JNK plays a key role in tau hyperphosphorylation in Alzheimer's disease models

Alzheimer's disease (AD) is a major clinical concern, and the search for new molecules to combat disease progression remains important. One of the major hallmarks in AD pathogenesis is the hyperphosphorylation of tau and subsequent formation of neurofibrillary tangles. Several kinases are involved in this process. Amongst them, c-Jun N-terminal kinases (JNKs) are activated in AD brains and are also associated with the development of amyloid plaques. This study was designed to investigate the contribution of JNK in tau hyperphosphorylation and whether it may represent a potential therapeutic target for the fight against AD. The specific inhibition of JNK by the cell permeable peptide D-JNKI-1 led to a reduction of p-tau at S202/T205 and S422, two established target sites of JNK, in rat neuronal cultures and in human fibroblasts cultures. Similarly, D-JNKI-1 reduced p-tau at S202/T205 in an in vivo model of AD (TgCRND8 mice). Our findings support the fundamental role of JNK in the regulation of tau hyperphosphorylation and subsequently in AD pathogenesis.     

Pituitary adenylate cyclase-activating polypeptide plays a key role in nitroglycerol-induced trigeminovascular activation in mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (PAC1, VPAC) are present in sensory neurons and vascular smooth muscle. PACAP infusion was found to trigger migraine-like headache in humans and we showed its central pro-nociceptive function in several mouse pain models. Nitroglycerol (NTG)-induced pathophysiological changes were investigated in this study in PACAP gene-deleted (PACAP^−/−) and wildtype (PACAP^+/+) mice. Chemical activation of the trigeminovascular system was induced by 10 mg/kg i.p. NTG. Light-aversive behavior was determined in a light-dark box, meningeal microcirculation by laser Doppler blood perfusion scanning and the early neuronal activation marker c-Fos with immunohistochemistry. NTG-induced photophobia both in the early (0-30 min) and late phases (90-120 min) due to direct vasodilation and trigeminal sensitization, respectively, was significantly reduced in PACAP^−/− mice. Meningeal blood flow increased by 30-35% during 4 h in PACAP^+/+ mice, but only a 5-10% elevation occurred from the second hour in PACAP^−/− ones. The number of c-Fos expressing cells referring to neuronal activation in the trigeminal ganglia and nucleus caudalis significantly increased 4 h after NTG in PACAP^+/+, but not in PACAP^−/− animals. Similar PAC1 receptor immunostaining was detected in both groups, which did not change 4 h after NTG treatment. PACAP-38 (300 μg/kg, i.p.) produced photophobia similarly to NTG and 30% meningeal vasodilatation for 30 min in PACAP^+/+, but not in PACAP^−/− mice. It significantly increased neural activation 4 h later in the trigeminal ganglia of both groups, but in the nucleus caudalis of only the PACAP^+/+ mice.We provide the first experimental results that PACAP is a pivotal mediator of trigeminovascular activation/sensitization and meningeal vasodilation related to migraine.     

Hippocampal up-regulation of NCAM expression and polysialylation plays a key role on spatial memory

Memory formation has been associated with structural and functional modifications of synapses. Cell adhesion molecules are prominent modulators of synaptic plasticity. Here, we investigated the involvement of the cell adhesion molecules, NCAM, its polysialylated state (PSA-NCAM) and L1 in spatial learning-induced synaptic remodeling and memory storage. A differential regulation of these adhesion molecules was found in the hippocampus of rats submitted to one training session in the spatial, but not cued, version of the Morris water maze. Twenty-four hours after training, synaptic expression of NCAM and PSA-NCAM was increased, whereas L1 appeared markedly decreased. The regulation of these molecules was spatial learning-specific, except for L1 reduction, which could be attributed to swimming under stressful conditions rather than to learning. Subsequent psychopharmacological experiments were performed to address the functional role of NCAM and PSA-NCAM in the formation of spatial memories. Rats received an intracerebroventricular injection of either a synthetic peptide (C3d) aimed to interfere with NCAM function, or endoneuraminidase, an enzyme that cleaves polysialic acid from NCAM. Both treatments affected acquisition of spatial information and lead to impaired spatial memory abilities, supporting a critical role of the observed learning-induced up-regulation of synaptic NCAM expression and polysialylation on spatial learning and memory. Therefore, our findings highlight NCAM as a learning-modulated molecule critically involved in the hippocampal remodeling processes underlying spatial memory formation.     

