Pheromone-triggered 'flipflopping' neural signals correlate with activities of neck motor neurons of a male moth, Bombyx mori

Male silkworm moths, Bombyx mori, exhibited sidewise movements of the head when they showed zigzagging walking in response to pheromonal stimulation. When the moth changed the direction of walking, the head angles also changed to those associated with the walking direction. The sidewise movements of the head were thought to be regulated by neck motor neurons which innervated the first cervical ventral muscles and the ventral muscles through a second cervical nerve. It has been reported that the state transition, resembling the 'flipflop' operation of an electrical circuit, in the spike activity of descending interneurons running in the ventral nerve cord to a thoracic motor system appears to be important in the pheromone-modulated turning of male B. mori. We recorded the activity of neck motor neurons in the second cervical nerve and the flipflopping activity in the ventral nerve cord simultaneously with multiple suction electrodes, in order to clarify the physiological functions of such flipflopping signals involved in the behavior. We demonstrated that the activity pattern of some neck motor neurons was correlated with the state transition of a flipflopping activity pattern triggered by the pheromones. The result suggests that the flipflopping activity pattern is correlated with the instruction of the zigzag turning during the pheromone-mediated walking of B. mori males.