Veteran image analysts please correct me there if im wrong.:
Pixel intensity is usually a variable of color or brightness. In grayscale images more intense pixels are whiter ones. In your image more intense pixels are “redder” ones (brighter, more saturated). So when you say you want to get the pixel intensity you would rather mean the distribution of intensities, which is a Histogram (Analyze -> Histogram).
What i understand you want is to get the number of red pixels, which would mean the area of the cytoskeleton. The workflow to achieve this is generally generating a binary image (Pixels you want to analyze (cytoskeleton) are white, background is black). For that you can threshold or segment the image in another way (weka segmentation for example). In this binary image you use Measure -> Analyze Particles to get Area, Perimeter, Width, Length, whatever you want (Use Analyze -> Set measurements to determine which parameters to measure).