Modulation of synaptic transmission at low temperatures by hibernation-related changes in ionic microenvironment in hippocampal slices of golden hamsters.

In hamsters, the entrance into hibernation is associated with a respiratory acidosis and elevation of the blood plasma concentrations of potassium, calcium, and magnesium. To investigate the effects of presumed hibernation-related ionic changes in the brain interstitium on neuronal function, the transmission properties of hippocampal slices prepared from golden hamsters were studied at low temperatures in vitro. Slices were investigated at 15-20 degrees C in artificial cerebrospinal fluid (ACSF) of variable composition (K+, 3-5 mM; Ca2+, 2-4 mM; Mg2+, 2-4 mM; pH 7.0-7.7). Population action potentials (population spikes, PS) of CA1 pyramidal cells were continuously evoked with 100-microseconds stimulus pulses delivered to the Schaffer collaterals/commissural fibers in intervals of 30 s. The PS amplitude was measured as a function of extracellular ion concentrations at given temperatures or as a function of temperature at a given ACSF composition. Elevation of [K+]o, [Mg2+]o, or [H+]o all reduced the PS amplitude at low temperatures, whereas elevation of [Ca2+]o increased the PS amplitude. In conclusion, changes in the ionic microenvironment occurring during entrance into hibernation presumably result in depression of synaptic transmission at low temperatures in the hamster hippocampus. The modulatory effect of ionic changes may be an important factor supporting a general depression of the brain during entrance into hibernation.