Interleukin-6: Its role and mechanisms in rescuing depression-like behaviors in rat models of depression.

Neuronal injury within specific brain regions is considered a critical risk factor in the pathophysiology of depression. However, the underlying mechanisms of this process, and thus the potential for development of novel therapeutic strategies in the treatment of depression, remain largely unknown. Here, we report that Il-6 protects against neuronal anomalies related with depression, in part, by suppressing oxidative stress and consequent autophagic and apoptotic hyperactivity. Specifically, we show that IL-6 is downregulated within the CA1 hippocampus in two animal models of depression and upregulated by antidepressants. Increasing levels of IL-6 in the CA1 region result in pleiotropic protective actions including reductions in oxidative stress and modulation of autophagy, anti-immuno-inflammatory activation and anti-apoptotic effects in CA1 neurons, all of which are associated with the rescue of depression-like behaviors. In contrast, IL-6 downregulation exacerbates neuronal anomalies within the CA1 region and facilitates the genesis of depression phenotypes in rats. Interestingly, in addition to attenuating oxidative damage, the antioxidant, N-acetylcysteine (NAC), is also associated with significantly decreased neuronal deficits and the display of depressive behaviors in rats. These results suggest that IL-6 may exert neuroprotection within CA1 neurons via pleiotropic mechanisms and may serve as a potential therapeutic target for the treatment of depression.

2R,4R-APDC, a Metabotropic Glutamate Receptor Agonist, Reduced Neuronal Apoptosis by Upregulating MicroRNA-128 in a Rat Model After Seizures.

This study aimed to study the protective effect of (2R,4R)-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC), a selective metabotropic glutamate receptor agonist, against hippocampal neuronal apoptosis induced by seizures in a rat model of pilocarpine-induced epilepsy. The Morris water maze test was used to assess the spatial memory abilities of epileptic rats with or without 2R,4R-APDC treatment. TUNEL assay was performed to examine neuronal apoptosis in hippocampus. Western blot was conducted to evaluate changes in the levels of caspase-3 and caspase-9 in hippocampus. Real-time PCR was used to determine the levels of microRNA-128 (miR-128) in hippocampus. The results of the Morris water maze test showed that the 2R,4R-APDC treatment reduced the escape latencies and swimming lengths of rats after seizures. The TUNEL assay showed that 2R,4R-APDC significantly counteracted seizure-induced cell apoptosis. The western blot confirmed this finding, demonstrating that the levels of cleaved caspase-3 and cleaved caspase-9 were potently decreased by 2R,4R-APDC in rat hippocampus after seizures. In addition, 2R,4R-APDC upregulated miR-128 expression levels in the hippocampus. A miR-128 mimic or inhibitor decreased or increased the percentage of TUNEL-positive cells in rats after seizures and 2R,4R-APDC treatment, respectively. The levels of both cleaved caspase-3 and cleaved caspase-9 were decreased in hippocampus exposed to the miR-128 mimic, whereas they were markedly increased in miR-128 inhibitor-treated hippocampus. In conclusion, 2R,4R-APDC protected hippocampal cells from cell apoptosis after seizures, possibly by upregulating miR-128.

COX-2 inhibition rescues depression-like behaviors via suppressing glial activation, oxidative stress and neuronal apoptosis in rats.

Depression is considered a neuropsychiatric condition which is associated with neuronal injury within specific brain regions. We previously reported that cyclo-oxygenase (COX)-2, a rate-limiting enzyme for prostaglandin E2 (PGE2) synthesis, significantly enhanced depressive-like disorders induced by chronic stress in rats. However, the underlying molecular mechanisms and identification of potential therapeutic targets for preventing neuronal injury associated with depression remain largely uncharacterized. Here, we show that COX-2 inhibition by celecoxib protects against neuronal injury through suppression of oxidative stress and, in this way, mediates its antidepressant effects. COX-2 is highly expressed in the hippocampal dentate gyrus (DG) of rat depression model and its activity is responsible for depression-like behaviors as demonstrated in two independent rat models of depression. Inhibition of COX-2 exerts neuroprotective actions in DG regions, including suppressing neuroinflammatory response, against oxidative stress and neuronal apoptosis, which are the critical risk factors for neuronal injury and pathophysiology of depression. Moreover, the antioxidant, N-acetylcysteine (NAC), significantly attenuates oxidative stress levels and dendritic spine deficiencies resulting from COX-2 overexpression; and, suppression of oxidative stress by NAC also significantly ameliorates depressive behaviors in rats. These findings suggest that selective inhibition of COX-2 ameliorates depression-like behaviors in rat models of depression. This selective inhibition of COX-2 appears to be protective against oxidative stress and neuronal deterioration resulting from chronic stress. Taken together, these findings have potentially important clinical implications with regard to the development of novel therapeutic approaches in the treatment of neuropsychiatric conditions like depression.

2R, 4R-APDC decreases cell proliferation in the dentate gyrus of adult rats: the effect of 2R, 4R-APDC on cell proliferation.

This study investigated the effects of group II metabotropic glutamate receptor agonist, 2R, 4R-4-aminopyrrolidine-2,4-dicarboxylate (2R, 4R-APDC), on cell proliferation in the dentate gyrus of adult rats. 2R, 4R-APDC at a dose of 1 and 10 nmol/day resulted in decreased bromodeoxyuridine immunoreactive cells in the dentate gyrus. In addition, we found that APDC treatment had no effect on the number of BrdU+ and GFAP(+)-labeled cells or BrdU+ and NeuN(+)-labeled cells compared with controls. These data suggest that group II metabotropic glutamate receptor is an important site for glutamate's regulation on cell proliferation in the dentate gyrus, but 2R, 4R-APDC had no effects on newborn cell's ability to differentiate into neurons or astrocytes.

Effects of the group II mGlu receptor agonist 2R,4R-APDC on dentate gyrus cell proliferation in the adult rat brain after diffuse brain injury.

OBJECTIVES: Diffuse brain injury (DBI) has been shown to increase the proliferation of granule cell precursors in the adult dentate gyrus (DG). However, the mechanism by which DBI-induced cell proliferation in the DG may enhance seizure susceptibility remains largely unknown. MATERIALS AND METHODS: Using bromodeoxyuridine (BrdU) immunohistochemistry, we examined the effects of group II metabotropic glutamate receptor (mGluR) agonist, 2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (2R,4R-APDC), on cell proliferation in the DG after DBI. RESULTS: It has been found that 2R,4R-APDC significantly blocked DBI-induced increase in the number of BrdU-positive cells in the DG, especially in hilus. In addition, double-label immunofluorescence staining showed that treatment with APDC did not affect the differentiation of newborn cells into neurons or astrocytes. Taken together, our findings indicate that the activation of mGluR system may inhibit the DBI-induced cell proliferation in the DG, but not the differentiation of newborn cells. DISCUSSION: It is suggested that 2R,4R-APDC has potential neuroprotection via inhibiting the aberrant neurogenesis induced by DBI, which is an important pathological basis of seizure or other abnormalities following DBI.