1. The Role And Mechanism Of N-acetylaspartate In The Central Amygdala In The Prevention Of Water Immersion Restraint-induced Gastric Ulcers In Rats With Monoamine Antidepressants 2. Adolescent Nicotine Exposure Is Susceptible To Stress-induced Depression

1.Effect and Mechanism of N-acetylaspartate in Central Amygdala in Preventing Water Immersion Restraint Induced Gastric Ulcer in Rats with Monoamine-based AntidepressantsStress shows both short-and long-term effects on the functions of the gastrointestinal tract,which ultimately leading to the development of a broad array of gastrointestinal disorders including inflammatory bowel disease(IBD),irritable bowel syndrome(IBS)and other functional gastrointestinal diseases.Among them,gastric ulcer is a common disease with many complications and recurrence easily.Serious complications such as gastric bleeding,ulcer perforation,and pyloric obstruction can be observed in patients get gastric ulcer.Previous studies have shown that the antidepressant duloxetine can protect rat gastric mucosal damage caused by water immersion restraint stress.The central nucleus of amygdala(CeA)plays a central role in physiologic and behavioral responses to fearful stimuli,stressful stimuli,and drug-related stimuli.The relationship between N-Acetyl aspartate(NAA)/creatine(Cr)ratio in the CeA and severity of gastric ulcer induced by WIRS and protective effect of duloxetine was determined in preliminary studies by proton magnetic resonance spectroscopy(,H-MRS).The results showed that the basic value of NAA/Cr is irrelevant with stress-induced gastric ulcer index,while duloxetine hydrochloride can significantly reduce the NAA/Cr ratio in CeA after 6h WIRS stress.Moreover,the ulcer index was negatively correlated with reduced NAA/Cr in CeA for all rats.Intra-CeA injection with NAA exacerbated the gastric mucosal damage caused by WIRS.The results indicated that changing the NAA/Cr content in CeA may be the mechanism by which duloxetine exerts the protective effect on gastric u.lcer.However,the mechanism by which duloxetine regulates the NAA content in CeA is still unknown.NAA is an enigmatic molecule present at exceptionally high concentrations in the brain.NAA is synthesized from aspartate and acetyl-coenzyme A in neurons by L-aspartate N-acetyltransferase(Asp-NAT).Aspartoacylase(ASPA)located in oligodendrocytes can degrade NAA into acetic acid and aspartic acid.N-acetylaspartylglutamate(NAAG)is synthesized from NAA and glutamate under the catalyzation of NAAG synthetase I(NAAGSI).Glutamate carboxypeptidase Ⅱ(GCP Ⅱ)and GCP Ⅲ located on the astrocyte membrane can hydrolyzed NAAG into NAA and glutamate.Considering the preventive protective effect of duloxetine hydrochloride on gastric ulcer injury induced by WIRS,we used Western blotting to detect the expression of five enzymes related to NAA metabolism in CeA at different time points during WIRS stress.The results showed that 0.5-h WIRS significantly reduced the expression of ASPA in CeA,suggesting that NAA content increased at this time.However,Nat81 and GCP Ⅱ in CeA decreased significantly after 3-h WIRS,suggesting the reduced NAA synthesis at this time due to the feedback effect.After 6-h WIRS,the NAAGSI in CeA had a significant increase,and the dynamic process of NAA metabolism finally maintain the NAA content in CeA.Prophylactic administration of 20 mg/kg duloxetine hydrochloride reversed the decrease in ASPA caused by 0.5-h WIRS.After 3-h WIRS,the NAAGSI in CeA increased significantly and this effect could last up for 6 hours,further reducing NAA content in CeA.Overexpression of ASPA in CeA reduces the damage of gastric mucosa induced by WIRS.We further tested the preventive protective effect other monoamine antidepressants,including amitriptyline(tricyclic agents,TCAs),moclobemide(monoamine oxidase inhibitors,MAOs)and fluoxetine(Selective 5-HT reuptake inhibitors,SSRIs)on WIRSinduced gastric ulcer on the expression of the above five enzymes in CeA,in order to explore the common molecular mechanisms of preventive protective effect of monoamine antidepressants on reducing the susceptibility of gastric ulcer injury induced by stress.The results show that the above three monoamine antidepressants can all reverse the decrease of ASPA in CeA induced by 0.5-h WIRS.In summary,ASPA in CeA may be a key mechanism for monoamine antidepressants to reduce the susceptibility to WIRS-induced gastric ulcer injury.Its increase reverses the increase in NAA in CeA caused by stress at the initial phase and makes the process of NAA decomposition and transformation in advance,reducing the damage caused by WIRS.2.Effect of Nicotine Exposure in puberty on the Susceptibility to Stress-induced Depression-like Behaviors in AdulthoodIn the past decades,the association between smoking and depression has been well documented in the literature.Smokers usually start smoking from adolescence or childhood.Among those who smoked from adolescence,the lifetime prevalence of major depression disorder(MDD)was significantly higher than those who never smoked,and among smokers,those with a lifetime history of MDD were less likely to have successfully quit smoking than those without a history of MDD.To explore when and how the relationship between smoking and depression was established,rats and mice were exposed to nicotine for 15 consecutive days in early adolescence(From postnatal day 30,PND 30)or late adolescence(From PND 50).In adulthood(PND 80),rats were subjected to chronic unpredictable mild stress(CUMS),and their depression-like behaviors were assessed by forced swimming and sucrose preference tests.The mice were tested for their social interaction ratio after sub-threshold social defeat stress.We found that in the rat and mouse models,nicotine exposure both in early and late adolescence increases the susceptibility to stress-induced depression-like behaviors in adulthood.The content of neurometabolites in specific brain regions of adult rats was measured by Proton magnetic resonance spectroscopy(1H-MRS).The results of 1H-MRS showed that both early and late adolescence nicotine exposure will increase the glx/Cr content in NAcR in adulthood,and the glx/Cr content in NAcR is positively correlated with immobility time after stress,which means with higher basic content of glx/Cr,rats would be more susceptible to stress-induced depression-like behaviors.This result indicates that the effects of nicotine exposure in adolescence on neurometabolites can continue into adulthood,and the change of the glutamate system in NAc may affect the susceptibility to stress-induced depression-like behavior.Western blot results showed that the level of mGluR2 in NAcR was significantly upregulated in mice exposed to nicotine during adolescence.Intra-NAcR infusion of mGluR2/3 agonist LY379278 followed by sub-threshold stress significantly reduced the social interaction ratio and increased immobility of mice,suggesting that mGluR2 in NAcR may mediate the stress-induced depression-like behavior.In summary,this study explored the effects of nicotine exposure in rats and mice in early and late adolescence on the susceptibility of stress-induced depression-like behaviors in adulthood.The result shows that in these two models,nicotine exposure in either early or late adolescence increases the susceptibility to stress-induced depression-like behaviors in adulthood.It suggests that the glx/Cr content in rat NAcR may be a molecular marker for predicting the susceptibility to stress-induced depression-like behavior.In mouse models,the increase in susceptibility is mediated by mGluR2 in NAcR.