The lamination of dentate gyrus afferents established during development is maintained following lesion-induced reactive growth in the adult. After partial deafferentation sprouts from undamaged afferents restore most synapses, while respecting the laminae relative boundaries. No evidence of trans-laminar sprouting has been found. Here, we review the information gathered during the last decade on the cellular and molecular bases of dentate synaptogenesis, with special attention to the role of glia during development and that of reactive glia after deafferentation. The interactions of neurons with astroglia and astroglial macromolecules, particularly proteoglycans, influence synapse segregation in the dentate gyrus, providing us with a reasonable explanation for afferent lamination.