An almost nontoxic tetrodotoxin analog, 5,6,11-trideoxytetrodotoxin, as an odorant for the grass puffer

Abstract

Toxic puffers contain the potent neurotoxin, tetrodotoxin (TTX). Although TTX is considered to serve as a defense substance, previous behavioral studies have demonstrated that TTX (extracted from the ovary) acts as an attractive pheromone for some toxic puffers. To determine the putative pheromonal action of TTX, we examined whether grass puffers (Takifugu alboplumbeus) can detect TTX using electrophysiological, morphological, and behavioral experiments. Electroolfactogram results suggest that the olfactory epithelium of grass puffers responded in a dose-dependent manner to a type of TTX analog (5,6,11-trideoxyTTX), although it did not respond to TTX. We also examined the attractive action of 5,6,11-trideoxyTTX on grass puffers by recording their swimming behavior under dark conditions. Grass puffers preferred to stay on the side of the aquarium where 5,6,11-trideoxyTTX was administered, and their swimming speed decreased. Additionally, odorant-induced labeling of olfactory sensory neurons using a fluorescent dextran conjugate or immunohistochemistry against phosphorylated extracellular signal regulated kinase (pERK) revealed that labeled olfactory sensory neurons were localized in the region surrounding "islets" where there was abundant cilia on the olfactory lamella. 5,6,11-trideoxyTTX has been known to accumulate in grass puffers, but its toxicity is much lower (almost nontoxic) than TTX. Our results suggest that grass puffers can detect 5,6,11-trideoxyTTX using their nose and may positively use this functionally unknown TTX analog as an olfactory chemoattractant.

Green spotted puffers can detect an almost nontoxic TTX analog odor using crypt olfactory sensory neurons

“…Previous studies reported that TTX attracts tiger puffer ( T. rubripes , Okita et al, 2013; Saito et al, 2000) and grass puffer ( T. alboplumbeus , Matsumura,1995; Noguchi et al, 2021). These puffers live in the seawater, but the green spotted puffer lives in brackish water.…”

“…Saito et al (2000) also reported that juvenile tiger puffers ( T. rubripes ) were attracted to TTX, and Okita et al (2013) reported that nose ablation eliminated the attractions of tiger puffers to TTX. Our electrophysiological and behavioral study has recently shown that an almost nontoxic TTX analog, 5,6,11-trideoxyTTX, acts as an olfactory chemoattractant for grass puffers (Noguchi et al, 2021). However, these studies have only been conducted on toxic puffers of the genus Takifugu .…”