To understand the repercussion of drug-evoked synaptic plasticity on the behavior of mesocorticolimbic DA system neural circuitry, synaptic transmission must be studied in a cell-type specific manner on identified inputs. In other words, future studies will have to resolve the origin of the synapses being monitored (i.e. which afferents are being stimulated), the detailed identity of the recorded neurons and the targets to which these neurons project. Approaches such as cell-type specific expression of fluorescent markers, retrograde labeling of neurons using in vivo injection of retrobeads or viruses, and expression of ChR2 or the inhibitory halorhodopsin in restricted sets of afferents by vector delivery into upstream brain areas will have to be applied in combination so that control of identified sets of synapses can be achieved (Witten et al., 2010; Stuber, 2010; Wall et al., 2010; Haubensak et al., 2010; Ciocchi et al., 2010).
