Effects of adrenalectomy on rhythmic and non-rhythmic aggressive behavior in the male golden hamster

Male golden hamsters, adrenalectomized and maintained by subcutaneous implants of deoxycorticosterone-acetate (adx-DOCA), show a loss of the nocturnal rhythm in aggression seen in sham operated (sham-op) animals. A similar loss of the nocturnal aggression rhythm is evident in hamsters adrenalectomized and implanted with separate pellets of DOCA and cortisol-acetate (adx-DOCA-cortisol). However, while Adx-DOCA animals do not differ from sham-op animals in the level of aggression summed over all tests (overall aggression), the overall aggression levels of the adx-DOCA-cortisol animals are significantly higher than the levels of either the adx-DOCA or sham-op animals. Nocturnal rhythms in locomotor activity persist in all three groups. it is suggested that circadian rhythms of the pituitary-adrenocortical axis are important for the expression of the aggression rhythm. A possible mechanism of action is discussed.