Forebrain steroid levels fluctuate rapidly during social interactions

Neurosteroids are powerful modulators of brain function and behavior, yet their dynamics within the brain have remained elusive. Using in vivo microdialysis in male zebra finches, we show that local estradiol levels increase rapidly within the forebrain during social interactions with females. Further, when males are exposed to other males’ song, local estradiol levels also increase and testosterone levels drop within a cortical/pallial auditory region that is analogous to mammalian auditory cortex. We also report that local estradiol and testosterone levels are differentially regulated in this same region by the conventional neurotransmitters glutamate and GABA, respectively. This study provides direct evidence that forebrain steroid levels are acutely and differentially regulated during social behavior, in a region-specific manner, and in a rapid time-course akin to that of traditional neuromodulators.