The Role Of Stimulating AgRP Neurons Or Inhibiting POMC Neurons Of Arcuate Nucleus In Chronic Unpredictable Stress-induced Depressive-like Behavior

PurposeNeurons producing melanocortin receptor agonist,a-melanocyte-stimulating hormone(MSH)derived from proopiomelanocortin(POMC),and antagonist,agouti-related protein(AgRP),are known to be sensitive to metabolic stress such as food deprivation and glucoprivation.However,how these neurons respond to emotional/psychological stress remained to be elucidated.It is reported that the melanocortinergic pathway is rapidly recruited by acute emotional stress and contributes to stress-induced anorexia and anxiety-like behavior evoking mRNA over expression of c-fos,a neuronal activation marker,in POMC and AgRP neurons of arcuate nucleus.Meanwhile,some studies have demonstrated that chronic unpredictable stress(CUS)induces a cognitive deficit and anxiety-like behavior in rats that is prevented by chronic antidepressant drug treatment.So we want to determine whether the melanocortinergic pathway is associated with neurobiological mechanisms underlying the cognitive and emotional consequences of chronic stress.If it exists,how POMC or AgRP neurons in arcuate nucleus respond to chronic unpredictable stress is the crucial in our study.MethodsThe homozygous AgRP-Ires-cre mice and C57BL mice were intercrossed to generate heterozygous AgRP-Ires-cre mice.The heterozygous AgRP-Ires-cre mice and heterozygous AgRP-Ires-cre mice were intercrossed to generate homozygous AgRP-Ires-cre mice and heterozygous AgRP-Ires-cre mice.The heterozygous POMC cre(Lowell B)mice and C57BL mice were intercrossed to generate heterozygous POMC cre(Lowell B)mice.Using designer receptors exclusively activated by designer drugs(DREADD)technology to provide specific and reversible regulation of neuronal activity in mice,we use cre-dependent,stimulatory DREADD-hM3Dq AAV in the AgRP-Ires-cre mice to Stimulate AgRP neuron,and use cre-dependent,inhibitory DREADD-hM4Di AAV in Pomc-cre(Lowell B)mice to inhibit Pomc neuron.We pretest FUST to divide the mice into two groups(mcherry and hm3d-mcherry or mcherry and hm4d-mcherry)before virus injection.2weeks after virus injection,the mice will be exposed to the 10-day CUS.We perform FUST to test whether the CUS model is successful on day 11.Next,we do the FUST with clozapine-N-oxide(CNO)injection on day 12.We perform sucrose preference test with CNO injection on day 13.We do the forced swimming test on day 14.The last we perform locomotor activity with CNO injection on day 15.ResultsIn the assessment of depression-like behavior experiment,we found that the baseline of female urine sniff time in female urine sniffing test after CUS was significantly decreasesd than female urine sniffing test before virus injection(P<0.05).The result suggests that the model was successful.We found that hm3d-mcherry group in female urine sniffing test after CNO injection was higher than mcherry group,there was no significant difference between mcherry and hm3d-mcherry groups in female urine sniffing test after CNO injection,but the baseline of female urine sniff time was increased than female urine sniffing test after CUS.In the mcherry group,the mice after CNO injection had higher tendency in female urine sniffing time than the mice before CNO injection using paired t-test.However,in the hm3d-mcherry group,the mice after CNO injection was significant increased the female urine sniff time than the mice before CNO injection(P<0.05).The results were similar as mcherry and hm4d-mcherry groups.In sucrose preference test(SPT),there was no difference between hm3d-mcherry group and mcherry group in 12 hours and 14 hours(P>0.05).There was no difference between mcherry and hm3d-mcherry groups in forced swimming test(FST)and locomotor activity after CNO injection(P>0.05).There was also no difference between mcherry and hm4d-mcherry groups in sucrose preference test,forced swimming test and locomotor activity after CNO injection(P>0.05).ConclusionBy the above results,it suggested that stimulating AgRP neurons or inhibiting Pomc neurons in arcuate nucleus reverse chronic unpredictable stress-induced depressive-like behavior in mice.