Acetylcholinesterase inhibition in the basolateral amygdala plays a key role in the induction of status epilepticus after soman exposure

Exposure to nerve agents induces intense seizures (status epilepticus, SE), which cause brain damage or death. Identification of the brain regions that are critical for seizure initiation after nerve agent exposure, along with knowledge of the physiology of these regions, can facilitate the development of pretreatments and treatments that will successfully prevent or limit the development of seizures and brain damage. It is well-established that seizure initiation is due to excessive cholinergic activity triggered by the nerve agent-induced irreversible inhibition of acetylcholinesterase (AChE). Therefore, the reason that when animals are exposed to lethal doses of a nerve agent, a small proportion of these animals do not develop seizures, may have to do with failure of the nerve agent to inhibit AChE in brain areas that play a key role in seizure initiation and propagation. In the present study, we compared AChE activity in the basolateral amygdala (BLA), hippocampus, and piriform cortex of rats that developed SE (SE rats) after administration of the nerve agent soman (154 μg/kg) to AChE activity in these brain regions of rats that received the same dose of soman but did not develop SE (no-SE rats). The levels of AChE activity were measured at the onset of SE in SE rats, 30 min after soman administration in no-SE rats, as well as in controls which received saline in place of soman. In the control group, AChE activity was significantly higher in the BLA compared to the hippocampus and piriform cortex. Compared to controls, AChE activity was dramatically lower in the hippocampus and the piriform cortex of both the SE rats and the no-SE rats, but AChE activity in the BLA was reduced only in the SE rats. Consistent with the notion that soman-induced neuropathology is due to intense seizures, rather than due to a direct neurotoxic effect of soman, no-SE rats did not present any neuronal loss or degeneration, 7 days after exposure. The results suggest that inhibition of AChE activity in the BLA is necessary for the generation of seizures after nerve agent exposure, and provide strong support to the view that the amygdala is a key brain region for the induction of seizures by nerve agents.     

12-Lipoxygenase plays a key role in cell death caused by glutathione depletion and arachidonic acid in rat oligodendrocytes

Oxidative injury to premyelinating oligodendrocytes (preOLs) in developing white matter has been implicated in the pathogenesis of periventricular leukomalacia, the lesion underlying most cases of cerebral palsy in premature infants. In this study, we investigated the pathways of OL death induced by intracellular glutathione (GSH) depletion. We found that the lipoxygenase (LOX) inhibitors AA-861 and BMD-122 (N-benzyl-N-hydroxy-5-phenylpentamide; BHPP), but not the cyclooxygenase (COX) inhibitor indomethacin, fully protected the cells from GSH depletion caused by cystine deprivation. Arachidonic acid (AA), the substrate for 12-LOX, potentiated the toxicity of mild cystine deprivation and at higher concentration was itself toxic. This toxicity was also blocked by 12-LOX inhibitors. Consistent with a role for 12-LOX in the cell death pathway, 12-LOX activity increased following cystine deprivation in OLs. Blocking 12-LOX with AA-861 effectively inhibited the accumulation of reactive oxygen species (ROS) induced by cystine deprivation. These data suggest that, in OLs, intracellular GSH depletion leads to activation of 12-LOX, ROS accumulation and cell death. Mature OLs were more resistant than preOLs to cystine deprivation. The difference in sensitivity was not due to a difference in 12-LOX activity but rather appeared to be related to the presence of stronger antioxidant defense mechanisms in mature OLs. These results suggest that 12-LOX activation plays a key role in oxidative stress-induced OL death.     

miR-6858 plays a key role in the process of melatonin inhibition of the malignant biological behavior of glioma

