Cortical and striatal levels of Bdnf mRNA and mature BDNF protein in YAC128 and Bdnf transgenic (BTg) mice. A, Representative in situ hybridization images showing levels of Bdnf mRNA in brains of WT, YAC128, BTg, and double transgenic (YAC;BTg) mice. The probes were ³⁵S-labeled antisense and sense RNAs corresponding to the Bdnf coding region. B, Representative Western blots showing levels of mature BDNF protein in the cerebral cortex and striatum. C, Quantification of Bdnf in situ hybridization signals in the cerebral cortex and striatum. The optical density of signals was measured on eight sections for each mouse (cortex: F_{3, 12} = 38.1, p < 0.0001; striatum: F_{3, 12} = 401.3, p < 0.0001; n=4–5 mice/genotype). D, Relative levels of mature BDNF in the cerebral cortex and striatum, as revealed by Western blots (cortex: F_{3, 14} = 80.89, p < 0.0001; striatum: F_{3, 20} = 6.997, p < 0.001; n=4–6 mice/genotype). Error bars represent standard errors. Multiple comparisons using t test: *, p < 0.05; **, p < 0.01.

Activation of the TrkB receptor in YAC128 and BTg mice. A–C, Representative Western blots showing levels of TrkB receptors, downstream effectors (Akt, Erk1/2, and PLC-γ1), and their activated (phosphorylated) forms (p-TrkB, p-Akt, p-Erk1/2, and p-PLC-γ1) in the cortex and striatum. D and E, Relative levels of TrkB receptors and downstream effectors in the cortex and striatum (n=4–9 mice per genotype). One-way ANOVA analyses revealed that there was a significant effect of genotype on levels of striatal Akt (F_{3, 23} = 9.609, p < 0.001) and striatal p-Akt (F_{3, 23} = 3.928, p < 0.05), but not for other protein levels. Error bars represent standard errors. Multiple comparisons using t test: *, p<0.05; **, p<0.01.

BDNF overexpression ameliorates motor dysfunction in YAC128 mice. A, Performance on rotarod tests. Tests were performed at 4, 9 and 16 months of ages (n = 10–38 mice per genotype at each time point). There was a significant effect of genotype (F_{3, 225} = 7.208, p < 0.001) and age (F_{2, 225} = 36.29, p < 0.0001), but no interaction between genotype and age. B Body weights of male mice (n = 5–19 mice per group at each time point). There was no significant effect of genotype (F_{3, 118} = 0.328, p = 0.805) and age (F_{2, 118} = 1.080, p = 0.343). C, Body weights of female mice (n = 4–19 mice per group at each time point). There was a significant effect of genotype (F_{3, 98} = 7.795, p < 0.001) and age (F_{2, 98} = 14.76, p < 0.0001), but no interaction between genotype and age. D, Time to cross beam. Beam walk tests were performed at 16 months of age. YAC128 mice took longer time to cross the beam than the other 3 genotypes of mice (F_{3, 85} = 8.005, p < 0.0001; n ≥ 19 mice per genotype). E, Percentage of mice that fell off the beam. F, Percentage of mice that stopped walking on the beam. G and H, Stride length and hind base width were measured when mice were at 13 months of age (Stride length: F_{3, 50} = 2.744, p = 0.0528; Hind base width: F_{3, 50} = 9.936, p < 0.0001; n = 11–17 mice per genotype). I, Muscle strength was measured when mice were at 14 months of age. There was a significant effect of genotype on muscle strength (F_{3, 49} = 3.226, p = 0.0304). Error bars indicate standard errors. Multiple comparisons with WT mice using t test: *, p < 0.05; **, p < 0.01. Comparisons between YAC128 mice and YAC;BTg mice using t test: #, p < 0.05; ##, p < 0.01.

