Fig. 4. Postfracture accumulation of mast cells (green ) in the dermis of the hind paw skin, and the effects of the substance P (neurokinin-1) receptor antagonist. Keratin (red ) is a marker for epidermal keratinocytes. (A ) Systemic treatment with the neurokinin-1 receptor antagonist LY303870 for 8 days blocked fracture-induced increases in the dermal mast cells. Scale bar = 100 μm. (B ) Quantification of immunostained mast cells in the dermis of saline vehicle (n = 9) and LY303870-treated fracture rats (n = 6). ***P < 0.001, versus  saline treated. Fx = fracture; LY = LY303870.