Locus of the effect of DA on EPSCs.

<p><b>A</b>: Current traces of the responses evoked by a pair of single local electrical stimuli 50 ms apart at holding membrane potentials of −100 mV to record the AMPA response before (1) and during (2) superfusion with DA (50 µM). 3: overlay of the responses before and during DA superfusion; the amplitude of the 2nd response in the presence of DA was scaled to match the amplitude of the 2nd response during control. Note that the 1st response proportionally decreased more than the 2nd response in the presence of DA and that there is no substantial changes in the time course of the EPSCs. Current traces represent the average of 6 sweeps and BMI (10 µM) was present in the superfusing medium throughout recording. Panel 4 (4. PPR) shows the average amplitude of the PPR from 12 neurons before and during superfusion with DA. * Statistically different from control, Student’s paired t-test, <i>P</i><0.05. <b>B</b>: Average holding membrane current before and during superfusion with DA (50 µM). No statistically significant differences were found at any holding membrane potential. <b>C</b>: current traces of the response evoked by local pressure ejection of glutamate (10 mM; vertical arrow) from a patch pipette before (1) and during (2) superfusion with DA (50 µM) at a holding membrane potential of –100 mV in the presence of tetrodotoxin (1 µM) and BMI (10 µM). 3: the overlay of the responses recorded in panels 1 and 2. 4: amplitude of the peak response recorded at a holding membrane potential of −100 mV for 5 neurons before and during superfusion with DA. No statistically significant difference in the amplitude of the glutamate response during control and during DA superfusion (Student’s paired <i>t</i>-test, <i>P</i>>0.75, n = 5).