Time-dependent effect of glutamate on long-term potentiation in the suprachiasmatic nucleus of rats

The effect of glutamate on optic nerve stimulation-evoked field potentials in rat suprachiasmatic nucleus (SCN) was examined in vitro. Glutamate application for 20 min induced long-term potentiation (LTP) of the field potentials in the SCN at nighttime, whereas that induced a weak LTP at daytime. On the other hand, application for 40 min induced LTP in the SCN during the daytime, whereas it induced a weak one at nighttime. These results indicate that the effect of glutamate is dependent on the application time and that the effect is influenced by the duration of glutamate exposure.