Behavioral Changes in Unilaterally 6-Hydroxy-Dopamine Lesioned Rats After Transplantation of Differentiated Mouse Embryonic Stem Cells Without Morphological Integration

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Abstract
Objective. Transplantation of fetal mesencephalic cells into the striatum has been performed in about 350 patients with Parkinson's disease and has been intensively studied in rat models of Parkinson's disease. Limited access to this material has shifted the focus toward embryonic stem (ES) cells. The grafting of undifferentiated ES cells to 6‐hydroxy‐dopamine (6‐OHDA)‐lesioned rats leads to behavioral improvements but may induce teratoma‐like structures. This risk might be avoided by using more differentiated ES cells. In this study, we aimed to investigate differentiated mouse ES cells regarding their in vivo development and fate after transplantation in the striatum in the 6‐OHDA rat model and the behavioral changes induced after transplantation. Methods. Mouse ES cells were differentiated on PA6 feeder cells for 14 days before grafting. Twenty to twenty‐five percent of the neurons obtained were positive for tyrosine‐hydroxylase (TH). PKH26‐labeled cells were transplanted in the striata of unilaterally 6‐OHDA‐lesioned rats. Results. Direct PKH26 fluorescence visualization and TH staining proved the existence of cell deposits in the striata of all grafted animals, indicating cell survival for at least 5 weeks posttransplantation. There was no evidence of tumor formation. Immunocytochemical staining showed glial immunoreactivity surrounding the grafted cell deposits, probably inhibiting axonal outgrowth into the surrounding host tissue. There was a significant reduction in amphetamine‐induced rotational behavior seen in grafted animals, which was not observed in sham‐operated animals. Conclusions. The findings of this study suggest that the amphetamine‐induced rotational behavioral test without histological confirmation is not proof of morphological integration with axonal outgrowth within the first 4 weeks posttransplantation.