The calcium receptor modulates the hyperpolarization-activated current in subfornical organ neurons

Here we report that neurons of the subfornical organ (SFO), a circumventricular structure devoid of a blood-brain barrier, show time-dependent, inward rectification indicative of the presence of a subthreshold, hyperpolarization-activated inward current (Ih). In whole-cell patch clamp experiments of isolated SFO neurons, we observed a Cs+-sensitive Ih in 47% of cells tested. Furthermore, we show that Ih is involved in the generation of evoked bursts in SFO neurons. An allosteric agonist of the extracellular calcium-sensing receptor (CaR) was found to potentiate Ih consistent with our previous observations of CaR-mediated bursting in SFO neurons. These studies indicate that a proportion of SFO neurons express Ih, and this may be one ionic mechanism through which bursting is regulated by various extracellular messengers.