Increased number of neurons expressing androgen receptor in the basolateral amygdala of pathologically aggressive dogs.

The present study aimed to determine the extent to which the androgen receptor (AR) is directly involved in the hormonal modulation of pathological canine aggressive behaviour in the basolateral nuclear group (BNG) of the amygdaloid body. A stereological quantification of AR-positive neurons was performed in the BNGs of normally behaving and aggressive male dogs. The BNG was selected because it is involved in sexual and behavioural activities that are influenced by androgens. In the aggressive dogs the BNG contained a significantly higher number of AR-positive neurons compared with normally behaving dogs suggesting differences in androgen activity within the BNGs of both the groups. However, additional mechanisms are likely to be involved because the AR-negative fraction of BNG neurons was also increased in the aggressive dogs. It was concluded that most of the AR was unliganded because a cytoplasmic staining pattern of AR positivity was observed in the canine BNG neurons. This indicates that genomic androgen actions, which are mediated through the AR are of minor importance in the testosterone modulation of canine aggression within the BNG. Other non-genomic mechanisms through which androgens may exert their action in the BNG are discussed. The aromatase pathway is suggested to be the main mechanism through which testosterone exerts its action within the BNG.