Figure 5. Lasting synaptic pruning in the forebrain motor nucleus HVC.

(A) Photomicrographs of dendrite segments from non-singing control animals (C), singing female canaries sacrificed after five months of testosterone treatment (T₁+), and non-singing individuals sacrificed 2.5 months after testosterone withdrawal (T₁-). (B) Compared to naive control birds (C), spine densities were significantly reduced in testosterone-treated, singing birds (T₁+), and remained significantly reduced up to 2.5 months after birds stopped singing by withdrawing testosterone (T₁-). (C) No significant differences in spine densities were observed in RA between the experimental periods. (D–F) The probability distribution of dendrites with different spine densities in HVC demonstrated a shift towards more dendrites with fewer spines in testosterone treated (T₁+), singing birds and testosterone removed (T₁-), non-singing birds compared to non-singing control birds. Columns in B-F represent the mean ± SEM and open circles indicate individual data points (a,b: p<0.01, ANOVA, n = 6 animals). Scale bar = 100 µm. Source data for spine quantifications are available in the Figure 5—source data 1.