Mass Start or Time Trial? Structure of the Nervous System and Neuroregeneration in Pygospio elegans (Spionidae, Annelida)

SIMPLE SUMMARY: We study how a common marine spionid, Pygospio elegans, regenerates its nervous system at the anterior and posterior ends. We use immunostaining techniques with antibodies against serotonin and FMRFamide to label the nervous system of intact and regenerating worms. Our findings show that the regeneration of the P. elegans central nervous system has common features with that of other annelids, while the regeneration of the peripheral nervous system depends on individual features. Comparing these findings with the results for other annelids provides valuable insights into both conservatism and plasticity in the mechanisms of nervous system regeneration. ABSTRACT: The spionid worm Pygospio elegans is a convenient model for regeneration studies due to its accessibility, high tolerance, and ease of maintenance in laboratory culture. This article presents the findings regarding neuroregeneration and the structure of the nervous system based on antibody labeling of serotonin and FMRFamide. We propose the main stages of central nervous system neurogenesis during regeneration: single nerve fibers, a loop structure, and neurons in the brain and segmental ganglia. Nerve fibers and receptor cells of the peripheral nerve system can be traced to different stages of regeneration. We also provide a comparison of our results with previous data on the structure and regeneration of the nervous system based on antibody labeling of catecholamines, gamma-aminobutyric acid, and histamine and with the results for other annelids.