Role of Neuroestrogens in Memory Acquisition and Recall in the Zebra Finch

Steroid hormones synthesized in the brain, known as neurosteroids, influence neuroplasticity and behavior, including learning and memory, as well as recovery from neural injury. In particular, estradiol has been identified as a neurosteroid affecting neuronal plasticity and thus may play a role in learning and memory. Neuroestrogens are produced from androgens by the enzyme aromatase that is expressed in the brain. In some songbirds, aromatase is expressed at high levels in the hippocampus (HP), a brain region crucial for vertebrate learning and memory. To determine whether performing a memory task regulates aromatase levels in the HP via gene expression, zebra finches were subjected to either a memory acquisition or a memory recall test that required the localization of a food source in a four-armed maze. Immediately after completing the behavioral test, the HP of each bird was removed and frozen.  Quantitative polymerase chain reaction (qPCR) was used to determine levels of aromatase mRNA in the HP of each individual. It is predicted that memory formation regulates aromatase via rapid modifications (i.e., phosphorylation of aromatase), while memory recall leads to longer-term regulation of gene expression. Therefore, it is expected that aromatase mRNA levels will be higher in birds using memory recall to successfully complete the behavioral task than in birds that have recently acquired the memory. Understanding the time course of aromatase expression will help further our knowledge of neuroestrogen production in the brain and its role in learning and memory.