The evolution of the serotonergic nervous system

Area of Science:

• Developmental Biology
• Neuroscience
• Evolutionary Biology

Background:

• The serotonergic nervous system plays a crucial role in development and function across diverse animal phyla.
• Understanding the evolutionary origins of neural structures provides insights into conserved developmental pathways.

Purpose of the Study:

• To describe and compare the development of the serotonergic nervous system in various invertebrate larvae.
• To investigate the evolutionary origins of the vertebrate serotonergic raphe system and neural tube.

Main Methods:

• Comparative analysis of serotonergic nervous system development across a wide range of invertebrate larvae (ctenophores, platyhelminths, nemerteans, etc.) and lampreys.
• Examination of larval brain (apical ganglion) and ciliary band innervation patterns.

Main Results:

• Spiralian protostome larvae (except nermerteans) exhibit a simple serotonergic pattern in the apical ganglion innervating the ciliary band.
• Deuterostome larvae (brachiopods, phoronids, echinoderms, enteropneusts) show numerous serotonergic neurons in the apical ganglion innervating the ciliary band, similar to lampreys.
• No evidence of dorsal-ventral orientation shifts in the lineage leading to chordates.

Conclusions:

• The vertebrate serotonergic raphe system likely originated in the larval brain of deuterostome invertebrates.
• The chordate neural tube may have evolved, in part, from the ciliary band of deuterostome invertebrate larvae.
• Suggests a conserved developmental origin for key neural structures across invertebrates and vertebrates.