Expression of Phosphorylated ERK1/2 and cFos Proteins in Vestibular Nuclei by Selective Stimulation of Horizontal Semicircular Canal

BACKGROUND: There is a little information about the effect of selective vestibular stimulation on the expression of activity-dependent metabolic markers in the vestibular nuclei. The purpose of this study was to evaluate effect of afferent excitation of the horizontal semicircular canal on expression of phosphorylated ERK1/2 (pERK1/2) and cFos proteins in the vestibular nuclei. METHODS: The horizontal semicircular canal of Sprague-Dawley rats was selectively stimulated by using the sinusoidal horizontal stimulator with 10-minute duration of stimulation. Conventional immunohistochemical method was used to visualize pERK1/2 or cFos immunoreactive neurons in the vestibular nuclei following rotation. RESULTS: Five minutes after stimulation of the horizontal semicircular canal there was a high expression of pERK1/2 protein in the medial vestibular nucleus among 4 major subnuclei of the central vestibular nuclear complex. On the contrary, immunoreactivity of cFos protein was observed in the medial and inferior vestibular nucleus 2 hours after horizontal sinusoidal rotation. The lateral vestibular nucleus was free from the expression of pERK1/2 and cFos proteins in response to excitation of the horizontal semicircular canal. However, in the vestibular nuclei of unilaterally labyrinthectomized rats expression of pERK and cFos proteins was markedly suppressed in ipsi-lesional side as well as contra-lesional side following stimulation of the horizontal semicircular canal. Furthermore no expression of pERK1/2 and cFos protein in the bilateral vestibular nuclei of bilaterally labyrinthectomized rats was noted after stimulation of the horizontal semicircular canal. CONCLUSIONS: Therefore these results of present study suggest that excitatory afferent signals from the peripheral vestibular receptors are essential for protein translation for pERK1/2 and cFos in response to stimulation of the semicircular canal.

Actions of Orphan Opioid on the Membrane Conductances and Synaptic Transmission in Rat Medial Vestibular Nucleus Neurons

BACKGROUND: The medial vestibular nucleus (MVN) is involved in the reflex control of the head and eyes, and the recovery of vestibular function after vestibular injuries. This study was performed to investigate the actions of the orphan opioid (nociceptin) on the membrane conductances and synaptic transmission in rat MVN neurons. METHODS: Whole cell patch clamp recordings were carried out in the brainstem slice of neonatal rats. RESULTS: Nociceptin (2 micro M) inhibited the spontaneous discharge in the majority (83%) of MVN neurons. This inhibition was insensitive to the non-specific opioid receptor antagonist naloxone (10 micro M), but was effectively antagonized by the selective opioid receptor-like 1 (ORL1) receptor antagonist, [Nphe1] nociceptin(1-13)NH2 (3 micro M). Nociceptin had no effect on the rate or amplitude of miniature inhibitory postsynaptic currents (mIPSCs). Nociceptin induced an outward current, and which was blocked by [Nphe1] nociceptin(1-13)NH2 in MVN neurons. Outward current reversed at -81 +/- 2 mV, which was close to the K+ equilibrium potential as calculated by the Nernst equation in 6 mM extracellular potassium solution. This indicates that the action of nociceptin involves postsynaptic receptors on the MVN neurons. CONCLUSIONS: These results suggest that nociceptin modulate neuronal excitability by activating a K+ conductance in postsynaptic neurons, not by modulation of synaptic transmission in MVN neurons.

Analysis of Role of Peripheral Vestibular Receptors on Orthostatic Tolerance using Heart Rate Variability in Rats

BACKGROUND: There is substantial evidence that the vestibular system is involved in the regulation of blood pressure. Heart rate variability (HRV) is useful to investigate the role of the peripheral vestibular receptors and the baroreceptors in the orthostatic tolerance. METHODS: EKG was recorded during postural changes with the head up either after sinoaortic denervation or after bilateral labyrinthectomies in Sprague-Dawley rats. HRV, including mean, standard deviation, coefficient of variation (CV), and power spectrum, were analyzed from R-R intervals of EKG. RESULTS: Phenylephrine increased low frequency region and sodium nitroprusside increased high frequency region in the power spectral analysis of HRV in anesthetized rats. Postural changes decreased blood pressure transiently and then increased blood pressure gradually in control rats, but the depression of blood pressure induced by postural change was greater in rats with both sinoaortic denervation and bilateral labyrinthectomies. The increase of CV of HRV just after sinoaortic denervation or bilateral labyrinthectomies represents an unstable heart rate in resting position, however, CV of HRV was increased markedly by postural change 7 days after bilateral labyrinthectomies. Postural change with sinoaortic denervation increased low-frequency region representing sympathetic activity, whereas bilateral labyrinthectomies increased highfrequency region representing parasympathetic activity in power spectral analysis. CONCLUSIONS: These results suggest that both the peripheral vestibular receptors and the baroreceptors have subsidiary action in orthostatic tolerance and the peripheral vestibular receptors regulate blood pressure during postural change through the sympathetic nervous system.

Hypertension-induced Posterior Reversible Encephalopathy Syndrome

Posterior reversible encephalopathy syndrome (PRES) involves predominantly posterior subcortical white matter and cortex. PRES is associated with an abrupt and severe increase in blood pressure or administration of various immuno-suppresants. We present a 18-year-old female with PRES. She was admitted to our hospital with seizures. She had been suffering from acute hypertension (170/100 mmHg) associated with acute renal failure. Brain MRI showed reversible biparietal cortical and subcortical edema. We report a case of hypertension-induced PRES associated with acute renal failure. (J Korean Neurol Assoc 19(5):541~543, 2001)