Differential effect of morphine on dopaminergic neurons in frontal cortex and striatum of the rat

Inhibition of dopamine synthesis by a single injection of α-methyl-para-tyrosine (200 mg/kg, i.p.) was complete from 30 to at least 300 min after administration. When morphine (20 mg/kg) was given intraperitonealy 30 min after α-MpT treatment an enhanced decline of dopamine was observed in frontal parts of the cortex but not in the striatum. These results indicate that morphine affects dopaminergic neurons in frontal parts of the cortex in a way differently from those in the striatum of the rat. This may be caused either by a difference in the properties of dopaminergic nerve endings in both structures or by an effect of morphine on the input to the cortical system which is lacking in the striatum.