Useful models of dendritic arbor formation are the "Xenopus" tadpoles, which are transparent in early stages of larval development and allow for dye-labeled neurons to be repeatedly imaged in the intact animal over several weeks. It has been observed from this and other models that there are rapid dendritic branch additions and retractions which lengthen the overall dendrite and accumulate more branches. This mirrors the development of axonal branches (both have a lifetime of approximately 10min). This activity decreases as neurons mature. Signals including glutamate from axon branches may increase branch additions.