Development of Inhibitory Activity of Sulpiride for Synaptic [3H]-Spiperone Binding in the Rat Striatum

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Abstract
To establish the functional development of striatal dopamine (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 mMNa+ compared to that in 70-day-old control animals but not by 50 µM 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 fractional maturity in fetuses at 18 days of gestation and that the Na+ dependence of the effect decreases during aging.