Aggressive behavior in adult male mice elevates serum nerve growth factor levels

By use of a specific and sensitive beta-nerve growth factor radioimmunoassay (beta NGF-RIA), serum beta NGF concentrations were measured in adult male Swiss-Webster mice under various physiological conditions. Animals killed on the day of arrival from the animal supplier showed wide variations (3-15 ng beta NGF/ml) in serum beta NGF levels. These levels significantly decreased if the animals were maintained under individually housed conditions for at least 6 days prior to death. Aggression caused by social contact between previously individually housed animals raised serum beta NGF levels by two orders of magnitude relative to serum beta NGF concentrations in nonaggressive mice. Testosterone propionate treatment (10 mg/animal) 5 days prior to death did not elevate serum beta NGF levels in individually maintained animals. However, the hormone pretreatment markedly augmented serum beta NGF levels in aggressive mice compared with the levels in hormone-treated nonaggressive animals. Removal of the submandibular-sublingual salivary glands 10 days prior to death completely abolished the increase in serum beta NGF due to aggression. The high serum beta NGF levels, as measured by competitive RIA in aggressive mice, were confirmed by a neurite outgrowth PC-12 bioassay system. In conclusion, serum beta NGF in adult male mice is subject to alteration by environmental stress.