The expression of large-conductance Ca2+-activated K+ (BK) channel protein in amygdala complex was higher in adult (8-10 weeks old) male rats than in female. Castration at 4-6 weeks old significantly reduced BK channel expression in amygdala to the level similar to that in female. Immunocytochemical analyses of pyramidal-like neurons isolated from amygdala revealed that somas with relatively large size were highly immunoreactive to both anti-androgen receptor (AR) and anti-BK channel antibodies, while those with smaller size were not. The double-immunopositive neurons were dominant (60%) among pyramidal-like neurons isolated from amygdala of male rats but rare among those from female. The membrane current sensitive to penitrem A, a BK channel blocker, was the major K+ current. component in large neurons and showed higher current-density than that in smaller ones. These results suggest the gender-dependent cell population expressing BK channels in amygdala complex and its up-regulation by AR stimulation. (C) 2008 Elsevier Inc. All rights reserved.