Abstract
Subfornical organ (SFO) is a brain center which controls body fluid homeostasis. Injection of noradrenaline (NA) into SFO caused a increase of water intake. Hemorrhage increased NA release in SFO area. Accordingly, noradrenergic activation on SFO neurons suggests to regulate body fluid balance. In the present study, the effects of NA and its analogues on 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 mM produced membrane depolarization (64%, 14 responsive neurons /22 neurons tested) and hyperpolarization (27%, 6/22 neurons). In the voltage clamp mode, NA application at 1-100 mM produced inward currents (63%, 33/52 neurons) and outward currents (27%, 14/52 neurons). These currents were not affected by the presence of TTX. In most of the neurons (15/21 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 α1 agonist phenylephrine. The phenylephrine-induced inward currents were inhibited by the α1 antagonist prazosin. In addition, the α2 agonist clonidine decreased the frequency of spontaneous GABAergic inhibitory postsynaptic currents (4/10 neurons). The results suggest that SFO neurons in rats are activated postsynaptically through α1 adrenoceptors, and that the activation is enhanced by suppressing GABAergic inhibitory synaptic inputs through presynaptic α2 adrenoceptors. [Jpn J Physiol 55 Suppl:S143 (2005)]
