The odor of a nontoxic tetrodotoxin analog, 5,6,11-trideoxytetrodotoxin, is detected by specific olfactory sensory neurons of the green spotted puffers

Abstract

Toxic puffers accumulate tetrodotoxin (TTX), a well-known neurotoxin, by feeding on TTX-bearing organisms and using it to defend themselves from predators. Our previous studies have demonstrated that toxic puffers are attracted to 5,6,11-trideoxytetrodotoxin (TDT), a nontoxic TTX analog that is simultaneously accumulated with TTX in toxic puffers and their prey. In addition, activity labeling using immunohistochemistry targeting neuronal activity marker suggests that TDT activates crypt olfactory sensory neurons (OSN) of the green spotted puffer. However, it remains to be determined whether individual crypt OSNs can physiologically respond to TDT and whether TDT is processed differently from other odors in the brain. By employing electroporation to express GCaMP6s in OSNs, we successfully identified a distinct group of oval OSNs that exhibited a specific calcium response when exposed to TDT in green spotted puffers. These oval OSNs showed no response to amino acids (AAs), which serve as food odor cues for teleosts. Furthermore, immunohistochemistry targeting neural activity markers revealed that TDT and AAs odors activate extensively overlapping areas in the dorsomedial olfactory bulb. These results suggest that while different types of OSNs detect TDT and AAs in the olfactory epithelium, these substances are processed as similar odors in the olfactory bulb. The TDT odor may act as a chemoattractant for finding conspecific toxic puffers and for feeding TTX-bearing organisms for effective toxification.