Activation of subfornical organ neurons in rats through pre- and postsynaptic -adrenoceptors

Honda, Eiko, Kentaro Ono, Shinji Kataoka, and Kiyotoshi Inenaga. Activation of subfornical organ neurons in rats through preand postsynaptic -adrenoceptors. Am J Physiol Regul Integr Comp Physiol 290: R1646–R1653, 2006. First published February 2, 2006; doi:10.1152/ajpregu.00801.2004.—The effects of noradrenaline (NA) and its analogs on subfornical organ (SFO) neurons in rat slice preparations were investigated by using whole cell patch-clamp recording. In the current-clamp mode, the application of NA at 10–100 M produced membrane depolarization (63%, 17 responsive neurons/27 neurons tested) and hyperpolarization (22%, 6/27 neurons). In the voltage-clamp mode, NA application at 1–100 M produced inward currents (69%, 42/61 neurons) and outward currents (23%, 14/61 neurons). These currents remained in the presence of TTX or both glutamate and GABA receptor antagonists. In most of the neurons (25/31 neurons) showing inward currents in the presence of NA, the membrane conductance was not changed by voltage ramps or hyperpolarizing pulse stimulation. Similar responses were obtained by the application of the 1-agonist phenylephrine. The phenylephrineinduced inward currents were inhibited by the 1-antagonist prazosin. The 2-agonist clonidine decreased the frequency of spontaneous GABAergic inhibitory postsynaptic currents (4/10 neurons). In addition, RT-PCR assay and immunohistochemical staining showed the existence of 1-adrenoceptors in the SFO. The results suggest that SFO neurons in rats are activated postsynaptically through 1-adrenoceptors and that the activation is enhanced by suppressing GABAergic inhibitory synaptic inputs through presynaptic 2-adrenoceptors.