Embryonic and mature astrocytes exert different effects on neuronal growth in rat ventral mesencephalic slice cultures

One obstacle with grafting of dopamine neurons in Parkinson’s disease is the insufficient ability of the transplant to reinnervate the host striatum. Another issue is the prospective interaction between the donor fetal tissue and the adult astrocytes of the host. To study nerve fiber growth and its interaction with immature/mature astrocytes, ventral mesencephalic (VM) organotypic rat tissue cultures from embryonic days (E) 12, E14, and E18 were studied up to 35 days in vitro (DIV), and co-cultures of E14 VM tissue and mature green fluorescent protein (GFP)-positive astrocytes were performed. Generally, nerve fibers grew from the tissue slice either in association with a monolayer of migrated astroglia surrounding the tissue (glial-associated), or distal to the astroglia as non-glial-associated outgrowth. The tyrosine hydroxylase (TH)-positive glial-associated nerve fiber outgrowth reached a plateau at 21 DIV in E12 and E14 cultures. In E18 cultures, TH-positive neurons displayed short processes and migrated onto the astrocytes. While the non-glial-associated nerve fiber outgrowth dominated the E14 cultures, it was found absent in E18 cultures. The GFP-positive cells in the VM and GFP-positive astrocyte co-cultures were generally located distal to the monolayer of migrated fetal astrocytes, a few GFP-positive cells were however observed within the astrocytic monolayer. In those cases TH-positive neurons migrated towards the GFP-positive cells. Both the non-glial- and glial-associated nerve fibers grew onto the GFP-positive cells. Taken together, the glial-associated growth has limited outgrowth compared to the non-glial-associated nerve fibers, while none of the outgrowth types were hampered by the mature astrocytes.