gms | German Medical Science

Objective: Grafting studies in the 6-OHDA rat model of PD have shown that only 8–10% of the grafted embryonic ventral mesencephalic (VM) dopaminergic (DAergic) cells survive. In order to increase this rate, we established a new two-step grafting protocol where a standard amount of VM cells is divided in half and grafted in two separate sessions with a certain time interval. Previous studies from our group revealed that this procedure provides a significantly higher cell survival rate and graft volume compared to the standard transplantation protocol. The aim of this study is to provide an insight into the mechanisms causing this effect by altering the amount of cells in the 1^st graft and by evaluating the two grafts independently using GFP⁺ cells.

Methods: 40 6-OHDA-lesioned adult rats were allotted to 3 two-step grafting groups, each with a time interim of 2, 5 or 9 days between the two transplantation sessions. Each group was sub-divided into 2 subgroups receiving either 2x10⁵ (GFP-) cells in the 1^st grafting and 2x10⁵ (GFP+) cells in the 2^nd (low cell number:2dL, 5dL, 9dL) or 4x10⁵ (GFP-)/2x10⁵ (GFP+) cells per animal respectively (high cell number:2dH, 5dH, 9dH).

As controls, 2 standard transplantation groups were grafted with the same combinations of cells in a single operation session each.

Results: Transplantation effects were evaluated by drug-induced rotation tests, performed 2, 3, and 6 weeks after the 1^st grafting. The animals were sacrificed 8 weeks after transplantation and graft survival was evaluated by stereology.

In the rotation test all transplanted groups showed significant compensation of the lesion indicating good graft survival and dopamine release.

Morphological analysis showed better survival of DAergic cells in the 2d groups in comparison to all other two-step grafting groups. The DAergic cell number in the 2dH group was 24% higher than in the 5dH and 39% higher than in the 9dH. Even greater were the differences (84% and 71%, respectively) for the comparison of the low cell number groups. In addition, grafts showed GFP+ (2^nd graft derived) vessel-like structures present in 60% of the 2dL transplants and 100% of the 2dH and 5dH transplants. These structures only formed in regions where both grafts overlapped and were completely absent in the standard group.

Conclusions: The double-grafting strategy offers a new model to study graft survival and integration, graft‑host and graft-graft interactions as well as the role of transplant vascularization in PD.