Effects of Phenylephrine on the Excitability of Medial Vestibular Nuclear Neurons in Rats

Coeruleo-vestibular pathway which connects locus coeruleus and vestibular nuclei is noradrenergic. This study was designed to elucidate the effects of phenylephrine on the spontaneous activity of acutely isolated medial vestibular nuclear neurons of rat by whole-cell patch-clamp technique. Sprague-Dawley rats, aged 14 to 16 days, were used. After enzymatic digestion, dissociated medial vestibular neurons were transferred to a recording chamber mounted on an inverted microscope, and spontaneous action potentials were recorded by standard patch-clamp techniques. In current-clamp mode, the frequency of spontaneous action potential of medial vestibular nuclear neurons was decreased by phenylephrine (n=15). Phenylephrine increased the amplitude of afterhyperpolarization without changes in the resting membrane potential and spike width. In voltage-clamp mode, the whole potassium currents of the medial vestibular nuclear neurons were increased by phenylephrine (n=12). These experimental results suggest that alpha-receptor mediates the inhibitory effects on the neuronal activity of the medial vestibular nuclear neuron.

Inhibitory Effects of Norepinephrine on the Potassium Current of Rat Medial Vestibular Nuclear Neurons

BACKGROUND: This study aimed to explore the effects of norepinephrine on the potassium currents of rat medial vestibular nuclear neurons by using the whole-cell patch clamp technique. METHODS: Sprague-Dawley rats aged 14 to 16 days were anesthetized with ether and decapitated. After enzymatic digestion, the portion of the medial vestibular nucleus neurons were obtained by micropunching. The dissociated neurons were transferred into a recording chamber mounted on an inverted microscope and potassium currents were recorded by standard patch-clamp techniques under voltage-clamp modes. RESULTS: Norepinephrine inhibited the whole potassium currents of the medial vestibular nuclear neurons. Outward potassium currents were more suppressed in 4 mM 4-aminopyridine and norepinephrine added solutions than 4 mM 4-aminopyridine only, but were not suppressed in 10 mM tetraethylammonium and norepinephrine added solutions compared to 10 mM tetraethylammonium only. CONCLUSIONS: These results suggest that norepinephrine blocks the delayed rectifier potassium channels in medial vestibular nuclear neurons.