Effects Of Hypothalamic Paraventricular Nucleus GLP-1 On Feeding And Gastric Motility In Rats And Its Potential Mechanism

Objective: Glucagon-like peptide-1(GLP-1)is one of the common anorexic neuropeptides,and GLP-1 receptors are widely distributed in the central nervous system.The hypothalamus is mainly involved in the regulation of food intake and satiety.Paraventricular nucleus(PVN),lateral hypothalamic area(LHA)and arcuate nucleus(ARC)are all distributed in the hypothalamus.The ventromedial hypothalamic nucleus(VMH),which is similar to PVN,is also one of the important nuclei in the hypothalamus involved in the inhibition of feeding.VMH plays a key role in regulating feeding behavior and satiety,and has a large number of neurons that express and secrete GLP-1.However,there is no report on the effects of GLP-1 on the feeding and gastric function in PVN and the mechanism of VMH on the gastric function or feeding regulation of PVN GLP-1ergic neurons.Therefore,this study aims to explore the effects of endogenous and exogenous GLP-1 on feeding,gastric motility and gastric emptying in rats,and to observe whether there is a GLP-1 nerve pathway between VMH-PVN and whether this pathway is involved in feeding and functional regulation.Methods: 1.Nucleus intubation method was used to intubate PVN or VMH according to rat brain atlas.2.The effects of microinjection of GLP-1 or GLP-1R antagonist Exendin 9-39(Ex9)into the nucleus of PVN on food intake,gastric motility and gastric emptying rate in rats were observed by feeding analysis,in vivo gastric motility recording and gastric emptying.3.The structure of VMH-PVN GLP-1 nerve pathway was observed by fluorescence gold retrograde tracing combined with fluorescence immunohistochemistry.4.The effects of 50?A electric stimulation on the intake,gastric motility and gastric emptying rate of VMH nuclei in rats were observed.VMH was stimulated by PVN after Ex9 injection.The effects of VMH on food intake,gastric motility and gastric emptying rate in rats were observed.VMH stimulation after.PVN was injected.Results:(1)The effect of microinjection of GLP-1 into PVN on the intake of rats showed that compared with NS group,the intake of GLP-1(10 pmol)by microinjection of PVN decreased significantly in 0-2 h(P < 0.05),but the cumulative intake of 0-4 h or 0-6 h did not change significantly(P > 0.05).Compared with GLP-1 group,microinjection of GLP-1+Ex9 mixture with PVN significantly increased the feeding intake of rats in 0-2 hours(P < 0.05),and the effect of GLP-1 on feeding inhibition disappeared.After microinjection of Ex9 into PVN,the cumulative intake of Ex9 did not change significantly(P > 0.05)at 0-2 h,0-4 h or 0-6 H.(2)The effect of microinjection of GLP-1 with PVN on gastric motility in rats showed that,compared with NS group,the gastric motility amplitude(P < 0.01)and frequency(P < 0.01)of rats began to decrease significantly after microinjection of GLP-1 with PVN for about 10 minutes,and continued to decrease for about 15 min.Compared with GLP-1 group,intravenous injection of GLP-1 receptor antagonist Ex9 + GLP-1 mixture in PVN significantly increased gastric contraction amplitude(P < 0.01)and contraction frequency(P < 0.01).However,there was no significant change in the amplitude or frequency of gastric motility(P > 0.05)after PVN was injected with Ex9 alone.(3)The effect of microinjection of GLP-1 with PVN on gastric emptying in rats showed that compared with NS group,microinjection of GLP-1 with PVN could significantly reduce gastric emptying rate in rats(P < 0.05).Compared with GLP-1 group,the gastric emptying rate of rats was significantly increased by microinjection of GLP-1 receptor antagonist Ex9 + GLP-1 into PVN(P < 0.05).When PVN was injected with Ex9 alone,there was no significant change in gastric emptying rate(P > 0.05).(4)Fluorescent gold retrograde tracing combined with immunohistochemical study showed that FG labeled neurons in VMH could be seen under fluorescence microscope 7 days after injection of 0.2 u L 3% fluorescent gold(FG)into rat.GLP-1 immunopositive neurons could be seen in the same section by immunofluorescence histochemical staining.Under the microscope,some GLP-1 immunopositive neurons coexisted with FG.The results suggest that some GLP-1 immunoreactive neurons in VMH emit nerve fibers that can be projected to PVN.(5)The effect of microinjection of GLP-1 into PVN before VMH stimulation showed that 50 A electric stimulation of VMH significantly reduced the intake of rats by 0-2 h(P < 0.05),0-4 h(P < 0.05)and 0-6 h(P < 0.05)compared with the sham electric stimulation group.When Ex9 was pre-injected into PVN,VMH was subsequently stimulated.Compared with VMH + NSPVN group,the intake of 0-2 h(P < 0.05),0-4 h(P < 0.05)and 0-6 h(P < 0.05)increased significantly.(6)The effect of microinjection of GLP-1 into PVN before VMH stimulation on gastric motility in rats showed that the gastric contraction amplitude(P<0.05)and frequency(P<0.05)decreased significantly after VMH stimulation for 3 min,and reached the lowest point about 18 min(amplitude)or 13 min(frequency)after VMH stimulation.Compared with the VMH + NSPVN group,the gastric contraction amplitude(P < 0.05)and frequency(P < 0.05)of the rats were significantly increased when GLP-1 receptor antagonist Ex9 was injected into the PVN before stimulating VMH.(7)The effect of microinjection of GLP-1 into PVN on gastric emptying in rats after VMH stimulation showed that compared with the sham-electric stimulation group,electrical stimulation of VMH could significantly reduce the gastric emptying rate(P < 0.05),but compared with the VMH + NS PVN group,the effect of electrical stimulation of VMH induced by pre-injection of Ex9 into PVN disappeared(P < 0.05).Conclusion: The exogenous GLP-1 of PVN participates in the negative regulation of feeding,gastric motility and gastric emptying in rats.There is a GLP-1 nerve pathway in VMH-PVN,which may be involved in the control of feeding,gastric motility and gastric emptying in rats.