IN-VITRO ELECTROPHYSIOLOGY OF RAT SUBICULAR BURSTING NEURONS

Intracellular recordings were used to study the electrophysiological p roperties of rat subicular neurons in a brain slice preparation in vit ro. Cells were classified as bursting neurons (n = 102) based on the f iring pattern induced by depolarizing current pulses. The bursting res ponse recorded at resting membrane potential (-66.1 +/- 6.2 mV, mean /- SD n = 94) was made up of a cluster of fast action potentials ridin g on a slow depolarization and was followed by an afterhyperpolarizati on. Tonic firing occurred at a membrane potential of approximately -55 mV. A burst also occurred upon termination of a hyperpolarizing curre nt pulse. Tetrodotoxin (TTX, 1 mu M) blocked the burst and decreased o r abolished the underlying slow depolarization. These effects were not induced by the concomitant application of the Ca2+ channel blockers C o2+ (2 mM) and Cd2+ (1 mM). Subicular bursting neurons displayed volta ge- and time-dependent inward rectifications of the membrane during de polarizing and hyperpolarizing current pulses. The inward rectificatio n in the depolarizing direction was abolished by TTX, while that in th e hyperpolarizing direction was blocked by extracellular Cst (3 mM), b ut not modified by Ba2+ (0.5-1 mM), TTX, or Co2+ and Cd2+. Tetraethyla mmonium (10 mM)-sensitive, outward rectification became apparent in th e presence of TTX. These results suggest that neurons in the rat subic ulum can display voltage-dependent bursts of action potentials as well as membrane rectification in the depolarizing and hyperpolarizing dir ections. These results also indicate that activation of a voltage-gate d Na+ conductance may be instrumental in the initiation of bursting ac tivity. (C) 1997 Wiley-Liss, Inc.