UC San Diego

The use of nudibranchs as experimental species for neuroethology has been pivotal to elucidating the basis of behavior. These shell-less molluscs are particularly well-suited, given their swimming and crawling behaviors and large, identifiable neurons. However, little is known about early life stages: how the neural system controls behavior during embryonic, larval, and juvenile stages remains unclear, mostly due to the intractability of embryos in species currently used for behavioral studies. Understanding central nervous system development and the formation of identifiable neurons are crucial for neuroethological studies. However, the embryonic origins of the central nervous system and the appearance of identified neurons after metamorphosis are unknown. Therefore, the aeolid nudibranch Berghia stephanieae has been established as an experimental system; this species' embryos are accessible, enabling the study of brain development. This study reports on methodology for labeling the central nervous system with various antibodies that recognize neurotransmitters, creates the most detailed larval and juvenile staging system in a nudibranch to date, and describes the expression patterns of neurotransmitters in the brain during these stages. The post-metamorphic juvenile brain is organized similarly to the adult brains of nudibranch neuroethological models. Gangliogensis of the larval and juvenile central nervous systems is described and quantified. Additionally, the central and peripheral nervous systems are described in detail throughout distinct larval and juvenile stages. Finally, landmark neurons were identified in post-metamorphic stages. These results provide a detailed atlas of neural development and quantification of those growth through ganglion cell counts and immunoreactive cell counts throughout time.