MicroRNAs (miRNAs), small non-coding RNA molecules with a length of 18–25 nucleotides, have been shown to be involved in mediating various malignant properties of GBM, including growth, invasion and angiogenesis. Here, we investigated whether miRNAs might be involved in mediating the suppression of malignant properties of GBM by melatonin (MEL), an amine hormone secreted by the pineal gland. Sequencing was performed to screen specifically for miRNAs induced by MEL in U87 and an orthotopically xenografted primary GBM cell line, GBM#P3. MiR-6858-5p was the most significantly up-regulated miR in GBM cell lines in response to MEL (~5 × ). Transfection of a mimic of miR-6858-5p into both cell lines led to a decrease in viability of ~ 50% at 72 h, confirming a suppressive role for miR-6858-5p in GBM. In contrast, an inhibitor of miR-6858-5p rescued GBM cells from MEL suppression of proliferation, migration and invasion. Analysis using Targetscan yielded candidate mRNAs targeted by miR-6858-5p, some of which are involved in the SIRT/AKT signaling pathway. In cells transfected with a mimic or an inhibitor of miR-6858-5p, levels of SIRT3 and downstream components of the AKT signaling pathway were suppressed or up-regulated, respectively, both in vitro and in an in vivo orthotopic xenograft model. Our results elucidated a novel molecular mechanism underlying MEL suppression of GBM, highlighting a role for miRNAs, and provide a potential therapeutic strategy for GBM.     

Ischemia-induced extracellular release of serotonin plays a role in CA1 neuronal cell death in rats.

BACKGROUND AND PURPOSE: Serotonin, via 5-HT2 receptors, exerts an excitatory effect on CA1 neurons and may play a role in ischemia-induced excitotoxic damage. To evaluate the role of serotonin in ischemia, both neurochemical and histopathological studies were performed. METHODS: Neurochemical studies included rats that were subjected to 12.5 or 20 minutes of normothermic ischemia by two-vessel occlusion plus hypotension, and extracellular serotonin levels were measured in the hippocampus (12.5 minutes' ischemia, n = 5) or striatum (20 minutes' ischemia, n = 13) by microdialysis. In the histopathological study the effect of 8 mg/kg ritanserin, a 5-HT2 antagonist, administered continuously from 30 minutes prior to ischemia until 1 hour of recirculation was evaluated in five rats subjected to 10 minutes of ischemia. After 3 days, the numbers of normal-appearing neurons in the CA1 subregions were counted. RESULTS: Ischemia of 12.5 minutes' duration induced a fourfold increase in serotonin in the hippocampus (mean +/- SEM baseline, 1.86 +/- 0.25 pmol/ml perfusate; during ischemia, 8.14 +/- 0.89 pmol/ml; p < 0.05 by analysis of variance). Twenty minutes of ischemia induced a 25-fold increase in serotonin in the dorsolateral striatum (baseline, 0.98 +/- 0.15 pmol/ml; ischemia, 24.4 +/- 5.93 pmol/ml; p < 0.001). The histopathological study demonstrated severe ischemic damage in all CA1 subregions of nontreated animals (medial, 34 +/- 16 normal-appearing neurons, middle, 52.2 +/- 22.9 neurons; lateral, 56.6 +/- 21.8 neurons). Treatment with ritanserin significantly attenuated ischemic damage (medial, 117.6 +/- 6.5 neurons; middle, 131.4 +/- 4.9 neurons; lateral, 130 +/- 7.5 neurons; p < 0.01 different from nontreated). CONCLUSIONS: Taken together, these results suggest that serotonin plays a detrimental role, mediated by 5-HT2 receptors, in the development of ischemic damage.     

Adenomatous polyposis coli plays a key role, in vivo, in coordinating assembly of the neuronal nicotinic postsynaptic complex

The neuronal nicotinic synapse plays a central role in normal cognitive and autonomic function. Molecular mechanisms that direct the assembly of this synapse remain poorly defined, however. We show here that adenomatous polyposis coli (APC) organizes a multi-molecular complex that is essential for targeting alpha3(*)nAChRs to synapses. APC interaction with microtubule plus-end binding protein EB1 is required for alpha3(*)nAChR surface membrane insertion and stabilization. APC brings together EB1, the key cytoskeletal regulators macrophin and IQGAP1, and 14-3-3 adapter protein at nicotinic synapses. 14-3-3, in turn, links the alpha3-subunit to APC. This multi-molecular APC complex stabilizes the local microtubule and F-actin cytoskeleton and links postsynaptic components to the cytoskeleton--essential functions for controlling the molecular composition and stability of synapses. This work identifies macrophin, IQGAP1 and 14-3-3 as novel nicotinic synapse components and defines a new role for APC as an in vivo coordinator of nicotinic postsynaptic assembly in vertebrate neurons.     

