The enzyme aromatase, which converts androgens into oestrogens, is widely expressed in neurons from different brain regions of male and female animals. These include brain areas involved in reproductive control and brain regions related to memory, emotion and cognitive processing. For example, in humans, aromatase immunoreactivity has been detected in, among other brain structures, pyramidal neurons and some interneurons in the cerebral cortex and the hippocampus147. In addition, aromatase has been detected at synapses in birds and mammals148–150.