Effects of olfactory bulb ablation and androgen on marking and agonistic behavior in male Mongolian gerbils (Meriones unguiculatus).

Male Mongolian gerbils, selected for high marking frequency, were paired with male opponents, and marking and fighting behavior were recorded. Animals then underwent castration, bilateral bulbectomy, unilateral bulbectomy, the combined operations, or a sham operation; and their behavior was again observed. All operated animals showed drastic reduction in both marking and aggressive encounters. Injections of testosterone propionate (TP) produced complete restoration of marking in castrates, but not in bilaterally or unilaterally bulbectomized animals or combined operates. The exhibition of aggression after injections of TP, however, was enhanced to supernormal levels in bulbectomized or bulbectomized-castrated animals. The results suggest the following: that removal of the olfactory bulbs may eliminate a critical neural input necessary for the normal expression of marking and agonistic; that although marking and fighting are influences by olfactory input and gonadal steroids, their regulatory mechanisms may not be identical; and that removal of the bulbs may sensitize a neural mechanism controlling aggression, thus potentiating its elicitation following administration of exogenous androgen.