Bulk application of fluorescent dyes into an area of interest allows us to visualize, by means of confocal microscopy, the gross morphology of particular neuronal pathways forming a complete system. By injecting fluorescent dyes possessing distinct optical characteristics into different brain areas, we can uncover putative overlapping of the axon terminals originating from the various regions. The immunostaining technique offers the opportunity to stain neuron populations based on the transmitter they utilize and/or to stain neural structures according to the presence of particular molecules, such as synapsin, which is present in all presynaptic terminals.