Skin perfusion changes in experimental neuropathic pain: sciatic nerve constriction

Laser Doppler flowmetry was used as a method of measurement of skin blood flow perfusion in an experimental rat model of neuropathic pain. The common sciatic nerve was microsurgically approached and four ligatures were loosely tied around the nerve (sciatic ligature group). Contralateral nerves were approached but not injured (sham procedure). All paws were studied before any surgical procedure (controls) and immediately, 24 h, 11 and 25 days after surgery. In each experiment, the skin perfusion was measured in the plantar surface of the hind paw, both in baseline conditions and after a heating test, where skin temperature around flowmeter probe reached 42 degrees C. The heating test produced an increase in skin perfusion that ranged between 70% and 80% in sham and normal paws. Nerve ligation induced no immediate changes in skin perfusion with a normal 65% increase after heating. However, 24 h later, baseline skin perfusion was significantly higher than preoperatively with smaller response to heating. This situation changed at 11 and 25 days, with baseline values significantly smaller than before surgery and responses to heating significantly higher. Nerve section in these previously ligated sciatic nerves produces a significant increase in skin perfusion. Our results suggest that vasomotor changes in the model of sciatic ligature are presumably related to a denervation hypersensitivity of skin blood vessels to vasoactive agents.