Yi Ling Yang

Systemic and intra-amygdala administration of glucocorticoid agonist and antagonist modulate extinction of conditioned fear

We examined the effect of glucocorticoid agonists on the extinction of conditioned fear in rats by using fear-potentiated startle. Systemic injection of glucocorticoid receptor agonists dexamethasone (DEX) (0.1, 0.5, and 1.0 mg/kg) and intra-amygdala infusion of RU28362 (0.5, 1.0, and 3.0 ng/side) prior to extinction training facilitated extinction of conditioned fear in a dose-dependent manner. Extinction of conditioned fear and circulating corticosterone levels were attenuated by administration of corticosteroid synthesis inhibitor metyrapone (25 mg/kg s.c.) 90 min before extinction training. The facilitation effect of DEX was dependent on repeated presentation of the conditioned stimulus rather than exposure to the experimental context, indicating this effect did not result from impaired expression of conditioned fear or accelerated forgetting. Intra-amygdaloid administration of the glucocorticoid receptor antagonist mifepristone (0.1, 0.2, and 0.5 ng/side, bilaterally) blocked extinction of conditioned fear and the facilitation effect of DEX in a dose-dependent manner. Mifepristone (2 ng/side) did not affect extinction but blocked the facilitating effect of DEX. Systemic administration of DEX after extinction training also facilitated extinction, suggesting that DEX may influence the memory consodilation phase of extinction. The Dose of dexamethsone or metyrapone used here did not influence fear-potentiated startle when administered before testing. Thus, it is unlikely that these drugs influenced extinction by increasing or disrupting CS processing. All results suggested that amygdaloid glucocorticoid receptors were involved in the extinction of conditioned fear.

Resveratrol Protects Rats from Aβ-induced Neurotoxicity by the Reduction of iNOS Expression and Lipid Peroxidation

Alzheimer disease (AD) is an age-dependent neurodegenerative disease characterized by the formation of β–amyloid (Aβ)-containing senile plaque. The disease could be induced by the administration of Aβ peptide, which was also known to upregulate inducible nitric oxide synthase (iNOS) and stimulate neuronal apoptosis. The present study is aimed to elucidate the cellular effect of resveratrol, a natural phytoestrogen with neuroprotective activities, on Aβ-induced hippocampal neuron loss and memory impairment. On adult Sprague-Dawley rats, we found the injection of Aβ could result in a significant impairment in spatial memory, a marked increase in the cellular level of iNOS and lipid peroxidation, and an apparent decrease in the expression of heme oxygenase-1 (HO-1). By combining the treatment with Aβ, resveratrol was able to confer a significant improvement in spatial memory, and protect animals from Aβ-induced neurotoxicity. These neurological protection effects of resveratrol were associated with a reduction in the cellular levels of iNOS and lipid peroxidation and an increase in the production of HO-1. Moreover, the similar neurological and cellular response were also observed when Aβ treatment was combined with the administration of a NOS inhibitor, N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME). These findings strongly implicate that iNOS is involved in the Aβ-induced lipid peroxidation and HO-1 downregulation, and resveratrol protects animals from Aβ-induced neurotoxicity by suppressing iNOS production.

Neuroprotective Effects of Resveratrol on MPTP-Induced Neuron Loss Mediated by Free Radical Scavenging

Resveratrol is a natural polyphenol and possesses many biological functions such as anti-inflammatory activity and protection against atherosclerosis and myocardial infraction. Parkinsons disease is a common progressive neurodegenerative disease. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is the most useful neurotoxin to induce Parkinsonism. The present study was carried out to elucidate the neuroprotective effect and possible mechanism of resveratrol on MPTP-induced striatal neuron loss. Sixty adult Balb/c mice were divided into four groups: sham operation, MPTP treatment (30 mg/kg, i.p.), MPTP combined with resveratrol administration (20 mg/kg, i.v.), and resveratrol treatment alone. Microdialysis and high-performance liquid chromatography were used to analyze dihydroxybenzoic acid (DHBA) that reflected the hydroxyl radical level. In the present study, we found MPTP chronic administration significantly induced motor coordination impairment in mice. After MPTP administration, the hydroxyl radical levels in substantia nigra were also significantly elevated and animals displayed severe neuronal loss. Resveratrol administration significantly protected mice from MPTP-induced motor coordination impairment, hydroxyl radical overloading, and neuronal loss. Our results demonstrated that resveratrol could elicit neuroprotective effects on MPTP-induced Parkinsonism through free radical scavenging.

Glutamate NMDA receptors within the amygdala participate in the modulatory effect of glucocorticoids on extinction of conditioned fear in rats.

