Chondroitin Fragments Are Odorants that Trigger Fear Behavior in Fish

• Published in: Current biology 2012-03, Vol.22 (6), p.538-544
• Main Authors: Mathuru, Ajay S., Kibat, Caroline, Cheong, Wei Fun, Shui, Guanghou, Wenk, Markus R., Friedrich, Rainer W., Jesuthasan, Suresh
• Format: Article
• Language: English
• Subjects: Animals; Behavior, Animal - drug effects; Behavior, Animal - physiology; Chondroitin - chemistry; Chondroitin - pharmacology; Chondroitin - physiology; Echinoidea; Fear - drug effects; Fear - physiology; fearfulness; fish; fish behavior; fractionation; larvae; Marine; neurons; odor compounds; Odorants - analysis; olfactory bulb; Olfactory Bulb - drug effects; Olfactory Bulb - physiology; predators; Skin - chemistry; Zebrafish - physiology
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2012.01.061

The ability to detect and avoid predators is essential to survival. Various animals, from sea urchins to damselfly larvae, use injury of conspecifics to infer the presence of predators [1–7]. In many fish [1, 8, 9], skin damage causes the release of chemicals that elicit escape and fear in members of the shoal. The chemical nature of the alarm substance (“Schreckstoff” in German) [1], the neural circuits mediating the complex response, and the evolutionary origins of a signal with little obvious benefit to the sender, are unresolved. To address these questions, we use biochemical fractionation to molecularly characterize Schreckstoff. Although hypoxanthine-3 N-oxide has been proposed to be the alarm substance [10, 11], it has not been reliably detected in the skin [12] and there may be other active components [13, 14]. We show that the alarm substance is a mixture that includes the glycosaminoglycan (GAG) chondroitin. Purified chondroitins trigger fear responses. Like skin extract, chondroitins activate the mediodorsal posterior olfactory bulb, a region innervated by crypt neurons [15] that has a unique projection to the habenula [16]. These findings establish GAGs as a new class of odorants in fish, which trigger alarm behavior possibly via a specialized circuit. [Display omitted] ► Schreckstoff, the alarm substance in fish, is a mixture ► Chondroitin, a glycosaminoglycan, is a component of the alarm substance ► Skin extract activates the mediodorsal posterior and lateral anterior olfactory bulb ► Purified chondroitin activates the mediodorsal posterior bulb