Xenogeneic adrenal medulla graft rejection rather than survival leads to increased rat striatal tyrosine hydroxylase immunoreactivity.

Adrenal medulla has often been used as a donor tissue for transplantation into damaged central nervous system, with functional effects ranging from very good to nonexistent. The grafts have often been associated with morphological evidence of stimulated recipient dopaminergic fiber plasticity. The interpretation of these results has been difficult due to variable but mostly poor graft survival. The present study combines two experiments which evaluated the effects of intrastriatal xenogeneic adrenal medullary cell suspension grafts on rat recipients. First, bovine adrenal medulla cell suspension grafts of various compositions were tested for their functional and morphologic effects on immunosuppressed hemiparkinsonian rats. In the second experiment, graft rejection was allowed to occur in half of the rats in order to determine a possible contribution of the inflammatory/immune response to increased dopaminergic fiber plasticity of the recipient. At 28 days, grafts of all cell types survived well in immunosuppressed rats, but none of the grafted cell types was associated with either an amelioration of amphetamine-induced rotation or an increase in striatal tyrosine hydroxylase immunoreactivity around the graft site. The latter phenomenon was observed only in the nonimmunosuppressed rats with rejected grafts. Our findings strongly support the role of inflammatory/immune response to grafting in stimulating dopaminergic fiber plasticity and in the appearance of sprouting.