A chemical probe (DECM-PhKA) was developed to study filopodia extension in glial cells with spatio-temporal control. Irradiating DECM-PhKA with blue light releases the neuroactive agonist phenylkainic acid with a half-lifetime of 61 seconds. The effect of rapid uncaging was demonstrated in U118-MG astrocyte cells. The agonist is released locally with high precision using an optic fiber to trigger calcium influx that leads to filopodia extension in the targeted cells. This chemical probe provides a new tool to study the contribution of kainate receptors in transduction of external signals at the single cell level using a physiologically compatible wavelength.