Inflammation with no axonal damage of the rat saphenous nerve trunk induces ectopic discharge and mechanosensitivity in myelinated axons

Inflammation along a nerve trunk with no frank axonal nerve damage produced by complete Freund's adjuvant (CFA) or Carrageenan is known to induce a pa inful peripheral neuropathy. In the present study, we examined the electrop hysiological properties of myelinated axons (spontaneous discharge and mech anical sensitivity) at the inflamed nerve site. The rat saphenous nerves we re exposed at mid-thigh level and wrapped in 2 mm wide bands of haemostatic oxidized cellulose (Oxycel (R)) that were saturated with undiluted CFA. In the control rats the Oxycel (R) was saturated with saline. At postoperativ e days (PODs) 2-5 and 6-10, fine axon bundles were teased from the nerve, a nd electrophysiological recordings performed. At both time points spontaneo us activity at the site of the application in CFA rats (PODS 2-5 = 9.9 +/- 2.5%: PODs 6-10 = 6.1 +/- 1.4%) was significantly higher than in the contro l animals (PODS 2-5 = 2.9 +/- 1.1%: PODS 6-10 = 1.6 +/- 1.4%: P = 0.03, P = 0.02, respectively). Mechanical sensitivity at both time points was signif icantly higher in CFA rats (PODS 2-5 = 12.6 +/- 3.1%: PODS 6-10 = 10.3 +/- 3.1%) than in saline rats (PODS 2-5 = 3.4 +/- 2.91%: PODS 6-10 = 0.8 +/- 1. 0%: P = 0.03, P = 0.04, respectively). This study clearly shows that perine ural inflammation with no axonal nerve damage induced by CFA application ar ound the nerve trunk elevates spontaneous activity and induces mechanosensi tivity in myelinated axons. (C) 2001 Elsevier Science Ireland Ltd. All righ ts reserved.