NGF antibody production as a result of repeated psychosocial stress in adult mice

Mouse intraspecific fighting, a classic form of psychosocial stress induced by social isolation, provokes a massive release of salivary NGF into the bloodstream while markedly increasing its synthesis in some hypothalamic areas. CD-1 male mice were isolated for 8 weeks and tested for aggressive behavior (20-min fighting sessions) twice a week over a period of six months until they were sacrificed and serum levels of antibodies against NGF analyzed. Adrenergic innervation of the iris (number of neurites/mm²), and NGF (pg/g) levels in the hypothalamus, hippocampus, and cortex were measured. About 40% of the mice developed antibodies against NGF (Positive mice). The adrenergic innervation of the iris was significantly lower in these mice than in mice that did not develop antibodies (Negative mice). In an activity/exploration test, the Positive mice spent significantly less time self-grooming than the Negative mice. Anti-NGF production might reflect an imbalance caused by repeated hyperactivation of the homeostatic mechanisms underlying adaptive responses to stress stimuli.