Fine structure of an octopaminergic neuron and its terminals

Abstract

The large octopaminergic dorsal unpaired median neuron of the locust that innervates the extensor tibiae muscle, DUMETi, was examined electronmicroscopically. Its soma contains many Golgi complexes apparently making dense-core vesicles similar to those found in peripheral branches and terminals. There are also larger stores of the dense material in the soma, especially near the exit of the principal neurite, that are not in vesicular form. Since the neurons can be penetrated and stimulated by microelectrodes, they form favorable subjects for direct studies of the control of neurosecretion. Preterminal fine branches of the neuron were located in proximal outer bundles of muscle fibers into which they had been traced electrophysiologically. They contain numerous large dense-core vesicles arrayed in rows near microtubules. These fine branches have a thick layer of collagenous connective tissue between the axon and the muscle fiber. Final terminals have varicosities containing many vesicles, lying inside the outer layers of the sarcolemmal complex of muscle fibers. They do not form synaptic structures. Terminals of another DUM neuron, one that innervates the dorsal longitudinal flight muscles (DUMDL), were similar in detail to those of DUMETi. DUMETi swelled about 20-fold in cross-sectional area above a ligature, in a 12-hr period, indicating that there is an extensive centrifugal flow of material in it, and sprouted a branch.

Mechanism of the Insect Enzyme, Tyramine β-Monooxygenase, Reveals Differences from the Mammalian Enzyme, Dopamine β-Monooxygenase

“…It is not known definitively whether T␤M is expressed in similar vesicles of the invertebrate nervous system. Octopamine, however, is associated with dense core vesicles of dorsal unpaired median neurons in locusts (29,30), and studies also have shown that T␤M is localized in octopaminergic neurons/cell bodies (of honeybees and lobster) (8,9,31). A recent study demonstrated that octopamine-containing cells of the Drosophila reproductive system, including vesicles of the ovarian sheath, were immunoreactive for T␤M.…”

Peripheral distribution of presynaptic sites of abdominal motor and modulatory neurons inManduca sexta larvae

“…At the ultrastractural level, dendritic neuronal processes in the central nervous system and peripheral neuromuscular terminals of the UM neurons appear to contain large dense-core vesicles, together with less numerous, small clear vesicles. However, dense-core vesicles, which are thought to contain octopamine, were never found in typical presynaptic specializations, suggesting that octopamine may be released nonsynaptically (Oertal et al, 1975;Hoyle et al, 1980;Kiss et al, 1984;Watson, 1984;Atwood et al, 1993;Rheuben, 1995;Pflü ger and Watson, 1995).…”

Octopamine immunoreactivity in the fruit fly Drosophila melanogaster

“…Octopamine regulates hormone release in cockroaches (Downer et al, 1984), induces lipid and carbohydrate metabolism in crickets (Fields and Woodring, 1991), and modulates feeding behavior of blowflies (Long and Murdock, 1983) and bees (Bicker and Menzel, 1989;Braun and Bicker, 1992). Additionally, both somatic and visceral muscles are innervated by octopaminecontaining endings in several insect species (see, e.g., Hoyle et al, 1980). Physiological studies indicate that octopamine has excitatory modulatory actions at these muscles (Hoyle, 1984;Hidoh and Fukami, 1987;Malamud et al, 1988).…”