N- β-alanyldopamine and N-acetyldopamine occurrence and synthesis in the central nervous system of Manduca sexta (L.)

Abstract

N- β-Alanyldopamine (NBAD), N-acetyldopamine (NADA), dopamine (DA), and 3,4-dihydroxyphenylalanine (DOPA) were detected in the brain and ganglia of the central nervous system of larval and adult tobacco hornworms, Manduca sexta, by reversed phase HPLC with electrochemical detection. NBAD predominated in larval neural tissue during development of the fifth instar and increased to peak concentrations of 936, 650 and 263 nmol g −1 in the abdominal ganglia, subesophageal plus thoracic ganglia and brain, respectively, at the wandering stage of development. Concentrations of all catecholamines decreased in the pharate pupa and were generally lowest in the adult nerve cord. DA was the second most abundant catecholamine in larval ganglia, but the primary catecholamine in adult ganglia. Relatively high levels of DOPA also occurred in the ganglia of wandering larvae but not at other times. NADA was detected only in the abdominal ganglia of day 3 larvae. N-Acyltransferases that catalyze synthesis of NBAD and NADA from DA also were present in abdominal ganglia, as demonstrated by analysis of in vitro cultures in which exogenous DA stimulated synthesis of both N-acylated catecholamines. Maximal NBAD synthesis occurred in ganglia removed from wandering stage larvae (9.3 nmol g −1 day −1), whereas NADA synthesis was highest in ganglia from pharate pupae (7.3 nmol g −1 day −1). Thus, N- β-alanylation and N-acetylation are competing metabolic reactions for DA in the hornworm's nervous system. The role played by the N-acylated catecholamines in M. sexta neurophysiology is unknown, but these compounds may be storage or inactive forms of the putative neurotransmitter DA.