Effect Of LHA-PVN Orexin-A Pathway On Gastric Motility And Gastric Acid Secretion In Rats And Its Regulation

Objective: Orexin A is one of the important brain-gut peptides secreted by the hypothalamus involved in feeding.The aim of this study is to investigate the effects of orexin A pathway on gastric motility and gastric acid secretion between the lateral hypothalamic(LHA)and paraventricular nucleus(PVN)and its underlying mechanisms.Methods: Healthy male Wistar rats were used,280-300 g.Using fluorescent gold retrograde tracing technique,the neuronal pathway between LHA and PVN was observed;Single neuron extracellular discharge recording was performed to observe the effect of orexin-A on the discharge activity of melanin-concentratinghormone(MCH)excitatory gastric distension(GD)neurons in PVN of hypothalamus;Electrical stimulation of LHA to observe the changes of firing frequency of orexin-A/MCH excitatory GD neurons in PVN and its effect on gastric motility;Recording of gastric motility was used to observe the effects of orexin-A microinjection of PVN on gastric motility,gastric acid secretion and gastric emptying in rats.Results:(1)Extracellular discharge study showed that microinjection of MCH in PVN significantly increased the discharge frequency of rat GD neurons(P<0.05).Microinjection of orexin-A in PVN significantly increased the frequency of MCH-excited/GD-responsive in rat(P<0.05).Pretreatment of MCH receptor antagonist ATC-0065 into the PVN could partially block the effect of orexin-A on the firing frequency of MCH-excited/GD-responsive neurons(P<0.05).Injection of ATC-0065 alone had no significant effect on the discharge of GD neurons(P>0.05).It suggests that orexin-A can promote the change of discharge frequency of MCH-excited/GD-responsive neurons in PVN,and MCH signaling pathway participates in the regulation of orexin-A on the firing frequency of GD neurons.(2)Electrical stimulation of LHA significantly increased the firing frequency of orexin-A/MCH excitatory GD neurons in PVN(P<0.05).Microinjection of orexin-A receptor antagonist SB334867 into PVN could partially block the stimulation of LHA on the firing frequency of GD neurons in PVN.It suggests that LHA can regulate the firing activity of orexin-A/MCH excitatory GD neurons in PVN.(3)Fluorescent retrograde tracing combined with fluorescent immunohistochemical staining showed that neurons labeled with orexin-A and fluorescent gold were visible in LHA.It suggests that some of the orexin-A immunopositive neurons in LHA can send nerve fibers to PVN.(4)Microinjection of orexin-A into PVN significantly increased the amplitude and frequency of gastric movement in rats(P<0.05),and reached a maximum in 10-15 min;PVN microinjection of orexin-A and ATC-0065 mixture,the promoting effect of orexin-A on gastric motility was partially inhibited(P<0.05).However,when PVN was injected with ATC-0065 or saline alone,there was no significant change in gastric motility(P>0.05).It suggests that the promoting effect of orexin-A on gastric motility may be partly mediated by MCH signaling pathway.(5)Pretreatment of SB334867 into the PVN followed by electrical stimulation of LHA,and the stimulation of LHA on gastric motility was inhibited(P<0.05),suggesting that the LHA-PVN orexin-A pathway is involved in the regulation of gastric motility.(6)After microinjection of orexin-A into PVN,rats’ gastric emptying increased rapidly and gastric acid secretion increased(P<0.05).Pretreatment of ATC-0065 can partially block the promoting effect of orexin-A on gastric emptying and gastric acid secretion(P<0.05).It suggests that orexin-A regulates gastric emptying and gastric acid secretion through the MCH pathway.Conclusion: This study found that PVN orexin-A can regulate the discharge activity of GD neurons through the MCH pathway and regulate gastric function.LHA contains orexin-A neurons that project to the PVN.It is speculated that LHA may be involved in the regulation of gastric function through orexin-A pathway.