Development of the larval serotonergic nervous system in the sea star Patiriella regularis as revealed by confocal imaging

Development of the nervous system in the larvae of the sea star Patiriella regularis was reconstructed in three dimensions. The optical sectioning and image processing capabilities of the confocal microscope made it possible to identify the precise location and timing of development of serotonergic cells in relation to subsequent development of larval features. Similaritie s between this system and the serotonergic systems in larvae of other echin oderms were explored. Neuronal-like immunoreactive cells and processes firs t appeared in late gastrulae as a collection of cells scattered across the animal pole. These cells subsequently gave rise to basal axons positioned a long the basal lamina. Immunopositive cells located in the stomodaeal regio n marked the beginnings of formation of the adoral ciliated band. Cells wer e also present in the mid-dorsal epithelium. Advanced bipinnaria had pyrami dal immunoreactive cells within the adoral band and ovoid immunoreactive ce lls within the preoral and postoral ciliated bands. Processes originating f rom neurons in the transverse region of the preoral ciliated band extended into the buccal cavity, suggesting that these cells have a sensory role in feeding. An anterior ganglion formed in the late bipinnaria, innervating th e preoral and postoral ciliated bands. This connection has not previously b een described. It thus appears that the ciliated bands in the bipinnaria la rvae of P. regularis communicate via serotonergic nerve tracts.