Modulation of a rhythmically active crayfish muscle by the neuropeptide proctolin

Abstract

Whole-animal studies have indicated that the neuromodulators octopamine, serotonin, and proctolin have multiple effects upon the central crustacean ventilatory system. We were interested in determining if these modulators have a complementary peripheral effect in augmenting the muscle power output in a ventilatory muscle. The availability of the biogenic amines and the presence of proctolin-like immunoreactivity in motor axons of the second maxilla indicate that the ventilatory system may be a target for those neuroactive substances. Intracellular recordings and isotonic muscle tension measurements were made on an isolated preparation of a ventilatory muscle. The amines and the peptide were applied by superfusion in normal saline. Of the three substances only protocolin had a modulatory action, which was seen as significant increases in both nerve-evoked and glutamate-evoked muscle contractions. An enhancement of the amplitude of excitatory postsynaptic potentials occurred at a subset of synapses.