Fig. 2.

D₁ MSNs displayed bidirectional Hebbian STDP dependent upon D₁ receptors. (A) LTP induction by a positive timing pairing protocol. EPSP amplitude and input resistance of the recorded cell were plotted as a function of time. The averaged EPSP traces before and after induction are shown at the top. Scale bars: 2 mV × 100 ms. (B) LTP induction (n = 10; P < 0.01, Wilcoxon test) was blocked by APV (50 μM) and MK-801 (20 μM). (C) LTD was not induced in D₁ neurons with a negative pairing. Plots and EPSP traces are from a single cell as in (A). Scale bars: 2 mV × 100 ms. (D) In the presence of D₁ receptor antagonist SCH23390 (3 μM), a negative timing pairing revealed LTD. But in the presence of CB₁ receptor antagonist AM-251 (2 μM), negative pairing failed to alter EPSP amplitude. (E) LTP induced by a positive timing pairing was blocked by SCH23390, revealing LTD. LTD induced in the presence of SCH23390 was disrupted by AM-251. (F) Schematic drawing shows that activation of D₁ and NMDA receptors evokes LTP and activation of mGluR5 receptor and CaV1.3 channels evokes LTD. Moreover, D₁ and mGluR5 receptor activation opposes each other in inducing plasticity.