Synaptophysin immunoreactivity in the hippocampus of Syrian Hamsters is not affected by natural hypothermia

Neurotransmission capacity in the hippocampus is affected by torpor in obligate hibernators such as European Ground Squirrels. We investigated whether torpor in Syrian Hamsters has similar effects. We measured immunoreactivity (IR) of the synaptic vesicle marker synaptophysin in Syrian Hamster hippocampus at different time points in the cycle of torpid and euthermic phases during hibernation. Hamsters were sacrificed in early (2.5 hr after arousal onset) and late (8.5 hr) stages of euthermic phases, and early (24.1 hr after torpor onset) and late (94.7 hr after torpor onset) stages of torpid phases. Synaptophysin IR showed no significant differences between these groups, nor did synaptophysin IR of continuously euthermic Syrian Hamsters in long-day (summer) conditions. It is concluded that torpor in Syrian Hamsters does not affect hippocampal neurotransmission capacity. This finding contrasts observations in European Ground Squirrels, Golden-mantled Ground Squirrels and European Hamsters, indicating reduction of synaptic transmission capacity in torpor. The findings are discussed in the framework of regulation of torpor bout duration.