Regional brain cholecystokinin changes as a function of friendly and aggressive social interactions in rats

Cholecystokinin (CCK) is the most abundant neuropeptide in the mammalian brain, and has been implicated in the regulation of a diversity of emotions and motivations including negative affect and stress responses. In this experiment, we assayed levels of CCK (CCK4/5 and CCK8) from tissue homogenates in intruder animals 6 h after resident-intruder inter-male aggression. Intruder animals that demonstrated submissive behavior (freezing and 22-kHz ultrasonic vocalizations) had higher levels of CCK in the tegmentum and posterior cortex as compared to non-submissive (i.e., "Friendly") intruder animals. Ultrasonic vocalizations (22-kHz) were positively correlated with CCK levels in the tegmentum, posterior cortex and pituitary. These data suggest that CCK may play a role in the generation of negative affective states indexed by 22-kHz ultrasonic calls in certain regions of the brain.