Androgens and estrogens induce seasonal‐like growth of song nuclei in the adult songbird brain

Abstract

In seasonally breeding songbirds, the brain regions that control song behavior undergo dramatic structural changes at the onset of each annual breeding season. As spring approaches and days get longer, gonadal testosterone (T) secretion increases and triggers the growth of several song control nuclei. T can be converted to androgenic and estrogenic metabolites by enzymes expressed in the brain. This opens the possibility that the effects of T may be mediated via the androgen receptor, the estrogen receptor, or both. To test this hypothesis, we examined the effects of two bioactive T metabolites on song nucleus growth and song behavior in adult male white-crowned sparrows. Castrated sparrows with regressed song control nuclei were implanted with silastic capsules containing either crystalline T, 5alpha-dihydrotestosterone (DHT), estradiol (E(2)), or a combination of DHT+E(2). Control animals received empty implants. Song production was highly variable within treatment groups. Only one of seven birds treated with E(2) alone was observed singing, whereas a majority of birds with T or DHT sang. After 37 days of exposure to sex steroids, we measured the volumes of the forebrain song nucleus HVc, the robust nucleus of the archistriatum (RA), and a basal ganglia homolog (area X). All three steroid treatments increased the volumes of these three song nuclei when compared to blank-implanted controls. These data demonstrate that androgen and estrogen receptor binding are sufficient to trigger seasonal song nucleus growth. These data also suggest that T's effects on seasonal song nucleus growth may depend, in part, upon enzymatic conversion of T to bioactive metabolites.

Seasonal-like growth and regression of the avian song control system: Neural and behavioral plasticity in adult male Gambel’s white-crowned sparrows

“…In canaries, systemic exposure to either DHT or E2 for eleven days does not increase song control nuclei volume or song rate, unlike T, which does increase HVC volume and song rate (Sartor et al, 2005). Systemic exposure to both an aromatizable androgen and an estrogen, however, produce full growth of song nuclei volumes and maximal song rate (Tramontin et al, 2003), RA soma area, and RA spontaneous firing rate (Park et al, 2005;Meitzen et al, 2007a). Exposure to the aromatase inhibitor ATD blocks the increase in RA soma area and spontaneous firing rate induced by LD photoperiod and systemic T (Meitzen et al, 2007a).…”

“…These metabolites have been implicated in song control system growth. In white-crowned sparrows, systemic exposure to either DHT (a nonaromatizable androgen) or E2 alone for 21 days results in substantial growth of song control nuclei (Tramontin et al, 2003), but not RA spontaneous firing rate or soma area (Park et al, 2005;Meitzen et al, 2007a). In canaries, systemic exposure to either DHT or E2 for eleven days does not increase song control nuclei volume or song rate, unlike T, which does increase HVC volume and song rate (Sartor et al, 2005).…”

Steroid Hormones Act Transsynaptically within the Forebrain to Regulate Neuronal Phenotype and Song Stereotypy

“…), 1.0 mm; outer diameter (o.d. ), 2.0 mm; length, 12 mm; VWR, West Chester, PA)] filled with crystalline 17-␤ estradiol, or testosterone, as in the study by Tramontin et al (2003). Some birds received two subcutaneous SILASTIC implants (i.d., 1.0 mm; o.d., 2.0 mm; length, 9 mm) of the aromatase inhibitor 1-4-6-androstatrien-3,17-dione (ATD; Sigma, St. Louis, MO) as in the study by Moore et al (2004).…”

Courtship and copulation in the adult male green anole: Effects of season, hormone and female contact on reproductive behavior and morphology

“…In male starlings, T increases the volume of song control nuclei more under conditions typical of the BS than NBS [8]. Parallel to behavioral changes, the volume of brain regions controlling song can increase due to the rise in T that occurs in the BS [3,4,16,19,59,69,81,83,84]. However, unlike the anole, increased song production in some birds contributes directly to enhancement of the morphology of song control nuclei [1,18,85].…”