Rats discriminate individual cats by their odor: possible involvement of the accessory olfactory system.

Social behavior in mammals often relies upon the discrimination of same-species individuals via olfactory processing of unique chemosensory signatures. The ability to identify individuals from a different species by their odor (heterospecific discrimination) is less well documented. Here we used a habituation-dishabituation paradigm to demonstrate that rats can discriminate individual cats by their odor. Rats were repeatedly exposed to a collar previously worn by a domestic cat. Strong initial defensive responses (hiding in a small box and vigilant "head out" behavior from the box entrance) habituated with repeated exposure to the same collar. Brain activation following repeated presentation of the same odor - as indexed by c-Fos expression - also habituated in accessory olfactory regions (mitral and granular layers of the posterior accessory olfactory bulb and posteroventral medial amygdala), as well as regions involved in defensive behavior, including the ventromedial and dorsal premammillary hypothalamic nuclei, basolateral amygdala and periaqueductal grey. When a collar taken from a different cat was presented to habituated rats, defensive responses (hiding, vigilance, suppression of grooming) were dishabituated, and c-Fos expression was reinstated in the accessory olfactory system and in defense-related hypothalamic, amygdaloid and brainstem nuclei. Results indicate that rats may process and store details of the chemosensory signatures of individual predators using the accessory olfactory system.