Aromatase expression and function in the brain and behavior: A comparison across communication systems in teleosts

Aromatase (Cyp19a1) is a steroidogenic enzyme that functions to convert aromatizable androgens into bioactive estrogens. The teleost brain is known to have the highest levels of aromatase activity among vertebrates, yet we know relatively little about the function of local estrogen production in teleost behavior. This review compares and contrasts the findings from behavioral studies in the visual, auditory, electrosensory, and olfactory systems, with expression studies in the brain and peripheral nervous system to identify pathways for aromatase effects on teleost behavior. I will first describe aromatase expression at the cellular level in the teleost brain. I will then review evidence for an effect of aromatase activity in sensory perception across different communication systems, followed by a comparison of its effects in the signal production circuitry of vocal and electrogenic teleosts. The findings presented demonstrate that aromatase expression is well conserved in the sensory afferent nerve fibers across communication systems, despite the paucity of study to date on the effects of locally produced estrogens in sensory perception. It is also apparent that there are numerous other locations of aromatase expression within sensory pathways, drawing attention to the need for more localized inhibition studies to understand the function of local estrogen production in distinct regions. The findings in the last section of this review show that differences in vocal call production in the plainfin midshipman fish likely involve differences in aromatase expression in the hindbrain control nucleus, whilst this relationship does not appear to be conserved in the brown ghost knifefish for electromotor production. Therefore, local estrogen function in signaling behavior at the organismal level likely differs between these communication systems, though its effects at the cellular level remain to be determined.