In rat prefrontal cortex (the prelimbic area of medial frontal cortex), the induction of long-term depression (LTD) and long-term potentiation (LTP) of glutamatergic synapses is powerfully modulated by dopamine. The presence of dopamine in the bathing medium facilitates LTD in slice preparations, whereas in the anesthetized intact brain, dopamine released from dopaminergic axon terminals in the prefrontal cortex facilitates LTP. Dopaminergic facilitation of LTD is at least partly achieved by postsynaptic biochemical mechanisms in which enzymatic processes triggered by dopamine receptor activation cooperate with those triggered by glutamate metabotropic receptor activation. Evidence suggests that dopamine facilitates LTP also in the slice condition. In this case, dopamine receptors must be pre-stimulated ('primed') before the application of high-frequency stimuli in the presence of dopamine. This procedure may mimic baseline stimulation of dopamine receptors that occurs under physiological conditions.
