Seasonal changes in inhibitory currents in rat hippocampus

Spontaneous inhibitory postsynaptic currents were recorded in voltage-clamped neurons (clamp potential −60 to −70 mV) in the pyramidal cell layer of the CA1 region of hippocampal slices from 3- to 4- month-old rats. The average time constant of decay of the currents progressively increased from March (early autumn) to July (mid-winter) and then declined progressively from July to November (late spring). The changes were statistically significant. It is suggested that such seasonal changes in the time course of inhibitory postsynaptic currents may have behavioural consequences and could explain the reported seasonal variations in the occurrence of disorders such as mania.