Expression of BDNF and trkB mRNAs in comparison to dopamine D1 and D2 receptor mRNAs and tyrosine hydroxylase-immunoreactivity in nigrostriatal in oculo co-grafts.

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, expresses potential effects on survival and outgrowth from dopaminergic neurons in ventral mesencephalon. In this study we have examined the expression of BDNF mRNA and its high affinity trkB receptor mRNA in the nigrostriatal system after grafting to the anterior chamber of the eye. The BDNF mRNA expression has been compared to the dopaminergic innervation of striatum as revealed by tyrosine hydroxylase (TH) immunohistochemistry and the development of D1 and D2 subtypes of the dopamine receptor mRNAs. Ventral mesencephalon and striatum anlage were either co-grafted or grafted alone and evaluated 2 weeks (immature grafts) or 6 weeks (mature grafts) after transplantation. In situ hybridization for BDNF revealed a positive signal over large neurons in the ventral mesencephalic grafts with an increased silver grain density in the mature grafts. The striatal grafts were negative for BDNF mRNA at both time points evaluated, but in situ hybridization for trkB truncated mRNA revealed increased silver grain density in both the ventral mesencephalic grafts and striatum, with a patchy appearance. The D1 and D2 mRNAs were expressed in a patchy pattern in the striatum both in single grafts and when co-implanted with ventral mesencephalon at both time points evaluated. Often the patches of D1 mRNA did not overlap with the D2 mRNA patches. TH-immunohistochemistry revealed positive neurons in all ventral mesencephalic grafts and a dense patchy innervation of the striatal co-grafts. In conclusion, the trkB truncated mRNA and the dopamine receptor mRNAs were expressed in the striatal graft independent of the contact to a ventral mesencephalic transplant and the dopaminergic input, and BDNF mRNA expression in the ventral mesencephalic transplants was independent of the contact to its striatal target.