Excess of leptin inhibits hypothalamic KiSS-1 expression in pubertal mice / 소아과

PURPOSE: Leptin has been considered a link between metabolic state and reproductive activity. Defective reproductive function can occur in leptin-deficient and leptin-excessive conditions. The aim of this study was to examine the effects of centrally injected leptin on the hypothalamic KiSS-1 system in relation to gonadotropin-releasing hormone (GnRH) action in the initial stage of puberty. METHODS: Leptin (1 microg) was injected directly into the ventricle of pubertal female mice. The resultant gene expressions of hypothalamic GnRH and KiSS-1 and pituitary LH, 2 and 4 hours after injection, were compared with those of saline-injected control mice. The changes in the gene expressions after blocking the GnRH action were also analyzed. RESULTS: The basal expression levels of KiSS-1, GnRH, and LH were significantly higher in the pubertal mice than in the prepubertal mice. The 1-microg leptin dose significantly decreased the mRNA expression levels of KiSS-1, GnRH, and LH in the pubertal mice. A GnRH antagonist significantly increased the KiSS-1 and GnRH mRNA expression levels, and the additional leptin injection decreased the gene expression levels compared with those in the control group. CONCLUSION: The excess leptin might have suppressed the central reproductive axis in the pubertal mice by inhibiting the KiSS-1 expression, and this mechanism is independent of the GnRH-LH-estradiol feedback loop.

L-NAME, a Non Selective Nitric Oxide Synthase, Affects Stress-Related Behaviors and Glial Cell-Derived Neurotrophic Factor Expression in Restrained Adolescent ICR Mice / 대한정신약물학회지

OBJECTIVE: Depending on genetic or environmental effects over adolescent development, typical behavioral responses come out in adolescence. Also, alteration of nitric oxide (NO) levels in the brain has been associated with modifications of stress related behavior. Present study was designed to investigate the possible influence of chronic stress from restraint on the generation of depression in adolescent mice, and also to evaluate whether NO has modulatory roles in the behavioral and biological reactions. METHODS: ICR mice exposed to stressful restraint, 2 h per day, was treated with NG-nitro L-arginine methyl ester (L-NAME) (10 mg/kg), a non-selective NO synthase (NOS) inhibitor. To evaluate depression-like behavior in the mice, forced swim test and open field test were performed after the last restraint. To investigate stress-induced changes in the expression level of glial cell-derived neurotrophic factor (GDNF), free-floating immunohistochemistry was performed. RESULTS: The results showed that stressed group has longer immobility time and less crossing number in forced swimming and open field test, and that these stress responses were significantly prevented by L-NAME. Furthermore, decreased GDNF expression in the hippocampus by stress was prevented to that of controls within the L-NAME treated group. CONCLUSION: The results suggest that stress and NO signaling could be involved in generation of depression in adolescence. It also suggested that GDNF might contribute to prevent stress-related behaviors.

Inhibition of eNOS/sGC/PKG Pathway Decreases Akt Phosphorylation Induced by Kainic Acid in Mouse Hippocampus

The serine/threonine kinase Akt has been shown to play a role of multiple cellular signaling pathways and act as a transducer of many functions initiated by growth factor receptors that activate phosphatidylinositol 3-kinase (PI3K). It has been reported that phosphorylated Akt activates eNOS resulting in the production of NO and that NO stimulates soluble guanylate cyclase (sGC), which results in accumulation of cGMP and subsequent activation of the protein kinase G (PKG). It has been also reported that PKG activates PI3K/Akt signaling. Therefore, it is possible that PI3K, Akt, eNOS, sGC, and PKG form a loop to exert enhanced and sustained activation of Akt. However, the existence of this loop in eNOS-expressing cells, such as endothelial cells or astrocytes, has not been reported. Thus, we examined a possibility that Akt phosphorylation might be enhanced via eNOS/sGC/PKG/PI3K pathway in astrocytes in vivo and in vitro. Phosphorylation of Akt was detected in astrocytes after KA treatment and was maintained up to 72 h in mouse hippocampus. 2 weeks after KA treatment, astrocytic Akt phosphorylation was normalized to control. The inhibition of eNOS, sGC, and PKG significantly decreased Akt and eNOS phosphorylation induced by KA in astrocytes. In contrast, the decreased phosphorylation of Akt and eNOS by eNOS inhibition was significantly reversed with PKG activation. The above findings in mouse hippocampus were also observed in primary astrocytes. These data suggest that Akt/eNOS/sGC/PKG/PI3K pathway may constitute a loop, resulting in enhanced and sustained Akt activation in astrocytes.

Bark Constituents from Mushroom-detoxified Rhus verniciflua Suppress Kainic Acid-induced Neuronal Cell Death in Mouse Hippocampus

Urushinol, a plant allergen, has significantly restricted the medical application of Rhus verniciflua, although it has been reported to possess a wide variety of biological activities such as anti-inflammatory, antioxidant, and anti-cancer actions. To reduce the urushinol content while maintaining the beneficial biological activities, mushroom-mediated fermentation of Rhus verniciflua was carried out and this method resulted in significantly attenuated allergenicity [1]. In the present study, to examine the neuroprotective properties of mushroom-fermented stem bark of Rhus verniciflua, two constituents were isolated from mushroom-fermented bark and their neuroprotective properties were examined in a mouse model of kainic acid (KA)-induced excitotoxicity. KA resulted in significant apoptotic neuronal cell death in the CA3 region of mouse hippocampus. However, seven daily administrations of RVH-1 or RVH-2 prior to KA injection significantly attenuated KA-induced pyramidal neuronal cell death in the CA3 region. Furthermore, pretreatment with RVH-1 and RVH-2 also suppressed KA-induced microglial activation in the mouse hippocampus. The present study demonstrates that RVH-1 and RVH-2 isolated from Rhus verniciflua and detoxified using mushroom species possess neuroprotective properties against KA-induced excitotoxicity. This leads to the possibility that detoxified Rhus verniciflua can be a valuable asset in herbal medicine.

