Dopamine–Glutamate Interactions Controlling Prefrontal Cortical Pyramidal Cell Excitability Involve Multiple Signaling Mechanisms

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Abstract
Although the importance of dopamine (DA) for prefrontal cortical (PFC) cognitive functions is widely recognized, the nature of DA actions in the PFC remains controversial. A critical component in DA actions is its modulation of glutamate transmission, which can be different when specific receptors are activated. To obtain a clear picture of cellular mechanisms involved in these interactions, we studied the effects of DA–glutamate coactivation on pyramidal cell excitability in brain slices obtained from developmentally mature rats using whole-cell patch-clamp recordings. Bath application of NMDA, AMPA, and the D1 agonistSKF38393induced concentration-dependent excitability increases, whereas bath application of the D2 receptor agonist quinpirole induced a concentration-dependent excitability decrease. The NMDA-mediated response was potentiated bySKF38393. This NMDA–D1 synergism required postsynaptic intracellular Ca2+and protein kinase A (PKA) and was independent of membrane depolarization. On the other hand, the excitatory effects of both NMDA and AMPA were attenuated by a D2 agonist. Surprisingly, the D2–NMDA interaction was also blocked by the GABAAantagonists bicuculline and picrotoxin, suggesting that the inhibitory action of D2 receptors on NMDA-induced responses in the PFC may be mediated by GABAergic interneurons. In contrast, the D2–AMPA interaction involves inhibition of PKA and activation of phospholipase lipase C–IP3and intracellular Ca2+at a postsynaptic level. Thus, the modulatory actions of D1 and D2 receptors on PFC pyramidal cell excitability are mediated by multiple intracellular mechanisms and by activation of GABAAreceptors, depending on the glutamate receptor subtypes involved.