Abstract
Extracellular single‐unit recording and iontophoresis were used to examine the effect of N‐methyl‐D‐aspartate (NMDA) and the competitive NMDA antagonist (+/−)‐4‐(3‐phosphonopropyl)‐2‐piperazine carboxylic acid (CPP) on the firing rate and firing pattern of A9 dopamine (DA) neurons in the rat. Administration of NMDA produced a dose‐dependent increase in firing rate (up to nearly 300% of baseline at the highest ejection current), which could be blocked by iontophoretic CPP. Low currents (2+ ionophore.