Plasminogen expression in the neonatal and adult mouse brain.

Tissue-type plasminogen activator (tPA) has been implicated in a variety of types of neural plasticity, including cell migration, occlusion-induced visual system plasticity, and learning. In the periphery, plasminogen serves as tPA's primary substrate; however, studies attempting to identify plasminogen in the central nervous system have produced mixed results. We have performed a comprehensive, multitechnique study examining plasminogen expression in the neonatal and adult mouse brain. Reverse transcription polymerase chain reaction (RT-PCR) and in situ hybridization reveal plasminogen mRNA in the cortex, hippocampus and cerebellum of both neonatal and adult C57BL/6 mice. Immunocytochemistry reveals plasminogen protein expression in these same brain regions. Notably, plasminogen expression in the cerebellum occurs in the granule cell and the Purkinje cell layers. tPA activity in these same regions is involved in granule cell migration during development and motor learning in adulthood. Therefore, these findings demonstrate that plasminogen is present in the central nervous system and localized to areas where it could serve as a substrate for plasticity-related increases in tPA activity.