Short-term regulation of information processing at the corticoaccumbens synapse.

In relation to expectation and delivery of reward, pyramidal neurons of the prefrontal cortex either switch from a single spiking mode to transient phasic bursting, or gradually increase their sustained tonic activity. Here, we examined how switching between firing modes affects information processing at the corticoaccumbens synapse. We report that increasing presynaptic firing frequency in a tonic manner either depresses or facilitates synaptic transmission, depending on initial probability of release. In contrast, repeated bursts of stimulation of cortical afferents trigger a new form of short-term potentiation of synaptic transmission (RB-STP) in the nucleus accumbens (NAc). RB-STP involves the regulation of axonal excitability mediated by 4-AP-sensitive potassium channels in afferent cortical neurons. Thus, in a tonic mode, information flow is tightly controlled by regulatory mechanisms at the level of presynaptic terminals, whereas switching to a bursting mode reliably enhances efficacy of information processing for all cortical afferents to NAc neurons.