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Trophic and tropic effects of striatal astrocytes on cografted mesencephalic dopamine neurons and their axons

Astrocytes from the ventral mesencephalon and from the striatum respectively promote the dendritic and axonal arborization of dopamine (DA) neurons in vitro. To test this response in vivo, astrocytes in primary cultures from the neonatal cerebral cortex, ventral mesencephalon, or striatum were coimplanted with fetal ventral mesencephalic tissue into the intact or DA‐denervated striatum of adult rats and these cografts examined after 3–6 months by tyrosine hydroxylase (TH) immunohistochemistry (intact recipients) or after 5–6 months by in vitro [H]DA‐uptake autoradiography (DA‐denervated recipients). In contrast with single ventral mesencephalic grafts, all types of cograft displayed a rather uniform distribution of TH‐immunoreactive perikarya. The average size of TH‐immunoreactive cell bodies was not significantly different in cografts containing cortical or mesencephalic astrocytes and in single ventral mesencephalic grafts, but it was significantly larger in cografts containing striatal astrocytes. Nevertheless, the number of [H]DA‐labeled terminals in the DA‐lesioned host striatum was clearly smaller with cografts of striatal astrocytes than with single mesencephalic grafts or with cografts containing cortical astrocytes. On the other hand, cografts of striatal astrocytes contained much higher numbers of [H]DA‐labeled terminals than the other types of graft or cograft. Thus, while cografted astrocytes in general influence the distribution of DA neurons within the graft, astrocytes from the neonatal striatum have a trophic effect on DA perikarya and a tropic effect on DA axons, keeping the latter within the graft.