Acute behavioural effects of corticosterone lack specificity but show marked context-dependency.

Rats were injected intraperitoneally with corticosterone (1 mg/kg). Ten min later they were submitted to dyadic encounters for 15 min. Rats naive to aggressive encounters responded to the corticosterone treatment by a reduction in resting times and an increase in exploration directed towards the novel environment. Resident rats acquainted with aggressive encounters responded to the treatment by a reduction of resting and an increase in threat behaviours. In resident rats acquainted with aggressive encounters and reared previously with a female an increase in attack frequency was noticed. It is concluded that an acute increase in blood corticosterone results in a stimulation of behaviour during social challenge, however, the specific effect is highly context dependent. These data confirm sporadic reports that noticed a behavioural stimulatory effect of acute corticosterone treatments. However, as far as a social challenge situation is concerned, the effect of corticosterone seems to be rather context then behaviour specific. Since corticosterone is known rather to change neuronal excitability than to activate neurons by itself, one can hypothesize that the context dependency of the effect is determined by the different configuration of activated centres in different situations. Attack may be stimulated by corticosterone only when centres involved in attack are already activated, that is, when a high frequency of attack is already present.