Neuroendocrine and neuroimmune modulation of High-impact signals

In most animals, social communication and sexual displays usually utilize visual and vocal signals controlled by the social decision-making network. In contrast, several avian taxa have evolved incredible sexually selected auditory signals that are produced by other means. For example, most woodpeckers use species-specific drumming sequences (slamming their heads on a hard substrate) as a way to attract mates and guard territories. Bearded manakins (Genus: Manacus) will rapidly snap their wings together (~60 snaps/sec) to achieve the same goals. These behaviors are mediated by bioactive steroid hormones (e.g., androgens), but little is known about how these hormones act in the brain to affect the activation and evolution of these behaviors. Our research aims to determine a) how androgens can impact the evolution and physiological trade-offs associated with high-impact displays in woodpeckers and manakins, and b) how steroid-sensitive regions in the downy woodpecker brain are interconnected and activate muscles that control drumming. By comparing our findings on these unique socio-sexual displays to the well-understood neuroendocrine circuitry that controls vocal signals (e.g., bird song), we hope to understand the evolution of the social decision-making network and cost-reducing neurophysiological traits to perform these behaviors.

Neuroendocrine modulation of the Social and reward-seeking networks

Sex steroid hormones can have drastic and rapid effects on the functioning of the reward system and reward-seeking behavior. Yet, traditional nodes of the reward system have a paucity of sex steroid receptors. The medial preoptic area of the hypothalamus, on the other hand, is incredibly sensitive to sex steroids and is a main node in the social network. My research in the Dominguez Lab demonstrated that medial preoptic area modulates the reward system’s response to rewards via direct inhibitory connections to dopamine-producing neurons in the ventral tegmental area. Neurotoxic lesions of the medial preoptic area also increase reward-seeking behavior. I found that steroid sensitive cells in the medial preoptic area project to the ventral tegmental area, which in turn affect reward-induced dopamine release in the nucleus accumbens. In turn, estrogen injections directly into the medial preoptic area increased reward-induced dopamine release 3-fold in the nucleus accumbens. These findings challenged the idea that sex steroids work directly on nodes of the reward system (e.g., nucleus accumbens), and provided evidence for obligatory interactions between the reward and the social behavior network—together known as the social decision-making network.

steroid synthesis in the social decision-making network

Steroid hormones are made in the periphery and circulate to the central nervous system to exert their behavioral effect…or so we thought. Steroid hormones can actually be synthesized in the brain from scratch (de novo) or from precursors. My research in the Soma Lab demonstrates that the mammalian brain has the all of the enzymes necessary to make androgens and estrogens from precursors or de novo. Using the gold-standard for steroid measurement (LC-MS/MS; see video), I showed that sex steroids levels are differentially regulated neural nodes of the social decision-making network. This means that, regardless of circulating levels of sex steroids, the brain can precisely control the local levels of steroids to ensure optimal function of the social-decision making network.