Expression of cholinergic markers in transplants of immature mouse neocortex into adult mouse parietal cortex.

Cerebral cortex of embryonic and newborn mouse was removed and transplanted into adult mouse neocortex to investigate whether the development of cholinergic markers would proceed normally after transplantation. It is shown that both AChE and muscarinic receptors developed in transplanted mouse neocortex. However, while muscarinic receptor binding increased to adult levels in transplants from both pre- and postnatal donors AChE staining intensity only achieved adult levels in tissue from postnatal donors. These results are in accordance with the normal developmental time course of the two different cholinergic markers, since muscarinic receptors appear prenatally in cortex while AChE becomes histochemically detectable after birth. These data suggest that the prenatal donor tissue, unlike the postnatal transplants, lacks an environmental signal for the appearance of AChE stained elements, that is, presumably host AChE fiber ingrowth. Transplantation of immature donor CNS tissue into adult host thus appears to be a useful paradigm to study the regulation of differentiation processes.