Functional characterization of dopaminergic neurons derived from rodent mesencephalic progenitor cells

Neural progenitor cells existing in the developing and adult brain retain the capacity to self renew and to produce the major cell types of the brain opening new avenues for restorative therapy of neuropsychiatric disorders. These cells can be grown in vitro while retaining the potential to differentiate into nervous tissue. A primary target for neurorestoration is Parkinson's disease, characterized by a continuous loss of the dopaminergic neurons in the substantia nigra pars compacta leading to dopamine depletion in the striatum and subsequent clinical symptoms including bradykinesia, rigidity and tremor. We established a protocol for long-term expansion and dopaminergic differentiation of rodent and human mesencephalic neural progenitor cells. Here we perform functional studies using both biochemical and electrophysiological techniques on dopaminergic neurons derived from rodent mesencephalic progenitor cells labeled with tyrosine hydroxylase (TH) gene promotor-driven expression of enhanced green fluorescence protein (EGFP). Thus, we demonstrate that these cells produce and release dopamine, express voltage-gated potassium and sodium currents, and fire action potentials. Furthermore, we detect a slowly activating hyperpolarization-activated inward cation current (I(h)), which is specific for dopaminergic neurons among present midbrain neurons. Our results demonstrate that differentiated mesencephalic progenitors exhibit some major morphological and functional characteristics of dopaminergic neurons. Therefore, these neural progenitor cells might serve as a useful source of dopaminergic neurons for studying the development and degeneration of these cells and may further serve as a continuous, on-demand source of cells for therapeutic transplantation in Parkinson's disease.