Neural control mechanisms of the pheromone‐triggered programmed behavior in male silkmoths revealed by double‐labeling of descending interneurons and a motor neuron

Abstract

Male silkmoths, Bombyx mori, exhibit a characteristic zigzagging behavior consisting of straight-line walking, zigzagging turns, and looping. The timing for shifting the turning direction is synchronized to the sideways head movements controlled by neck motor neurons (NMNs) including a cervical ventral NMN (cv1-NMN). It has been suggested that this programmed behavior is instructed by two types of activity patterns descending from the brain and the thoracic ganglion: one is a phasic excitation and the other is a state-dependent activity similar to the flipflop in electric memory circuits. These activities are shown by certain descending interneurons contained in two subsets of DNs, Group-I and -II DNs. However, it is not yet well understood which DNs are directly related to instructing this behavior. In order to understand neural control mechanisms of this programmed behavior, we investigated the morphological relationship between these DNs and the cv1-NMN, which is an index of this programmed behavior. We applied a double-labeling technique combining backfilling of the cv1-NMN and intracellular staining of single DNs. 3D confocal images revealed overlapping regions between the Group-I, -II DNs and the cv1-NMN. Group-IIA and -IID, which showed typical flipflop activities, Group-IIC DNs, which showed phasic excitation, and Group-IB DNs, which showed long-lasting inhibition had many overlapping regions on the cv1-NMNs. Our results indicate that the programmed behavior is instructed by these types of DNs.

Dynamic use of optic flow during pheromone tracking by the male silkmoth, Bombyx mori

“…Speculation of the neural mechanisms and pathways underlying dynamic use of optic flow during the pheromonetriggered behavioural response Earlier studies on the neural mechanism underlying pheromonetriggered behavioural responses have demonstrated that surge and zigzagging are controlled by two different neural circuits (Kanzaki, 2004;Wada and Kanzaki, 2005). Neural activity during surge shows a phasic response in a descending motor pathway, whereas zigzagging shows so-called 'flip-flop' activity, which is a longlasting tonic response generated by the premotor centre of the silkmoth's brain (Iwano et al, 2010;Wada and Kanzaki, 2005).…”

“…When the silkmoth detects an additional pheromone cue, this behavioural sequence restarts from the beginning (Kanzaki, 1996;Kanzaki, 1998;Kanzaki et al, 1992). Previous neurophysiological studies on this pheromone-triggered behaviour have demonstrated that two neural circuits control behaviour during surge and zigzagging and that the loop is presumably a part of zigzagging and controlled by the same neural circuit (Kanzaki, 1996;Kanzaki, 2004;Wada and Kanzaki, 2005). Hence, from now on, we will discuss behaviour during surge and zigzagging only.…”

“…Moreover, studies on the visual response of silkmoths have suggested that some descending interneurons in the ventral nerve cord show responses to moving visual stimuli (optic flow) (Olberg, 1983) and that the silkmoth uses visual information to compensate for unintentional turning (Ando et al, 2013;Minegishi et al, 2012). Although the behavioural and neurophysiological basis of the pheromone-plume tracking of the male silkmoth has been well studied (Kanzaki, 1996;Kanzaki, 2004;Wada and Kanzaki, 2005), how the silkmoth uses visual information for pheromone-plume tracking during different behavioural states (surge and zigzagging) remains unclear.…”

Pattern Generation by Network composed of Oscillators and Capacitive Couplers

“…For simplicity, we omit the phase of straight-line walking from the target. This simplification is supported by [26], which indicated that the neural circuit for straightline walking and that for zigzag turning and looping are di erent. The right and left inputs in Fig.…”

Humanitarian Demining Using an Insect Based Chemical Unmanned Aerial Vehicle

“…The activity of these, so called, flip/flop neurons is directly correlated with the body orientation and zigzagging of the moth while tracing a pheromone trail. Moreover, the orientation switches appear to be caused by the difference of pheromone concentration in the anteanne (Olberg 1993;Mishima & Kanzak 1998;Wada & Kanzaki 2005). Therefore, olfactory stereo information is used in our model to trigger the orientation changes whenever the sensor reading difference of two chemo-sensors is above threshold (Fig.…”