Abstract
The subfornical organ (SFO) is a forebrain structure that is related to drinking behavior, cardiovascular regulation, vasopressin release and sodium appetite. It has been recently reported that SFO neurons projecting to hypothalamus have large IA. We electrophysiologically classified acute dissociated SFO neurons (n=60) under the presence of 300 nM tetrodotoxin (TTX) into three types; Type-I, -II and -III neurons showed fast exponential decay components (time constant, τ<100 ms, n=9), slower (100 ms<τ<400 ms, n=17) and further slower (τ>500 ms, n=34) at +20 mV voltage-step from -70 mV, respectively. As some Type-III neurons (n=10) showed fast exponential decay components by the addition of CdCl2, they were further classified to Type-IIIa and other neurons were classified to Type-IIIb. Under the presence of TTX and CdCl2, IAs were isolated by -40 mV prepulse before voltage-steps. Some Type-IIIb neurons (n=7) did not show IA. Although all Type-I and -IIIa neurons showed larger IA; rates of the peak amplitudes of IA vs that of whole-cell currents were over 0.43. RT-PCR assay revealed that the SFO has mRNA of Kv1.4, Kvβ1, Kv3.4, Kv4.1, Kv4.2, Kv4.3, but not Kv3.3. All Type-II neurons showed exponential slowly decay components that was not inhibited by -40 mV prepulse and 1 mM tetraethylammonium (TEA) sensitive (presumed Kv3.4). Under the presence of TTX, CdCl2 and TEA, recovery rate of IA fitted to double-exponential function; τ of rapid component was under 300 ms (presumed Kv4-family) and τ of slow component was over 1 s (presumed Kv1-family). [Jpn J Physiol 54 Suppl:S132 (2004)]
