An octopaminergic neurone modulates neuromuscular transmission in the locust

Abstract

OCTOPAMINE, a biogenic amine, occurs widely in the nervous systems of vertebrates and invertebrates^1–3. 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 lobster^5,6 from which a calcium-dependent release of octopamine has been demonstrated^7,8. 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 invertebrates^1,3. 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.