Two- and three-dimensional neuropeptidomic landscape in the central nervous system of an invertebrate chordate, Ciona robusta.

Neuroanatomical information on neuropeptidergic neurons provides crucial clues to understanding the functions of neuropeptides and the cerebral structure-function relationships. In this study, we constructed comprehensive two- and three-dimensional atlases of 23 neuropeptides in the central nervous system (CNS) of an invertebrate chordate, Ciona robusta, at the single-cell level using a mass spectrometry imaging workflow. The neuropeptidomic atlases revealed that the cerebral ganglion is divided into three functional areas, dorso-rostral, dorso-caudal, and ventral areas. Particularly, the distribution of Ciona tachykinin, cholecystokinin, and neurotensin-like-peptide demonstrated the basal cerebral structure-function relationships in reproductive regulation in Ciona. The atlases also demonstrated the unexpected colocalization of multiple neuropeptides and the differential localization of gene-related peptides yielded from a single precursor, which cannot be unraveled by any transcriptomic analyses. Collectively, the present study provides a foundation for investigating various neuropeptidergic functions of the invertebrate chordate CNS and the evolution of chordate neuropeptidergic systems.