Spontaneous activity of axotomized afferent neurons after L5 spinal nerve injury in rats.

After mechanical injury of a peripheral nerve some axotomized afferent neurons develop spontaneous activity, which is thought to trigger abnormal pain behavior in rats and neuropathic pain in humans. Here, we analysed the ectopic activity in axotomized afferent fibers recorded from the L5 dorsal root in different time periods after L5 spinal nerve lesion and the effects of sympathectomy on it. The following results were obtained: (1) Up to 6 hours after spinal nerve transection there was almost no spontaneous activity in axotomized afferents, except short-lasting injury discharges at the time of transection; (2) Three to 8 days following spinal nerve lesion, the rate of spontaneous activity was 7.

Distribution of sensory properties among axotomized cutaneous C-fibres in adult rats.

A few hours after peripheral axons of cutaneous afferent neurons have been transected, some of their novel endings become excitable by physical or chemical stimuli. It has been assumed that these axon endings preferentially respond to those stimuli which have excited their previous receptive endings. We studied the prevalence of sensory properties among 784 unmyelinated sural nerve fibres which had been axotomized 2-24 h before, by applying mechanical and thermal forces to the nerve lesion site.

Inflammatory mediators sensitize acutely axotomized nerve fibers to mechanical stimulation in the rat.

Many axotomized myelinated as well as unmyelinated cutaneous nerve fibers are sensitive to mechanical stimuli applied to the cut nerve end within a few hours after nerve lesion. Here we investigated the influence of inflammatory mediators on this ectopic mechanosensitivity after cutting and ligating the sural nerve in anesthetized rats. Neural activity was recorded from single axons in filaments teased from the sural or sciatic nerve proximally to the lesion site 2-33 hr after axotomy.

Algesics excite axotomised afferent nerve fibres within the first hours following nerve transection in rats.

The direct consequences of a peripheral nerve injury at the lesion site itself are often twofold: axons of afferent (and efferent) nerve fibres are transected and the tissue surrounding the nerve injury site is inflamed. Recent studies have shown that a few hours after nerve transection, axotomised myelinated (A) and unmyelinated (C) afferents may respond to mechanical and thermal stimuli applied to the cut nerve end. Here, 5-24 h after sural nerve ligation and transection we studied the ectopic excitability of axotomised cutaneous A and C fibres by chemical agents, most of which excite afferent terminals in skin.

Neomycin and gadolinium applied to an L5 spinal nerve lesion prevent mechanical allodynia-like behaviour in rats.

In male Wistar rats, the left ventral ramus of the L5 spinal nerve (RvL5) was cut, and animals were tested for allodynia-like behaviour in response to mechanical stimuli which were applied with von Frey hairs (4.3-205 mN) to the plantar skin of the hindpaw supplied by the intact L4 spinal nerve. After surgery, allodynia-like behaviour was evoked prominently on the operated (left) side and weakly on the contralateral (right) side.