Subcellular compartmentalization of aromatase is sexually dimorphic in the adult zebra finch brain

Abstract

ABSTRACT:The vertebrate brain is a source of estrogen (E) via the expression of aromatase (E-synthase). In the zebra finch (Taeniopygia guttata), despite documented dimorphisms in E-action, no differences are detectable in circulating E, or the neural levels of aromatase transcription, activity, or somal protein expression. Studies of aromatase expression at the lightand electron-microscope levels reveal greater numbers of fibers and presynaptic boutons in adult males relative to females. We assayed aromatase activity and content in synaptosomes and microsomes from the anterior [containing lMAN and Area X (males)] and posterior telencephalon (containing HVC and RA) of adult birds. In contrast to non-song birds and mammals, both cell fractions contain abundant aromatase measurable in terms of activity (enzyme assays) and content (Western blots) with minimal enrichment in microsomes. From brain homogenates of identical concentration, aromatase activity was higher in the synaptosomal relative to the microsomal fraction, in males relative to females, and in the posterior compared to anterior telencephalon. These effects were driven by high levels of synaptosomal aromatase in the male posterior telencephalon. These data suggest that males possess more aromatase per presynaptic bouton, or a greater number of aromatase-containing presynaptic boutons than females in the posterior telencephalon. Further, the present report reveals synaptic aromatization as a considerable source of E in the zebra finch brain, and supports the idea that telencephalic synapses in and around the adult male song production nuclei may be exposed to higher levels of E compared to the female brain. ' 2006 Wiley Periodicals, Inc. J Neurobiol 67: 1-9, 2007

A Quantification of the Injury‐Induced Changes in Central Aromatase, Oestrogenic Milieu and Steroid Receptor Expression in the Zebra Finch

“…As reported previously (34), the antibody against aromatase recognises a single band at approximately 55 kDa in zebra finch tissue (Fig. 1A).…”

Sex-specific, rapid neuroestrogen fluctuations and neurophysiological actions in the songbird auditory forebrain

“…Aromatase, the enzyme that synthesizes estrogens, is expressed and active within presynaptic terminals in some neuronal circuits (Naftolin et al 1996;Peterson et al 2005;Rohmann et al 2007;Saldanha et al 2000). Alongside estrogen production in brain, novel actions have been identified in which estrogens rapidly modulate ion channel receptors on neuronal membranes.…”

The importance of neural aromatization in the acquisition, recall, and integration of song and spatial memories in passerines

“…Newer evidence from ultrastructural studies supports this contention as we now have a greater understanding of the acute and rapid alterations in synaptic E 2 provision via the presynaptic expression and activity of aromatase (Peterson et al, 2005;Rohmann et al, 2007).…”

“…Immunoelectron microscopy reveals an abundance of aromatase in presynaptic boutons and postsynaptic dendrites at this locus, the former being more abundant in males than in females (Peterson et al, 2005). Correspondingly, aromatase activity is higher in synaptosomal than microsomal fractions from tissue homogenates and in males relative to females (Rohmann et al, 2007).…”