Quantitative correlation between tetanus-induced decreases in extracellular calcium and LTP.

Decreases in the extracellular calcium concentration ([Ca2+]o), induced by tetanization of the Schaffer collaterals in rat hippocampal slices, were measured by means of Ca2+-sensitive microelectrodes. The amount of long term potentiation (LTP) of the evoked field potentials, induced by this tetanus, was determined. A positive correlation was found between the amplitude of the tetanus induced decrease in [Ca2+]o and the amount of LTP that was elicited. The N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-phosphonovalerate decreased both the tetanus-induced decreases in [Ca2+]o and the amount of LTP that was induced. We conclude that the amount of Ca2+ that enters the cell during a tetanus is of major importance in the induction process of LTP.