Physiological Significances for Expression of Immediate Early Gene Protein by Change of Arterial Pressure in Vestibular Nuclear Complex of Adult Rats / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The purpose of this research was to evaluate physiological significances of expression of immediate early gene proteins in the vestibular nuclear complex by change of arterial pressure (AP) in adult Sprague-Dawley rats. MATERIALS AND METHOD: Record AP and inject either sodium nitroprusside (SNP) or phenylnephrine to change AP. Either fast or slow removal of blood from the femoral artery was made to induce different rapidity in reduction of AP. Blood supply to the inner ear was temporally blocked by clamping anterior inferior cerebellar artery (AICA). Immunohistochemical staining and image analysis for cFos, FosB, Krox, and JunB proteins were performed 2, 6, 12 hours after change of AP. RESULTS: The selective expression of cFos protein was observed in the medial vestibular nucleus (MVN) following reduction of AP. The number of cFos positive neurons peaked at 2 hours and then rapidly reduced, returning to the normal value 24 hours after SNP injection. And cFos protein expression was also well correlated with that of AP reduction at 2 hours of SNP injection. The rapid falling of AP caused a significant expression of cFos protein but slow withdrawal of blood did a minimal change of cFos protein expression. In addition, there was a significant expression of cFos protein following the increase of AP by single injection of phenylnephrine. Unilateral occlusion of AICA resulted in the significant expression of cFos protein in bilateral MVN. Furthermore, bilateral ablation of vestibular endorgans resulted in significant reduction of cFos expression by AICA occlusion in MVN. CONCLUSION: These results suggest that cFos protein is a marker for neuronal excitation in vestibular complex in response to rapid changes in the arterial blood pressure and that medial vestibular nuclei plays an important role in signaling the process of cardiovascular information coming from the peripheral vestibular apparatus.

Neuronal Activity of the Vestibular Nuclei Following Acute Hypotension in Rats

The role of peripheral vestibular receptors in acute hypotension was investigated in anesthetized rats. Acute hypotension was induced by either intravenous infusion of sodium nitroprusside (SNP) or by experimental hemorrhage, and electrical activity and expression of cFos-like immunoreactive (cFL) protein were measured in the medial vestibular nuclei (MVN). Blood pressure decreased proportionately to the does of intravenous SNP and to the volume of the hemorrhage. Blood pressure decreased 10, 30, 50% for the 5, 10, 15ng/kg SNP injection, respectively, and also decreased 30 and 50% after 1- and 2-ml blood loss, respectively, due to hemorrhage. In animals with intact labyrinths, acute hypotension induced by either intravenous infusion of SNP or hemorrhage produced different electrical activities with three different patterns in type I and II neurons of MVN. The responses of type I neurons showed excitatory in 2/3 of recorded neurons and inhibitory or no change in 1/3 of neurons, while the responses of type II neurons showed inhibitory in 2/3 of recorded neurons and excitatory or no change in 1/3 of neurons. In unilateral labyrinthectomized animals, 2/3 of type I neurons ipsilateral to the lesion showed an inhibitory response, and 2/3 of contralateral type I neurons showed an excitatory response after the induction of acute hypotension. The response patterns of type II neurons were opposite from those of the type I neurons. After 30% decrease in blood pressure, cFL protein expressed in the bilateral vestibular nuclei of control animals with intact labyrinths. Expression of cFL protein increased significantly proportionately to the reduction of blood pressure. The unilateral labyrinthectomized animals with acute hypotension produced expression of cFL neurons in contralateral vestibular nuclei to the lesion side, but not in ipsilateral vestibular nuclei. However, cFL protein was not expressed in bilateral vestibular nuclei after acute hypotension in bilateral labyrinthectomized animals. These results suggest that the peripheral vestibular receptors might play a significant role in controlling blood pressure following acute hypotension via activation of type I neurons and inhibition of type II neurons in the vestibular nuclei.

Changes in Excitability of Neurons in Rat Medial Vestibular Nucleus Following Vestibular Neurectomy

Intrinsic excitabilities of acutely isolated medial vestibular nucleus (MVN) neurons of rats with normal labyrinth and with undergoing vestibular compensation from 30 min to 24 h after unilateral vestibular deafferentation (UVD) were compared. In control rats, proportions of type A and B cells were 30 and 70%, respectively, however, the proportion of type A cells increased following UVD. Bursting discharge and irregular firing patterns were recorded from 2 to 12 h post UVD. The spontaneous discharge rate of neurons in the ipsilesional MVN increased significantly at 2 h post-UVD and remained high until 12 h post-UVD in both type A and type B cells. After-hyperpolarization (AHP) of the MVN neurons decreased significantly from 2 h post-UVD in both types of cells. These results suggest that the early stage of vestibular compensation after peripheral neurectomy is associated with an increase in intrinsic excitability due to reduction of AHP in MVN neurons.

