Physiological adaptations to prolonged fasting in the overwintering striped skunk (Mephitis mephitis)

From In Vitro Data to In Vivo Interspecies Danger Communication: A Study of Chemosensing via the Mouse Grueneberg Ganglion

Simple Summary

The mouse olfactory system is essential for danger detection with a critical role in the Grueneberg ganglion subsystem. This organ, which is localized at the tip of the nose, is implicated in the recognition of kairomones, or chemical cues released by predators which allow interspecies communication. These kairomones, which are present in the secretions of predators, will induce fear-related behaviours in mice. It is not yet known how the Grueneberg ganglion neurons can detect these molecules; however, three specific bitter taste receptors, known as TAS2Rs, that are present in the Grueneberg ganglion play a role in this detection. Here, using in vitro, ex vivo and in vivo experimental approaches, we identified two novel and potent sources of kairomones that are recognized by the mouse Grueneberg ganglion neurons, namely the biological secretions from the raccoon (Procyon lotor) and the skunk (Mephitis mephitis).

Abstract

In the wild, mice have developed survival strategies to detect volatile cues that warn them of potential danger. Specific olfactory neurons found in the Grueneberg ganglion olfactory subsystem can detect alarm pheromones emitted by stressed conspecifics, as well as kairomones involuntarily released by their predators. These volatile chemical cues allow intra- and interspecies communication of danger, respectively. Alarm pheromones, kairomones and bitter taste ligands share a common chemical motif containing sulfur or nitrogen. Interestingly, three specific bitter taste receptors (TAS2Rs) have been found in the Grueneberg ganglion neurons that are implicated in danger signalling pathways. We have recently developed a TAS2R–expressing heterologous system that mimics the Grueneberg ganglion neuron responses after kairomone stimulation. Here, we demonstrated by in vitro, ex vivo and in vivo experiments that the biological secretions from the raccoon (Procyon lotor) and the skunk (Mephitis mephitis) were acting as potent sources of kairomones. They activated the Grueneberg ganglion neurons and induced fear-related behaviours in mice. Identification of new sources of semiochemicals is a first step towards an understanding of the interspecies danger communication that takes place in the Grueneberg ganglion.

Hematocrit of mammals (Artiodactyla, Carnivora, Primates) at 1500m and 2100m altitudes

The rise in hematocrit (Hct) is one of the hallmarks of human acclimatization to high altitude and, in chronic conditions, reflects the hypoxia-induced polycythemia. However, it is not a uniform response among domestic species and it is not found in Andean camelids, species long adapted to high altitudes. Hence, we asked to what extent the polycythemia of humans is common among mammals. Hct data were collected from captive mammals of three orders (Primates, Artiodactyla, Carnivora), 70 specimens of 33 species at ∼1500m altitude (barometric pressure Pb=635mmHg) and 296 specimens of 64 species at ∼2100m (Pb=596mmHg), long-term residents at those altitudes. Sea level values and data in men and women at the corresponding altitudes were from a compilation of literature sources. At either altitude Hct was significantly higher than at sea level both in men and women; the increase (ΔHct) for genders combined averaged 3.4% (±0.7 SEM) at 1500m and 5.4% (±0.3) at 2100m. Differently, among the three mammalian orders studied a significant increase in Hct occurred only in females of Carnivora (at 1500m) and in males of Primates (at 2100m). The average ΔHct of all species combined was 0.8% (±0.7) at 1500m and 1.5% (±0.4) at 2100m, both significantly less than in humans (P<0.001). At 2100m the average ΔHct of nine species long adapted to high altitude was 0.4% (±1), significantly less than in non-adapted species (P<0.001). A polycythemic response like that of men and women at 2100m occurred in less than 10% of the mammals examined. We conclude that, at least for the altitudes studied, a minimal polycythemia is a general feature of both high-altitude adapted and non-adapted species, and the magnitude of the human response is exceptional among mammals.