Survival and function of dissociated rat dopamine neurones grafted at different developmental stages or after being cultured in vitro.

The in vitro culture approach was combined with the cell suspension grafting technique to examine whether the maturation of dopamine (DA) neurones in vitro imposed similar limitations on their ability to survive grafting as when they are allowed to develop in situ in the fetus. The functional capacity, survival and growth of DA neurones from 2.5- and 7-day-old cultures, grafted to rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway, was compared with similar grafts freshly prepared from fetal donors of embryonic days 14, 16 and 20. Grafts of freshly dissociated mesencephalic DA neurones, taken from embryonic day 14-16 donors and 2.5-day-old cultures, generally survived well and markedly reduced amphetamine-induced rotational asymmetry in the recipient rats. However, when cultured for 7 days prior to grafting, or when taken from 20-day-old fetuses, the mesencephalic DA neurones survived very poorly and the grafts did not have any functional effects. Plating of aliquots of cell suspension used for grafting indicated that the survival rate of dissociated DA neurones is in the same order of magnitude when grown in vitro (about 2 DA neurones per 1000 cells) as when grafted in vivo to the rat striatum (about 1-5 DA neurones per 1000 cells). When the number of surviving grafted DA neurones was plotted against the behavioural effects of the grafts, a threshold number of around 100-200 DA neurones was found necessary to obtain a marked reduction (greater than 50%) in amphetamine-induced rotational asymmetry. Moreover, the survival of 300-500 DA neurones seemed to produce a 'ceiling effect' beyond which additional surviving DA neurones gave rise to little or no further effect on the amphetamine-induced rotational behaviour.