diminished NMDAergic activity during early development. © 2014 Wiley Periodicals, Inc.     

Early continuous white noise exposure alters l‐α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid receptor subunit glutamate receptor 2 and γ‐aminobutyric acid type a receptor subunit β3 protein expression in rat auditory cortex

Auditory experience during the postnatal critical period is essential for the normal maturation of auditory function. Previous studies have shown that rearing infant rat pups under conditions of continuous moderate‐level noise delayed the emergence of adult‐like topographic representational order and the refinement of response selectivity in the primary auditory cortex (A1) beyond normal developmental benchmarks and indefinitely blocked the closure of a brief, critical‐period window. To gain insight into the molecular mechanisms of these physiological changes after noise rearing, we studied expression of the AMPA receptor subunit GluR2 and GABA_A receptor subunit β3 in the auditory cortex after noise rearing. Our results show that continuous moderate‐level noise rearing during the early stages of development decreases the expression levels of GluR2 and GABA_Aβ3. Furthermore, noise rearing also induced a significant decrease in the level of GABA_A receptors relative to AMPA receptors. However, in adult rats, noise rearing did not have significant effects on GluR2 and GABA_Aβ3 expression or the ratio between the two units. These changes could have a role in the cellular mechanisms involved in the delayed maturation of auditory receptive field structure and topographic organization of A1 after noise rearing. © 2009 Wiley‐Liss, Inc.     

Protein kinase Cγ is a signaling molecule required for the developmental speeding of α‐amino‐3‐hydroxyl‐5‐methyl‐4‐isoxazole‐propionate receptor kinetics

A key step in the maturation of glutamate synapses is the developmental speeding of α‐amino‐3‐hydroxyl‐5‐methyl‐4‐isoxazole‐propionate receptor (AMPA‐R) kinetics, which occurs via a switch in receptor subtypes. However, the molecular components required for the switch in receptors are unknown. Here, we used the zebrafish preparation to show that activation of protein kinase C (PKC)γ is necessary for the developmental speeding of AMPA‐R kinetics. Targeted knockdown of PKCγ with an antisense morpholino oligonucleotide [PKCγ‐morpholino (PKCγ‐MO)], prevents the normal speeding up of AMPA‐R kinetics in Mauthner cells. PKCγ‐MO‐injected embryos are incapable of trafficking AMPA‐Rs following application of phorbol 12‐myristate 13‐acetate or PKCγ. PKCγ‐MO‐injected embryos do not hatch or exhibit the C‐start escape response. Increasing synaptic activity (33 h post‐fertilization embryos) by application of an elevated K⁺ medium or by application of N‐methyl‐d ‐aspartate induces rapid PKCγ‐dependent trafficking of fast AMPA‐Rs to synapses. Our findings reveal that PKCγ is a molecular link underlying the developmental speeding of AMPA‐Rs in zebrafish Mauthner cells.     

Clinical and genetic associations of autoantibodies to 3‐hydroxy‐3‐methyl‐glutaryl‐coenzyme a reductase in patients with immune‐mediated myositis and necrotizing myopathy

Introduction: Inhibition of 3‐hydroxy‐3‐methyl‐glutaryl‐coenzyme A reductase (HMGCR) with statins may trigger idiopathic inflammatory myositis (IIM) or immune‐mediated necrotizing myopathy (IMNM). Anti‐HMGCR antibodies have been detected in patients with IIM/IMNM. We aimed to determine the associations of anti‐HMGCR in IIM/IMNM. Methods: Anti‐HMGCR antibodies were detected by ELISA in sera from patients with IIM/IMNM. Results: Anti‐HMGCR antibodies were detected in 19 of 207 patients with IIM/IMNM, and there was a trend toward an association with male gender (P = 0.079). Anti‐HMGCR antibodies were associated strongly with statin exposure (OR = 39, P = 0.0001) and HLA‐DRB1*11 (OR = 50, P < 0.0001). The highest risk for development of anti‐HMGCR antibodies was among HLA‐DR11 carriers exposed to statins. Univariate analysis showed a strong association of anti‐HMGCR antibodies with diabetes mellitus (P = 0.008), which was not confirmed by multiple regression. Among anti‐HMGCR⁺ patients there was a trend toward increased malignancy (P = 0.15). Conclusions: Anti‐HMGCR antibodies are seen in all subtypes of IIM and IMNM and are associated strongly with statin use and HLA‐DR11. Muscle Nerve 52 : 196–203, 2015     

Mechanisms of status epilepticus: α‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor hypothesis

