| The vestibuiar nuclei is the located site of the second neurons receiving the vestibuiar primary afferents, and integrates the information from the vestibuiar organ and other afferents, and regulates the body motions through the efferent projections. Variable motion, change of gravity and posture or head position could excite vestibuiar receptor, and then the vestibuiar system could modulate body posture, eye-movement, muscle strain so as to maintain the body balance, at the same time, it could rapidly modulate the circulation, respiration and other visceral activity for keeping the stabilization of internal environment. At present, it is believed that the motion sickness happened in riding, navigation or aviation is mostly induced by the abnormal activity of vestibuiar system. Therefore, it has become one of the focuses that the mechanism of the vestibuiar system in modulating the visceral activity, especially the mechanism of nausea and vomiting produced by visceral discomfort. The illumination of the mechanism has important academic and practical significance which to prevent and treat motion sickness, and to develop anti-motion sickness medicament.The neural substrate of nausea and vomiting is still unknown, however the mechanism that most rodent have not action of vomiting is also need to investigate. Early years, administering emetic drugs—cisplatin by intraperitoneal injection in cat to express Fos, which discover the Fos positive neurons were most located in AP, NTS, lateral tegmental, nucleus retroambiguus, DMV and RMg, especially in the arc area from NTS and lateral tegmental to VLM. The arc area was believed the brief vomiting center. After intraperitoneal injected CCK or LiCl in ferret, the Fos positive neurons were most located in DVC, VLM, lateral tegmental, ROb, LPB, Gi and LC in brainstem, as well as in SON, PVN, Ce, BST. Because rat has not vomiting activity and obvious vomiting indicator, so it is hardly used in the study of neural mechanism of vomiting. Now it is unclear whether there is similar emetic area in non-emetic animals.The vestibuiar signal that induced motion sickness certainly effect vomiting center, then produce nausea and vomiting. In 1977, Porter etc. injected tetramethylrhodamine dextran in caudal vestibuiar nucleus in rat, and found there was direct projection from vestibuiar nucleus to DVC, they presumed that the direct projection played an important role in vestibule-viscus modulation. However Takeda etc. believed the neural pathway from vestibuiar nucleus to DVC was as follows: vestibuiar nucleus → ventral tegmental nucleus → hippocampus → tuberomammillary nucleus → DVC. But the hypothetic indirect pathway was based on some dispersive literatures and has not sequential morphological studies on the level of optical microscope or electron microscope. Some data indicated that there was the direct projection from vestibuiar nucleus to VLM, LPGi, Amb, PBN and so on, which could modulate the visceral activity. However the neural substrate of nausea and vomiting induced by vestibuiar signal is still unknown.Because the rat has not vomiting activity, if it is used as experimental animal to study motion sickness, in the rat nerve system, we must indicate whether there is similar vomiting centre with emetic animal, and whether the similar response to emetic drug or abnormal vestibuiar stimulation is the same with emetic animal, and whether there is the direct or indirect projection from the vestibuiar nucleus that receive vestibuiar afferents to vomiting center—DVC. Therefore, the following experiments were processed by using tracing technique, immunohistochemicaltechnique and other technique in Sprague-Dawley rat in present study. (1) Administering emetic drugs—cisplatin by intraperitoneal injection or stimulating vestibule by offer vertical axis rotation (OVAR) to observe the distribution of the Fos positive neurons in brains and compare the similarities and differences with the response of emetic animal in vomiting centre for revealing the possible location of vomiting centre in the rat. (2) To study the direct or indirect projection from vestibular nucleus to DVC to reveal the neural pathway of vestibular signal to vomiting centre, and offer the morphologic data for researching the mechanism of motion sickness in future. The results were as follows:1. The distribution of the Fos positive neurons induced by intraperitoneal injection of emetic drugs—cisplatin and stimulating vestibule by OVAR in rat brain.The results that expression of Fos in central nerve system in rat were induced by emetic drugs—cisplatin were as follows: (1) In the forebrain, there were a great deal of Fos positive neurons in SON and PVN in hypothalamus, and the density of the Fos positive neurons were increased significantly in the experimental group than in the control group (P<0.01). (2) In the brainstem, there were abundant Fos positive neurons in AP, NTS (especially medial and subpostrema subnuclei), LPB, and the density of the Fos positive neurons were increased significantly in the experimental group than in the control group (P<0.01). In addition, the distribution of the Fos positive neurons also located in ECu, Sp5 and RPa. The Fos positive neurons were also observed in MVe, SpVe and Gia and Tz. There were sporadic Fos positive neurons in DMV, Amb, RMg and LC.The results that the expression of Fos in neuron of central nerve system in rat was induced by OVAR were as follows: (1) There were a great deal of Fos positive neurons in SON and PVN in hypothalamus, and the density of the Fos positive neurons were increased significantly in the experimental group than in the control group (P<0.01). The Fos positive neurons were also found in Ce, ZI, AH, LH and PVN. (2) There were abundant Fos positive neurons in AP, NTS, DMV, VLM, LPGi, and the density of the Fos positive neurons were increased significantly in the experimental group than in the control group (P<0.01). In addition, plenty of Fos positive neurons were also located in MVe, SpVe, Amb, PCRt, Sp5, PrH, LPB, LC and dorsal tegmental nucleus. There were scattered Fos positive neurons in RPa, IOC, RMg, SOI and TZ. 2. The indirect projection from vestibular nucleus to DVCAfter PHA-L was injected in MVe and SpVe respectively, many PHA-L-labeled fibers and terminals were found in VLM, LPGi, Gia, Amb, PBN, RMg and RPa, which modulate visceral activity. But there were sporadic PHA-L-labeled fibers in NTS and DMV and there were no PHA-L-labeled terminals. So we presumed that the few projection maybe the fiber pass by, and believed that there is no direct projection from vestibular nucleus to DVC.After FG was injected in DVC, many FG-labeled neurons were found in PCRt, LPGi, VLM, Gia, KF, LPB, LC, dorsomedial part of Sp5 and Pr5, but there were sporadic FG-labeled neurons in vestibular nucleus. After PHA-L was injected in MVe or SpVe and FG was injected in DVC in the same rat, the overlap area of the PHA-L-labeled fibers and terminals and FG-labeled neurons were only found in VLM and LPGi.The results above indicated: (1) Emetic drug could induce visceral discomfort but not vomiting activity in rat, and there was similar emetic area with the emetic animal in rat's central nerve system. The results suggest that there was absence of modulation mechanism associated with vomiting activity in rat central nerve system. (2) The visceral response induced by OVAR...
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