Figure 4. Effect of DA receptor agonists on the EPSCs.
EPSCs were evoked at 0.2 Hz in the presence of bicuculline (20 μM), strychnine (0.5 μM) and D-AP5 (25 μM). The holding potential was −60 mV. A, lack of effect of the D1-like receptor agonist SKF 81297 (30 μM) on the evoked EPSCs. The traces are the averaged traces of 20 consecutive responses in control, 4 min after the onset of drug application, and 4 min after washout of the drug, respectively. B, inhibitory effect of the D2-like receptor agonist quinpirole (30 μM) on the evoked EPSCs. The traces are the averaged traces of 20 consecutive responses in control, 2 min after the onset of drug application, and 4 min after washout of the drug, respectively. C, summarized histograms showing the means ± s.e.m. of the inhibitory effects of SKF 81297, quinpirole and DA. All agonists were applied at 30 μM. The value of DA was derived from the concentration-response curve in Fig. 3. Values for SKF 81297, quinpirole and DA were 8.04 ± 5.02% (n = 9), 51.1 ± 7.10% (n = 6) and 41.6 ± 2.57% (n = 29), respectively. The difference in the effects between SKF 81297 and quinpirole or SKF 81297 and DA was significant (P < 0.001), whereas the difference between quinpirole and DA was not significant (P = 0.15).