Prenatal ethanol exposure persistently impairs NMDA receptor-dependent activation of extracellular signal-regulated kinase in the mouse dentate gyrus

The dentate gyrus (DG) is the central input region to the hippocampus and is known to play an important role in learning and memory. Previous studies have shown that prenatal alcohol is associated with hippocampal-dependent learning deficits and a decreased ability to elicit long-term potentiation (LTP) in the DG in adult animals. Given that activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling cascade by NMDA receptors is required for various forms of learning and memory, as well as LTP, in hippocampal regions, including the DG, we hypothesized that fetal alcohol-exposed adult animals would have deficits in hippocampal NMDA receptor-dependent ERK1/2 activation. We used immunoblotting and immunohistochemistry techniques to detect NMDA-stimulated ERK1/2 activation in acute hippocampal slices prepared from adult fetal alcohol-exposed mice. We present the first evidence linking prenatal alcohol exposure to deficits in NMDA receptor-dependent ERK1/2 activation specifically in the DG of adult offspring. This deficit may account for the LTP deficits previously observed in the DG, as well as the life-long cognitive deficits, associated with prenatal alcohol exposure.     

A pharmacogenetic inducible approach to the study of NMDA/alphaCaMKII signaling in synaptic plasticity

We recently introduced an inducible pharmacogenetic approach where pharmacological manipulations can be used to reveal recessive mutant phenotypes in a temporally controlled manner. This approach takes advantage of synergisms between pharmacological and genetic manipulations to alter the function of specific signaling pathways. For example, mice heterozygous for a point mutation (T286A) in the alpha-calcium/calmodulin-dependent kinase II (alphaCaMKII) gene show normal learning and memory. However, a concentration of an NMDA receptor antagonist (CPP) that does not affect learning in wild-type (WT) littermates, reveals learning deficits in this heterozygote (alphaCaMKII(T286A+/-)). Here, we show that pretetanic application of a concentration of CPP (0.1 microM) ineffective in WT hippocampal slices induced deficits in alphaCaMKII(T286A+/-) slices in hippocampal long-term potentiation (LTP), a mechanism thought to be involved in learning and memory. Importantly, posttetanic application of CPP (0.1 microM) had no effect on the expression or maintenance of LTP in hippocampal slices from alphaCaMKII(T286A+/-) mice. Thus, this pharmacogenetic approach allowed us to demonstrate that NMDA receptor-dependent autophosphorylation of alphaCaMKII is required during the induction but not maintenance of LTP. This ability to temporally induce recessive mutant phenotypes could be applicable to a broad range of problems and genetic systems.     

Reduction of Phosphorylated Synapsin I (Ser-553) Leads to Spatial Memory Impairment by Attenuating GABA Release after Microwave Exposure in Wistar Rats

Background

Abnormal release of neurotransmitters after microwave exposure can cause learning and memory deficits. This study investigated the mechanism of this effect by exploring the potential role of phosphorylated synapsin I (p-Syn I).

Methods

Wistar rats, rat hippocampal synaptosomes, and differentiated (neuronal) PC12 cells were exposed to microwave radiation for 5 min at a mean power density of 30 mW/cm². Sham group rats, synaptosomes, and cells were otherwise identically treated and acted as controls for all of the following post-exposure analyses. Spatial learning and memory in rats was assessed using the Morris Water Maze (MWM) navigation task. The protein expression and presynaptic distribution of p-Syn I and neurotransmitter transporters were examined via western blotting and immunoelectron microscopy, respectively. Levels amino acid neurotransmitter release from rat hippocampal synaptosomes and PC12 cells were measured using high performance liquid chromatograph (HPLC) at 6 hours after exposure, with or without synapsin I silencing via shRNA transfection.

Results

In the rat experiments, there was a decrease in spatial memory performance after microwave exposure. The expression of p-Syn I (ser-553) was decreased at 3 days post-exposure and elevated at later time points. Vesicular GABA transporter (VGAT) was significantly elevated after exposure. The GABA release from synaptosomes was attenuated and p-Syn I (ser-553) and VGAT were both enriched in small clear synaptic vesicles, which abnormally assembled in the presynaptic terminal after exposure. In the PC12 cell experiments, the expression of p-Syn I (ser-553) and GABA release were both attenuated at 6 hours after exposure. Both microwave exposure and p-Syn I silencing reduced GABA release and maximal reduction was found for the combination of the two, indicating a synergetic effect.

