High resolution image analysis of EM48-positive aggregates indicates major age-dependent differences.

<p>Young (3 week) and old (15 month) rats received a stereotaxic injection of lentiviral vectors encoding Htt171-82Q (2 µl, 200 ng/µl of p24). Histological evaluation was carried out 4 weeks after infection using EM48 immunohistochemistry and image analysis software. The number of EM48 positive objects (aggregates) was determined from images obtained using a 50× objective at different focal depths (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0004637#s4" target="_blank">Materials and Methods</a>) so that very small EM48 positive objects could be detected. Typical images acquired at 50× objective in a young rat (<i>A</i>) and an old rat (<i>C</i>). <i>B</i> and <i>D</i> correspond to zoomed images of the rectangles in A and B. Note the high resolution of the images allows reliable detection of even small aggregates. <i>E</i>, Histograms showing the distribution of small objects as a function of size (apparent cross-sectional area) in two animals, indicating that the proportion of very small aggregates in old rats is approximately ten fold higher than in young animals.