Temporal changes in neuronal activity of the bilateral medial vestibular nuclei following unilateral labyrinthectomy in rats

To investigate the changes in the responses of vestibular neurons with time during vestibular compensation, the resting activity and dynamic responses of type I and II neurons in the medial vestibular nuclei to sinusoidal angular acceleration were recorded following unilateral labyrinthectomy (ULX) in Sprague-Dawley rats. The unitary extracellular neuronal activity was recorded from the bilateral medial vestibular nuclei with stainless steel microelectrodes of 3~5 MOMEGA before ULX, and 6, 24, 48, 72 hours, and I week after ULX under pentobarbital sodium anesthesia (30 mg/kg, i.p.). Gain (spikes/s/deg/s) and phase (in degrees) were determined from the neuronal activity induced by sinusoidal head rotation with 0.05, 0.1, 0.2, and 0.4 Hz. The mean resting activity before ULX was 16.7+/-8.6 spikes/s in type I neurons (n=67, M+-SD) and 14.5+/-8.4 spikes/s in type II neurons (n=43). The activities of ipsilateral type I and contralateral type 11 neurons to the lesion side decreased markedly till 24 hr post-op, and a significant difference between ipsilateral and contralateral type I neurons sustained till 24 hr post-op. The gain at 4 different frequencies of sinusoidal rotation was depressed in all neurons till 6 or 24 hr post-op and then increased with time. The rate of decrease in gain was more prominent in ipsilateral type I and contralateral type 11 neurons immediately after ULX. Although the gain of those neurons increased gradually after 24 hours, it remained below normal levels. The phase was significantly advanced in all neurons following ULX. These results suggest that a depression of activities in ipsilateral type I and contralateral type II neurons is closely related with the occurrence of vestibular symptoms and restoration of activities in those neurons ameliorates the vestibular symptoms.

Studies on the Vestibular Compensation after Contralateral Labyrinthectomy in Unilateral Labyrinthectomized Rats / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Vestibular compensation is a process of behavioral recovery following unilateral labyrinthectomy (ULX). The neural plasticity in vestibular compensation was assessed by observing changes of behavioral response and c-Fos expression following contralateral labyrinthectomy (second labyrinthectomy) in ULX rats. MATERIAL AND METHODS: Contrala-teral labyrinthectomy was performed 2 weeks after ULX in Sprague-Dawley rats, each weighing 250-300 gm. Changes of spontaneous nystagmus, head tilt, and c-Fos expression in the medial vestibular nucleus (MVN) and nucleus prepositus hypoglossi (PrH) were measured. RESULT: In ULX, spontaneous nystagmus with the slow phase directed to the lesion side was 3.5+/-0.5 beats/sec and head tilt deviated to the lesion side was 71+/-16 degrees just after ULX. Spontaneous nystagmus disappeared within 72 hours, but head tilt was maintained at 28+/-8 degrees until 2 weeks after ULX. The number of c-Fos proteins 2 hours after ULX was 81+/-25 and 212+/-63 in MVN of the lesion side and the intact side, respectively. And PrH showed 136+/-37 in the lesion side and 94+/-19 in the intact side, which was opposite of MVN in spatial expression of c-Fos. In second labyrinthectomy, direction of spontaneous nystagmus and head tilt was opposite to the first ULX and their decrement was faster. c-Fos was expressed more in the MVN of the first labyrinthectomized side than in the second one and PrH showed the opposite pattern to MVN, which was opposite to the first ULX in spatial expression. CONCLUSION: These results suggest that recovery of vestibuloocular reflex in vestibular compensation is accomplished by restoration of neuronal activity in the central nervous system including MVN and PrH.

c-fos Expression in Medial Vestibular Nucleus of Guinea Pigs After Unilateral Labyrinthectomy / 听力学及言语疾病杂志

Objective To investigate the c-fos ex pr ession in guinea pigs' medial vestibular neuleus (MVN) following unilateral laby rinthectomy (UL). Methods Twenty-seven SCO guinea pigs were randomly divide d into nine groups, three in each group. After resection of right labyrinth,th e immunohistological staining of c-fos was performed. Fos-like immunoreactivity (FLI) was analyzed at fifteen minutes, and 1?2?6?8?12 and 24 h, and 2 and 7 days after UL. Results Results showed no Fos expression in the control g roup. By contrast, Fos was consistently induced in the UL guinea pigs. Asymmetri cal labeling was found in the bilateral medial vestibular nucleus, with more Fos -like neurons in the ipsilateral MVN of the lesioned side than that in the contr alateral MVN(P