Conclusion

p-Syn I (ser-553) was found to play a key role in the impaired GABA release and cognitive dysfunction that was induced by microwave exposure.     

Fragile X mental retardation protein is required for chemically-induced long-term potentiation of the hippocampus in adult mice

Fragile X syndrome (FXS), a common form of inherited mental retardation, is caused by the lack of fragile X mental retardation protein (FMRP). The animal model of FXS, Fmr1 knockout mice, have deficits in the Morris water maze and trace fear memory tests, showing impairment in hippocampus-dependent learning and memory. However, results for synaptic long-term potentiation (LTP), a key cellular model for learning and memory, remain inconclusive in the hippocampus of Fmr1 knockout mice. Here, we demonstrate that FMRP is required for glycine induced LTP (Gly-LTP) in the CA1 of hippocampus. This form of LTP requires activation of post-synaptic NMDA receptors and metabotropic glutamateric receptors, as well as the subsequent activation of extracellular signal-regulated kinase (ERK) 1/2. However, paired-pulse facilitation was not affected by glycine treatment. Genetic deletion of FMRP interrupted the phosphorylation of ERK1/2, suggesting the possible role of FMRP in the regulation of the activity of ERK1/2. Our study provide strong evidences that FMRP participates in Gly-LTP in the hippocampus by regulating the phosphorylation of ERK1/2, and that improper regulation of these signaling pathways may contribute to the learning and memory deficits observed in FXS.     

Iron mediates N-methyl-D-aspartate receptor-dependent stimulation of calcium-induced pathways and hippocampal synaptic plasticity

Iron deficiency hinders hippocampus-dependent learning processes and impairs cognitive performance, but current knowledge on the molecular mechanisms underlying the unique role of iron in neuronal function is sparse. Here, we investigated the participation of iron on calcium signal generation and ERK1/2 stimulation induced by the glutamate agonist N-methyl-D-aspartate (NMDA), and the effects of iron addition/chelation on hippocampal basal synaptic transmission and long-term potentiation (LTP). Addition of NMDA to primary hippocampal cultures elicited persistent calcium signals that required functional NMDA receptors and were independent of calcium influx through L-type calcium channels or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors; NMDA also promoted ERK1/2 phosphorylation and nuclear translocation. Iron chelation with desferrioxamine or inhibition of ryanodine receptor (RyR)-mediated calcium release with ryanodine-reduced calcium signal duration and prevented NMDA-induced ERK1/2 activation. Iron addition to hippocampal neurons readily increased the intracellular labile iron pool and stimulated reactive oxygen species production; the antioxidant N-acetylcysteine or the hydroxyl radical trapper MCI-186 prevented these responses. Iron addition to primary hippocampal cultures kept in calcium-free medium elicited calcium signals and stimulated ERK1/2 phosphorylation; RyR inhibition abolished these effects. Iron chelation decreased basal synaptic transmission in hippocampal slices, inhibited iron-induced synaptic stimulation, and impaired sustained LTP in hippocampal CA1 neurons induced by strong stimulation. In contrast, iron addition facilitated sustained LTP induction after suboptimal tetanic stimulation. Together, these results suggest that hippocampal neurons require iron to generate RyR-mediated calcium signals after NMDA receptor stimulation, which in turn promotes ERK1/2 activation, an essential step of sustained LTP.     

Decreased calcium/calmodulin-dependent protein kinase II and protein kinase C activities mediate impairment of hippocampal long-term potentiation in the olfactory bulbectomized mice

Olfactory bulbectomized (OBX) mice showed significant impairment of learning and memory-related behaviors 14 days after olfactory bulbectomy, as measured by passive avoidance and Y-maze tasks. We here observed a large impairment of hippocampal long-term potentiation (LTP) in the OBX mice. Concomitant with decreased acetylcholinesterase expression, protein kinase C (PKC)alpha autophosphorylation and NR1(Ser-896) phosphorylation significantly decreased in the hippocampal CA1 region of OBX mice. Both PKCalpha and NR1(Ser-896) phosphorylation significantly increased following LTP in the control mice, whereas increases were not observed in OBX mice. Like PKC activities, calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation significantly decreased in the hippocampal CA1 region of OBX mice as compared with that of control mice. In addition, increased CaMKII autophosphorylation following LTP was not observed in OBX mice. Finally, the impairment of CaMKII autophosphorylation was closely associated with reduced pGluR1(Ser-831) phosphorylation, without change in synapsin I (site 3) phosphorylation in the hippocampal CA1 region of OBX mice. Taken together, in OBX mice NMDA receptor hypofunction, possibly through decreased PKCalpha activity, underlies decreased CaMKII activity in the post-synaptic regions, thereby impairing LTP induction in the hippocampal CA1 region. Both decreased PKC and CaMKII activities with concomitant LTP impairment account for the learning disability observed in OBX mice.     

