BICUCULLINE INCREASES THE INTRACELLULAR CALCIUM RESPONSE OF CA1 HIPPOCAMPAL-NEURONS TO SYNAPTIC STIMULATION

Intracellular calcium levels were measured by ratio imaging of Fura-2- injected CA1 pyramidal neurons during repetitive electrical stimulatio n of the Schaffer collaterals in rat hippocampal slices. Baseline intr acellular calcium levels of 102 nM increased to 190 nM during a 3-s st imulus train of 5 Hz. Bicuculline (20 muM) significantly enhanced this stimulus-dependent rise in intracellular calcium, while the baseline calcium levels remained unchanged. Concomitantly performed extra- and intracellular electrophysiological recordings indicate that the increa sed calcium response in the presence of bicuculline is linked to a pro longation of the excitatory postsynaptic potential and the induction o f multiple action potentials. The bicuculline-induced increased calciu m response could have long-term implications for cell function and eve ntually lead to cell degeneration.