Prolonged seizures of status epilepticus (SE) result from failure of mechanisms of seizure termination or activation of mechanisms that sustain seizures. Reduced γ‐aminobutyric acid type A receptor–mediated synaptic transmission contributes to impairment of seizure termination. However, mechanisms that sustain prolonged seizures are not known. We propose that insertion of GluA1 subunits at the glutamatergic synapses causes potentiation of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic receptor (AMPAR)‐mediated neurotransmission, which helps to spread and sustain seizures. The AMPAR‐mediated neurotransmission of CA1 pyramidal neurons was increased in animals in SE induced by pilocarpine. The surface membrane expression of GluA1 subunit–containing AMPARs on CA1 pyramidal neurons was also increased. Blockade of N‐methyl‐d ‐aspartate receptors 10 minutes after the onset of continuous electrographic seizure activity prevented the increase in the surface expression of GluA1 subunits. N‐methyl‐d ‐aspartate receptor antagonist MK‐801 in conjunction with diazepam also terminated seizures that were refractory to MK‐801 or diazepam alone. Future studies using mice lacking the GluA1 subunit expression will provide further insights into the role of GluA1 subunit–containing AMPAR plasticity in sustaining seizures of SE.     

Non‐classical mechanism of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor channel block by fluoxetine

Antidepressants have many targets in the central nervous system. A growing body of data demonstrates the influence of antidepressants on glutamatergic neurotransmission. In the present work, we studied the inhibition of native Ca²⁺‐permeable and Ca²⁺‐impermeable α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) receptors in rat brain neurons by fluoxetine. The Ca²⁺‐impermeable AMPA receptors in CA1 hippocampal pyramidal neurons were weakly affected. The IC₅₀ value for the inhibition of Ca²⁺‐permeable AMPA receptors in giant striatal interneurons was 43 ± 7 μm . The inhibition of Ca²⁺‐permeable AMPA receptors was voltage dependent, suggesting deep binding in the pore. However, the use dependence of fluoxetine action differed markedly from that of classical AMPA receptor open‐channel blockers. Moreover, fluoxetine did not compete with other channel blockers. In contrast to fluoxetine, its membrane‐impermeant quaternary analog demonstrated all of the features of channel inhibition typical for open‐channel blockers. It is suggested that fluoxetine reaches the binding site through a hydrophobic access pathway. Such a mechanism of block is described for ligands of sodium and calcium channels, but was never found in AMPA receptors. Molecular modeling suggests binding of fluoxetine in the subunit interface; analogous binding was proposed for local anesthetics in closed sodium channels and for benzothiazepines in calcium channels.     

Ischemia preconditioning protects astrocytes from ischemic injury through 14‐3‐3γ

Stroke is a leading cause of death and disability, and new strategies are required to reduce neuronal injury and improve prognosis. Ischemia preconditioning (IPC) is an intrinsic phenomenon that protects cells from subsequent ischemic injury and might provide promising mechanisms for clinical treatment. In this study, primary astrocytes exhibited significantly less cell death than control when exposed to different durations of IPC (15, 30, 60, or 120 min). A 15‐min duration was the most effective IPC to protect astrocytes from 8‐hr‐ischemia injury. The protective mechanisms of IPC involve the upregulation of protective proteins, including 14‐3‐3γ, and attenuation of malondialdehyde (MDA) content and ATP depletion. 14‐3‐3γ is an antiapoptotic intracellular protein that was significantly upregulated for up to 84 hr after IPC. In addition, IPC promoted activation of the c‐Jun N‐terminal kinase (JNK), extracellular signal‐related kinase (ERK)?1/2, p38, and protein kinase B (Akt) signaling pathways. When JNK was specifically inhibited with SP600125, the upregulation of 14‐3‐3γ induced by IPC was almost completely abolished; however, there was no effect on ATP or MDA levels. This suggests that, even though both energy preservation and 14‐3‐3γ up‐regulation were turned on by IPC, they were controlled by different pathways. The ERK1/2, p38, and Akt signaling pathways were not involved in the 14‐3‐3γ upregulation and energy preservation. These results indicate that IPC could protect astrocytes from ischemia injury by inducing 14‐3‐3γ and by alleviating energy depletion through different pathways, suggesting multiple protection of IPC and providing new insights into potential stroke therapies. © 2015 Wiley Periodicals, Inc.     