Involvement of microglia activation in the lead induced long-term potentiation impairment

Exposure of Lead (Pb), a known neurotoxicant, can impair spatial learning and memory probably via impairing the hippocampal long-term potentiation (LTP) as well as hippocampal neuronal injury. Activation of hippocampal microglia also impairs spatial learning and memory. Thus, we raised the hypothesis that activation of microglia is involved in the Pb exposure induced hippocampal LTP impairment and neuronal injury. To test this hypothesis and clarify its underlying mechanisms, we investigated the Pb-exposure on the microglia activation, cytokine release, hippocampal LTP level as well as neuronal injury in in vivo or in vitro model. The changes of these parameters were also observed after pretreatment with minocycline, a microglia activation inhibitor. Long-term low dose Pb exposure (100 ppm for 8 weeks) caused significant reduction of LTP in acute slice preparations, meanwhile, such treatment also significantly increased hippocampal microglia activation as well as neuronal injury. In vitro Pb-exposure also induced significantly increase of microglia activation, up-regulate the release of cytokines including tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS) in microglia culture alone as well as neuronal injury in the co-culture with hippocampal neurons. Inhibiting the microglia activation with minocycline significantly reversed the above-mentioned Pb-exposure induced changes. Our results showed that Pb can cause microglia activation, which can up-regulate the level of IL-1β, TNF-α and iNOS, these proinflammatory factors may cause hippocampal neuronal injury as well as LTP deficits.     

Wip1 phosphatase modulates both long-term potentiation and long-term depression through the dephosphorylation of CaMKII

Synaptic plasticity is an important mechanism that underlies learning and cognition. Protein phosphorylation by kinases and dephosphorylation by phosphatases play critical roles in the activity-dependent alteration of synaptic plasticity. In this study, we report that Wip1, a protein phosphatase, is essential for long-term potentiation (LTP) and long-term depression (LTD) processes. Wip1-deletion suppresses LTP and enhances LTD in the hippocampus CA1 area. Wip1 deficiency-induced aberrant elevation of CaMKII T286/287 and T305 phosphorylation underlies these dysfunctions. Moreover, we showed that Wip1 modulates CaMKII dephosphorylation. Wip1^?/? mice exhibit abnormal GluR1 membrane expression, which could be reversed by the application of a CaMKII inhibitor, indicating that Wip1/CaMKII signaling is crucial for synaptic plasticity. Together, our results demonstrate that Wip1 phosphatase plays a vital role in regulating hippocampal synaptic plasticity by modulating the phosphorylation of CaMKII.     

ERK Inhibition Rescues Defects in Fate Specification of Nf1-Deficient Neural Progenitors and Brain Abnormalities

Germline mutations in the RAS/ERK signaling pathway underlie several related developmental disorders collectively termed neuro-cardio-facial-cutaneous (NCFC) syndromes. NCFC patients manifest varying degrees of cognitive impairment, but the developmental basis of their brain abnormalities remains largely unknown. Neurofibromatosis type 1 (NF1), an NCFC syndrome, is caused by loss-of-function heterozygous mutations in the NF1 gene, which encodes neurofibromin, a RAS GTPase-activating protein. Here, we show that biallelic Nf1 inactivation promotes Erk-dependent, ectopic Olig2 expression specifically in transit-amplifying progenitors, leading to increased gliogenesis at the expense of neurogenesis in neonatal and adult subventricular zone (SVZ). Nf1-deficient brains exhibit enlarged corpus callosum, a structural defect linked to severe learning deficits in NF1 patients. Strikingly, these NF1-associated developmental defects are rescued by transient treatment with an MEK/ERK inhibitor during neonatal stages. This study reveals a critical role for Nf1 in maintaining postnatal SVZ-derived neurogenesis and identifies a potential therapeutic window for treating NF1-associated brain abnormalities.     

