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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.

Laser Doppler flowmetry was used as a method of measurement of skin blood flow perfusion in an experimental rat model of peripheral nerve section. The common sciatic nerve was microsurgically approached and cleanly severed (sciatic transection group). Contralateral nerves were approached but not injured (sham procedure). All paws were studied before any surgical procedure (controls) and immediately, 24 hours, 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. Sham operated paws showed no differences from control unoperated paws. The heating test produced an increase in skin perfusion that ranged between 70% and 80% in sham and normal paws. Sciatic nerve section produces an immediate increase of 36.7% in blood flow with an additional increase of 27.5% after heating. In the following studies, on days 1, 11 and 25 baseline skin perfusion showed no changes in relation to preoperative values and heating induced only a small increase in perfusion.

Deafferentation pain has been related to abnormal electrical hyperactivity in the neurons of the sensory relays in the central nervous system. This electrical activity resembles the epileptoid pattern observed in experimental epileptoid foci. With the aim of preventing this hyperactivity, rats were given long-term treatment with phenobarbital after sciatic transection and dorsal cervical rhizotomy. Daily intramuscular injections of saline solution or 5 and 10 mg/kg of phenobarbital were administered for 20 days, starting 10 days before surgery. Larger doses of phenobarbital delayed the onset and reduced the severity of autotomy. In a test of acute pain, the effect of intraperitoneal (1-16 mg) and intrathecal (100-500 micrograms) phenobarbital was studied by measuring the "tail-flick" response latency. Intraperitoneal phenobarbital did not modify acute pain, but 500 micrograms of intrathecal phenobarbital increased the threshold of pain. These results indicate that (a) phenobarbital, a drug with anticonvulsant activity, reduces deafferentation behavior in rats, and (b) intrathecal phenobarbital has an antinociceptive action in acute experimental pain.

The role of microfascicular double ligation and interligature coagulation in the prevention of painful neuroma was studied in an experimental model of section of the sciatic nerve in the rat. The experimental parameters used were the onset of autotomy and the weekly autotomy score. The autotomy of the denervated limb is a behavioral pattern that occurs in the experimental animal after the severing of peripheral nerves and has been related to anomalous electrical activity originating from the neuroma. Microfascicular ligation was performed immediately after section of the sciatic nerve or 10 days later. The results were compared to those of control groups treated with simple nerve section or simple neuroma resection 10 days after nerve section. The results show that immediate or delayed microfascicular ligation has no effect on pain as measured by the development of autotomy.