Modulation of predatory odor processing following lesions to the dorsal premammillary nucleus.

Previous studies have shown that electrolytic lesions of the dorsal premammillary nucleus (PMd) produce robust reductions in responsivity of rats to the presence of a live predator as well as to its odor, suggesting a critical role for the PMd in the modulation of defense. The present study investigated whether disruptions in defensive responding were specific to predators or if they may indicate a more general deficit in responding to pheromonal odors. Sexually naive male rats with bilateral ibotenic acid lesions of the PMd were exposed to the odor of a female rat in estrus as well as to the presence of cat odor, and, a live cat. PMd lesions produced a dramatic reduction in freezing and avoidance to the cat odor; and, reductions in freezing, enhanced activity and risk assessment to cat exposure. However, PMd lesions produced no changes in response to the presentation of the female odorant. These results confirm earlier findings of attenuation in defensiveness following electrolytic PMd lesions while extending these findings to suggest that the reduced defensiveness occurs specifically in response to predatory odors.