Tetanus during a high extracellular calcium pulse overrides the block of long-term potentiation seen at 20 degrees C in the hamster hippocampal slice.

Extracellular CA1 pyramidal cell activity was measured at different temperatures in hamster hippocampal slices with bath Ca2+ concentration set at either 2.0 mM or 4.5 mM. Records taken before and after tetanic stimulation of Schaffer collateral/commissural pathways were compared to determine if long-term potentiation (LTP) developed. LTP, which cannot be elicited at 20 degrees C with 2.0 mM calcium in the bath, was elicited at 20 degrees C when a tetanus was administered during a high calcium (4.5 mM) pulse. This LTP was limited to the tetanized pathway and was blocked by APV. Moreover, to elicit LTP at 20 degrees C, high (4.5 mM) extracellular calcium was needed both during and for several minutes following the tetanus. We conclude that mechanisms responsible for a thermal block of LTP are sensitive to calcium and that the thermal block can be overcome by increasing the amount of calcium that enters a cell during a tetanus.