how to distinguish between neighbouring cells?

[Tinah]

Hello,
I am trying to distinguish between neighboring fluorescent cells in ImageJ. Since the intensities are similar at each of the cell's membranes I am unable to outline one cell without it being affected by its neighbor when I process it. With single cells I can easily convert the image to binary, threshold, and then measure the area. Does anyone have an idea of how to manually tell ImageJ that I want to exclude neighboring intensities?

Thanks,
tina