Short Communication Octopamine in a Neurohaemal Area within the Antennal Heart of the American Cockroach

A great deal of research suggests that octopamine functions as a neuromodulator, neurotransmitter and neurohormone in insects (Orchard, 1982; Evans, 1985; Hoyle, 1985). Especially high concentrations of this biogenic amine have been reported for neurohaemal tissue such as the corpora cardiaea and the neurohaemal organs of the medial nervous system (Evans, 1985). In the presented paper, octopamine is shown to occur in another neurohaemal area located within the antennal heart of the cockroach, Periplaneta americana. The antennal heart is a circulatory organ consisting of two ampullae that are attached to the frontal cuticle, medial to the bases of the antennae (Fig. 1A). The ampullae are interconnected by a transverse muscle which functions as a dilator, expanding the lumina of both ampullae simultaneously upon contraction; the elasticity of the ampullae walls returns them to their original shape during relaxation of this muscle (Pawlowa, 1895; Pass, 1985). Within the walls of the ampullae numerous interstitial neurosecretory terminals can be found which are clearly neurohaemal releasing sites (Beattie, 1976; Pass, Agricola, Birkenbeil & Penzlin, 1988). Neuroanatomical investigations employing cobalt ionophoresis revealed that these terminals originate from neurones in the suboesophageal ganglion. Among other neurones unpaired cells were stained which strongly resemble, in their morphology and location, the well-known dorsal unpaired median (DUM) neurones (Passed al. 1988). As all individually investigated DUM neurones are octopaminergic (Evans, 1985; Orchard & Lange, 1985), a search was made for the presence of octopamine in the antennal heart.