Altered burst responses in hippocampal CA3 neurons injected with EGTA

Intracellular injection of EGTA abolished the hyperpolarization seen after spontaneous and evoked bursts of action potentials in hippocampal CA3 neurons. Simultaneously recorded, orthodromically elicited IPSPs were relatively unaffected by this treatment. It is concluded that CA3 neurons generate at least two types of hyperpolarization: one resulting from a calcium-mediated potassium conductance and the other from increased conductance to chloride.