Neurokinin-1 receptor in the basolateral nuclear group of the canine amygdala—Comparative study in normal and aggressive dogs

Substance P and its NK-1 receptor are involved in the modulation of aggressive behavior. Because of the role of the basolateral nuclear group (BNG) of the amygdala in canine aggression, neurokinin-1 receptor (NK-1) immunoreactivity in this brain region was assessed stereologically in 7 normally behaving and 6 pathologically aggressive dogs. The first aim of this study was to obtain information about the absolute number of neurons expressing the NK-1 receptor in the canine BNG because absolute numbers of neurons expressing the NK-1 receptor are not documented in literature. Additionally, an exploratory comparison was made between NK-1 expressing neurons in the BNGs of normally behaving and aggressive dogs. Results showed a very low amount (1–2%) of BNG neurons containing the NK-1 receptor in both groups. Aggressive dogs had significantly more NK-1-receptor-positive BNG neurons than normal dogs, but the numerical densities and fractions of receptor-positive neurons did not differ significantly between both groups. Combined with the fact that aggressive dogs have 27% more neurons in their BNGs than normal dogs, as reported in a previous study, these findings suggest a limited role for the NK-1-receptor-positive neurons within the BNG in the modulation of canine aggression. The present report of absolute numbers of neurons expressing the NK-1 receptor in the canine BNG could however be useful for further quantitative studies.