Extracellular ATP has an important role as neurotransmitter and neuromediator, by activating P2X and P2Y purinergic receptors in the nervous system. P2X receptors are ligand-gated ion channels which are permeable for calcium and monovalent cations. To this time, seven subunits (P2X₁-P2X₇) of these receptors, being able to form homo or heteromeric functional channels, have been cloned. P2X receptors are abundantly distributed, and functional responses are seen in neurons, glia, epithelia, endothelia, bone, muscle, and hemopoietic tissues. The molecular composition of native receptors is becoming understood, and many cells express more than one type of P2X receptor. Besides being involved in innumerous physiological processes and neuronal signal transmission, P2X receptor gene expression is regulated during neuronal differentiation in vitro and in vivo.  We have studied differential gene expression of P2X₂ and P2X₆ receptors, belonging to the most predominant P2X receptors in the brain, during neuronal differentiation of P19 embryonal carcinoma cells as in vitro model for early neuronal development. Following treatment with retinoic acid (10^-6M), these cells undergo neuronal differentiation, which is complete after 7 to 9 days when differentiated cells express neuron-specific proteins.   RT-PCR experiments were used for detection of gene expression of P2X₂ and P2X₆ receptors. Additionally, in situ hybridization experiments were realized to confirm the results obtained by RT-PCR.  We demonstrate that P2X₂ receptors are expressed more intensively from day 4 on of differentiation when cells become post-mitotic and undergo neuronal maturation. P2X₆ receptor gene expression is present throughout neuronal differentiation, whereby an alternatively spliced form being predominantly expressed. As the splice variant codes for a truncated receptor protein, we suggest that alternative splicing contributes to the regulation of functional P2X₆ receptors during neuronal differentiation.