Effects Of Orexin On Acute High Fat Diet Consumption Induced Activation Of LHA-VTA Pathway

Objective:Orexin,a neuropeptide found in the hypothalamus,is involved in many physiological functions such as energy metabolism,sleep,wakefulness,and feeding.The purpose of this study was to investigate the role of orexin in the activation of the lateral hypothalamus(LHA)-hypothalamus ventral tegmental area(VTA)pathway in high-fat diet and its underlying mechanism.Methods:Adult male C57BL6/J mice,20-30 g.They were divided into regular chow(RC)group,high fat diet(HFD)group and high fat diet control group.Regular chow(carbohydrates 28.8%,protein 25.5%,fat 3.6%,fiber 27.4%,minerals 8.1%,humidity 6.7%;energy: 2.5 kcal/g);high fat diet group(carbohydrates 22.5%,protein 22.8%,fat 21.1%,fiber 23%,minerals 5.6%,humidity 5%;energy: 3.9 kcal/g);In order to distinguish potential effects of HFD itself and those of higher food intake,a pair-fed controlgroup consisting of mice exposed to amounts of HFD similar tothose eaten by mice exposed to RC was included.The effect of high-fat diet on 2h mice food intake and calorie intake were observed;Fluorogold retrograde tracing combined with fluorescence immunohistochemistry method was used to observ LHA-VTA orexin neural pathway;Immunohistochemistry and intraperitoneal injection of OX1 R receptor antagonist SB334867 were used to observe the influence of high fat diet on the expression of c-fos and orexin of VTA and LHA in mice;To investigate the role and potential mechanism of orexin in the activation of LHA-VTA pathway in high-fat diet.Results:(1)Compared with the regular chow group,2h food intake of high-fat diet mice increased significantly(P<0.05),2h calorie intake increased significantly(P<0.05),but 2h food intake of high-fat diet control group had no significant change(P>0.05).It suggests that high-fat diet can induce food intake in mice.(2)Fluorogold retrograde tracing combined with fluorescence immunohistochemistry assay showed that VTA injection of fluorescent gold in 7 days,In LHA,neurons with fluorescent gold labeling were observed,and orexin immunofluorescence staining was used to study the expression of orexin positive cells in LHA partially labeled fluorescent gold.It is suggested that some orexin neurons in LHA may send fibers to VTA.(3)Acute high-fat diet significantly increased the expression of c-fos in VTA(P<0.05)in mice,but there was no significant change in c-fos expression in LHA(P>0.05).It suggests that high-fat diet can activate midbrain limbic system neurons.(4)Acute high-fat diet significantly increased the proportion of orexin neurons expressing c-fos in mice LHA(P<0.05),suggesting that high fat diet can activate orexin neurons in LHA.(5)Intraperitoneal injection of OX1 R antagonist SB334867 significantly reduced the expression of c-fos in VTA of mice fed with high fat diet(P<0.05),but there was no significant change in c-fos expression in LHA(P>0.05).It is suggested that orexin signaling can regulate the activation of VTA neurons induced by high-fat diet.Conclusion:LHA-VTA has a orexin neural pathway;The increased food intake of mice induced by high-fat diet may be related to the activation of neurons in the mesolimbic system;the LHA-VTA orexin signaling pathway is involved in the regulation of feeding induced by high fat diet.