In the many kinds of neuronal transmitters, ATP is a newcomer. Extracellular ATP is known to play several roles as neurotransmitter, neuromodulator and trophic factor in the nervous system. Many functions of extracellular purines are reported in numerous brain areas, where they affect both glial cells and neurons. In developing cerebellar cortex, purinergic stimulation of the inhibitory input to Purkinje cells primarily mediated by activation of P₂X receptors, and the inhibitor of ATP-degrading enzymes suggested endogenous ATP would be released 2 weeks later after birth, however, little is known about the developmental modulation of the released ATP. Recently, we developed a new ATP imaging system using ATP requiring redox enzyme, and observed distribution and transition of ATP release in the developing cerebellar cortex. ATP was released to 100 µM glutamate stimulation and observed in the lower molecular layer and granular layer. The ATP release was increased drastically at postnatal day 10 (P10), and decreased gradually to P14 with depending manner of extracellular [Ca²⁺]. Both AMPA and NMDA could induce ATP release, whereas whereas trans-ACPD could not. In addition, Valproate application to embryonic day 16 p. o. increased ATP release with glutamate stimulation earlier. In this study, we would report expression and distribution of P₂X receptors and glutamate receptors, and discuss the molecular mechanism of ATP signaling.