Born with Silurian global warming: Defensive role of TRPV1 in caudal neurosecretory system (CNSS) in flounder.

The caudal neurosecretory system (CNSS), unique to fish, emerged during the Silurian global warming period and appears to have an inevitable connection with "heat." Although TRPV1 is known to be a key molecule mediating high-temperature perception in fish, its role in CNSS remains unknown. Here, we found that TRPV1 located on Dahlgren cells in CNSS, is involved in sensing high-temperatures and helps flounder to respond correctly. Specifically, in the context of mild high-temperatures, Dahlgren cells expressing Urotensin I (UI) are the main active cell subpopulation. TRPV1 promotes the activation of the UI cell subpopulation by activating excitatory receptors, which in turn facilitates freezing behavior in flounder. When the accumulated temperature in the abdomen reaches avoidance high-temperatures, the firing activity of the UI cell subpopulation is inhibited, which is related to the TRPV1-mediated activation of NR3A. Accordingly, a subpopulation of Urotensin II (UII) cells was activated. Meanwhile, the expression of genes related to dopamine receptors and acetylcholine synthesis are significantly elevated, thereby mediating the avoidance behavior of flounder to escape from injury. Overall, these studies collectively elucidate the complex adaptive mechanisms employed by flounder in response to high-temperature fluctuations, with a special emphasis on the importance of CNSS temperature sensing.