Fig. 3: Histological analysis of extracellular matrix and synapse proteins in the aging mesolimbic dopamine system.

a Areas within the ventral tegmental area (VTA) and nucleus accumbens (NAc) histologically examined. Experiments were performed once on a single cohort of mice. b Photomicrographs of tyrosine hydroxilase (TH) and Wisteria floribunda agglutinin (WFA) from a young-adult (4 months) and late-middle-aged (18 months) mouse (left). Right: binarized images used for quantification. c Boxplots depicting VTA and NAc WFA field-of-view coverage (%) in young-adult (black; n = 8 mice) and late-middle-aged mice (gray; n = 10 mice; n-way ANOVA; post-hoc Tukey-Kramer; two-sided; Age: p = 0.026). d Photomicrographs of hyaluronan and TH in young-adult and late-middle-aged mice (left). Right: binarized images used for quantification. e Boxplots depicting VTA and NAc hyaluronan filed-of-view coverage in young-adult (black; n = 12 mice) and late-middle-aged (gray; n = 12 mice) mice (n-way ANOVA; post-hoc Tukey-Kramer; two-sided; Age: p = 0.23). f Photomicrographs of Homer2, VGlut1, and TH in young-adult and middle-aged mice. Insets depict the field of view outlined by the white squares. Circles delineate synapses with presynaptic and postsynaptic elements. g Boxplots of VTA and NAc homer2 densities (n-way ANOVA; post-hoc Tukey-Kramer; two-sided; Age: p = 0.98; n = 7 young and n = 6 aged mice). h Photomicrographs of hyaluronan, homer2, and TH in the VTA and NAc of a young-adult mouse. Bottom panels are equivalent to top panels with the addition of the TH channel. Arrows highlight putative hyaluronan-homer2 colocalized puncta and squares depict homer2 puncta not associated with hyaluronan. Right: schematic ECM-synapse proximity analysis. Experiments were performed once on a single cohort of mice. i Densities of homer2 within 0.5 µm of hyaluronan compared to when rotating 1 channel 90 degrees (paired t-test; two-sided; VTA: p = 0; NAc: p = 0.003; n = 8 young and n = 8 aged mice). In all boxplots, boxes represent the interquartile range (IQR; 25–75 percentiles), middle lines the median, and whiskers extend ± 1.5*IQR. Source data are provided in the file Source Data - Fig. 3 and all statistics are provided in Supplementary Data 6. * represents p < 0.05, ** represents p < 0.01, *** represents p < 0.001 for each statistical test.