The role of neurotrophins in the seasonal-like growth of the avian song control system - PubMed (original) (raw)

The role of neurotrophins in the seasonal-like growth of the avian song control system

Anne Marie Wissman et al. J Neurosci. 2009.

Abstract

The avian song control system undergoes pronounced seasonal plasticity in response to photoperiod and hormonal cues. The action of testosterone (T) and its metabolites in the song nucleus HVC is both necessary and sufficient to promote breeding season-like growth of its efferent nuclei RA (robust nucleus of the arcopallium) and Area X, suggesting that HVC may release a trophic factor such as brain-derived neurotrophic factor (BDNF) into RA and X. BDNF is involved in many forms of adult neural plasticity in other systems and is present in the avian song system. We used a combination of in situ hybridization and intracerebral infusions to test whether BDNF plays a role in the seasonal-like growth of the song system in adult male white-crowned sparrows. BDNF mRNA levels increased in HVC in response to breeding conditions, and BDNF infusion into RA was sufficient to promote breeding-like changes in somatic area and neuronal density. Expression of the mRNA for the Trk B receptor of BDNF, however, did not vary with seasonal conditions in either HVC or RA. Local blockade of BDNF activity in RA via infusion of Trk-Fc fusion proteins inhibited the response to breeding conditions. Our results indicate that BDNF is sufficient to promote the seasonal plasticity in somatic area and cell density in RA, although NT-3 may also contribute to this process, and suggest that HVC may be a presynaptic source of increased levels of BDNF in RA of breeding-condition birds.

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Figures

Figure 1.

Figure 1.

Dark-field photomicrographs of in situ hybridization showing BDNF mRNA expression in HVC (A) and RA (B) of birds in the four treatment groups. Arrows delineate the borders of the song nuclei. Boxes indicate area from which pallial measurements were taken. Scale bars, 300 μm. Quantitative analysis of BDNF mRNA expression in HVC (C) and RA (D). Data are expressed as a ratio of the grain density within the song nucleus versus the surrounding pallial region. Bars are group means ± SEM, and each point represents one bird. Letters above bars represent statistically different groups (Tukey's HSD p < 0.05).

Figure 2.

Figure 2.

Dark-field photomicrograph (A) and quantitative analysis (B) of TrkB mRNA expression in RA in the different treatment groups. Arrows delineate the borders of RA. Data in B are expressed as a ratio of the grain density within the song nucleus versus the surrounding pallial region. Bars are group means ± SEM, and each point represents one bird.

Figure 3.

Figure 3.

Comparison of RA somatic area (A), neuronal density (B), and volume (C) in birds infused with one of four concentrations of BDNF near RA on one side of the brain. Bars are group means ± SEM; numbers inside bars indicate number of birds in each group (each number refers also to adjoining bar from opposite hemisphere). Value of p from Tukey's HSD, comparison between ipsilateral and contralateral side. Symbols above bars represent differences between ipsilateral and contralateral sides (Tukey's HSD); *p < 0.001; †p = 0.058.

Figure 4.

Figure 4.

Comparison of HVC somatic area (A) and neuronal density (B) across hemispheres in birds infused with vehicle or the highest dose of BDNF. Bars are group means ± SEM; numbers inside bars indicate number of birds in each group.

Figure 5.

Figure 5.

Comparison of RA somatic area (A) and neuronal density (B) across hemispheres in birds infused with saline, TrkB-Fc alone, TrkC-Fc alone, or TrkB&C-Fc. Bars are group means ± SEM; numbers inside bars indicate number of birds in each group. *p = 0.059 (Tukey's HSD), comparison between ipsilateral and contralateral side.

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