Ontogenesis of embryonic porcine ventral mesencephalon in the perspective of its potential use as a xenograft in Parkinson's disease.

Human fetal neural dopaminergic tissue can be transplanted and can ameliorate neurological deficiencies in patients with Parkinson's disease (PD). Donor tissue from other species has been used experimentally for several years in animal experiments and is now being considered an attractive alternative, particularly from a donor species that breeds in large litters, e.g., the pig. We have studied the early ontogenetic development of the mesencephalic dopaminergic system in the pig, utilising an anti-tyrosine hydroxylase (TH) immunocytochemical technique, and demonstrated the earliest appearance of its cell bodies at embryonic day 20 (E20). We compared the porcine data with those of human fetal development, as revealed by the same technique. Embryonic dopaminergic cell groups resembling the A8, A9, and A10 of the rat are present in the pig and differentiate into the homologous cell groups of human, although interesting quantitative differences are apparent. In the pig, prolonged presence of immature characteristics of TH-immunoreactive (TH-i.r.) cell bodies was observed, notwithstanding the early outgrowth of TH-i.r. axons into the ganglionic eminence. In the human, on the other hand, cell divisions and maturation of dendrites have progressed to a further degree than in the pig, before such distinct outgrowth of axons takes place. In pig embryos of 28 days, cells in the ventral mesencephalon had differentiated into TH containing neurons, which indicates their potential to synthesize dopamine. In spite of their differentiation, these cells still showed immature morphological features (rounded cell bodies with undifferentiated, short processes). Dopamine synthesis by these cells was demonstrated in previous studies by the high performance liquid chromatographic technique (HogenEsch et al. [1993] Can. J. Neurol. Sci. 20(suppl. 4):P.S. 235). In a separate paper, we have described that these porcine 28-day dopaminergic cells retain their potential for development and outgrowth in culture (van Roon et al. [1995] Res. Neurol. Neurosci. 7:199-205). We conclude that the ventral mesencephalon in pig embryos of 28 days is a potential source of dopaminergic neurons to be used as a xenograft in PD.