A TETRODOXIN-INSENSITIVE SODIUM CURRENT INITIATES BURST FIRING OF NEOCORTICAL NEURONS

The ability to generate burst discharges is a widespread phenomenon in central neurons and often has been attributed to Ca2+ currents. The d iversity of burst patterns seems to be at variance with a single mecha nism. Selected neocortical bursting neurons were examined by intracell ular recordings. Selective blockers and pulse protocols were applied t o characterize the crucial components of bursting activity. In the pre sence of tetrodotoxin and Ca2+ channel antagonists a transient depolar ization persists, which shares the activation and deinactivation prope rties with the burst. The sensitivity to Naf removal and resistance to tetrodotoxin suggests a tetrodotoxin-insensitive Na+ current as the c rucial component in neocortical bursting neurons. A tetrodotoxin-insen sitive Na+ current has been isolated in neocortical bursting neurons. The biophysical properties of this current allow for burst firing at f requencies up to about 12 Hz. This tetrodotoxin-insensitive Na+ may ge nerate the alpha-rhythm of the electroencephalogram by effectively syn chronizing arrays of follower cells. The implications of the intrinsic currents of bursting neurons for the initiation of epileptic discharg es are discussed.