Characterization of ionic currents of cells of the subfornical organ that project to the supraoptic nuclei

The subfornical organ (SFO) is a forebrain structure that converts peripher al blood-borne signals reflecting the hydrational state of the body to neur al signals and then through efferent fibers conveys this information to sev eral central nervous system structures. One of the forebrain areas receivin g input from the SFO is the supraoptic nucleus (SON), a source of vasopress in synthesis and control of release from the posterior pituitary. Little is known of the transduction and transmission processes by which this convers ion of systemic information to brain input occurs. As a step in elucidating these mechanisms, the present study characterized the ionic currents of di ssociated cells of the SFO that were identified as neurons that send effere nts to the SON. A retrograde tracer was injected into the SON area in eleve n-day-old rats. After three days for retrograde transport of the label, the SFOs of these animals were dissociated and plated for tissue culture. The retrograde tracer was used to identify the soma of SFO cells projecting to the SON so that voltage-dependent ionic currents using whole-cell voltage c lamp methods could be studied. The three types of currents in labeled SFO n eurons were characterized as a 1) rapid, transient inward current that can be blocked by tetrodotoxin (TTX) characteristic of a sodium current; 2) slo w-onset sustained outward current that can be blocked by tetraethylammonium (TEA) characteristic of a delayed rectifier potassium current; and 3) rema ining outward current that has a rapid-onset and transient characteristic o f a potassium A-type current. (C) 1999 Elsevier Science B.V.