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Summary 1.Earlier reports from this and other laboratories have indicated that wide variations exist in estimates of the concentrations of norepinephrine in the brain and heart of the snailHelix aspersa. This is a report on investigations of norepinephrine concentrations inHelix aspersa tissues using high-performance liquid chromatography with electrochemical detection. In addition, the effects of treatment with some amino acid precursors or enzyme inhibitors on the concentrations of norepinephrine, dopamine, 5-hydroxytryptamine, and some of their metabolites were investigated.2.The levels of norepinephrine in the brain were low (46 ng/g) in comparison to dopamine (2.1)εg/g) and 5-hydroxytryptamine (2.6εg/g). Epinephrine was not observed in either snail heart of snail nervous tissue.3.Administration ofl-3,4-dihydroxyphenylalanine resulted in elevated snail brain dopamine, while 3,4-dihydroxyphenylserine treatment increased norepinephrine. Treatment with blockers of tyrosine hydroxylase and aromatic-l-amino acid decarboxylase reduced dopamine concentrations without affecting 5-hydroxytryptamine.4.The dopamine metabolite 3,4-dihydroxyphenylacetic acid was observed only after administration ofl-3,4-dihydroxyphenylalanine or dopamine and then only in very small amounts. At no time was the dopamine metabolite homovanillic acid or the 5-hydroxytryptamine metabolite 5-hydroxyindoleacetic acid observed in brain, heart, or whole-body extracts of the snail.5.Incubation of nervous tissue with either dopamine or 5-hydroxytryptamine resulted in the production of electrochemically active metabolites which were identified by oxidation characteristics and cochromatography with synthesized standards as theγ-glutamyl conjugates of the amines. Treatment of snails with 5-hydroxytryptamine or dopamine also resulted in the production ofγ-glutamyl conjugates.6.The present experiments show that great care must be exercised when measuring monoamines and their metabolites in gastropod tissues by highperformance liquid chromatography with electrochemical detection. |
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