ICYMI: Lamprey Study Raises Questions About Sympathetic Nervous System Evolution

In a discovery more than 340 million years in the making, a study published April 17 in Nature calls into question the evolutionary origins of the sympathetic nervous system across species.

Researchers from the California Institute of Technology studying the primitive jawless sea lamprey (Petromyzon marinus) noticed the developing animal appeared to have sympathetic neurons located outside its intestine. For centuries, scientists maintained only jawed vertebrates possessed such sympathetic neurons — the neurons guiding the flight-or-fight response. Further investigation revealed the animal had bunches of sympathetic neurons along its trunk, expressing many genes related to the fight-or-flight system. 

In particular, these sympathetic neurons produced enzymes called tyrosine hydroxylase (TH), important for the synthesis of norepinephrine — a neurotransmitter and hormone helping activate movement. The team found a subset of these TH-positive cells originated from the animal’s neural crest — the collection of stem cells that migrate across the developing embryo to produce various cell types in an organism.

Big Picture: Findings from the 19th century suggested only jawed vertebrates had sympathetic neurons in their trunks. However, finding norepinephrine, or noradrenaline, present in the lamprey’s sympathetic nervous system puts into question the origins of how the system has evolved. The team suggested this finding may have been previously missed, as the sea lamprey’s sympathetic nervous system grows much later in development than other organisms and results in fewer neurons.

Read More: Lampreys have ‘fight or flight’ cells, challenging ideas about nervous system evolution. Science News

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