Fig. 7: Histological analysis of extracellular matrix deposition on dopamine neurons in behaviorally characterized aging mice.

a Left: photomicrographs of immunohistochemically labeled hyaluronan and proteoglycan link protein 1 (HAPLN1), aggrecan, and tyrosine hydroxylase (TH) from the ventral tegmental area (VTA) of a late-middle-aged mouse. Numbered images in middle panel correspond to numbered fields of view within white squares in the left panels. Right panels depict the fields of view delineated by white squares in middle panel. Right: photomicrographs depicting HAPLN1 and aggrecan deposition on dopamine neuron surfaces, and the peri-dopamine neuron region of interest used to estimate protein abundances at neuronal membranes. Experiments were performed once on a single cohort of mice. b Boxplots depicting field of view coverage of HAPLN1 and aggrecan in the VTA of young-adult (black; n = 8 mice), aging-unimpaired (AU; green; n = 6 mice), and aging-impaired (AI; yellow; n = 4 mice) mice (n-Way ANOVA; post-hoc Tukey-Kramer; HAPLN: p = 0.022; Aggrecan: p = 0.25). c Boxplots depicting HAPLN1-DA neuron, aggrecan-DA neuron, and HAPLN1-aggrecan-DA neuron puncta densities in young-adult (n = 8 mice), aging-unimpaired (AU; n = 6 mice), and aging-impaired (AI; n = 4 mice) mice (n-Way ANOVA; two-sided; HAPLN1-DA: p = 0.029; Aggrecan-DA: p = 0.62; HAPLN-Aggrecan-DA: p = 0.031). d Schematic of the analysis strategy used to examine hyaluronan and Homer2 on dopamine neurons (Homer-DA neuron). Experiments were performed once on a single cohort of mice. e Boxplots depicting homer-DA neuron puncta densities in young-adult (black) and late-middle-aged (gray) sedentary (squares) and behavior-trained (triangles) mice (n-way ANOVA; two-sided; Behavior: p = 0.65; n = 8 young-sedentary; 12 young-behavior; 8 middle-aged-sedentary; 12 middle-aged-behavior mice). f Relationship between homer-DA neuron puncta densities and performance on foraging task (robust regression; two-sided; Young: p = 0.91; Middle-aged: p = 0.039). g Scatter plots of hyaluronan-DA neuron puncta densities plotted against Homer2-DA neuron puncta densities in sedentary and behavior-trained mice (robust regression; two-sided; Young Sedentary: p = 0.34; Middle-aged Sedentary: p = 0.14; Young Behavior: p = 0.0036; Middle-aged Behavior: p = 0.0068). In all boxplots, boxes represent interquartile ranges (IQR; 25–75 percentiles), middle lines represent medians, and whiskers extend +/− 1.5*IQR. Source data are provided in the file Source Data - Fig. 7 and all statistics are provided in Supplementary Data 6. * represents p < 0.05.