Iron efflux from astrocytes plays a role in remyelination

How iron is delivered to the CNS for myelination is not well understood. We assessed whether astrocytes can provide iron to cells in the CNS for remyelination. To study this we generated a conditional deletion of the iron efflux transporter ferroportin (Fpn) in astrocytes, and induced focal demyelination in the mouse spinal cord dorsal column by microinjection of lysophosphatidylcholine (LPC). Remyelination assessed by electron microscopy was reduced in astrocyte-specific Fpn knock-out mice compared with wild-type controls, as was proliferation of oligodendrocyte precursor cells (OPCs). Cell culture work showed that lack of iron reduces the ability of microglia to express cytokines (TNF-α and IL-1β) involved in remyelination. Furthermore, astrocytes in culture express high levels of FGF-2 in response to IL-1β, and IGF-1 in response to TNF-α stimulation. FGF-2 and IGF-1 are known to be important for myelination. Reduction in IL-1β and IGF-1 were also seen in astrocyte-specific Fpn knock-out mice after LPC-induced demyelination. These data suggest that iron efflux from astrocytes plays a role in remyelination by either direct effects on OPCs or indirectly by affecting glial activation.     

Broca's area plays a causal role in morphosyntactic processing

Although there is strong evidence that Broca's area is important for syntax, this may simply be a by-product of greater working memory and/or cognitive control demands for more complex syntactic structures. Here we report an experiment with event-related transcranial magnetic stimulation (TMS) to investigate whether Broca's area plays a causal role in morphosyntactic processing when both working memory and cognitive control demands are low. Participants were presented with word pairs that could either agree or disagree in grammatical number or gender while receiving stimulation to Broca's area or to the right intraparietal sulcus (a control site). Stimulation of Broca's area significantly reduced the advantage for grammatical relative to ungrammatical word pairs. In contrast, stimulation of control site left this grammaticality advantage unchanged. The interaction between grammaticality and stimulation was specific to Broca's area, suggesting a clear involvement of the region in morphosyntactic processing.     

IL-1 type I receptor plays a key role in mediating the recruitment of leukocytes into the central nervous system

This study investigates the role of type I IL-1 receptor (IL-1R1) in mediating the recruitment of leukocytes into the brain parenchyma in mice. Intracerebroventricular (icv) injection of interleukin IL-1beta induced infiltration of leukocytes between 8 and 72 h after the injection. Leukocytes were rarely found in the brain tissue of saline-injected animals. At 8h after IL-1beta injection, leukocytes were seen lining the blood vessels of the brain and sparsely scattered infiltration of leukocytes was found in the cortex. Peak infiltration of leukocytes, which distributed evenly throughout the brain, was seen at 16 h post-injection. The number of leukocytes in the brain declined thereafter and no leukocytes were found 72 h post-injection. This phenomenon was replicated in mice deficient in lymphotoxin-alpha (LT(alpha)), IL-6, interferon (IFN)-gamma receptor, or the tumor necrosis factor (TNF)-alpha receptor, but abrogated in animals deficient in IL-1R1. ICV injection of IFN-gamma or TNF-alpha, but not IL-6 or IL-12, also induced leukocyte infiltration into the brain. Injection of IL-1beta, IFN-gamma, TNF-alpha, IL-6, and IL-12 induced IL-1beta expression in the brain, with IL-6 and IL-12 being the least effective. Leukocyte infiltration induced by icv IFN-gamma and TNF-alpha was also abrogated in IL-1R1-knockout animals. The induced infiltrating leukocytes were identified as neutrophils. Chronic infection with Trypanosoma brucei resulted in the recruitment of T cells, but no other cell types, into the brain. This did not occur in IL-1R1-knockout mice. Thus, IL-1R1 appears to be important for the recruitment of leukocytes across the blood-brain barrier.     

