Distribution Of Dopamine Receptors In The Lateral Hypothalamic Nucleus And Their Potential Role In Gastroparesis Rats With Parkinson’s Disease

BackgroundGastroparesis is a common non-motor system symptom in patients of Parkinson’s disease（PD）,but the mechanism remains unknown.The lession of dopaminergic neurons,which predominate in substantia nigra（SN）,leads to PD.We have previously demonstrated that the neurons in the SN project to the lateral hypothalamic nucleus（LH）and the dorsal motor nucleus of vagus（DMV）receives the neural projection from LH by the means of anterograde and retrograde neural tracing technology.Orexin A（OXA）is predominately expressed in the LH.It has been reported that OXA can alter the gastric motility through the orexin receptor 1（OX1R）in DMV.We speculated that SN damage might cause OXA alteration in LH,then lead to DMV functional disorder,and this SN-LH-DMV pathway might play an important role in the modulation of gastric motility.However,the distribution and expression of dopamine receptors（DR）,especially localization with OXA neurons,in the LH is unknown.ObjectivesTo investigate the distribution of tyrosine hydroxylase（TH）,D1 and D2 in the LH and their co-localization with OXA neurons.The alternations of D1,D2 and OXA in the LH,and OX1R and choline acetyltransferase（ChAT）in the DMV were observed in the rats with bilateral SN injection of 6-OHDA.The present study may provide morphological evidences for DA/DR and OXA/OXR promoting gastric motility through SN-LH-DMV pathway.Methods1.To determine the location of SN,LH,and DMV in the rat brain by Nissl staining.2.The anterograde tracer BDA was microinjected into the left SN to determine whether BDA-labeled fibers could be observed in the LH and DMV.3.Rats were anesthetized by intraperitoneal injection with chloral hydrate（0.4 g/kg）and placed on stereotaxic instrument.Two small areas of the skull were exposed（coordinates:anteroposterior,–5.6 mm;mediolateral,±2.0 mm;dorsoventral,–7.5 mm）,and 6-OHDA was injected with a 10μl Hamilton syringe.Control groups were injected with 0.05%ascorbic acid/saline.The rats injected with 6-OHDA in the SN were referred to as 6-OHDA rats.4.Double-label immunofluorescence was performed to assess the distribution patterns of OXA,TH,D1 and D2 in the LH.5.Double-label immunofluorescence was performed to assess the distribution patterns of ChAT and OX1R in the DMV.6.Changes in OX1R and ChAT protein expressions in dorsal medulla oblongae were detected by western blot.7.Observation of changes in gastric motility in rats by X-ray of animals Results1.The anterograde tracer BDA was microinjected into the left SN.After 7 days,a dense BDA stained area was located at the injection area,the left SN pars compacta.Dense puncta and irregular curved BDA positive nerve fibers were observed in the LH.However,no BDA positive fibers were observed in the DMV.2.A considerable quantity of dopamine receptor 1 and 2 was expressed in the LH,and the OX1R in the DMV.3.Nearly all of the D1-immuoreactve（IR）neurons were also OXA-positive while only a few neurons expressed both D2 and OXA in the LH,and the DR-positive neurons were surrounded by the dopaminergic neural fibers.4.In the DMV,OX1R were colocalized with choline acetyltransferase（ChAT）-labeled motor neurons.5.When dopaminergic neurons in the SN were destroyed,the expression of D1 and OXA in the LH was significantly decreased,while D₂ had no statistical change.Further more the reduced OX1R and ChAT expression in the DMV were observed.6.6-OHDA rats exhibited delayed gastric emptying.ConclusionsSN might regulate the function of OXA-positive neurons via D1 receptor,which then affect the motor neurons in the DMV through OX1R.The gastric motility malfunction induced by SN lesion might be related to the alteration of SN-LH-DMV pathway.The present study may provide morphological evidences for promoting gastric motility through SN-LH-DMV pathway.