Biogenic Monoamines in the Brain and the Corpus Cardiacum Between Albino and Normal Strains of the Migratory Locust, Locusta migratoria

Abstract

Biogenic monoamines and related compounds were analyzed in the brain and the corpus cardiacum of normal and albino strains of the migratory locust, Locusta migratoria, using a three-dimensional HPLC system with multiple coulometric electrochemical detection. Evidence for the following metabolic pathways was obtained: tyrosine-4 → dihydroxyphenylalanine ( l-dopa) → dopamine → norepinephrine → epinephrine; dopamine → 3-0-methyl dopa → homovanillic acid, and dopamine → 3,4-dihydroxyphenylacetic acid → homovanillic acid in the case of catecholamines; tyrosine-4 → tyramine → hydroxyphenylacetic acid and tyramine → octopamine in the case of phenolamines; and tryptophan → 5-hydroxytryptamine → 5-hydroxyindoleacetic acid and tryptophan → kynurenine in the case of indolealkylamines. The proposed kynurenine pathway is reported for the first time in the neuroendocrine system of an insect. The clearest difference between the albino and control insects was associated with kynurenine. Kynurenine was absent from brain and corpus cardiacum of the fifth instar nymphs on day 0. It was found on day 1 of the fifth nymphal instar and on day 0 of adulthood. However, in albino nymphs, the level was half of that in the controls and kynurenine was not detected in the female brain on day 1. The possible involvement of kynurenine in the development of body color is discussed.