Meeting Abstract
Estrogens (E) affect vertebrate brain and behavior throughout the lifespan. Given the diversity of E-dependent behaviors, targets, and sources, the spatial and temporal precision of E-delivery is of considerable interest. In the songbird, while aromatase is widely expressed, E-sensitive loci, such as the hippocampus (HP) and HVC have few to no aromatase-expressing neuronal profiles. Using immunoelectron microscopy, we detected aromatase in presynaptic boutons and post-synaptic dendrites in the zebra finch HP and HVC, areas where somal aromatase was low to undetectable. Thus, synapses may be provided with E with extreme precision, perhaps to the exclusion of adjacent structures. Local application of the aromatase inhibitor ATD to the HP, reduced local E, and impaired learning and performance on a spatial memory task. Thus, constitutive HP aromatization, likely at the synapse, is a critical modulator of HP-dependent function. We have also found that aromatase can be induced by mechanical damage in vimentin-positive reactive astrocytes and radial glia; cells that do not express aromatase in the unperturbed homeotherm brain. This induction is considerable, as mechanical injury almost doubles immunoreactive aromatase and almost quadruples local E around the injury. We now focus on the interaction between injury-dependent aromatase and the innate immune system. In adults of both sexes, mechanical injury first induces cytokine expression in microglia followed by the astrocytic aromatase. E, synthesized by glia is a potent inflammatory as its removal and replacement, sustains and reduces cytokine expression respectively. Taken together, these studies reveal the remarkable and dynamic specificity of E-provision in the vertebrate brain underscoring the considerable spatial and temporal precision of E-provision, and its influence on brain structure and function.
