The rate of decline of α-methyl- m -tyramine (MMTA) from the corpus striatum of the rat can be altered by drugs acting on the dopamine (DA) receptor. By the use of this false dopaminergic transmitter, amine release by drugs acting directly on the neurone can be distinguished from that by drugs acting indirectly via DA receptor interaction. The rate of disappearance of MMTA is much slower than that of DA after tyrosine hydroxylase inhibition, but the combination of synthesis blockade and monoamine oxidase blockade greatly slowed the rate of DA decline, suggesting that normally much DA is metabolized intraneuronally. The decline rate of MMTA appears to accurately reflect the striatal DA neurone impulse flow rate under normal conditions or after administration of drugs which act only to alter impulse flow.
