From social behavior to neural circuitry: steroid hormones rapidly modulate advertisement calling via a vocal pattern generator.

Across vertebrates, androgens are rapidly elevated within minutes in response to aggressive or reproductive stimuli, yet it is unclear what the causal relationship is between fast androgen elevation and the ongoing (minute-by-minute) expression of behavior. This study tested the hypothesis that rapid increases in plasma steroid levels induce similarly rapid increases in both vocal behavior and the neurophysiological output of a central pattern generator that governs vocal behavior. In Gulf toadfish (Opsanus beta), males call to attract females to their nesting sites, and both males and females vocalize in aggressive interactions. Previous field experiments with males showed that simulated territorial challenges produce rapid and concurrent elevations in ongoing calling behavior and circulating levels of the teleost-specific androgen 11-ketotestosterone (11kT), but not the glucocorticoid cortisol. The current field experiments showed that non-invasive (food) delivery of 11kT, but not cortisol, induced an elevation within 10 min in the ongoing calling behavior of males. Electrophysiological experiments revealed that intramuscular injections of either 11kT or cortisol, but neither testosterone nor 17-beta-estradiol, induced increases within 5 min in the output of the vocal pattern generator in males, whereas only cortisol had similarly fast effects in females. The field behavioral results support predictions generated by the challenge hypothesis and also parallel the 11kT-dependent modulation of the vocal pattern generator in males. The cortisol effect on the vocal pattern generator in both sexes predicts that glucocorticoids regulate vocalizations in non-advertisement contexts. Together, these experiments provide strong support for the hypothesis that surges in circulating steroid levels play a causal role in shaping rapid changes in social behavior (vocalizations) through non-genomic-like actions on neural (vocal motor) circuits that directly encode behavioral patterning.