Previous work has demonstrated that subfornical organ neurons exhibit spontaneous action potentials interspersed with periods of membrane potential oscillation. We used whole cell patch clamp recording to investigate properties of these oscillations. The amplitude, but not the frequency, of the oscillations exhibited voltage dependence. The oscillations were unaffected by application of blockers for gamma-amino-n-butyric acid type A (GABA(A)) and glutamate receptors, nor were they affected by application of Cd2+ to block Ca2+ channels, or Cs+ to block hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channels. The oscillations, however, were abolished by the application of tetrodotoxin, indicating a role for voltage-gated Na+ channels. Voltage clamp experiments demonstrated that the activation of persistent Na+ current, but not transient Na+ current, matched with the voltage dependence of activation of the oscillation.