Expression of P2X purinoceptors during rat brain development and their inhibitory role on motor axon outgrowth in neural tube explant cultures

Extracellular ATP is well known as a neurotransmitter and neuromodulator in the CNS of adults. However, little is known about the involvement of ATP during the development of mammalian brain. In the present study, we have examined the expression pattern of P2X receptor subtype mRNA and protein during perinatal rat brain development (from embryonic day (E) 10 to postnatal day (P) 16 brain). While P2X₃ receptors appeared early at E11, they declined in the stages that follow. P2X₂ and P2X₇ receptors were expressed from E14 onwards, while P2X₄, P2X₅ and P2X₆ receptors were expressed from P1 onwards. P2X₁ receptor expression was not observed in any of the developmental ages examined. We investigated the effect of 100μM ATP and α,β-methylene ATP (α,β-meATP; selective agonist for P2X₁, P2X_2/3 and P2X₃ receptors) on motor axon outgrowth in collagen-embedded neural tube explant cultures. Both ATP- and α,β-meATP-treated neural tubes showed a significant reduction in neurite outgrowth compared with the control explants. This inhibitory effect could not be reproduced by uridine triphosphate. In conclusion, all P2X receptor subtypes, except for P2X₁, were strongly represented in the developing rat brain. ATP was shown to inhibit motor axon outgrowth during early embryonic neurogenesis, most likely via the P2X ₃ receptor. It is speculated that P2X₇ receptors may be involved in programmed cell death during embryogenesis and that P2X₄, P2X₅ and P2X₆ receptors might be involved in postnatal neurogenesis.