Distribution of nNOS-ir neurons within the mouse arcuate nucleus (Arc). Comparison among females in different stages of the cycle (proestrus and diestrus) and males. Scale bar: 150 μm. The histogram reports the quantitative differences in the number of nNOS-ir cells (mean ± standard error). * = p < 0.05 in comparison to males; °° = p < 0.01 in comparison to estrus female; ^^ = p < 0.01 in comparison to proestrus females.