O-Linked β-N-Acetylglucosamine (O-GlcNAc) Site Thr-87 Regulates Synapsin I Localization to Synapses and Size of the Reserve Pool of Synaptic Vesicles

O-GlcNAc is a carbohydrate modification found on cytosolic and nuclear proteins. Our previous findings implicated O-GlcNAc in hippocampal presynaptic plasticity. An important mechanism in presynaptic plasticity is the establishment of the reserve pool of synaptic vesicles (RPSV). Dynamic association of synapsin I with synaptic vesicles (SVs) regulates the size and release of RPSV. Disruption of synapsin I function results in reduced size of the RPSV, increased synaptic depression, memory deficits, and epilepsy. Here, we investigate whether O-GlcNAc directly regulates synapsin I function in presynaptic plasticity. We found that synapsin I is modified by O-GlcNAc during hippocampal synaptogenesis in the rat. We identified three novel O-GlcNAc sites on synapsin I, two of which are known Ca²⁺/calmodulin-dependent protein kinase II phosphorylation sites. All O-GlcNAc sites mapped within the regulatory regions on synapsin I. Expression of synapsin I where a single O-GlcNAc site Thr-87 was mutated to alanine in primary hippocampal neurons dramatically increased localization of synapsin I to synapses, increased density of SV clusters along axons, and the size of the RPSV, suggesting that O-GlcNAcylation of synapsin I at Thr-87 may be a mechanism to modulate presynaptic plasticity. Thr-87 is located within an amphipathic lipid-packing sensor (ALPS) motif, which participates in targeting of synapsin I to synapses by contributing to the binding of synapsin I to SVs. We discuss the possibility that O-GlcNAcylation of Thr-87 interferes with folding of the ALPS motif, providing a means for regulating the association of synapsin I with SVs as a mechanism contributing to synapsin I localization and RPSV generation.     

Motivational Disturbances and Effects of L-dopa Administration in Neurofibromatosis-1 Model Mice

Children with neurofibromatosis type 1 (NF1) frequently have cognitive and behavioral deficits. Some of these deficits have been successfully modeled in Nf1 genetically-engineered mice that develop optic gliomas (Nf1 OPG mice). In the current study, we show that abnormal motivational influences affect the behavior of Nf1 OPG mice, particularly with regard to their response to novel environmental stimuli. For example, Nf1 OPG mice made fewer spontaneous alternations in a Y-maze and fewer arm entries relative to WT controls. However, analysis of normalized alternation data demonstrated that these differences were not due to a spatial working memory deficit. Other reported behavioral results (e.g., open-field test, below) suggest that differential responses to novelty and/or other motivational influences may be more important determinants of these kinds of behavior than simple differences in locomotor activity/spontaneous movements. Importantly, normal long-term depression was observed in hippocampal slices from Nf1 OPG mice. Results from elevated plus maze testing showed that differences in exploratory activity between Nf1 OPG and WT control mice may be dependent on the environmental context (e.g., threatening or non-threatening) under which exploration is being measured. Nf1 OPG mice also exhibited decreased exploratory hole poking in a novel holeboard and showed abnormal olfactory preferences, although L-dopa (50 mg/kg) administration resolved the abnormal olfactory preference behaviors. Nf1 OPG mice displayed an attenuated response to a novel open field in terms of decreased ambulatory activity and rearing but only during the first 10 min of the session. Importantly, Nf1 OPG mice demonstrated investigative rearing deficits with regard to a novel hanging object suspended on one side of the field which were not rescued by L-dopa administration. Collectively, our results provide new data important for evaluating therapeutic treatments aimed at ameliorating NF1-associated cognitive/behavioral deficits.     

Kinase suppressor of Ras1 compartmentalizes hippocampal signal transduction and subserves synaptic plasticity and memory formation

The ERK/MAP kinase cascade is important for long-term memory formation and synaptic plasticity, with a myriad of upstream signals converging upon ERK activation. Despite this convergence of signaling, neurons routinely activate appropriate biological responses to different stimuli. Scaffolding proteins represent a mechanism to achieve compartmentalization of signaling and the appropriate targeting of ERK-dependent processes. We report that kinase suppressor of Ras (KSR1) functions biochemically in the hippocampus to scaffold the components of the ERK cascade, specifically regulating the cascade when a membrane fraction of ERK is activated via a PKC-dependent pathway but not via a cAMP/PKA-dependent pathway. Specificity of KSR1-dependent signaling also extends to specific downstream targets of ERK. Behaviorally and physiologically, we found that the absence of KSR1 leads to deficits in associative learning and theta burst stimulation-induced LTP. Our report provides novel insight into the endogenous scaffolding role of KSR1 in controlling kinase activation within the nervous system.     

