Complicated vertebrates have networks of neurons that interact directly with groups of muscle fibres. Simpler invertebrates have fewer neurons yet manage to perform complex gymnastics by modulating the nerve signals that are sent to muscle tissue. They do this through a specialised type of neuron that releases modulator peptides. The peptides modulate the message by altering the release of neurotransmitter at the synapse and by making the muscle cell more or less responsive when it receives the message.
Proctolin is a modulator peptide that is released by a neuron that affects the dorsal muscles of Idotea emarginata. Proctolin was already known to modulate muscle contraction by triggering a phosphorylation cascade that opened calcium channels. But Sabine Kreissl and her colleagues in Konstanz suspected that proctolin might also mediate a response at the level of the contractile machinery. She set out to investigate.
Kreissl used muscular stimulation with caffeine to...
