Time-window for sensitivity to cooling distinguishes the effects of hypothermia and protein synthesis inhibition on the consolidation of long-term memory

The effects of hypothermia on memory formation have been examined extensively, and while it is clear that post-training cooling interferes with the process of consolidation, the nature of the temperature sensitive processes disrupted in this way remain poorly defined. Post-training manipulations that disrupt consolidation tend to be effective during specific time-windows of sensitivity, the timing and duration of which are directly related to the mechanism through which the treatment induces amnesia. As such, different treatments that target the same basic processes should be associated with similar time-windows of sensitivity. Using this rationale we have investigated the possibility that cooling induced blockade of long-term memory (LTM) stems from the disruption of protein synthesis. By varying the timing of post-training hypothermia we have determined the critical period during which cooling disrupts the consolidation of appetitive long-term memory in the pond snail Lymnaea. Post-training hypothermia was found to disrupt LTM only when applied immediately after conditioning, while delaying the treatment by 10 min left the 24 h memory trace intact. This brief (<10 min) window of sensitivity differs from the time-window we have previously described for the protein synthesis inhibitor anisomycin, which was effective during at least the first 30 min after conditioning [Fulton, D., Kemenes, I., Andrew, R. J., & Benjamin, P. R. (2005). A single time-window for protein synthesis-dependent long-term memory formation after one-trial appetitive conditioning. European Journal of Neuroscience, 21, 1347–1358]. We conclude that hypothermia and protein synthesis inhibition exhibit distinct time-windows of effectiveness in Lymnaea, a fact that is inconsistent with the hypothesis that cooling induced amnesia occurs through the direct disruption of macromolecular synthesis.