Development of inhibitory activity of sulpiride for synaptic [3H]-spiperone binding in the rat striatum

To establish the functional development of striatal dopamine2 (DA2) receptors, the effects of NA+ and GTP on the potency of sulpiride in competing for specific [3H]-spiperone binding were investigated in the striatum of developing rats. The IC50 value of sulpiride for specific [3H]-spiperone binding was 31-fold decreased by 100 mM Na+ compared to that in 70-day-old control animals but not by 50 microM GTP. In the presence of Na+, the IC50 of sulpiride was low in fetuses at 18 days of gestation and high at 360 days of postnatal life. It is suggested that the Na+-dependent binding of sulpiride to DA2 receptors probably reaches functional maturity in fetuses at 18 days of gestation and that the Na+ dependence of the effect decreases during aging.