Permissive role of insulin in the expression of long-term potentiation in the hippocampus of immature rats

Many studies indicate that impairment in insulin signaling leads to learning and memory deficits. However, previous studies failed to establish a clear role of insulin in long-term potentiation (LTP), the best cellular model of memory formation. Here we show that while insulin pretreatment did not affect LTP magnitude in the adult rat hippocampus, it facilitated LTP expression in the immature hippocampus. The tyrosine kinase inhibitor AG-1024 abolished the effect of insulin in young rats, suggesting the involvement of the insulin receptor. On the other hand, increasing extracellular glucose concentration failed to facilitate LTP and application of an insulin-responsive glucose transporter-4 inhibitor did not impair the effect of insulin. These results suggest that the facilitatory action of insulin on LTP is not an indirect effect on glucose homeostasis/utilization. Involvement of the MAPK/ERK pathway, a known downstream pathway of insulin signaling, was revealed by pretreatment with PD98059, which blocked the insulin-mediated LTP facilitation. Consistent with this, high-frequency stimulation induced a significant increase in the level of phosphorylated Erk-2 in insulin-treated hippocampus. Taken together, these results suggest that insulin may be an essential factor in the immature brain, allowing the expression of LTP to facilitate learning and memory.     

Neurofibromin binds to caveolin-1 and regulates ras, FAK, and Akt

Neurofibromin (Nf1) is an approximately 280 kDa protein having tumor suppressor function, presumably by virtue of its GTPase activating domain, but little is known regarding molecular aspects of its effector pathways. Caveolin-1 (Cav-1) regulates diverse signaling molecules and has itself been implicated as a tumor suppressor. Here we demonstrate that Nf1 binds to Cav-1's scaffolding domain and co-immunoprecipitates with Cav-1. Analysis of Nf1's primary structure reveals four potential caveolin binding domains, and interestingly, in individuals with neurofibromatosis I, missense mutations occur with high frequency in 3 of the 4 putative domains. We show that Nf1 modulates ras, Akt, and focal adhesion kinase pathways, thereby affecting cytoskeletal organization; moreover, Nf1's effects on signaling are altered when lipid rafts and caveolae are disrupted by cholesterol depletion. These novel findings provide insight into possible signaling mechanisms of Nf1 and suggest that together Nf1 and Cav-1 may coordinately regulate cell growth and differentiation.     

Deletion of the ryanodine receptor type 3 (RyR3) impairs forms of synaptic plasticity and spatial learning.

Deletion of the ryanodine receptor type 3 (RyR3) results in specific changes in hippocampal synaptic plasticity, without affecting hippocampal morphology, basal synaptic transmission or presynaptic function. Robust long-term potentiation (LTP) induced by repeated, strong tetanization in the CA1 region and in the dentate gyrus was unaltered in hippocampal slices in vitro, whereas weak forms of plasticity generated by either a single weak tetanization or depotentiation of a robust LTP were impaired. These distinct physiological deficits were paralleled by a reduced flexibility in re-learning a new target in the water-maze. In contrast, learning performance in the acquisition phase and during probe trial did not differ between the mutants and their wild-type littermates. In the open-field, RyR3(-/-) mice displayed a normal exploration and habituation, but had an increased speed of locomotion and a mild tendency to circular running. The observed physiological and behavioral effects implicate RyR3-mediated Ca(2+) release in the intracellular processes underlying spatial learning and hippocampal synaptic plasticity.     

Motor deficits in neurofibromatosis type 1 mice: the role of the cerebellum

Neurofibromatosis type 1 (NF1) is an autosomal dominantly inherited disease, characterized by various neurocutaneous symptoms, cognitive impairments and problems in fine and gross motor performance. Although cognitive deficits in NF1 have been attributed to increased release of the inhibitory neurotransmitter γ-amino butyric acid (GABA) in the hippocampus, the origin of the motor deficits is unknown. Cerebellar Purkinje cells, the sole output neurons of the cerebellar cortex, are GABAergic neurons and express neurofibromin at high levels, suggesting an important role for the cerebellum in the observed motor deficits in NF1. To test this, we determined the cerebellar contribution to motor problems in Nf1(+/-) mice, a validated mouse model for NF1. Using the Rotarod, a non-specific motor performance test, we confirmed that, like NF1 patients, Nf1(+/-) mice have motor deficits. Next, to evaluate the role of the cerebellum in these deficits, mice were subjected to cerebellum-specific motor performance and learning tests. Nf1(+/-) mice showed no impairment on the Erasmus ladder, as step time and number of missteps were not different. Furthermore, when compensatory eye movements were tested, no performance deficits were found in the optokinetic reflex and vestibulo-ocular reflex in the dark (VOR) or in the light (VVOR). Finally, Nf1(+/-) mice successfully completed short- and long-term VOR adaptation paradigms, tests that both depend on cerebellar function. Thus, despite the confirmed presence of motor performance problems in Nf1(+/-) mice, we found no indication of a cerebellar component. These results, combined with recent clinical data, suggest that cerebellar function is not overtly affected in NF1 patients.     