Isolated gluteal and paravertebral muscle weakness due to anti‐3‐hydroxy‐3‐methylglutaryl‐coenzyme a reductase antibody–associated necrotizing autoimmune myopathy

Introduction: A 56‐year‐old man with a distant history of statin use presented with progressive isolated very proximal lower limb and truncal weakness. Electromyogram (EMG) showed isolated gluteal and lumbar paraspinal muscle involvement. Methods: Gluteus medius muscle biopsy was performed under general anesthesia. Results: The biopsy showed a pauci‐inflammatory necrotizing myopathy. Serum antibodies to 3‐hydroxy‐3‐methylglutaryl‐coenzyme A reductase (HMGCR) were positive. He has since partially responded to corticosteroids and methotrexate. Conclusions: Anti‐HMGCR–associated necrotizing autoimmune myopathy (NAM) can present in a restricted form after cessation of a statin. Biopsy of a symptomatic but uncommonly studied muscle is worthwhile. Muscle Nerve 54 : 150–152, 2016     

Exercise modifies α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor expression in striatopallidal neurons in the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine‐lesioned mouse

The α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic‐acid‐type glutamate receptor (AMPAR) plays a critical role in modulating experience‐dependent neuroplasticity, and alterations in AMPAR expression may underlie synaptic dysfunction and disease pathophysiology. Using the 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) mouse model of dopamine (DA) depletion, our previous work showed exercise increases total GluA2 subunit expression and the contribution of GluA2‐containing channels in MPTP mice. The purpose of this study was to determine whether exercise‐dependent changes in AMPAR expression after MPTP are specific to the striatopallidal (D₂R) or striatonigral (D₁R) medium spiny neuron (MSN) striatal projection pathways. Drd₂‐eGFP‐BAC transgenic mice were used to delineate differences in AMPAR expression between striatal D₂R‐MSNs and D₁R‐MSNs. Striatal AMPAR expression was assessed by immunohistochemical (IHC) staining, Western immunoblotting (WB) of preparations enriched for postsynaptic density (PSD), and alterations in the current–voltage relationship of MSNs. We found DA depletion results in the emergence of GluA2‐lacking AMPARs selectively in striatopallidal D₂R‐MSNs and that exercise reverses this effect in MPTP mice. Exercise‐induced changes in AMPAR channels observed after DA depletion were associated with alterations in GluA1 and GluA2 subunit expression in postsynaptic protein, D₂R‐MSN cell surface expression, and restoration of corticostriatal plasticity. Mechanisms regulating experience‐dependent changes in AMPAR expression may provide innovative therapeutic targets to increase the efficacy of treatments for basal ganglia disorders, including Parkinson's disease. © 2013 Wiley Periodicals, Inc.     

MLK3‐MKK3/6‐P38MAPK cascades following N‐methyl‐D‐aspartate receptor activation contributes to amyloid‐β peptide‐induced apoptosis in SH‐SY5Y cells

Amyloid‐β peptide (Aβ) has been implicated in the development of Alzheimer's disease (AD), but the underlying molecular mechanisms remain unclear. The present study explores the proapoptosis signaling evoked by N‐methyl‐D‐aspartate (NMDA) receptors in Aβ neurotoxicity. Oligomeric Aβ25–35 incubation resulted in significant apoptosis of neuronal SH‐SY5Y cells. Preadministration of the potent NMDA receptor antagonist MK801 promoted neuronal survival. Both NVP‐AAM077 and Ro25–6981, GluN2A‐ and GluN2B‐subunit‐selective NMDA receptor antagonists, respectively, showed effects similar to those of MK801, supporting a critical role of GluN2A‐ or GluN2B‐containing NMDA receptors in Aβ neurotoxicity. Exposure to oligomeric Aβ25–35 increased the phosphorylation (activation) of mixed‐lineage kinase 3 (MLK3), dual‐specific mitogen‐activated protein kinase kinase 3/6 (MKK3/6), and P38 mitogen‐activated protein kinase (P38MAPK) in SH‐SY5Y cells. Inhibition of P38MAPK activation by SB239063 had a neuroprotective effect. K252a attenuated the phosphorylation of MLK3, MKK3/6, and P38MAPK but also partially prevented SH‐SY5Y cells apoptosis. MK801, NVP‐AAM077, and Ro25–6981, abrogated the MLK3‐MKK3/6‐P38MAPK activation induced by oligomeric Aβ25–35. These results suggest that the activation of GluN2A‐ or GluN2B‐containing NMDA receptors is responsible for the activation of MLK3‐MKK3/6‐P38MAPK cascades, which contributes to Aβ‐mediated cell apoptosis. © 2014 Wiley Periodicals, Inc.