Tyrosine Hydroxylase Content of Residual Striatal Dopamine Nerve Terminals Following 6‐Hydroxydopamine Administration: A Flow Cytometric Study

Fluorescence‐activated cell sorting based on im‐munolabeling with a monoclonal antibody to tyrosine hydroxylase and a fluorescein‐conjugated secondary antibody was used to identify striatal synaptosomes derived from ni‐grostriatal dopamine nerve terminals. The amount of tyrosine hydroxylase immunoreactivity in dopaminergic striatal synaptosomes prepared from control rats was compared to the amount in dopaminergic synaptosomes prepared from rats that had received intraventricular injections of 6‐hydroxy‐dopamine. Although the absolute number of dopaminergic synaptosomes was decreased in lesioned animals, those residual dopamine terminals present contained more tyrosine hydroxylase than did dopamine terminals from control rats. Both the decrease in the absolute number of dopamine terminals and the increase in tyrosine hydroxylase immunoreactivity in residual terminals were proportional to the extent of the lesion, as determined by measurement of striatal dopamine levels. These results suggest that an increase in the amount of tyrosine hydroxylase protein in residual terminals may represent one compensatory mechanism by which residual dopamine neurons maintain normal striatal function after partial destruction of the nigrostriatal dopamine projection.