Expression of tyrosine hydroxylase mRNA in transplanted fetal dopamine neurons

Expression of genes coding for synthesis of secretory products has been shown to be an important index of neuronal activity. Gene expression in transplanted fetal substantia nigra (SN) was examined for the first time, utilizing in situ hybridization with a probe for tyrosine hydroxylase mRNA. Three months after implantation, the grafts contained many labeled neurons. Compared to host SN neurons, the grafted dopaminergic cells expressed more message for the enzyme, while they showed lower amounts of the enzyme itself. This result suggests that a molecular approach applied to neural transplantation can detect important if subtle differences in graft cell activity.