Glucocorticoid effects on open field running and aggression.

Abstract

The effects of glucocorticoid injections on open field running behavior and aggression were examined in rodents. The first experiment was designed to test the effects of corticosterone injections on food and water dominance and spontaneous aggression in rats. Data suggested that corticosterone may affect certain aspects of dominance in rats, but not all. The second experiment examined the differences in open-field activity between dominant and subordinate mice. Data verified earlier findings that the dominant male runs significantly more than the subordinate in the open-field situation, and has smaller adrenal glands. The goal of the third experiment was to test the effects of manipulated blood levels of corticosterone or dexamethasone on open-field running and aggressive behavior of male mice. Different surgical treatments were also utilized to control the amount of endogenous corticosterone and/or testosterone present. The results showed that corticosterone had very little effect on the establishment of dominance. Open field running behavior was depressed by a high dose of corticosterone in castrated animals, while little effect was seen in animals receiving a low dose. Effects of corticosterone on open-field running were short-lived and reversible. Once injections were discontinued, running jumped significantly in a type of "rebound". The high dose of corticosterone increased open-field running of adrenalectomized animals. Corticosterone had little effect on open-field running in intact animals and animals that were both adrenalectomized and castrated. Unlike corticosterone, dexamethasone did not decrease open-field running behavior in castrated animals. Since dexamethasone has effects similar to those of corticosterone on metabolism, and pituitary secretion of ACTH, it is unlikely that the corticosterone effect on running is mediated by one of these peripheral actions. On the other hand, since the hippocampus binds orticosterone to a much greater degree than dexamethasone, the motor effects of the hormone may be mediated by this part of the CNS. It is concluded that, while glucocorticoids apparently are not critically involved in the establishment of dominance relations, they are critically involved in the behavior of the submissive animal once dominance is established.