Cryopreservation and storage of embryonic rat mesencephalic dopamine neurons for one year: comparison to fresh tissue in culture and neural grafts.

Blocks of embryonic rat ventral mesencephalic tissue containing the developing A8-A10 dopamine (DA) cell groups were cryopreserved and stored for approximately 1 year, at which time this tissue was thawed, dissociated into a cell suspension, and compared to a similar preparation of fresh mesencephalic tissue for viability in tissue culture and neural grafts. Estimates of total cell number immediately prior to plating in culture indicated that cryopreserved tissue yields fewer cells, but when this reduced cell number is compensated for, and equal numbers of cells were plated in culture, approximately equal total numbers of neurons, as well as tyrosine hydroxylase (TH)-positive neurons, were present in cultures from cryopreserved and fresh tissue. Grafting of equal numbers of fresh and cryopreserved mesencephalic cells into the striatum of adult rats with large unilateral lesions of the nigrostriatal DA pathway tended to yield smaller grafts with fewer surviving TH-positive cells with less extensive neuronal processes when tissue was previously cryopreserved. However, grafts derived from freeze-stored tissue provided a similar time-course and extent of behavioral recovery in amphetamine-induced rotational tests to that provided by fresh tissue grafts. Taken together, our findings indicate that while cryopreservation of mesencephalic tissue has its costs--reduced cell yield in cultures and grafts, and compromised morphology in grafts--sufficient numbers of cryopreserved neurons survive the grafting procedure to ameliorate behavioral signs of DA depletion in the lesioned rat model.