Electrophysiological properties of neural stem cell-derived midbrain neurons reveal functional dopaminergic differentiation as prerequisite for therapeutic approaches

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 strategies 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 isolation, long-term expansion and dopaminergic differentiation of rodent and human mesencephalic neural progenitor cells. Here we perform functional studies using electrophysiological techniques on midbrain neurons derived from rodent mesencephalic progenitor cells. We could show that these cells express A-type currents as well as TEA-sensitive delayed rectifier potassium channels as well as ttx-sensitive sodium currents, and fire action potentials. Furthermore, we detect a slowly activating hyperpolarization-activated inward cation current (Ih), which is specific for dopaminergic neurons among present midbrain neurons. Finally, we measured the response to various concentrations of GABA, glutamate or N-methyl-D-aspartate. The characteristics of GABA-induced currents were typical for GABAA receptors. Nine out of 10 cells expressing glutamate-induced currents also showed functional NMDA receptors with amplitudes of approx. 27% of the mean glutamate amplitude. Our results demonstrate that differentiated mesencephalic progenitors exhibit some major morphological and functional characteristics of dopaminergic neurons. Therefore, these neural progenitor cells might be suitable for regenerative therapeutic approaches in Parkinson's disease.