Figure 4.

Representative MEA tracings from a rat receiving kynurenine (KYN; 50 mg/kg, i.p.). Top two tracings: MEA signal from the glutamate-sensitive site (GluOx) and its adjacent background sentinel. The third trace from the top reflects the self-referenced signal (Self Ref) of the GluOx channel against the sentinel background. Deflections along the vertical axis reflect changes in concentration (μM), and the horizontal axis depicts time (hr). The total recording session extended for 6 hrs after kynurenine administration (note 3 hr break in time axis). Kynurenine produces a steady decline in the glutamate signal, reaching a maximum decrease of 2.1 μM by the end of the recording session (see Table 1 for group data). A control local infusion of glutamate (0.25 mM) rapidly elicits the characteristic phasic glutamate signal (8.5 μM increase), demonstrating that the MEA remained sensitive to changes in glutamate levels at the nadir of the kynurenine effect. Note that the abrupt drop in baseline, prior to the glutamate infusion, is an artifact reflecting disruption of background current due to the removal of the dummy cannula and the insertion of the infusion cannula. Bottom tracing: self-referenced signal from an animal that received a control saline injection (0.9%, i.p.), demonstrating stability of the basal glutamate signal.