Transient expression of laminin immunoreactivity in the developing rat hippocampus

We have isolated and characterized a polyclonal antibody that recognizes the extracellular matrix glycoprotein laminin. In the developing rat hippocampus, in addition to staining the basal laminae of blood vessels and the glia limitans, this antibody detects a punctate deposit of non-basal lamina laminin that appears transiently, disappearing on E18. The punctate laminin is distributed throughout the hippocampus from the border of the ependyma and the neuropil to the pial surface, but is particularly concentrated in the presumptive molecular layer (marginal zone). Electron microscopy showed that the punctate laminin was in the extracellular space on the surfaces of cell bodies and, more commonly, their processes. In double-labelling experiments in which neurites were labelled with tau or MAP2 antibodies, there were occasional cases where neurites came into direct contact with punctate laminin. These observations suggest a role for laminin in hippocampal development and possibly in neurite outgrowth.