Stanniocalcin 2 Enhances Cell Proliferation on Dentate Gyrus of Hippocampus in ICR Mice / 대한정신약물학회지

OBJECTIVE: Stanniocalcin 2 (STC2) is a glycoprotein hormone that is widely expressed in mammalian kidney, heart, and thymus. However, the potential function of STC2 in the brain is less understood. In this study, we investigated whether treatment with STC2 influenced cell proliferation and neurogenesis in imprinting control region (ICR) mice. METHODS: 100 nM STC2 and 5'-bromo-2'-deoxyuridine (BrdU) (50 mg/kg) were administered intracerebroventricularly and intraperitoneally, respectively. On days 1 and 21 after the BrdU injection, sections of STC2-treated group and controls were carried out immunohistochemistry using anti-BrdU and anti-phosphor-cAMP-response element-binding protein (CREB) antibody. RESULTS: We found that the number of BrdU-positive cells was significantly increased in the hippocampal dentate gyrus (DG), compared with controls. Next, we observed that CREB phosphorylation was decreased in the hippocampal DG of STC2-treated group versus the controls. CONCLUSION: These results suggest that STC2 treatment may increase cell proliferation by increasing CREB phosphorylation in the subgranular zone of the DG.

Kainic Acid-induced Neuronal Death is Attenuated by Aminoguanidine but Aggravated by L-NAME in Mouse Hippocampus

Nitric oxide (NO) has both neuroprotective and neurotoxic effects depending on its concentration and the experimental model. We tested the effects of NG-nitro-L-arginine methyl ester (L-NAME), a nonselective nitric oxide synthase (NOS) inhibitor, and aminoguanidine, a selective inducible NOS (iNOS) inhibitor, on kainic acid (KA)-induced seizures and hippocampal CA3 neuronal death. L-NAME (50 mg/kg, i.p.) and/or aminoguanidine (200 mg/kg, i.p.) were administered 1 h prior to the intracerebroventricular (i.c.v.) injection of KA. Pretreatment with L-NAME significantly increased KA-induced CA3 neuronal death, iNOS expression, and activation of microglia. However, pretreatment with aminoguanidine significantly suppressed both the KA-induced and L-NAME-aggravated hippocampal CA3 neuronal death with concomitant decreases in iNOS expression and microglial activation. The protective effect of aminoguanidine was maintained for up to 2 weeks. Furthermore, iNOS knockout mice (iNOS-/-) were resistant to KA-induced neuronal death. The present study demonstrates that aminoguanidine attenuates KA-induced neuronal death, whereas L-NAME aggravates neuronal death, in the CA3 region of the hippocampus, suggesting that NOS isoforms play different roles in KA-induced excitotoxicity.

Celecoxib Attenuates Kainic Acid-induced Neuronal Cell Death Through Suppression of Microglial c-Jun N-terminal Kinase Phosphorylation

In the present study, neuroprotective property of celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, and its underlying mechanism were examined in the animal model of kainic acid (KA)-induced excitotoxicity. KA, administered intracerebroventricularly (i.c.v.), induced marked neuronal cell death with concurrent microglial activation and subsequent induction of inducible nitric oxide synthase (iNOS) in the hippocampus. Histopathological analysis demonstrated that celecoxib (100 mg/kg), pre-treated 1 hr before or post-treated 2 hr after KA i.c.v. injection, significantly attenuated KA-induced death of pyramidal neurons in CA3 region. Celecoxib obviously suppressed KA-induced microglial activation and subsequent iNOS expression. KA- induced phosphorylation of c-Jun N-terminal kinases (JNK) was attenuated with celecoxib treatments. The results of the present study demonstrate that suppression of JNK phosphorylation by celecoxib contributes to its neuroprotective action against KA-induced excitotoxicity suggesting that celecoxib may be a potentially valuable in the treatment of acute brain pathologies associated with excitotoxic neuronal damage such as epilepsy, stroke, and traumatic brain injury.

Melatonin Induces Akt Phosphorylation through Melatonin Receptor- and PI3K-Dependent Pathways in Primary Astrocytes

Melatonin has been reported to protect neurons from a variety of neurotoxicity. However, the underlying mechanism by which melatonin exerts its neuroprotective property has not yet been clearly understood. We previously demonstrated that melatonin protected kainic acid-induced neuronal cell death in mouse hippocampus, accompanied by sustained activation of Akt, a critical mediator of neuronal survival. To further elucidate the neuroprotective action of melatonin, we examined in the present study the causal mechanism how Akt signaling pathway is regulated by melatonin in a rat primary astrocyte culture model. Melatonin resulted in increased astrocytic Akt phosphorylation, which was significantly decreased with wortmannin, a specific inhibitor of PI3K, suggesting that activation of Akt by melatonin is mediated through the PI3K-Akt signaling pathway. Furthermore, increased Akt activation was also significantly decreased with luzindole, a non-selective melatonin receptor antagonist. As downstream signaling pathway of Akt activation, increased levels of CREB phoshorylation and GDNF expression were observed, which were also attenuated with wortmannin and luzindole. These results strongly suggest that melatonin exerts its neuroprotective property in astrocytes through the activation of plasma membrane receptors and then PI3K-Akt signaling pathway.