siRNA-mediated GABAB receptor at early fetal rat brain upon acute and chronic ethanol exposure: Down regulation of PKA and p-CREB expression

Binge-like Prenatal Ethanol Exposure Causes Impaired Cellular Differentiation in the Embryonic Forebrain and Synaptic and Behavioral Defects in Adult Mice

An embryo’s in-utero exposure to ethanol due to a mother’s alcohol drinking results in a range of deficits in the child that are collectively termed fetal alcohol spectrum disorders (FASDs). Prenatal ethanol exposure is one of the leading causes of preventable intellectual disability. Its neurobehavioral underpinnings warrant systematic research. We investigated the immediate effects on embryos of acute prenatal ethanol exposure during gestational days (GDs) and the influence of such exposure on persistent neurobehavioral deficits in adult offspring. We administered pregnant C57BL/6J mice with ethanol (1.75 g/kg) (GDE) or saline (GDS) intraperitoneally (i.p.) at 0 h and again at 2 h intervals on GD 8 and GD 12. Subsequently, we assessed apoptosis, differentiation, and signaling events in embryo forebrains (E13.5; GD13.5). Long-lasting effects of GDE were evaluated via a behavioral test battery. We also determined the long-term potentiation and synaptic plasticity-related protein expression in adult hippocampal tissue. GDE caused apoptosis, inhibited differentiation, and reduced pERK and pCREB signaling and the expression of transcription factors Pax6 and Lhx2. GDE caused persistent spatial and social investigation memory deficits compared with saline controls, regardless of sex. Interestingly, GDE adult mice exhibited enhanced repetitive and anxiety-like behavior, irrespective of sex. GDE reduced synaptic plasticity-related protein expression and caused hippocampal synaptic plasticity (LTP and LTD) deficits in adult offspring. These findings demonstrate that binge-like ethanol exposure at the GD8 and GD12 developmental stages causes defects in pERK–pCREB signaling and reduces the expression of Pax6 and Lhx2, leading to impaired cellular differentiation during the embryonic stage. In the adult stage, binge-like ethanol exposure caused persistent synaptic and behavioral abnormalities in adult mice. Furthermore, the findings suggest that combining ethanol exposure at two sensitive stages (GD8 and GD12) causes deficits in synaptic plasticity-associated proteins (Arc, Egr1, Fgf1, GluR1, and GluN1), leading to persistent FASD-like neurobehavioral deficits in mice.

The Modulatory Effect of Metformin on Ethanol-Induced Anxiety, Redox Imbalance, and Extracellular Matrix Levels in the Brains of Wistar Rats

The study investigated the potential neuroprotective effects of metformin (MET) on alcohol-induced neurotoxicity in adult Wistar rats. The animals were randomized in four groups (n = 10): control, alcohol (ALC), ALC + MET, and MET. ALC (2 g/kg b.w.) and MET (200 mg/kg b.w.) were orally administered for 21 days, once daily. For the ALC + MET group, MET was administered 2 h after ALC treatment. On day 22, the open field test (OFT) and elevated plus maze (EPM) were performed. MET improved global activity and increased the time spent in unprotected open arms, decreased oxidative stress, both in the frontal lobe and in the hippocampus, and increased neuroglobin expression in the frontal cortex. Histopathologically, an increased neurosecretory activity in the frontal cortex in the ALC + MET group was noticed. Thus, our findings suggest that metformin has antioxidant and anxiolytic effects and may partially reverse the neurotoxic effects induced by ethanol.

Dexmedetomidine protects rats from postoperative cognitive dysfunction via regulating the GABAB R-mediated cAMP-PKA-CREB signaling pathway

This work attempts to discuss whether dexmedetomidine (Dex) can protect rats from postoperative cognitive dysfunction (POCD) through regulating the γ-aminobutyric acid-_B receptor (GABA_B R)-mediated cyclic adenosine monophosphate (cAMP) - protein kinase A (PKA) - cAMP-response element binding (cAMP-PKA-CREB) signaling pathway. Sprague-Dawley rats were divided into a non-surgical group (Control), a surgical group (Model), a surgical group treated with Dex (Model + Dex), a surgical group treated with GABA_B R antagonist (Model + CGP 35348) and a surgical group treated with Dex and GABA_B R agonist (Model + Dex + Baclofen). Cognitive and memory functions were evaluated by Y-maze test and open-field test. The neuronal morphology of the hippocampus was observed by hematoxylin and eosin staining and neuronal apoptosis was by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling method. Inflammatory factors and cAMP levels were detected by enzyme-linked immunosorbent assay while expressions of GABA_B R and PKA-CREB pathway-related molecules by Western blot. Compared with control rats, the model rats exhibited reduced alternation rates with a prolonged time spent in the central zone; meanwhile, levels of tumor necrosis factor-α and interleukin-1β and the apoptotic index, as well as GABA_B R1 and GABA_B R2 expressions were increased in the model rats, but the cAMP-PKA-CREB pathway was inhibited (all P < 0.05). When treated with either Dex or CGP 35348, the surgical rats displayed an opposite tendency concerning the above factors as compared to the model rats (all P < 0.05). Furthermore, Baclofen, the agonist of GABA_B R, could reverse the protective effect of Dex against POCD in rats. Dex protects rats from POCD possibly via suppressing GABA_B R to up-regulate the cAMP-PKA-CREB signaling pathway, thereby alleviating the hippocampal inflammation caused by surgical trauma.