A critical role for the glial-derived neuromodulator D-serine in the age-related deficits of cellular mechanisms of learning and memory

Age-associated deficits in learning and memory are closely correlated with impairments of synaptic plasticity. Analysis of N-methyl-D-aspartate receptor (NMDAr)-dependent long-term potentiation (LTP) in CA1 hippocampal slices indicates that the glial-derived neuromodulator D-serine is required for the induction of synaptic plasticity. During aging, the content of D-serine and the expression of its synthesizing enzyme serine racemase are significantly decreased in the hippocampus. Impaired LTP and NMDAr-mediated synaptic potentials in old rats are rescued by exogenous D-serine. These results highlight the critical role of glial cells and presumably astrocytes, through the availability of D-serine, in the deficits of synaptic mechanisms of learning and memory that occur in the course of aging.     

Berberine Inhibits the Release of Glutamate in Nerve Terminals from Rat Cerebral Cortex

Berberine, an isoquinoline plant alkaloid, protects neurons against neurotoxicity. An excessive release of glutamate is considered to be one of the molecular mechanisms of neuronal damage in several neurological diseases. In this study, we investigated whether berberine could affect endogenous glutamate release in nerve terminals of rat cerebral cortex (synaptosomes) and explored the possible mechanism. Berberine inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP), and this phenomenon was prevented by the chelating extracellular Ca²⁺ ions and the vesicular transporter inhibitor bafilomycin A1, but was insensitive to the glutamate transporter inhibitor DL-threo-beta-benzyl-oxyaspartate. Inhibition of glutamate release by berberine was not due to it decreasing synaptosomal excitability, because berberine did not alter 4-AP-mediated depolarization. The inhibitory effect of berberine on glutamate release was associated with a reduction in the depolarization-induced increase in cytosolic free Ca²⁺ concentration. Involvement of the Ca_v2.1 (P/Q-type) channels in the berberine action was confirmed by blockade of the berberine-mediated inhibition of glutamate release by the Ca_v2.1 (P/Q-type) channel blocker ω-agatoxin IVA. In addition, the inhibitory effect of berberine on evoked glutamate release was prevented by the mitogen-activated/extracellular signal-regulated kinase kinase (MEK) inhibitors. Berberine decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synapsin I, the main presynaptic target of ERK; this decrease was also blocked by the MEK inhibition. Moreover, the inhibitory effect of berberine on evoked glutamate release was prevented in nerve terminals from mice lacking synapsin I. Together, these results indicated that berberine inhibits glutamate release from rats cortical synaptosomes, through the suppression of presynaptic Cav2.1 channels and ERK/synapsin I signaling cascade. This finding may provide further understanding of the mode of berberine action in the brain and highlights the therapeutic potential of this compound in the treatment of a wide range of neurological disorders.     

The HMG-CoA reductase inhibitor lovastatin reverses the learning and attention deficits in a mouse model of neurofibromatosis type 1

Neurofibromatosis Type 1 (NF1) is a common neurological disorder caused by mutations in the gene encoding Neurofibromin, a p21Ras GTPase Activating Protein (GAP). Importantly, NF1 causes learning disabilities and attention deficits. A previous study showed that the learning and memory deficits of a mouse model of NF1 (nf1+/-) appear to be caused by excessive p21Ras activity leading to impairments in long-term potentiation (LTP), a cellular mechanism of learning and memory. Here, we identify lovastatin as a potent inhibitor of p21Ras/Mitogen Activated Protein Kinase (MAPK) activity in the brain. Lovastatin is a specific inhibitor of three-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, used commonly for the treatment of hypercholesterolemia. We report that lovastatin decreased the enhanced brain p21Ras-MAPK activity of the nf1+/- mice, rescued their LTP deficits, and reversed their spatial learning and attention impairments. Therefore, these results demonstrate that lovastatin may prove useful in the treatment of Neurofibromatosis Type 1.