An octopaminergic neurone modulates neuromuscular transmission in the locust

OCTOPAMINE, a biogenic amine, occurs widely in the nervous systems of vertebrates and invertebrates1–3. It has been found in single neurones in the central nervous system of the marine mollusc, Aplysia4 and also in peripheral neurosecretory neurones in the lobster5,6 from which a calcium-dependent release of octopamine has been demonstrated7,8. Specific octopamine receptors9 and octopamine activated adenylate cyclases10 have also been found in invertebrate nervous tissue. This has led to the suggestion of a neurotransmitter role for octopamine in invertebrates1,3. In the absence, however, of an example in which the effect of stimulating an identified octopamine containing neurone on its identified target or end organ is known, the true function of octopamine remains obscure. This paper aims to demonstrate that octopamine is the neurotransmitter of a single identified neurone in the locust Schistocerca americana gregaria. This neurone, which is shown to contain octopamine, innervates a muscle where it functions as a neuromodulator by potentiating the synaptic potential and tension produced by an identified motoneurone. That this function is mediated by the release of octopamine on stimulation is supported by the action of exogenously applied octopamine.