Figure 1.

Criteria for the levels of basal, Ca²⁺- and K⁺-evoked hippocampal serotonin releases. (a) At least 6 h after starting the perfusion with MRS, the serotonin level in hippocampal perfusate was measured. After confirming the stabilization of extracellular serotonin level, the serotonin level was measured for 120 min as control data (basal release). After determination of basal release, perfusion medium was switched to 3.4 mM Ca²⁺ including MRS for 20 min (Ca²⁺-evoked stimulation). After confirming the stabilization of extracellular serotonin level, perfusion medium was switched to 50 mM K⁺ including MRS for 20 min (K⁺-evoked stimulation). (b) The value of Ca²⁺-evoked serotonin release was defined as the level of basal extracellular serotonin level subtracted from the maximal extracellular serotonin level during Ca²⁺-evoked stimulation. The level of K⁺-evoked release was defined as the level of basal extracellular level subtracted from the maximal extracellular level during K⁺-evoked stimulation.