Continuous infusion of acidified saline around the rat sciatic nerve produces thermal hyperalgesia

Recent observations using both clinical and animal models have suggested that acidosis may initiate pain and sensitization. In the present study, we examined if changing the acidic environment around the rat sciatic nerve resulted in thermal hyperalgesia. Fresh solutions of preservative-free saline (PFS) and unbuffered PFS acidified to pH 3.5 were continuously infused around the left rat sciatic nerve for 7 days. Rats receiving unbuffered, acidified PFS developed a progressive thermal hyperalgesia that was maximal on infusion day 6. Unbuffered, acidified PFS significantly decreased the perineural pH (pH 6.9 +/- 0.15, P < 0.05), and decreasing perineural pH values were significantly correlated with increasing thermal hyperalgesia (r = 0.91) for individual rats. While it is likely that multiple factors play a role in the development of neuropathic pain, these data demonstrate that an acidic environment around the sciatic nerve will produce thermal hyperalgesia.