Thermal effects on long-term potentiation in the hamster hippocampus.

Extracellular CA1 pyramidal cell activity was measured at different temperatures in hippocampal slices from the Syrian hamster (Mesocricetus auratus), a hibernator. Control records taken before and after tetanic stimulation of Schaffer collateral/commissural pathways were compared to determine if long-term potentiation (LTP) was established. LTP (an enhancement of the population spike amplitude or population synaptic response following tetanus) was elicited in slices at temperatures above 22 degrees C, but not in slices at temperatures of 20 degrees C. When LTP was established at temperatures above 24 degrees C, however, lowering the temperature to 20 degrees C did not abolish the LTP. Furthermore, when a tetanus was delivered at 20 degrees C and the bath temperature was then raised above 22 degrees C, LTP was established. These results for step changes in temperature suggest that the sequence of cellular mechanisms leading to LTP is activated, but then arrested in slices maintained at a constant temperature of 20 degrees C. Assuming this type of activity in the slice parallels in vivo hippocampal activity, it follows that the ability to elicit LTP in CA1 hippocampal pyramidal cells is lost when the core temperature of an animal entering hibernation falls to 20 degrees C.