The hardness of food plays an important role in food selection behavior in rats

To examine the importance of the hardness of foods, we conducted behavioral and electromyographical experiments in Wistar male rats using three kinds of pellets, a hard commercially made pellet (MF), a hard privately produced pellet (H) and a soft privately produced pellet (S). MF and H had the same hardness but contained different ingredients, and S and H had the same ingredients but different degrees of hardness (S相似文献   

FGF plays a subtle role in oligodendrocyte maintenance in vivo

Numerous in vitro studies indicate that fibroblast growth factors (FGFs) play a role in both the development and maintenance of oligodendrocytes. Addition of FGF to mature oligodendrocytes in culture was reported to downregulate the expression of genes encoding proteins of the myelin sheath and to induce a loss of myelin compaction. In this study, a model was developed to functionally block FGF signaling in oligodendrocytes in vivo, by generating transgenic mice expressing a dominant-negative FGF receptor (FGFR1), under the control of the myelin basic protein (MBP) promoter. To demonstrate the effectiveness of this model, truncated FGFR1 was first overexpressed in an FGF-responsive cell line in vitro. It was confirmed that FGF-signalling was blocked in these cells. Subsequently, five independent transgenic lines (“MBP-FRD”) were generated. Three lines expressing the highest level of the transgene were further studied. Initial investigation by Western blot and light microscopic analyses revealed no apparent alterations in myelination of the MBP-FRD mouse brains. However, ultrastructural analysis of myelinated optic nerve fibres from two independent MBP-FRD lines revealed a significant increase in myelin thickness as a function of fibre diameter for both transgenic lines (13% and 16% increase). This increase in myelin thickness was not accompanied by alterations in myelin compaction. These results support the idea that FGF signaling in oligodendrocytes plays a role in the modulation of axon myelination in vivo. J. Neurosci. Res. 49:404–415, 1997. © 1997 Wiley-Liss, Inc.     

The cerebellum plays a role in conscious episodic memory retrieval

The cerebellum has traditionally been considered to be primarily dedicated to motor functions. Its phylogenetic development and connectivity suggest, however, that it also may play a role in cognitive processes in the human brain. In order to examine a potential cognitive role for the cerebellum in human beings, a positron emission tomography (PET) study was conducted during a "pure thought experiment": subjects intentionally recalled a specific past personal experience (consciously retrieved episodic memory). Since there was no motor or sensory input or output, the design eliminated the possibility that cerebellar changes in blood flow were due to motor activity. During silent recall of a consciously retrieved episodic memory, activations were observed in the right lateral cerebellum, left medial dorsal thalamus, medial and left orbital frontal cortex, anterior cingulate, and a left parietal region. These activations confirm a cognitive role for the cerebellum, which may participate in an interactive cortical-cerebellar network that initiates and monitors the conscious retrieval of episodic memory.     

Both endogenous and exogenous ACh plays antinociceptive role in the hippocampus CA1 of rats

Summary. The present study examines the effect of acetylcholine (ACh), muscarinic acetylcholine receptors (mAChRs) agonist pilocarpine and mAChRs antagonist atropine on the pain-evoked response of pain-excited neurons (PEN) and pain-inhibited neurons (PIN) in the hippocampal CA1 of rats. The trains of electric impulses applied to the sciatic nerve were used as noxious stimulation. The discharges of PEN and PIN in the hippocampal CA1 were recorded by glass microelectrode. The results showed that intrahippocampal microinjection of ACh (2 μg/1 μl) or pilocarpine (2 μg/1 μl) decreased the frequency of discharge of PEN, and increased the frequency of discharge of PIN evoked by the noxious stimulation in the hippocampal CA1, while intrahippocampal administration of atropine (0.5 μg/1 μl) produced opposite response. On the basis of the above findings, we can deduce that ACh and mAChRs are involved in the modulation of nociceptive information transmission in the hippocampal CA1. Correspondence: Man-Ying Xu, Department of Physiology, Harbin Medical University, Harbin 15 0081, Heilongjiang Province, China     

ATP plays a role in neurite stimulation with activated mast cells

Previously, we showed that nerve-mast cell cross-talk can occur bidirectionally and that substance P is a mediator to activate mast cells. Here, we have studied the mediators to activate nerves cocultured with mast cells. Addition of antigen to the cocultures of superior cervical ganglia (SCG) and rat basophilic leukemia cells (RBLs) elicited Ca(2+) response in RBLs and after a lag period induced Ca(2+) signal in SCG neurites. Pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (purinergic receptor antagonist) or apyrase (ATP-hydrolyzing enzyme) reduced the Ca(2+) signals in neurites, indicating that ATP released from activated mast cells was one of important mediators to activate nerves.