Abstract

Neuropeptides are endogenous active substances that are present in nervous tissues and participate in behavioral and physiological processes of the animal system. Locomotor behavior is basic to predation, escape, reproduction in animals, and neuropeptides play an important role in locomotion. In this study, the function of pedal peptide-type neuropeptide (PDP) in the process of locomotor behavior of the sea cucumber Apostichopus japonicus was evaluated. The locomotor behavior of A. japonicus was recorded by infrared camera before and after PDP administration, and muscle physiology was studied by ultra performance liquid chromatography and quadrupole time-off-light mass spectrometry (UPLC-Q-TOF-MS) to clarify the potential physiological mechanisms. The results showed that PDP enhanced the cumulative duration of moving significantly at the 7th h after injection, and reduced the mean and maximum velocity by 16.90 and 14.22% in A. japonicus. The data of muscle metabolomics suggested that some significantly changed metabolites were related to locomotor behavior of sea cucumbers. The decreases of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) might result in the increases of lysophosphatidylcholines (lysoPC) and lysophosphatidylethanolamine (lysoPE), and suggested the change of fluidity and permeability in the muscle cell membrane, which would affect the physiology and function of muscle cells, and finally alter the locomotor behavior. In addition, the increased level of arachidonic acid (ARA) might activate K+ ion channels and then affect the signaling of muscle cells, or promote the sensitivity of muscle cells to Ca2+ and then result in the contractility of longitudinal muscles in sea cucumbers. ARA was also involved in the linoleic acid metabolism which was the only pathway that disturbed significantly after PDP administration. In conclusion, PDP participated in the regulation of locomotor behavior in the sea cucumber, and the decreased PE and PC, increased lysoPC, lysoPE and ARA might be the potential physiological mechanisms that responsible for behavioral effects of PDP in A. japonicus.

Highlights

  • Neuropeptides generally refer to endogenous active substances that are present in nervous tissues and participate in the functions of animal nervous system

  • The distances of sea cucumbers moved per hour ranged from 115.05 to 176.84 cm in the control group (CON) group and 120.57 to 188.31 cm in the peptide-type neuropeptide injected (PDP) group, and they increased to some extent after PDP administration, but were not statistically significant (Figure 1A; F = 7.235, p > 0.05)

  • The average total distance moved per hour after injection was 12.50 ± 1.29 m in the CON group and 14.05 ± 1.85 m in the PDP group

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Summary

Introduction

Neuropeptides generally refer to endogenous active substances that are present in nervous tissues and participate in the functions of animal nervous system. They are characterized by low contents, high activities, extensive functions and complex mechanisms. Locomotor behavior is basic to predation, escape, habitat dominance, reproduction in animals, and a number of studies were focused on the functions and mechanisms of neuropeptides in locomotion (He et al, 2013; Pauls et al, 2019). With the decoding of whole-genome and the application of transcriptomics and proteomics in A. japonicus, the neuropeptides in A. japonicus were recently identified (Chen et al, 2019), which provide the foundation to study the functions of neuropeptides in locomotor behavior in this species

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