A method of differentiating adult stem cells, such as those derived from a teratocarcinoma cell line, the Ntera2/D1 clone (NT2). The developed cells exhibit a stable neurotransmitter phenotype without the required use of growth factors or retinoic acid in differentiation process, which may be difficult to completely remove during commercial production. An identification of specific neurotransmitters is possible in these differentiated NT2-derived neurons (NT2-N) after 30 days in culture or 30 days survival in vivo. The invention includes a method to stably differentiate neuronal stem/precursor cells to a neuronal phenotype for use in cell replacement therapy for neurodegenerative disease, stroke or spinal cord injury. At least four different types of neurons are produced from this method of differentiation: dopaminergic, cholinergic, GABAergic and glutaminergic. Additionally, since the cells are a cancer stem cell prior to differentiation, they may serve as a model system for developing anti-cancer therapies aimed at the cancer stem cell, rather than the more differentiated daughter cell.