Transformation of leech microglial cell morphology and properties following co-culture with injured central nervous system tissue

When the leech central nervous system (CNS) is injured, microglial cells mi grate to the site of the lesion. It is possible that the injured CNS releas es diffusible substances that alter the properties of microglial cells; to investigate this, microglial cells were cultured in the presence of injured or uninjured CNS tissue, Grown on Concanavalin A (Con-A), 75 % of microgli al cells are rounded in shape and are avoided by growing neurites, However, when chains of leech ganglia with damaged connectives were cultured on Con -A next to microglial cells, many of the microglial cells changed their mor phology, The number of rounded cells present decreased to 48 %, 4 % became spindle-shaped and 48 % had an intermediate form. In addition, the presence of crushed ganglionic chains allowed more growth of neurites across microg lial cells than occurred under control conditions, although round-shaped mi croglia were still avoided by growing neurites, Similar changes in microgli al cells were produced in cells plated on Con-A in the presence of conditio ned medium from crushed ganglionic chains. Hence, a diffusible substance fr om injured CNS tissue caused the morphology of the microglial cells plated on Con-A to become more like that of microglia plated on laminin, on which only 22 % Of the cells are rounded while the remainder are spindle-shaped a nd are readily crossed by neurites, Changes in morphology were not observed when microglial cells were cultured with frozen and crushed ganglionic cha ins or with uncrushed chains. These experiments demonstrate that substances released from damaged leech CNS cause microglial cells plated on Con-A to change their morphology and the way in which they interact with cells morph ology and growing neurites.