Regulation Of Ghrelin Pathway In Arcuate Nucleus-Hippocampus On Gastric Distraction Afferent Information And Gastric Motility

Objective:To investigate the effects of ghrelin on the discharge of gastric distention sensitive neurons in the hippocampus and the gastric motility.Methods: The expression of GHSR-1a in the hippocampus was observed by PCR,western-blotting and immunofluorescence histochemical staining.The projection of ghrelin neurons in the arcuate nucleus(Arc)to the hippocampal CA1 region was observed by retrograde tracing and fluorescence immunohistochemical staining.Single cell external discharge recording combined with electrical stimulation of Arc was used to observe the effects of ghrelin,[d-lys-3]-GHRP-6 on the activity of neurons in hippocampal CA1 region,and the regulation of Arc-ghrelin pathway on gastric afferent information.The effects of microinjection of ghrelin into hippocampus CA1 on gastric motility in rats were observed by using in vivo gastric motility recording method.To observe the regulation and potential mechanism of Arc-hippocampal ghrelin pathway on gastric motility combined with electrical stimulation of the Arc and injection of [d-lys-3]-GHRP-6 into CA1 of the hippocampus.Results: Microinjection of ghrelin into hippocampus,the frequency of 58 neurons(61.05%)increased in 95 gastric distention excitatory(GD-E)neurons showing excitatory effect,and the discharge frequency of 22 neurons decreased showing inhibitory effect.There are 15 neurons no response.In 51 gastric distention inhibitory(GD-I)neurons,the firing of 50.98% neurons(26/51)increased,the firing of 14 neurons decreased,and 11 neurons did not respond.If ghrelin receptor antagonist [d-Lys-3]-GHRP-6 is injected into the hippocampal CA1 region,the stimulatory effect of ghrelin(P<0.05)can be completely blocked.It is suggested that ghrelin is involved in the regulation of gastric afferent information,and this effect may be achieved by the ghrelin 1A receptor.Electrical stimulation of Arc activates most of the gastric distention sensitive neurons in the hippocampal CA1 region.There are 58 GD-E neurons in hippocampal CA1,and electrical stimulation of Arc 38 neurons(38/58,65.52%)showed a significant increase in firing rate,the frequency of 12 GD-E neurons reduced,and 8 neurons no response.After electrical stimulation of Arc,the discharge of 18 neurons(69.23%)increased,the discharge of 3 neurons decreased,and the 5 neurons did not respond in the 26 GD-I neurons.Pre-injection of ghrelin receptor antagonist [D-Lys-3]-GHRP-6 in hippocampal CA1 region,then electrical stimulation of Arc,the discharge of gastric distention sensing neurons in CA1 region of hippocampus was significantly decreased by electrical stimulation of Arc compared with the control group injected in hippocampal CA1 area of NS(P<0.05).In vivo gastric motility results showed that hippocampal microinjection of ghrelin,gastric motility of rats was significantly enhanced.The amplitude of contraction was significantly increased,the frequency of contraction was significantly increased,and there was dose dependent relationship(P<0.05~0.01).However this effect can be blocked by [d-Lys-3]-GHRP-6 injection in the hippocampal CA1 region.PCR,Western blot and immunofluorescence histochemical staining showed that there were expressions of GHSR-1a m RNA and immunoreactive cells in hippocampus.Fluorescent gold(FG)retrograde tracing combined with fluorescence immunohistochemical staining revealed that ghrelin/FG double labeled neurons were present in the hippocampal CA1 region,suggesting that ghrelin neurons in the hippocampus CA1 region fibers projecting to Arc.Conclusion: There is a ghrelin nerve and functional pathway in the hippocampal CA1-Arc.The pathway involved in gastric mechanical distraction afferent information and gastric motility regulation,and this regulatory effect may be achieved via the ghrelin receptor signaling pathway.