Recent results show that brain glucocorticoids are involved in the dysregulation of fear memory extinction in post-traumatic stress disorder patients. The present study was aimed to elucidate the possible mechanism of glucocorticoids on the conditioned fear extinction. To achieve these goals, male SD rats, fear-potentiated startle paradigm, and Western blot were used. We found that (1) systemic administration of the synthetic glucocorticoid agonist dexamethasone (DEX) facilitated extinction of conditioned fear in a dose-dependent manner (0.05, 0.1, 0.5, or 1.0 mg/kg, i.p.); (2) systemic administration of the glutamate NMDA receptor antagonist (±)-HA966 (6.0 mg/kg, i.p.) and intra-amygdala infusion of the NMDA receptor antagonists MK801 (0.5 ng/side, bilaterally) or D,L-2-amino-5-phosphonovaleric acid (AP5, 2.0 ng/side, bilaterally) blocked the DEX facilitation effect; (3) the corticosteroid synthesis inhibitor metyrapone (25 mg/kg. s.c.) blocked extinction and this was prevented by co-administration of NMDA receptor agonist D-cycloserine (DCS, 5.0 mg/kg, i.p.); (4) co-administration of DEX and DCS in subthreshold doses provided a synergistic facilitation effect on extinction (0.2 and 5 mg/kg, respectively). Control experiments indicated that co-administration of DEX and DCS did not alter the expression of conditioned fear and the effect was not due to lasting damage to the amygdala. These results suggest that glutamate NMDA receptors within the amygdala participate in the modulatory effect of glucocorticoids on extinction.

Extracellular signal-regulated kinase-mediated IL-1-induced cortical neuron damage during traumatic brain injury

Traumatic brain injury (TBI) is one of the most prevalent causes of morbidity and mortality in youth. Interleukin-1 (IL-1) has many roles in the brain in addition to mediating glial inflammatory response; it has also been implicated in neurodegenerative diseases. We demonstrated the signal transduction pathway of IL-1 overproduction-induced cortical neuron loss during TBI. A calibrated weight-drop device (450 g weight and 2m height) was used to induce TBI in adult male Sprague-Dawley rats under general anesthesia (sodium pentobarbital: 40 mg/kg, i.p.). Expression of interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), extracellular signal-regulated kinase (ERK), Jun, and p-38 were determined by Western blotting and RT-PCR. Neuronal damage was evaluated by microscopic examination. We found both mRNA and proteins of cortical IL-1alpha and IL-1beta increased three hours after TBI. Phosphorylation of ERK significantly increased but there were no significant effects on cortical expression of ERK, Jun and p-38. Administration of ERK inhibitor, PD98059, IL-1alpha antibody and IL-1beta antibody protected animals from TBI-induced neuronal damage. Our results suggest that TBI-induced cortical neuron death was mediated by the IL-1 receptor through ERK phosphorylation.

NKCC1-mediated traumatic brain injury-induced brain edema and neuron death via Raf/MEK/MAPK cascade

Objective:Brain edema is one of the characteristic features of patients with severe traumatic brain injury. The aim of this study was to examine the effects of Na+-K+-2Cl− co-transporter on traumatic brain injury-induced brain edema and neuron damage and to elucidate the relationship between Na+-K+-2Cl− co-transporter and mitogen-activated protein kinase (MAPK) cascade. Design:Laboratory investigation. Setting:University research laboratory. Subjects:Male Wistar rats weighing 350–400 g. Interventions:Anesthetized animals were subjected to a weight-drop device (450-g weight, 1.8-m height) to induce traumatic brain injury. Measurements and Main Results:The expression of Na+-K+-2Cl− co-transporter and phosphorylation of MAPK cascade were determined by Western blot test. We also analyzed the degree of brain edema and neuronal damage in this study. We found that the messenger RNA and protein of Na+-K+-2Cl− co-transporter were up-regulated mainly in hippocampus neurons from 2 to 24 hrs after traumatic brain injury. After traumatic brain injury, animals displayed severe brain edema and neuron damage. The phosphorylation of extracellular signal-regulated kinase, MAPK kinase, and Raf also was significantly elevated after traumatic brain injury. Bumetanide (15.2 mg/kg), a specific Na+-K+-2Cl− co-transporter inhibitor, significantly attenuated the neuronal damage and brain edema after traumatic brain injury by decreasing the phosphorylation of Raf/MEK/ERK cascade proteins. Conclusions:The present study suggests that Na+-K+-2Cl− co-transporter plays an important role in TBI-induced brain edema and neuronal damage via activation of MAPK cascade.

