Activation of a G protein-coupled inwardly rectifying K+ current and suppression of Ih contribute to dexmedetomidine-induced inhibition of rat hypothalamic paraventricular nucleus neurons

Background: alpha(2)-Adrenoceptor agonist has been reported to produce inhibition of arginine vasopressin release, diuresis, and sympatholytic effects. However, its mechanisms of central action remain incompletely understood. Hypothalamic Paraventricular nucleus (PVN) neurons, which are in direct contact with noradrenergic synapses and are controlled by the hyperpolarization-activated currents, are called I-h (H current). The effect of dexmedetomidine, a highly selective and potent agonist, at alpha(2) adrenoceptors on I-h is unknown. The purpose of this study was to examine the effects of dexmedetomidine on the PVN neuron, which is involved in the arginine vasopressin release and autonomic regulation. Methods: The authors investigated the effects of dexmedetomidine on the membrane properties in PVN magnocellular neurons and an I-n in PVN parvocellular neurons with a whole cell patch clamp technique using a rat brain slice preparation. Results: Dexmedetomidine dose-dependently hyperpolarized PVN magnocellular neurons. in the voltage clamp mode, dexmedetomidine induced an outward current, with a reversal potential of -94 mV, and this was shown to depend on the external concentration of K+. Pretreatment with Ba2+ or peptide toxin tertiapin blocked hyperpolarization induced by dexmedetomidine. The effect of dexmedetomidine was blocked by an alpha(2)-adrenoceptor antagonist, yohimbine. I-h was suppressed dose dependently by dexmedetomidine in PVN parvocellular neurons. Pretreatment with Cs+ occluded the I-h suppression by dexmedetomidine. Yohimbine blocked the Ih suppression by dexmedetomidine. The I-h sensitive to dexmedetomidine was weakly modulated by intracellular cyclic adenosine monophosphate. Conclusions: Dexmedetomidine inhibited PVN magnocellular neurons by activation of the G protein-coupled inwardly rectifying K+ current and inhibited PVN parvoceBular neurons by suppression of I-h.