BDNF overexpression corrects deficits of YAC128 mice in a simple swimming test. Animals were 12 months old and included 13 WT mice, 18 BTg mice, 12 YAC128 mice, and 11 YAC;BTg mice. A, Average latency for mice to reach the platform in three trials on day 3. YAC128 mice took longer time to reach the platform than WT mice (F_{3, 53} = 4.49, p < 0.01). B. Quantification of the path taken to the platform. Mice swimming initially toward the platform were given a score of 0, whereas mice swimming initially away from the platform were given a score of 1. YAC128 mice made significant more errors in initiating the task than the other three genotypes of mice (F_{3, 53} = 10.71, p < 0.0001). Error bars indicate standard errors. Multiple comparisons using t test: *, p < 0.05; ***, p < 0.001.

BDNF overexpression prevents striatal atrophy in YAC128 mice at 16 months of age. A, Brain weight (F_{3, 85} = 23.62, p < 0.0001; n ≥ 19 mice/genotype). B, Striatum volume (F_{3, 21} = 12.61, p < 0.0001; n = 5–8 brains/genotype). C, Cortical volume (F_{3, 23} = 2.38, p = 0.0958; n = 5–10 brains/genotype). D, Counts of striatal neurons. Striatal neurons were revealed by NeuN immunohistochemistry (F_{3, 20} = 8.07, p = 0.0010; n = 5–7 mice/genotype). E. Soma size of striatal neurons (F_{3, 12} = 5.144, p < 0.05; n = 4 mice/genotype). Error bars indicate standard errors. Multiple comparisons using t test: *, p < 0.05; **, p < 0.01; ***, p < 0.001.

Effects of BDNF overexpression on gene expression of striatal neurons in YAC128 mice. A, Representative in situ hybridization images showing striatal levels of mRNAs for dopamine receptor D2 (Drd2), enkephalin (Penk), dopamine receptor D1a (Drd1a), and substance P (Tac1) in four genotypes of mice. B, Relative levels of Drd2, Penk, Drd1a, and Tac1 mRNAs in the striatum (n = 4 mice per genotype). Significant differences in abundance among the four genotypes were found for Drd2 mRNA (F_{3, 12} = 16.01, p < 0.001), Penk mRNA (F_{3, 12} = 13.16, p < 0.001), and Tac1 mRNA (F_{3, 12} = 4.328, p < 0.05) but not for Drd1a mRNA (F_{3, 12} = 1.479, p = 0.270). C, Representative Western blot of striatal DARPP-32. D, Relative levels of DARPP-32 in the striatum were not significantly different among four genotypes of mice (F_{3, 14} = 1.600, p = 0.234; n = 6 WT mice and 4 mice for each of the other 3 genotypes). Error bars represent standard errors. Multiple comparisons using t test: *, p < 0.05; **, p < 0.01.

BDNF overexpression does not affect dendritic arborization of striatal medium-sized spiny neurons (MSNs). A, Representative dendritic arbors of MSNs in four genotypes of mice. B–E, Quantification of node number, intersection, total dendrite length, and dendritic endings in each traced MSN. For each genotype, 40 MSNs from 4 mice were traced. No significant differences were detected between the four genotypes (Node number: F_{3, 12} = 0.104, p = 0.956; intersections: F_{3, 12} = 0.159, p = 0.922; dendritic length: F_{3, 12} = 0.121, p = 0.946; dendritic endings: F_{3, 12} = 0.144, p = 0.932).

BDNF overexpression in the forebrain normalizes spine abnormalities of MSNs in YAC128 mice at 16 months of age. A, Representative images of distal dendrites of MSNs in four genotypes of mice. B, Spine density as a function of distance from the soma in a major dendrite of MSNs (n = 4 mice; ten neurons were analyzed in each mouse). Two-way ANOVA analysis indicates a significant difference in spine density between genotypes (F_{3, 12} =15.42, p < 0.0001). Post hoc tests show significant difference in spine density between WT and YAC128 at 60, 90, 100, 110, and 130 μm from the soma and between YAC128 and YAC;BTg at 60–110 μm from the soma (p < 0.05). C, Spine length of MSNs in four genotypes of mice. There was a significant effect of genotype on spine length (F_{3, 156} = 2.778, p < 0.05; n = 40 neurons from 4 mice per genotype). D, Distribution of spine length (n = 4 mice per genotype). Approximately 750 spines in each brain were quantified. Error bars represent standard errors. Multiple comparisons using t test: *, p < 0.05; **, p < 0.01.