Sun Seek Min

NMDA receptor-independent long-term depression correlates with successful aging in rats.

Some individuals maintain high cognitive functioning at older ages. Here we show that mechanisms for long-term depression differ in aged rodents that maintain cognitive performance compared to young adults. Our results imply that cognitive abilities may be sustained in aged individuals by a switch in synaptic plasticity mechanisms.

Multiple Receptors Coupled to Phospholipase C Gate Long-Term Depression in Visual Cortex

Long-term depression (LTD) in sensory cortices depends on the activation of NMDA receptors. Here, we report that in visual cortical slices, the induction of LTD (but not long-term potentiation) also requires the activation of receptors coupled to the phospholipase C (PLC) pathway. Using immunolesions in combination with agonists and antagonists, we selectively manipulated the activation of α1 adrenergic, M1 muscarinic, and mGluR5 glutamatergic receptors. Inactivation of these PLC-coupled receptors prevents the induction of LTD, but only when the three receptors were inactivated together. LTD is fully restored by activating any one of them or by supplying intracellular d-myo-inositol-1,4,5-triphosphate (IP3). LTD was also impaired by intracellular application of PLC or IP3 receptor blockers, and it was absent in mice lacking PLCβ1, the predominant PLC isoform in the forebrain. We propose that visual cortical LTD requires a minimum of PLC activity that can be supplied independently by at least three neurotransmitter systems. This essential requirement places PLC-linked receptors in a unique position to control the induction of LTD and provides a mechanism for gating visual cortical plasticity via extra-retinal inputs in the intact organism.

Chronic brain inflammation impairs two forms of long-term potentiation in the rat hippocampal CA1 area.

Neuroinflammation plays an important role in the progression of Alzheimers disease (AD) and is characterized by the presence of activated microglia. We investigated whether chronic neuroinflammation affects the induction of N-methyl-d-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) and NMDAR-independent LTP which is expressed by voltage-dependent calcium channel (VDCC). Chronic neuroinflammation was induced by administration of lipopolysaccharide (LPS) (28 days, 0.35 microg/h) to the fourth ventricle. The Morris water maze test was conducted to measure the memory impairment and then excitatory postsynaptic potentials were recorded extracelluarly from stratum radiatum in the rat hippocampal CA1 area to examine the changes in synaptic plasticity induced by LPS infusion. Chronic administration of LPS induced remarkable memory impairment. The field recording experiments revealed that the induction of both NMDAR-dependent LTP and NMDAR-independent LTP were impaired in the hippocampal Schaffer collateral-CA1 synapse in animals chronically infused with LPS. The present results show that chronic neuroinflammation can lead to the impaired spatial memory and attenuation of VDCC-dependent LTP as well as NMDAR-dependent LTP. The attenuation of synaptic plasticity may be caused by the impairment of both NMDAR and L-type Ca2+ via elevated levels of inflammatory proteins, which may underlie aspects of dementia.

Antidepressant-like effect of Salvia sclarea is explained by modulation of dopamine activities in rats

AIM OF THE STUDY The purpose of the present study was to screen aromatic essential oils that have antidepressant effects to identify the regulatory mechanisms of selected essential oils. MATERIALS AND METHODS The antidepressant effects of essential oils of Anthemis nobilis (chamomile), Salvia sclarea (clary sage; clary), Rosmarinus officinalis (rosemary), and Lavandula angustifolia (lavender) were assessed using a forced swim test (FST) in rats. Rats were treated with essential oils by intraperitoneal injection or inhalation. Serum levels of corticosterone were assessed by enzyme-linked immunosorbent assay (ELISA). RESULTS Among the essential oils tested, 5% (v/v) clary oil had the strongest anti-stressor effect in the FST. We further investigated the mechanism of clary oil antidepression by pretreatment with agonists or antagonists to serotonin (5-HT), dopamine (DA), adrenaline, and GABA receptors. The anti-stressor effect of clary oil was significantly blocked by pretreatment with buspirone (a 5-HT(1A) agonist), SCH-23390 (a D(1) receptor antagonist) and haloperidol (a D(2), D(3), and D(4) receptor antagonist). CONCLUSIONS Our findings indicate that clary oil could be developed as a therapeutic agent for patients with depression and that the antidepressant-like effect of clary oil is closely associated with modulation of the DAnergic pathway.

