| According present researches, in anesthetize rats, acute hypotension after intravenous injection of sodium nitroprusside (SNP) could increase vestibular nerve afferent impulses to excite to increase number of pERK1/2-immunoreactive neurons in the MVN, and consider that Glutamate was the main neurotransmitter in this process. At the same time, vestibular organ could regulate blood pressure and electrical activity. pERK1/2immunoreactive neurons were meaningful to detect neuron activation as the marker. In this study, the blood pressure was recording by inserting a catheter into artery of all experimental animals after anesthesia. The acute hypotension was induced by injecting Sodium Nitroprusside into vein, making blood pressure lower about50%. Using the immuno-histochemistry and pharmacological methods observed the change of pERK1/2immunoreactive neurons, NMDA agonist and blocker affect expression of pERKl/2immunoreactive neurons to discuss the possible receptor mechanism of Glu-NMDA.Wistar rats (220±30g in weight) were used and they were divided into three groups:the intact labyrinthine group; the unilateral labyrinthine group; NMDA receptor group. And the intact labyrinthine group consisted of the control group with injecting normal saline and experimental group with sodium nitroprusside. The unilateral labyrinthine group in which peripheric vestibular organ was damaged by injecting Arsanilic acid into inner ear contained the unilateral labyrinthine acute phase (24h,48h) and the chronic phase(2W), after acute hypotension we observed the expression of pERK1/2immunoreactive neurons at5min,10min,20min,40min points in the MVN. The NMDA receptor group was divided into NMDA agonist group with injecting NMDA and blocker group with injecting MK-801. In their control groups cerebrospinal fluid (ACSF) and normal saline were respectively instead of agonist or blocker and sodium nitroprusside. All animals were conscious.Results:1. The pERK1/2-immunoreactive neurons were significantly expressed bilaterally after5min,10min,20min,40min following SNP-induced acute hypotension in the MVN in intact labyrinthine conscious rats. And it was most significant at5minute and10minute points. But in the control group, few numbers of pERK1/2-immunoreactive neurons were detected in the MVN. There were significant differences between control and SNP injection groups.2. There was significant expression of pERK1/2-immunoreactive neurons in the contra-lateral MVN in unilateral labyrinthine rats at different time points. However, few number of pERK1/2-immunoreactive neurons were apparent in the ipsilateral MVN in unilateral labyrinthine conscious rats of acute phase3. On the chronic phase (2W), there was significant expression of pERK1/2-immunoreactive neurons in the contra-lateral MVN at different time points following acute hypotension induced by SNP in conscious rats. However, few number of pERK1/2-immunoreactive neurons were apparent in the ipsilateral MVN4. After intracerebroventricular microinjection of NMDA, the pERK1/2-immunoreactive neurons were significantly expressed bilaterally in the MVN of intact labyrinthine conscious rats. And it was significant difference compared with the control group with intracerebroventricular microinjection of artificial cerebrospinal fluid (ACSF)(P<0.001).5.In the control group, after intracerebroventricular microinjection of ACSF, pERK1/2-immunoreactive neurons were detected significantly bilaterally in the MVN after inducing SNP in intact labyrinthine conscious rats. But after intracerebroventricular microinjection of MK-801, few number of pERKl/2immunoreactive neurons were expressed in the MVN following acute hypotension. There were significant differences between control and MK-801groups (P<0.001)Conclusions:1. Acute hypotension after intravenous injection of sodium nitropruss (SNP) could increase the number of pERK1/2-immunoreactive neurons in conscious rats.2. Acute hypotension in conscious rats, increasing expression of pERK1/2-immunoreactive neurons in the MVN was inhibited by labyrinthectomy.3. The Glu-NMDA receptor probably taked part in the process in which expression of pERK1/2-immunoreactive neurons was increased in the MVN following acute hypotension in conscious rats. |
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