Testosterone and brain-derived neurotrophic factor interactions in the avian song control system - PubMed (original) (raw)

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Testosterone and brain-derived neurotrophic factor interactions in the avian song control system

E A Brenowitz. Neuroscience. 2013.

Abstract

Interaction between steroid sex hormones and brain-derived neurotrophic factor (BDNF) is a common feature of vertebrate brain organization. The avian song control system provides an excellent model for studying such interactions in neural circuits that regulate song, a learned sensorimotor behavior that is often sexually dimorphic and restricted to reproductive contexts. Testosterone (T) and its steroid metabolites interact with BDNF during development of the song system and in adult plasticity, including the addition of newborn neurons to the pallial nucleus HVC and seasonal changes in structure and function of these circuits. T and BDNF interact locally within HVC to influence cell proliferation and survival. This interaction may also occur transsynpatically; T increases the synthesis of BDNF in HVC, and BDNF protein is then released on to postsynaptic cells in the robust nucleus of the arcopallium (RA) where it has trophic effects. The interaction between sex steroids and BDNF is an example of molecular exploitation, with the evolutionarily ancient steroid-receptor complex having been captured by the more recently evolved BDNF. The functional linkage of sex steroids to BDNF may be of adaptive value in regulating the trophic effects of the neurotrophin in sexually dimorphic and reproductively relevant contexts.

Copyright © 2012 IBRO. Published by Elsevier Ltd. All rights reserved.

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Figures

Figure 1

Figure 1

Simplified schematic sagittal view of the avian song control system showing the distribution of steroid receptors. Black arrows connect nuclei in the main descending motor circuit, and gray arrows connect nuclei in the anterior forebrain circuit. Abbreviations: AM- nucleus ambiguus; DLM, Dorsolateral nucleus of the medial thalamus; lMAN, lateral portion of the magnocellular nucleus of the anterior nidopallium; nXIIts, the tracheosyringeal portion of the hypoglossal nucleus; RA, the robust nucleus of the arcopallium; RAm – nucleus retroambigualis; syrinx, vocal production organ; V, lateral ventricle; X, area X of the medial striatum.

Figure 2

Figure 2

Song nuclei of Spotted Towhees represented in 3-D, from a caudal perspective. HVC, RA, and area X are each larger in 3-dimensional extent in breeding-condition birds (shown in gray) than in non-breeding-condition birds (shown in white). Figure adapted from (Bentley and Brenowitz, 2002).

Figure 3

Figure 3

Seasonal changes in androgen receptor expression in HVC of Song Sparrows. Bottom panel: AR mRNA is expressed at higher levels in HVC of breeding birds (adapted from Fraley et al., 2010). Scale-bar = 0.5 mm. Top panel: The density and immunostaining intensity of cells positive for AR-like protein are greater in HVC of breeding sparrows. Note that nonbreeding birds have fainter staining within cell nuclei (adapted from Soma et al., 1998). Scale bar = 20 µm.

Figure 4

Figure 4

Dark-field photomicrographs of in situ hybridization showing seasonal change in BDNF mRNA expression in HVC of White-crowned Sparrows. BDNF is expressed at higher levels in HVC of breeding birds. Arrows delineate the ventral border of HVC. Scale bar, 300 µm.

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