Cholecystokinin in intracerebral transplants.

Fetal mesencephalic tissue containing dopamine and cholecystokinin-immunoreactive neurons was grafted to the striatum of adult host rats, either as solid pieces of tissue or as cell suspensions. The dopaminergic innervation of the striatum was previously ablated unilaterally by neurotoxin. Immunohistochemical analysis using antibodies to cholecystokinin and tyrosine hydroxylase was performed at least 8 weeks after grafting. Neurons immunoreactive to tyrosine hydroxylase or cholecystokinin, as well as neurons immunoreactive to both compounds were found in the transplants. In the solid tissue grafts the proportions of neurons exhibiting either CCK- or tyrosine hydroxylase-like immunoreactivity to neurons exhibiting both immunoreactivities were similar to those seen in intact ventral mesencephalon. This suggests that these neurons are able to maintain and express their transmitter phenotypy when transplanted to an ectopic location. An extensive outgrowth of fibers containing tyrosine hydroxylase-like immunoreactivity, but apparently lacking cholecystokinin-like immunoreactivity, was observed in the host striatum. Cholecystokinin-immunoreactive fibers were found in a narrow zone immediately adjoining the graft. The results suggest the possibility that growth-regulating mechanisms in the denervated host striatum selectively favor the ingrowth of fibers from the appropriate dopaminergic neuronal subset.