Running Head: Neural Activity in the Amygdala to Predator Odor

24 Chemosensory cues signalling predators reliably stimulate innate defensive responses in 25 rodents. Despite the well documented role of the amygdala in predator odor-induced fear, 26 the relative contribution of the specific nuclei that comprise this structurally heterogeneous 27 structure is conflicting. In an effort to clarify this we examined neural activity, via 28 electrophysiological recordings, in amygdala subnuclei to controlled and repeated 29 presentations of a predator odor; cat urine. Defensive behaviors, characterised by 30 avoidance, decreased exploration and increased risk assessment were observed in adult 31 male hooded Wistar rats (n=11) exposed to a cloth impregnated with cat urine. 32 Electrophysiological recordings of the amygdala (777 multi-unit clusters) were subsequently 33 obtained in freely-breathing anesthetised rats exposed to cat urine, distilled water and 34 eugenol via an air-dilution olfactometer. Recorded units selectively responded to cat urine 35 and frequencies of responses were distributed differently across amygdala nuclei; medial 36 amygdala (MeA) demonstrated the greatest frequency of responses to cat urine (51.7%), 37 followed by the baso-lateral and -medial nuclei (18.8%), and lastly the central amygdala 38 (3.0%). Temporally, information transduction occurred primarily from the cortical and MeA 39 (ventral divisions) to other amygdala nuclei. Interestingly, MeA subnuclei exhibited distinct 40 firing patterns to predator urine, potentially revealing aspects of the underlying 41 neurocircuitry of predator odor processing and defensiveness. These findings highlight the 42 critical involvement of the MeA in processing olfactory cues signalling predator threat and 43 converge with previous studies to indicate that amygdala regulation of predator-odor 44 induced fear is restricted to a particular set of subnuclei which primarily include the MeA, 45 particularly the ventral divisions. 46