In seasonally-breeding songbirds, testosterone during the breeding season is sufficient for many animals to sing courtship song to a female. In fact, testosterone implanted into even one brain region (the medial preoptic area; mPOA) can activate courtship singing. But what about for males that do not possess the resources they need to breed successfully? European starlings require a nesting cavity to raise their young, and males court females by singing and advertising a defended nest cavity.
I manipulated male starling testosterone levels and whether or not males had access to a nesting cavity and found that only males with both testosterone and in possession of a nesting cavity sang to an introduced female. Testosterone, but not a nesting cavity, contributed to changes in patterns of mRNA expression in the mPOA. This led us to suggest that testosterone prepares to brain for courtship behavior, but in the absence of necessary resources, the mPOA is prevented from stimulating the behavior. See the published study in Hormones and Behavior.
I’m currently following up on what systems could be inhibiting the mPOA in the absence of necessary breeding resources. I’ve started by characterizing cells that receive input from both opioid and dopamine neurochemical systems (double-immunofluorescent labeling shown on left).