Photoperiod influences the ontogenetic expression of aromatase and estrogen receptor alpha in the developing tilapia brain.

Neural development is determined not only by genetic regulation, but also by environmental cues. Central estrogen-forming/estrogen-sensitive systems play an important role in the neural development of the brain. In the present study, the quantitative reverse transcription-polymerase chain reaction method was used to investigate the effects of photoperiod on the ontogenetic expression of aromatase and estrogen receptor alpha (ERalpha) in the developing tilapia brain. Before day 5 post-hatch, brain aromatase mRNA expression was significantly decreased by constant light but not influenced by constant darkness. During this period, brain ERalpha mRNA expression was significantly increased under both constant light and constant darkness. Between days 5 and 10, and between days 10 and 15, neither brain aromatase nor brain ERalpha expression was altered under constant darkness and constant light. These results indicate that the ontogenetic expression of brain aromatase and brain ERalpha is not via a light-inducing process but influenced by a light-entraining signal during the very early period of development.