Identification of pyridine analogs as new predator-derived kairomones

Abstract

In the wild, animals have developed survival strategies relying on their senses. The individual ability to identify threatening situations is crucial and leads to increase in the overall fitness of the species. Rodents, for example have developed in their nasal cavities specialized olfactory neurons implicated in the detection of volatile cues encoding for impending danger such as predator scents or alarm pheromones. In particular, the neurons of the Grueneberg ganglion (GG), an olfactory subsystem, are implicated in the detection of danger cues sharing a similar chemical signature, a heterocyclic sulfur- or nitrogen-containing motif. Here we used a “from the wild to the lab” approach to identify new molecules that are involuntarily emitted by predators and that initiate fear-related responses in the recipient animal, the putative prey. We collected urines from carnivores as sources of predator scents and first verified their impact on the blood pressure of the mice. With this approach, the urine of the mountain lion emerged as the most potent source of chemical stress. We then identified in this biological fluid, new volatile cues with characteristic GG-related fingerprints, in particular the methylated pyridine structures, 2,4-lutidine and its analogs. We finally verified their encoded danger quality and demonstrated their ability to mimic the effects of the predator urine on GG neurons, on mice blood pressure and in behavioral experiments. In summary, we were able to identify here, with the use of an integrative approach, new relevant molecules, the pyridine analogs, implicated in interspecies danger communication.

Alarm pheromone and kairomone detection via bitter taste receptors in the mouse Grueneberg ganglion

“…Using as bait the chemical structures of the mouse AP SBT and of the predator-derived kairomones [ 3 , 19 ], which are sulphated and nitrogenated heterocyclic compounds, we identified a new category of putative GG ligands that possess a chemically related structure (Fig. 1a ).…”

“…To test whether these ligands can evoke behavioural responses, we exposed B6 mice to the newly identified GG ligands (2-EP, CYC and PTU) in a set of open field behavioural experiments in which the animals had no physical accessibility to the tested cues [ 19 ] and compared the results obtained with the ones recorded in the presence of the known kairomones TMT and 2,6-DMP (Fig. 2a ).…”

“…Indeed, kairomones are volatile molecules present in and emitted by the anal glands, urine or feces of mice predators, such as 2,4,5-trimethylthiazoline (TMT) from the fox [ 11 ], 2,6-dimethylpyrazine (2,6-DMP) from the bobcat [ 12 ], 2-propylthietane (2-PT) from the stoat [ 13 ] and trimethylene sulphide (TS) or 1,3-dithiolane (1,3-DT) from several Mustelidae [ 14 ]. We demonstrated earlier that these molecules also activate mouse GG neurons [ 3 ] and that they have, as well, the ability to induce fear-related behaviours in mice [ 3 , 15 – 19 ]. These observations confer to the GG a double role, as it detects both intra- and interspecific danger signals, which bear a conserved chemical structure.…”

“…In our approach to identify the signalling pathways activated by danger signals, we took advantage of the chemical structure of previously identified GG ligands [ 3 , 19 ] to screen chemical libraries, and we found a category of compounds already known as bitter tastants. We therefore set out to find if the ability to taste bitter chemicals, which is used by organisms to warn them against ingestion of toxic or spoiled food [ 25 , 26 ], might also be adopted by the GG olfactory subsystem to detect structurally related chemicals.…”

Guanylyl cyclase‐G is an alarm pheromone receptor in mice

“…Because GG activation by SBT evokes reactions associated with fear and stress in mice (Brechbuhl et al, 2013b), we next analyzed whether SBT might also affect blood pressure in a GC-G-dependent manner since acute stress has been reported to increase arterial blood pressure in mice (Farah et al, 2004;Takahashi, 2014;Brechbuhl et al, 2015). In fact, exposure to SBT elicited a significant rise of both systolic and diastolic blood pressure in WT mice, whereas SBT failed to substantially increase systolic ( Fig 6A) and diastolic ( Fig 6B) blood pressure in GC-G-KO animals.…”