Analysis of Octopamine, Dopamine, 5-Hydroxytryptamine and Tryptophan in the Brain and Nerve Cord of the American Cockroach

The monohydroxy analogue of norepinephrine, octopamine (OA), appears as a trace amine in a variety of vertebrate tissues (Yui et al., 1980; Boulton and Juorio, 1981), and is a primary component of the insect nervous system (Evans, 1980). In insects, OA serves as a neurotransmitter, neuromodulator and neurohormone (Orchard, 1982) and has been proposed as the sympathomimetic effector of physiological responses to excitation (Hoyle, 1975; Downer, 1979). The demonstrated importance of OA in insects, together with its potential significance in vertebrates, indicates the need for a convenient, sensitive procedure for simultaneous determination of OA and other monoamines in small amounts of biological tissue. High performance liquid chromatography (HPLC) with electrochemical detection (E1CD) has been used successfully to estimate catecholamines and 5-hydroxytryptamine (5-HT) (Shoup, 1982), but the high potential required to electro-oxidize OA has generally excluded this compound from such analyses (Bailey et al., 1982). The problem of detection has recently been resolved by the use of two coulometric detectors in series (Martin et al. 1983). Eluant from the HPLC column is first exposed to a detector set at a relatively low potential which effects complete oxidation of catecholamines; the eluant then passes to a second detector which is set at the higher potential required for oxidation of phenolamines.