Upregulation of NF-E2-related factor-2-dependent glutathione by carnosol provokes a cytoprotective response and enhances cell survival

Aim:To explore whether glutathione (GSH) increased through Nrf-2 activation is involved in the cytoprotective effects of carnosol in HepG2 cells.Methods:Human hepatoma cell line HepG2 were exposed to rosemarry essential oil or carnosol. Cell viability was measured using an Alamar blue assay. The production of intracellular GSH was determined using monochlorobimane. The level of protein or mRNA was examined by Western blotting or RT-PCR, respectively.Results:Rosemarry essential oil (0.005%–0.02%) and carnosol (5 and 10 mol/L) increased the intracellular GSH levels and GSH synthesis enzyme subunit GCLC/GCLM expression. Rosemary essential oil and carnosol increased nuclear accumulation of Nrf2 and enhanced Nrf2-antioxidant responsive element (ARE)-reporter activity. Transfection of the treated cells with an Nrf2 siRNA construct blocks GCLC/GCLM induction. Furthermore, pretreatment of the HepG2 cells with essential oil and carnosol exerted significant cytoprotective effects against H2O2 or alcohol. In TNFα-treated cells, the nuclear translocation and transcriptional activity of NF-κB was abolished for 12 h following carnosol pretreatment. Cotreatment with GSH also suppressed NF-κB nuclear translocation, whereas cotreatment with BSO, a GSH synthesis blocker, blocked the inhibitory effects of carnosol.Conclusion:This study demonstrated that Nrf2 is involved in the cytoprotective effects by carnasol, which were at least partially mediated through increased GSH biosynthesis.

Hippocampal Neurogenesis after Traumatic Brain Injury Is Mediated by Vascular Endothelial Growth Factor Receptor-2 and the Raf/MEK/ERK Cascade

Adult neurogenesis occurs in the subgranular zone of the hippocampal dentate gyrus, and can be modulated by physiological and pathological events. We examined the effect of vascular endothelial growth factor (VEGF), and the correlation between VEGF and the Raf/MEK/ERK cascade in neurogenesis after traumatic brain injury (TBI). The expression of VEGF and the phosphorylation level of Raf/MEK/ERK were analyzed by Western blot, and TBI-induced neurogenesis was determined by immunofluorescence labeling and confocal microscopic detection. Hippocampal VEGF began to increase after 12 h, and reached a peak at day 7. Along with the upregulation of VEGF, neurogenesis in the hippocampus also increased. Administration of the VEGF antisense oligodeoxynucleotide, or the VEGF receptor-2 antagonist SU1498 (10 μg, ICV), attenuated the phosphorylation of the MAPK cascade proteins and caused a decrease in neurogenesis in the hippocampus. Similarly, administration of the ERK inhibitor PD98059 (500 ng, ICV) also exhibited a suppressive effect on neurogenesis. Our results indicate that VEGF plays an important role in neurogenesis after TBI, and that the process involves VEGF receptor-2 and the Raf/MEK/ERK cascade.

Bumetanide administration attenuated traumatic brain injury through IL-1 overexpression.

Abstract Objective: To examine the effects of administration of bumetanide, a specific NKCC1 inhibitor, on traumatic brain injury (TBI)-induced interleukin-1 (IL-1) expression. Methods: TBI model was induced by the calibrated weight drop device (450 g in weight, 2.0 m in height) in adult rats based on procedures previously reported. One hundred and sixty Wistar rats were divided into sham-control group and experimental group for time course works of TBI. The expression of IL-1β brain edema and neuronal damage were determined in these animals after TBI. Results: We found that both mRNA and protein of IL-1β were up-regulated in the hippocampus 3–24 hours after TBI. Animals displayed severe brain edema and neuron damage after TBI. Bumetanide (15 mg/kg), a specific Na+ −K+ −2Cl− cotransporter inhibitor, significantly attenuated the TBI-induced neuronal damage by IL-1β overexpression. The present study suggests that administration of bumetanide could significantly decreased TBI-induced inflammatory response and neuronal damage.

Behavioral and synaptic circuit features in a zebrafish model of fragile X syndrome.

Fragile X syndrome (FXS) is the most frequent inherited form of human mental retardation. It is characterized by cognitive impairment and physical and behavioral problems and is caused by the silencing of fmr1 transcription and the absence of the fmr1 protein (FMRP). Recently, animal models of FXS have greatly facilitated the investigation of the molecular and cellular mechanisms of this loss-of-function disorder. The present study was aimed to further characterize the role of FMRP in behavior and synaptic function by using fmr1 knockout zebrafish. In adult zebrafish, we found that fmr1 knockout produces the anxiolytic-like responses of increased exploratory behavior in light/dark and open-field tests and avoidance learning impairment. Furthermore, electrophysiological recordings from telencephalic slice preparations of knockout fish displayed markedly reduced long-term potentiation and enhanced long-term depression compared to wild-type fish; however, basal glutamatergic transmission and presynaptic function at the lateral (Dl) and medial (Dm) division of the dorsal telencephalon synapse remained normal. Taken together, our study not only evaluates the mechanism of FRMP but also suggests that zebrafish have valuable potential as a complementary vertebrate model in studying the molecular pathogenesis of human fragile X syndrome.