Differential effects of excitotoxic basolateral and corticomedial lesions of the amygdala on the behavioural and endocrine responses to either sexual or aggression-promoting stimuli in the male rat.

The effects of discrete excitotoxic lesions of the basolateral (BL) and corticomedial (CM) amygdaloid areas on both male rat sexual behaviour and inter-male agonistic behaviour were investigated. The effects of the same lesions on the hormonal responses (luteinising hormone (LH) following sexual behaviour, corticosterone following aggressive interactions) which accompany these behavioural responses were measured. Basolateral lesions had no effect on male sexual behaviour but significantly reduced the level of aggressive inter-male behaviour. However, the increase in plasma corticosterone concentration which occurs after such an interaction was not affected by basolateral lesions. In contrast, corticomedial lesions did not affect inter-male offence but severely affected copulatory behaviour, including a significant decrease in the males' investigation of the receptive female. However, the increase in plasma LH concentrations induced by the presence of a receptive female was not affected by the CM lesion. These results demonstrate a dissociation between the two amygdaloid regions with respect to the contributions made to the two social behaviours under study. This anatomical division may reflect differential amygdaloid sensory control of these behaviours. A further dissociation between amygdaloid contribution to behavioural and hormonal responses was also revealed. Neither hormonal response showed a parallel decline with the relevant behavioural response, suggesting that neither the basolateral nor corticomedial amygdaloid complex is responsible for coordinating behavioural and endocrine responses to a specific stimulus.