Differential effects of global versus local testosterone on singing behavior and its underlying neural substrate

Abstract

Steroid hormones regulate multiple but distinct aspects of social behaviors. Testosterone (T) has multiple effects on learned courtship song in that it regulates both the motivation to sing in a particular social context as well as the quality of song produced. The neural substrate(s) where T acts to regulate the motivation to sing as opposed to other aspects of song has not been definitively characterized. We show here that T implants in the medial preoptic nucleus (POM) of castrated male canaries (Serinus canaria) increase song rate but do not enhance acoustic features such as song stereotypy compared with birds receiving peripheral T that can act globally throughout the brain. Strikingly, T action in the POM increased song control nuclei volume, consistent with the hypothesis that singing activity induces neuroplasticity in the song control system independent of T acting in these nuclei. When presented with a female canary, POM-T birds copulated at a rate comparable to birds receiving systemic T but produced fewer calls and songs in her presence. Thus, POM is a key site where T acts to activate copulation and increase song rate, an appetitive sexual behavior in songbirds, but T action in other areas of the brain or periphery (e.g., HVC, dopaminergic cell groups, or the syrinx) is required to enhance the quality of song (i.e., stereotypy) as well as regulate context-specific vocalizations. These results have broad implications for research concerning how steroids act at multiple brain loci to regulate distinct sociosexual behaviors and the associated neuroplasticity.activity-driven plasticity | singing motivation | preoptic area S teroid hormones such as testosterone (T) can have multiple effects on physiology, morphology, and behavior (1-4). These pleiotropic effects of steroids allow coordinating suites of traits into an organized functional response (5, 6). In the case of the regulation of behavior, both motivational and performance aspects of behavior as well cognitive components are often activated by the same hormone (2, 7). The neural sites of steroid action coordinating these distinct aspects of an integrated behavioral response have not been well characterized. In this study, we investigated the site of hormone action in relation to the activation of different aspects of birdsong to illustrate how such an integrated regulation can occur.Birdsong is a species-typical, stereotypic set of usually long, learned, complex vocalizations produced in reproductive contexts (8). A discrete network of interconnected brain nuclei orchestrates song learning and production (from here on called the song control system or SCS) (3, 9-11). Areas such as HVC (acronym is proper name) and the robust nucleus of the arcopallium (RA) regulate the production of song, whereas areas such as Area X and LMAN are involved in song learning. These forebrain nuclei can undergo remarkable plasticity in response to seasonally changing T (12, 13; see refs. 2 and 14 for review). There is also evidence that other factors such as singing ac...

Dissociable Effects on Birdsong of Androgen Signaling in Cortex-Like Brain Regions of Canaries

“…In line with previous work, our goal was to place each cannula near but not into HVC or RA (Meitzen et al, 2007;Alward et al, 2013Alward et al, , 2016c. Thus, implants were placed lateral to HVC and dorsolateral to RA.…”

“…Birds were anesthetized using isoflurane gas (3-4%) and implanted subcutaneously with T-filled SILASTIC implants (Dow Corning; outside diameter ϭ 1.65 mm, inside diameter ϭ 0.76 mm; 12 mm in length filled with 10 mm of T, Sigma-Aldrich T-1500; RRID: CHEBI:17347) in the same fashion as in our previous studies (Alward et al, 2013(Alward et al, , 2016c. We implanted all birds with subcutaneous T given observations in our laboratory and others that some males sing at very low rates (Calder, 1970;Alward et al, 2016b) and that laboratory held males have lower plasma T concentrations than wild-caught individuals even when held on long days (Calder, 1970;Meitzen et al, 2007). Implanting all birds with T thus increased experimental and statistical power.…”

“…We used an identical implant procedure as in our previous work but performed bilateral instead of unilateral implants (Alward et al, 2013(Alward et al, , 2016c. Birds were bilaterally implanted with 27-gauge cannulae targeting HVC or RA filled with crystalline flutamide (Sigma-Aldrich, Flutamide F9397; RRID: CHEBI:5132) or left empty as a control.…”

“…Indeed, lesions in different parts of HVC lead to changes in neural activity in a highly topographical manner (Stauffer et al, 2012) and medial versus lateral portions of HVC regulate distinct features of song (Basista et al, 2014). This technique has been used previously in neuroendocrine studies and shown to be effective in delivering the compound of interest while avoiding damage to the nucleus of interest, which could lead to confounding effects (Meitzen et al, 2007;Alward et al, 2013Alward et al, , 2016c.…”

“…Recent research makes it clear that T has nonredundant effects on song production in both the brain and the periphery (for review, see Alward et al, 2017). We know for example that the motivation to sing can be activated by T acting outside the song system in the medial preoptic nucleus (POM; Alward et al, 2013). However, song stimulated by T action only in the POM lacks stereotypy and the simultaneous implantation in HVC rescues the deficit (Alward et al, 2016c).…”