Catalepsy induced by α-methyl-p-tyrosine and d-amphetamine: The rÔle of catecholamine metabolism

The effect of inhibition of monoamine oxidase (MAO), catechol-O-methyltransferase (COMT) and Dopa-decarboxylase on the catalepsy induced by d-amphetamine in -methyl-p-tyrosine (-MpT) treated rats has been investigated.Administration of an MAO inhibitor concomitant with -MpT slightly antagonized the cataleptic state, but when given 2 h later was without an appreciable effect. Only when an inhibitor was injected at an extremely high dose level 18 h prior to -MpT did catalepsy fail to develop.Following COMT inhibition the cataleptic state was enhanced. After Dopa decarboxylase inhibition the catalepsy developed as usual for the first 3 h post-amphetamine, but then declined in intensity.It is concluded that neither deaminated nor O-methylated products are responsible for the development of catalepsy. In fact, the indication is that the catalepsy may be antagonised by an O-methylated derivative. A possible explanation for the action of the Dopa decarboxylase inhibitor is discussed.