Among over 2000 species in the monophyletic Nudipleura clade, fewer than 70 species have been observed to exhibit swimming behavior. Swimming behavior is produced by rhythmically flexing whole body in dorsal-ventral direction or left-right direction. These two types of behavior appear to have evolved independently several times on the phylogenetic history. Nudibranchs Tritonia and Pleurobranchaea are phylogenetically distant, but they both show dorsal-ventral swimming. There are at least two homologous neurons in the swim central pattern generator (CPG) circuits of these species. They both employ serotonergic neuromodulation of synaptic strength within the CPG circuits. The left-right swimmers distributed widely in among nudibranchs. Since Melibe and Dendronotus belong to a clade of genera that all swim with left-right body flexions, their swimming behaviors are likely homologous. However, their swim CPGs differ in both cellular composition and in the details of the neural mechanisms. Thus in Nudipleura, there are similar behaviors that have evolved independently through parallel use of homologous neurons, yet employing two distinct neural mechanisms without changing the behavioral outputs.

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Since we ourselves are animals, the fact that animals can move doesn’t surprise us very much. However, once you look inside the body, you may notice that animal motion is not an easy task. Animals make motions by controlling muscles arraying in every position in the body. The motion patterns are generated by an intricately wired neural network. How the complicated neural circuits produce orchestrated and well-coordinated animal motion is one of the fundamental questions in neuroscience. In this review article, I introduce neural circuits in fly larvae, where the circuit mechanisms underlying motion have been intensively delved in a cellular level. Fly larvae are segmented along the body axis and exhibit various motor patterns such as forward locomotion, backward locomotion and bending by coordinating contraction of each segment. Many researchers over the world, including our group, have identified several key interneurons involved in the larval motor patterns. By comparing the larval circuits with the motor circuits in other species, commonality in the mechanisms of motor control will be explored.

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A model of two separate, but mutually coupled, circadian oscillators has been proposed to explain behavioral rhythm in nocturnal rodents: an evening (E) oscillator, which drives the activity onset and entrains to dusk, and a morning (M) oscillator, which drives the end of activity and entrains to dawn. Behavioral rhythm in mammals is controlled by circadian oscillator in the hypothalamic suprachiasmatic nucleus (SCN), indicating the E and M oscillators are located in the SCN. However, their localization in the SCN has not been shown. By using bioluminescence imaging of Period1-luciferase mouse we identified four regional oscillators in horizontal slices of the SCN. The first two regions are the respective sites for the E and M oscillators, and the third region is possibly a site for mediating photic signals to the former oscillators. The last region receives light information from the retina through the direct retinal projection. Histological analyses had indicated the SCN consists of two parts, core and shell. We identified the four regions by oscillatory function and light responsiveness. Our finding will be a valuable information for further study to reveal a regional function of the SCN.

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Flying is a characteristic ability in insects, and the study on insect flight has mainly focused on several model insects, desert locusts, files and hawkmoths. Among them, the desert locusts are the most successful models for finding a fundamental principle in animal locomotion, central pattern generator. The blowflies and fruit flies are the excellent models for sensory-motor control as agile flyers, and the latter have become more powerful model organisms in neuroscience by the recent advances in genetic methods. The hawkmoths are large, powerful and agile flyers, and have a lot of intermediate features between locusts and flies, which are useful characteristics considering the diversity of insect flight mechanisms. In this review, I introduced our recent progress in the study of hawkmoth flight, focusing on proprioceptive feedback, flight muscle control during free flight and thoracic deformation by muscle contraction, which are closely coupled together during flapping flight. I also introduced some recent unique findings in hawkmoth flight reported by other groups, which shows diversity of flight control in insect species. Finally, I discuss future direction for the integrative understanding of insect flight mechanism.

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