The efficacies of various agents that affect monoamine synthesis, oxidation and methylation were evaluated in the scallop, Placopecten magellanicus, through the use of high performance liquid chromatography with electrochemical detection. 2. Central ganglia, labial palps and feet from animals bathed in 10(-5) M or 10(-4) M alpha-methyl-p-tyrosine for 1 day followed by 3-6 day recovery in artificial sea water had significantly reduced concentrations of 3,4-dihydroxyphenylalanine, norepinephrine, epinephrine, dopamine and 3,4-dihydroxyphenylacetic acid. 3. Central ganglia, labial palps and feet from scallops incubated in 10(-5) M or 10(-4) M para-chlorophenylalanine for 1 day followed by a 3-6 day wash in artificial sea water had significantly reduced concentrations of 5-hydroxytryptophan, 5-hydroxytryptamine and 5-hydroxy-3-indoleacetic acid. 4. Monamine oxidase inhibitors (administered at 10(-4) M for 1 day followed by a 2-day recovery) significantly decreased the concentrations of 3,4-dihydroxyphenylalanine and 5-hydroxy-3-indolacetic acid and increased the concentrations of their corresponding precursors in tissues. Deprenyl, a monoamine oxidase type B inhibitor, generally had more potent effects than pargyline, which inhibits monoamine oxidase type B and type A. Clorgyline, a monoamine oxidase type A specific inhibitor, showed few significant effects on the levels of the monoamines or their precursors or metabolites. 5. Bath application of 10(-4) M 3,5-dinitrocatechol, a blocker of catechol-O-methyl transferase, resulted in significant decreases in the concentrations of normetanephrine and metanephrine in nervous and other tissues and increased the levels of their corresponding precursors, dopamine, norepinephrine and epinephrine. 6. Generally, treatments that appeared to directly cause changes in levels of catecholaminergic compounds indirectly resulted in inverse changes in levels of indolaminergic compounds, and vice versa. This suggests an interaction between these transmitter systems. 7. The detection of monoaminergic compounds and dramatic changes in their concentrations following various drug effects strongly suggests the presence of mammalian-type metabolic pathways leading to synthesis and subsequent inactivation of monoamines.