Anti-inflammatory effects of anethole in lipopolysaccharide-induced acute lung injury in mice

AIMS Anethole, the major component of the essential oil of star anise, has been reported to have antioxidant, antibacterial, antifungal, anti-inflammatory, and anesthetic properties. In this study, we investigated the anti-inflammatory effects of anethole in a mouse model of acute lung injury induced by lipopolysaccharide (LPS). MAIN METHODS BALB/C mice were intraperitoneally administered anethole (62.5, 125, 250, or 500mg/kg) 1h before intratracheal treatment with LPS (1.5mg/kg) and sacrificed after 4h. The anti-inflammatory effects of anethole were assessed by measuring total protein and cell levels and inflammatory mediator production and by histological evaluation and Western blot analysis. KEY FINDINGS LPS significantly increased total protein levels; numbers of total cells, including macrophages and neutrophils; and the production of inflammatory mediators such matrix metalloproteinase 9 (MMP-9), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and nitric oxide (NO) in bronchoalveolar lavage fluid. Anethole (250mg/kg) decreased total protein concentrations; numbers of inflammatory cells, including neutrophils and macrophages; and the inflammatory mediators MMP-9, TNF-α and NO. In addition, pretreatment with anethole decreased LPS-induced histopathological changes. The anti-inflammatory mechanism of anethole in LPS-induced acute lung injury was assessed by investigating the effects of anethole on NF-κB activation. Anethole suppressed the activation of NF-κB by blocking IκB-α degradation. SIGNIFICANCE These results, showing that anethole prevents LPS-induced acute lung inflammation in mice, suggest that anethole may be therapeutically effective in inflammatory conditions in humans.

Basal blood corticosterone level is correlated with susceptibility to chronic restraint stress in mice

Corticosterone is released in response to stress and manifests as various bodily stress responses in rodents. While corticosterone reflects acute adaptive responses, how the basal steady-state corticosterone level relates to the subsequent stress response is largely unknown. Here, we investigated how basal corticosterone levels can affect the susceptibility to chronic restraint stress in mice. We designed a longitudinal experiment, enabling us to compare the basal corticosterone level and the subsequent response to repeated restraint stress within the same animal. We found that the mice had differential changes in plasma corticosterone levels, which either increased or decreased, with exposure to chronic stress. These differential changes reflected the differential stress susceptibility of the mice, as evaluated by changes in body weight. The extent of the changes in corticosterone level during chronic stress exposure was predicted by the basal corticosterone level. In addition, the behavioral consequence of chronic stress was also correlated with the basal corticosterone level prior to chronic stress experience. These data reveal that the basal steady-state corticosterone level is a predictor of stress susceptibility or resilience to subsequent stress exposures.

Neuregulin-1 prevents amyloid β-induced impairment of long-term potentiation in hippocampal slices via ErbB4.

Neuregulin-1 (NRG1) participates in numerous neurodevelopmental processes and plasticity of the brain. Despite this, little is known about its role in Alzheimers disease (AD). Amyloid β (Aβ) peptide is generally believed to play a critical role in the pathogenesis of AD. The present study examined the effect of synthetic Aβ₁₋₄₂ peptides on long-term potentiation (LTP) in the CA1 region of mice hippocampal slices, a cellular model of learning and memory. We found that application of a test dose of Aβ₁₋₄₂ (200 nM) significantly inhibited the development of LTP without affecting basal synaptic transmission. Pretreatment with NRG1 effectively prevented Aβ₁₋₄₂-induced impairment of LTP, an effect that was dose-dependent. This LTP-restoring action of NRG1 was almost completely abolished by blocking ErbB4, a key NRG1 receptor, suggesting that NRG1 acts through ErbB4 to exert its protective action on LTP. The present study thus provides the first demonstration that NRG1/ErbB4 protects against Aβ-induced hippocampal LTP impairment, suggesting that NRG1 may be a promising candidate for the treatment of early-stage AD.

The essential oil of Citrus bergamia Risso induces vasorelaxation of the mouse aorta by activating K(+) channels and inhibiting Ca(2+) influx.

The aim of this study was to explore the effect of the essential oil of Citrus bergamia Risso (bergamot) on mouse blood vessels and to analyse the mechanism of this effect from a pharmacological perspective.

Dexibuprofen (S(+)-isomer ibuprofen) reduces microglial activation and impairments of spatial working memory induced by chronic lipopolysaccharide infusion.

Non-steroidal anti-inflammatory drugs (NSAIDs) have been proposed as a therapeutics to reduce the risk of Alzheimers disease (AD). The present study shows that the peripheral administration of dexibuprofen (S(+)-isomer ibuprofen), which causes less gastric damage and has better anti-inflammatory effects than ibuprofen, reduces the microglial activation in the cortex and hippocampus, and reduces the phosphorylation of extracellular signal-regulated kinases in the hippocampus, which has been induced by chronic infusion of lipopolysaccharide (LPS) into the fourth ventricle of Wistar rats. The effects of dexibuprofen on impairments of spatial working memory induced by LPS infusions were measured with a trial-unique matching-to-place task in a water maze which assessed memory for place information over varying delays. When performing the water maze task, the rats with the LPS infusions showed spatial working memory impairments relative to the rats with the artificial cerebrospinal fluid. Daily administrations of dexibuprofen reduced the spatial working memory impairment induced by the chronic LPS infusion. The results indicate that NSAID treatments using dexibuprofen significantly attenuate the processes that drive the pathology associated with AD and that this process may involve the suppression of microglial activation.

Effects of 1,8‐cineole on hypertension induced by chronic exposure to nicotine in rats

The monoterpenic oxide 1,8‐cineole is a major component of many essential oils. We investigated its effects on systolic blood pressure (SBP) and oxidative stress in rats chronically exposed to nicotine.