Alarm pheromone that aggravates stress-induced hyperthermia is soluble in water.

We previously reported that stressed male Wistar rats released alarm pheromone from the perianal region, which aggravated stress-induced hyperthermia and increased Fos expression in the mitral/tufted cell layer of the accessory olfactory bulb in recipient rats. In this study, we attempted to obtain this pheromone in water using these responses as bioassay parameters. Water droplets were collected from the ceiling of a box in which no animal was placed, or from a box in which an anesthetized donor rat was given electrical stimulation to either the neck or perianal regions in order to induce neck odor or alarm pheromone release, respectively. Then we placed one of the three kinds of water-containing filter papers on the wall of a recipient's home cage and observed heart rate, body temperature and behavioral responses, as well as Fos expression in the main and accessory olfactory bulbs of the recipient. The water collected from the box containing the alarm pheromone was found to generate a reproduction of all of the responses seen in the animal that had been directly exposed to alarm pheromone in our previous studies. These results suggest that the alarm pheromone is soluble in water.