Prenatal alcohol exposure inducing the apoptosis of mossy cells in hippocampus of SMS2-/- mice

In order to understand the mechanisms of alcohol-induced neuroapoptosis through the ceramide pathway, sphingomyelin synthase 2 knockout (SMS2-/-) mice were used to make the prenatal alcohol exposure model, and the role of ceramide regulation on alcohol-induced neuroapoptosis was studied in the offspring. Initially the levels of serum sphingomyelin (SM) were detected with enzymatic method in P0 pups after alcohol exposure in parents. Then the apoptosis of mossy cells in the offspring hippocampus was investigated after prenatal alcohol exposure with immunohistochemistry and TUNEL assay. Finally the expression of activated Caspase 8 and activated Caspase 3 in the offspring hippocampus was detected with Western blot analysis. Our results showed that SM levels were down-regulated in a dose-dependent manner (p<0.05) after prenatal alcohol exposure in wild-type (WT) and SMS2-/- pups. However, SM levels of serum in SMS2-/- pups were significantly lower than that in WT pups (p<0.01). Furthermore, we found that mossy cells were very sensitive to alcohol-induced neuroapoptosis. In both WT pups and SMS2-/- pups, the number of apoptotic mossy cells in the hippocampus increased after prenatal alcohol exposure in a dose dependent manner (p<0.05) and decreased with the growing age. Compared with WT pups, the number of apoptotic mossy cells in the hippocampus of SMS2-/- pups increased (p<0.05). Western blotting showed that the expression of activated Caspase 8 and activated Caspase 3 of hippocampal tissue in WT pups and SMS2-/- pups increases after prenatal alcohol exposure, consistent with results from TUNEL assay and immunocytochemistry. Our study suggests that mossy cells may be the easily attacked cells for fetal alcohol spectrum disorder (FASD), and ceramide is involved in the alcohol-induced neural apoptosis. The mechanism probably lies in the accumulated ceramide in SMS2 mice, and the increase of activated Caspase 8 and Caspase 3 promotes alcohol-induced neuroapoptosis.

Ceramide is involved in alcohol-induced neural proliferation

Prenatal alcohol exposure, especially during early pregnancy, can lead to fetal alcohol syndrome. The pharmacological and toxicological mechanisms of ethanol are related to the effects of ceramide. In this study, we established an alcohol exposure model in wild-type mice and in knockout mice for the key enzyme involved in ceramide metabolism, sphingomyelin synthase 2. This model received daily intragastric administration of 25% ethanol, and pups were used at postnatal days 0, 7, 14, 30 for experiments. Serology and immunofluorescence staining found that ethanol exposure dose-dependently reduced blood sphingomyelin levels in two genotypes of pups, and increased neural cell proliferation and the number of new neurons in the hippocampal dentate gyrus. Western blot analysis showed that the relative expression level of protein kinase C α increased in two notypes of pups after ethanol exposure. Compared with wild-type pups, the expression level of the important activator protein of the ceramide/ceramide-1-phosphate pathway, protein kinase C α, was reduced in the hippocampus of sphingomyelin synthase 2 knockouts. Our findings illustrate that ceramide is involved in alcohol-induced neural proliferation in the hippocampal dentate gyrus of pups after prenatal ethanol exposure, and the mechanism may be associated with increased pression of protein kinase C α activating the ceramide/ceramide-1-phosphate pathway.

Overexpression of serum response factor in astrocytes improves neuronal plasticity in a model of early alcohol exposure

Neuronal plasticity deficits underlie many of the cognitive problems seen in fetal alcohol spectrum disorders (FASD). We have developed a ferret model showing that early alcohol exposure leads to a persistent disruption in ocular dominance (OD) plasticity. Recently, we showed that this deficit could be reversed by overexpression of serum response factor (SRF) in the primary visual cortex during the period of monocular deprivation (MD). Surprisingly, this restoration was observed throughout the extent of visual cortex and most of the cells transfected by the virus were positive for the astrocytic marker GFAP rather than the neuronal marker NeuN. Here we test whether overexpression of SRF exclusively in astrocytes is sufficient to restore OD plasticity in alcohol-exposed ferrets. To accomplish that, first we exposed cultured astrocytes to Sindbis viruses carrying either a constitutively active form of SRF (SRF+), a dominant negative (SRF-) or control Green Fluorescent Protein (GFP). After 24h, these astrocytes were implanted in the visual cortex of alcohol-exposed animals or saline controls one day before MD. Optical imaging of intrinsic signals showed that alcohol-exposed animals that were implanted with astrocytes expressing SRF, but not SRF- or GFP, showed robust restoration of OD plasticity in all visual cortex. These findings suggest that overexpression of SRF exclusively in astrocytes can improve neuronal plasticity in FASD.