Study On The Distribution Of Dopamine Receptors In The Dorsal Motor Nucleus Of Vagus(DMV)and The Projection Of Substantia Nigra To DMV

BackgroundParkinson’s disease(PD)is a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons in the substantia nigra(SN).About 90%of PD patients suffer from gastrointestinal problems such as gastroparesis and constipation,which at present is poorly understood,scarcely investigated.Gastric motility is directly regulated by the dorsal motor nucleus of vagus(DMV).The result of autopsy in PD patients shows the degenerative morphology not only in SN,but also in DMV.We previously have reported that destroying bilateral SN decreased the acetylcholine transferase immunoreactivity in dorsal vagus complex(DVC)and gastric motor dysfunction in rats.DVC composes of DMV and nucleus of the solitary tract(NTS).DMV plays an important role in the regulation of gastrointestinal function.Dopamine(DA)exerts potent neuromodulatory effects on the motoneurons in the DMV via dopamine receptors(DRs),which implies that cross talking may be existed between DMV and SN.ObjectivesThe present study aims to investigate the distribution of DRs D1-and D2-immunoreactive(IR)neurons and their neurochemical phenotypes in the DMV of rats and to study the projection between DMV and SN in rats.Methods1.Nissl Staining.2.Double-labeling immunofluorescence technique combined with confocal microscopy.3.The expression change of D1,D2 receptor protein in DMV after 6-OHDA lesion.4.FG,a retrograde tracer,was injected into left side of DVC.The FG positive neurons were detected in the SN after 3 days.BDA,anterograde tracer,was injected into left side of SN.The BDA positive nerve fibers were detected in the DMV after 7 days.Results1.A large amount of choline acetyltransferase(ChAT)-IR and a few tyrosine hydroxylase(TH)-IR neurons were observed in DMV.2.A considerable quantity of D1 and D2 was expressed throughout the DMV.Nearly all of the ChAT-IR neurons were also Di-IR and D2-IR.3.A lot of TH-IR fibers surrounding Di-and D2-IR neurons were found in DMV.4.The protein expression of Di receptor was declined and D2 receptor was enhanced in DMV after lesion of bilateral SN by 6-OHDA.5.FG positive neurons were found in hypothalamic paraventricular nucleus(PVN),lateral hypothalamus(LH),inferior olive(IO),and locus coeruleus(LC),but not in SN and striatum after the injection of FG in DVC.6.BDA positive fibers were observed in striatum,globus pallidus,LC,and LH,but not in DVC after the injection of BDA in SN.Conclusions1.The wide distribution of D1 and D2 in the cholinergic and catecholaminergic neurons in the DMV of rats.The DRs might play an important role in the regulation of DA on the activity of cholinergic and catecholaminergic neurons in the DMV.D2 receptor expression may be related to the 6-OHDA rat gastric motility disorders.2.The SN neurons do not directly innvervate the DVC in rats.DVC might be indirectly regulated by SN through hypothalamus or LC,which provide the morphology evidence for the possible mechanism underlying the gastrointestinal disorder in PD patients.