Substrates for vocal‐acoustic plasticity: Neuroestrogen and steroid hormone receptor expression in midshipman fish.

Abstract

In a teleost fish, the midshipman Porichthys notatus, androgens and estrogen rapidly modulate vocal motor patterning and contribute to seasonal changes in the frequency encoding of the eighth nerve. To identify potential sites of action of these steroids, as well as local estrogen synthesis (via conversion from testosterone by the enzyme aromatase), in situ hybridization was employed to identify estrogen receptor alpha (ER), androgen receptor (AR), and aromatase mRNA distribution in vocal and auditory circuitry. AR expression was more widespread than ER and found at all levels of the vocal motor pathway and in vocal‐acoustic integration centers, while aromatase was particularly abundant in the vocal motor system. Both AR and ER were identified in midbrain and forebrain auditory nuclei and in the saccular epithelium of the inner ear, the main auditory end organ in midshipman and most teleosts. Aromatase was found in ganglion nerve cells of the eighth nerve, suggesting that the ear itself is a local source of estrogen driving peripheral auditory plasticity. In sum, expression of steroid receptors in vocal and auditory nuclei, and the inner ear, support neurophysiological evidence for the role of estrogen and androgens as modulators of vocal output and auditory encoding in midshipman fish. [Work supported by NIMH, NIH, and NSF.]