Blocking neuroestrogen synthesis modifies neural representations of learned song without altering vocal imitation accuracy in developing songbirds

Abstract

Birdsong, like human speech, is learned early in life by first memorizing an auditory model. Once memorized, birds compare their own burgeoning vocalizations to their auditory memory, and adjust their song to match the model. While much is known about this latter part of vocal learning, less is known about how initial auditory experiences are formed and consolidated. In both adults and developing songbirds, there is strong evidence suggesting the caudomedial nidopallium (NCM), a higher order auditory forebrain area, is the site of auditory memory consolidation. However, the mechanisms that facilitate this consolidation are poorly understood. One likely mechanism is 17β-estradiol (E2), which is associated with speech-language development and disorders in humans, and is abundant in both mammalian temporal cortex and songbird NCM. Circulating E2 is also elevated during the auditory memory phase, and in NCM immediately after song learning sessions, suggesting it functions to encode recent auditory experience. Therefore, we tested a role for E2 production in auditory memory consolidation during development using a comprehensive set of investigations to ask this question at the level of neuroanatomy, neurophysiology, and behavior. Our results demonstrate that while systemic estrogen synthesis blockade regulates juvenile song production, inhibiting E2 synthesis locally within NCM does not adversely affect song learning outcomes. Surprisingly, early life E2 manipulations in NCM modify the neural representations of birds' own song and the model tutor song in both NCM and a downstream sensorimotor nucleus (HVC). Further, we show that the capacity to synthesize neuroestrogens remains high throughout development alongside substantial changes in NCM cell density across age. Taken together, these findings suggest that E2 plays a multifaceted role during development, and demonstrate that contrary to prediction, unilateral post-training estrogen synthesis blockade in the auditory cortex does not negatively impact vocal learning. Acute downregulation of neuroestrogens are therefore likely permissive for juvenile auditory memorization, while neuroestrogen synthesis influences communication production and representation in adulthood. AntibodiesAntibodies and dilutions for aromatase and parvalbumin were identical to those used in Ikeda et al. (2017). Briefly, we used a polyclonal anti-aromatase primary antibody raised in rabbit (1:2,000; a generous gift from Dr. Colin Saldanha), and a monoclonal anti-parvalbumin primary antibody raised in mouse (1:10,000; Millipore MAB1572; RRID: AB_2174013). Secondary antibodies included goat antirabbit Alexa 488 (1:500; Thermo Fisher Scientific Inc.), and goat anti-mouse Alexa 647 (1:100; Thermo Fisher Scientific Inc.). ProcedureBrain sections were first manually washed 3 x in 0.1 M PB, followed by 3 x 15-minute washes in 0.1 M PB on a plate shaker, followed by a 2-hour incubation at room temperature with 10% normal goat serum (Vector) in 0.3 % PBT. Tissue was then transferred to a 10% normal goat...

Estrogen and sex-dependent loss of the vocal learning system in female zebra finches

“…We were also surprised to see that chronic exemestane treatment in females caused some females to produce 1-2 repeated syllables in a song-like manner, even though they had atrophied song nuclei. Prior studies have shown that acute aromatase inhibition can suppress the rate of singing in zebra finches and canaries (Alward et al, 2016;Vahaba et al, 2019;Walters and Harding, 1988), but no changes in song learning acuity have been reported (Merten and Stocker-Buschina, 1995;Vahaba et al, 2019). Perhaps the more potent and longterm application of the estrogen inhibitor we used revealed an unknown involvement of estrogen in vocal learning.…”