We have shown that we can effect a localized and constant perfusion of small (∼10-50 μm) synaptic regions for minutes up to ∼ 1 hr. This type of treatment mimics the tonic presence of neurotransmitters and modulators. Synaptic events, and many modulatory events, however, occur phasically. Similarly, activation of signaling pathways such as MAPK (Wu et al., 2001) and CREB (Kida et al., 2002) are sensitive to the timing and pattern of stimulation. The 3-inlet design of the μLP chamber allows increased temporal control of the perfusate. Using the advantages of laminar flow, which is defined by a no-slip boundary condition, if there is lower pressure in the center well delivering the perfusate, the outer two wells containing medium will merge resulting in an effective evacuation of the perfusate from the central region. This property can be used to rapidly turn on and off the perfusate. As an initial demonstration of this principle, we fluctuated the pressure in the center well to effect a pulsatile delivery of the Alexa Fluor 488 dye with subsecond resolution (Figure 4D).
