INWARD SODIUM CURRENT INVOLVEMENT IN REGENERATIVE BURSTING ACTIVITY OF RAT MAGNOCELLULAR SUPRAOPTIC NEURONS INVITRO

1. The rat hypothalamic slice preparation was used to investigate the involvement of inward Na+ currents as well as inward Ca 2+ currents in the generation of bursting activity by supraoptic (SON) neurones. Intracellular records were made from thirty-two SON neurones which showed regenerative bursting activity. The bursting activity consisted of spontaneous, intermittent bursts of action potentials with subsequent silent periods. During the bursts, plateau potentials on which action potentials were superimposed were frequently observed. 2. Perfusion of a low-Na+ medium, a tetrodotoxin (TTX)-containing medium or a Ca2+-free medium suppressed the regenerative bursting activity. 3. Addition of 3-10 mum veratridine to Ca 2+-free medium elicited regenerative bursting activity and spontaneous plateau potentials. The veratridine-induced regenerative bursting activity and plateau potentials were blocked by 1 muM TTX. Addition of 5 mm TEA allowed regenerative bursting activity to persist in Ca 2+-free medium. 4. These results suggest that TTX-sensitive Na+ inward currents as well as Ca2+ inward currents contribute to the generation of bursting activity in rat SON cells.