Distribution Of Dopamine Receptors In The Paraventricular Nucleus Of Rats And Morphological Observation Of Its Association With Glucose Metabolism

BackgroundParkinson's disease?PD?is a kind of central nervous degenerative disease that occurs in the elderly.Its main pathological sympotoms is the massive loss of dopamineic neurons in the substantia nigra?SN?.PD is often accompanied by both motor and non-motor symptoms.Although the classic motor characteristics can be attributed to the loss of nigrostriatal dopaminergic cells,the performance of non-motor symptoms can reflect more complex causes.Non-motor symptoms mainly include neuroendocrine and metabolic abnormalities.Studies have shown that patients with PD will occured the symptoms of glucose metabolism disorder at an early stage.Dopamine is an important neurotransmitter of catecholamines in the brain.It is involved in the regulation of many functions such as behavior,cognition,exercise,emotion,neuroendocrine and cardiovascular function.Dopamine receptors are widely distributed in human bodys,especially in the brain.The hypothalamic paraventricular nucleus?PVN?plays a crucial role in maintaining the homeostasis of the in vivo environment.It is the primary driver of the hypothalamic-pituitary-adrenal?HPA?axis response,with a large number of corticotropin releasing hormone?CRH?neurons,which acting on the pituitary gland to promote the release of adrenocorticotropic hormone?ACTH?into the pituitary portal vein of the median eminence.ACTH is released from the pituitary gland and propagates through the systemic circulation to the adrenal cortex.In the adrenal cortex causes the synthesis and secretion of glucocorticoids,which involved in the body's blood glucose regulation.Previous study by our research team had been found that there is a projection of dopaminergic nerve fibers from the SN to the PVN.It implies that on PD condition,the decrease of dopaminergic fibers in the SN which projects into the PVN may cause abnormal of the HPA pathway,which may in turn result to the disorder of blood glucose regulation.In order to investigate the mechanism of the effect of dopamine receptors in the PVN on blood glucose,the expression of dopamine receptor 1 and 2?D₁ and D₂?in the PVN was detected by immunofluorescence and western blot?WB?.This study may provide important morphological evidence for the dopamine regulating glucose metabolism through the dopamine receptors on the CRH neurons.ObjectivesTo study the changes of glucose tolerance and ACTH,corticosterone?CORT?on the HPA axis,the alteration of expression of D₁ and D₂,and co-labeling of D₂ and CRH neurons in the PVN between the control and 6-hydroxydopamine?6-OHDA?model group.The present study may provide a morphological basis for the possible mechanisms of glucose metabolism disorders in PD patients.Methods1.Injecting 6-OHDA into rat SN by brain stereotaxic instrument in order to destroy the expression of tyrosine hydroxylase?TH?between SN dopaminergic neurons.2.The 2 h glucose tolerance test was used to detect the changes of blood glucose in the control group and the 6-OHDA model group.3.Radioimmunoassay was used to detect the levels of ACTH and CORT in plasma and tissues.4.It is used Nissl staining to locate the layers of the brain core mass that associated with it.5.The damage of TH in the SN of rat was detected by immunohistochemical.6.The expression of TH/D₁,TH/D₂ and D₂/CRH in the PVN were detected by immunofluorescence double labeling,and the protein content of TH,D₁,D₂ and CRH neurons was detected by WB.Results1.Model identification:The results of Nissl staining showed that the number of neurons in the SN site of 6-OHDA-treated rats was significantly reduced,the Nissl bodys were blurred,the particle and density were decreased.And the immunohistochemical result showed that the number of TH immunopositive neurons in the SN was significantly reduced.2.After intraperitoneal injection of glucose in the 6-OHDA model group,blood glucose was significantly higher at 15 and 30 min compared with the control group,indicating that the glucose tolerance was decreased.3.Compared with the control group,the plasma CORT and ACTH in the pituitary tissues of the 6-OHDA group showed an increasing trend,indicating that the HPA axis of the 6-OHDA group was activated.4.D₁ and D₂ were expressed in each subdivisions of the PVN in the control group,and D₁ was co-labeling with vasopressin?VP?and oxytocin?OT?in the lateral magnocellular part?PaLM?,so as D₂.5.In the PVN,a large amount of TH fibers surrounded with the D₁ or D₂ positive neurons.In the control group,most of the TH immunoreactive?IR?positive neurons in the PaLM were co-labeling with D₁ or D₂,and CRH/D₂ was also co-labelled abundantly.In the6-OHDA model group,the expression of D₂ and TH-IR positive neurons was significantly decreased,CRH-IR positive neurons was increased,and D₁ was not significantly changed.ConclusionsD₁ and D₂ are widely expressed in the PVN.They are not only in the VP and OT neurons,but also in the CRH neurons.Damaging SN caused by 6-OHDA is able to induce abnormal of glucose metabolism suggesting that SN dopaminergic neurons are involved in the regulation of D₂ mediated CRH neurons through SN-PVN projection.The present study provides morpharologic evidences for the PD patients often companies with disordered glucose metabolism.