Fearful behavior, body size, and serum IGF-I levels in nervous and normal pointer dogs

Panic disorder in adult humans is associated with disturbances in hypothalamic-growth hormone (GH) function and children with emotional deprivation or severe anxiety develop growth retardation. Nervous pointer dogs, a genetic animal model of panic disorder or severe anxiety, are characterized by extreme fearfulness and avoidance of novel stimuli. This experiment investigated indices of body stature, weight, and insulin-like growth factor I (IGF-I) levels in a colony of purebred nervous and purebred normal pointer dogs. The genetic line of nervous dogs had significantly greater scores of fearfulness, lower total body weights, lower weight/height ratio, and lower serum IGF-I levels than the normal line of pointer dogs. There was an inverse relationship between degree of fearfulness and total body weight in female, but not male, dogs. Stepwise logistic regression analysis indicated that the severity of fear behaviors, height, and weight were significantly associated with IGF-I levels. The best predictor of IGF-I levels in the dogs, however, was the severity of fearful behaviors elicited by exposure to novel stimuli and humans. These observations suggest that the neurobiological substrates of alarm, arousal, and fear influence hypothalamic-GH-somatomedin-mediated effects on weight and, to a lesser extent, height. Findings are discussed in terms of their relevance to future research in humans with anxiety disorders.