| Objective: To observe the effect of Lateral hypothalamic nucleus(LHA)-ventral tegmental area(VTA)Orexin-A pathway on the discharge activity of gastric distension(GD)responsive neurons and gastric emptying in rats.Methods: The expression of Orexin-A receptor(OX-1R)in VTA was detected by fluorescence immunohistochemistry in healthy male Wistar rats.After fluorescent gold(FG)was injected into VTA,the coexistence of Orexin-A/FG in LHA was observed by FG retrograde tracking combined with fluorescence immunohistochemistry.The effect of gastric distension(GD)on the discharge activity of VTA neurons was observed.Rats were given Orexin-A via VTA nuclei,and extracellular discharges of single unit neuron was used to observe the discharge activity of GD responsive neurons in VTA.Phenol red quantitative method was used to determine the gastric emptying in rats.The changes of the discharge activity of GD responsive neurons and the gastric emptying in rats were observed after Orexin-A microinjection in VTA or electrical stimulation of the LHA,and the effect of SB334867 preadministration,an antagonist of Orexin-A receptor,was observed in VTA.Results:(1)The results of fluorescence immunohistochemical staining showed that Orexin-A receptor immunoreactive neurons expressed in VTA of rats.(2)FG retrograde tracing combined with fluorescence immunohistochemistry showed that some Orexin-A positive neurons in LHA could emit nerve fibers projecting to VTA.(3)Electrophysiological study showed that,of the 79 neurons recorded in VTA,58 GD-sensitive neurons were recorded in the VTA.Among them,41 showed excitatory effects(GD-E)and 17 showed inhibitory effects(GD-I).(4)Out of the 41 GD-E neurons,the discharge frequency of 28 of 41(28/41,68.29%)was significantly increased significantly from 6.14±1.22 Hz to 9.21±1.43 Hz(P<0.05)and 9 of 41(9/41,21.95%)was declined from 6.87±1.46 Hz to 4.13±1.12 Hz following microinjection of orexin-A into VTA(P<0.05).Out of GD-I neurons,the discharge frequency of 12 of 17(12/17,70.59%)was significantly rised from 6.03 ± 1.42 Hz to 9.22 ± 1.90 Hz(P<0.05)and 4 of 17(4/17,23.53%)was decreased from 6.23 ± 1.01 Hz to 3.12±0.92 Hz(P<0.05).After preadministration of orexin-A receptor antagonist SB334867 into VTA,the effect of Orexin-A on GD sensitive neurons was completely blocked(P>0.05).(5)31 Orexin-A reactived GD-E neurons in VTA were recorded after electrical stimulation of LHA,of which 22(22/31,70.97%)neurons showed further excitatory effects,the frequency of discharge increased from 5.41± 1.98 Hz to 9.55±3.35 Hz(P<0.05),6(6/31,19.35%)neurons discharges were weakened from 6.15±2.06 Hz to 3.49±1.27 Hz(P<0.05);In Orexin-A sensitive GD-I neurons,the discharge frequency of 11(11/17,64.71%)neurons were significantly rised from 5.28±1.28 Hz to 9.65±2.29 Hz,while 4(4/17,29.41%)neurons were significantly reduced from 6.91±1.78 Hz to 4.02±1.06 Hz(P < 0.05).VTA was pre-injected with Orexin-A receptor antagonist SB-334867,and then LHA was electrically stimulated,the increase of GD-sensitive neurons discharge frequency activated by Orexin-A was significantly inhibited(P<0.05).(6)The results of gastric emptying study showed that the gastric emptying of rats was significantly increased by microinjection of Orexin-A in VTA(P < 0.05)and pre-microinjection of SB-334867 into VTA could partly block this effect(P < 0.05).Electrical stimulation of LHA significantly enhanced gastric emptying in rats(P < 0.05).Similarly,SB-334867 was microinjected in VTA and then stimulated LHA,the enhancement of gastric emptying induced by electrical stimulation was significantly reduced(P < 0.05).Conclusion: There is an orexinergic neural pathway from LHA to VTA,which may be involved in the regulation of gastric motility. |
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