Evidence for a command neuron controlling calling song in the cricket Gryllus assimilis

In invertebrates stereotypical behaviours may be controlled by command neurons. In the field cricket Gryllus bimaculatus a command neuron descending from the brain controls the generation of rhythmic wing movements underlying calling song. We analysed if a corresponding command neuron also exists in other cricket species. Our intracellular recording and stimulation experiments point to a putative command neuron for calling song in G. assimilis, although the structure of the neuron could not be revealed. When this neuron was depolarised to generate 50 AP/s the cricket raised its forewings into singing position, it started rhythmic wing movements and produced the typical species-specific calling song. Further enhancing the spike rate of the neuron increased the chirp repetition rate but not the pulse repetition rate. Blocking the spike activity of the neuron by hyperpolarizing current injection reduced the chirp repetition rate and could terminate singing activity. Our evidence indicates that the two species, G. assimilis and G. bimaculatus, have homologous neurons for controlling calling song, which may be a conserved phenotype across cricket species.