Dopaminergic innervation of the rat globus pallidus characterized by microdialysis and immunohistochemistry

The present study examined the dopaminergic innervation of the rat globus pallidus by in vivo microdialysis and immunohistochemistry in more detail. Using tyrosine hydroxylase immunohistochemistry, two classes of dopaminergic fibers were distinguished morphologically in the globus pallidus. Unilateral infusion of 6-hydroxydopamine into the substantia nigra produced a loss of dopaminergic fiber density in the globus pallidus which was correlated with the nigral extent of the lesion. These findings are in line with the notion that a degenerative loss of nigral dopaminergic cell bodies might also affect the dopamine input of extrastriatal structures such as the globus pallidus. Using in vivo microdialysis, we tested whether dopamine measured in the globus pallidus is of neuronal origin. Perfusion of tetrodotoxin induced a strong and transient decrease of pallidal dopamine. The tetrodotoxin-sensitivity of pallidal dopamine demonstrates the functional significance of the nigropallidal dopaminergic innervation.