Tyrosine Hydroxylase Immunoreactivity and Monoamine and Metabolite Levels in Cryopreserved Human Fetal Ventral Mesencephalon

Both fresh and cryopreserved-thawed human fetal ventral mesencephalon have been used for preclinical research and implantation into the brains of patients with Parkinson's disease. Further characterization and an evaluation of the effects of cryopreservation on immunocytochemical and neurochemical markers of monoamine neurons in human fetal ventral mesencephalic tissue are reported here. Fresh and cryopreserved-thawed human fetal mesencephalic tissue of 7-10 weeks fetal age was analyzed for the presence of tyrosine hydroxylase-like immunoreactivity and levels of dopamine (DA), norepinephrine, serotonin, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole acetic acid. After fixation, cryopreserved-thawed mesencephalic tissue exhibited cellular tyrosine hydroxylase-like immunoreactivity identical to that seen in fresh tissue. The levels of DA, norepinephrine, serotonin, and 5-hydroxyindole acetic acid in the cryopreserved thawed tissue were the same as the levels in fresh tissue. The levels of DOPAC were higher, and those of HVA were lower, in the cryopreserved-thawed tissue compared to the levels in fresh tissue. The changes in the levels of the DA metabolities, DOPAC and HVA, without corresponding change in the levels of the parent monoamine in cryopreserved-thawed tissue, indicate ongoing metabolic activity in DA-containing neurons. These results further suggest that cryopreservation and subsequent thawing does not have a measurable adverse effect on DA biosynthesis in the human fetal mesencephalon. The presence of the monoamines and their metabolites in the ventral mesencephalon at 7-10 weeks of fetal age coincides well with the early presence of immunocytochemical markers of monoamine neurons and reflects the early function of the nuclear groups containing specific monoamine neurotransmitters.