Further evidence for ‘pain-related’ behaviours in a model of unilateral peripheral mononeuropathy

Abstract

A model of experimental peripheral neuropathy producing pain-related disorders has recently been described in the rat. The present study aimed to investigate, using a different and quantifiable behavioural approach, the abnormal pain-related sensations in the animals. The neuropathy was produced by 4 ligatures tied loosely around the common sciatic nerve. 6-8 days after surgery, most of the rats exhibited pain-related disorders ipsilateral to the sciatic ligation, which became maximal 2 weeks after surgery. Mechanical noxious stimulation (pinching of the hind paw) revealed hyperalgesia in all the animals. Rats also exhibited allodynia when tested with the vocalization threshold test to paw pressure (mean vocalization thresholds were 65.5 +/- 3.6% of the preoperative control, P less than 0.01, n = 95). Tests using heat (40, 42, 44, 46 degrees C) and cold (10 degrees C) stimulation (immersion of the rat's hind paw in a bath until it was observed to struggle) indicated hyperalgesia to noxious heat (decrease of 30% in the immersion duration (ID) at a temperature of 46 degrees C), and allodynia to non-noxious heat (decrease of 30% in the temperature of the struggle threshold) and to cold stimulation (decrease by 40% in the ID). In addition, the animals showed modifications in the spontaneous postures of the affected hind paw in a natural setting, suggesting a 'spontaneous' pain-related behaviour (the mean 'pain' rating, derived from the technique used for the formalin test and numbered 0-5, was 2.8 +/- 0.4, P less than 0.01, n = 12). Lastly, sensitized responses were observed to mechanical stimulation after thermal stimulation in the non-noxious range applied to the lesioned but not the non-lesioned paw. The time course of pain-related disorders was comparable whatever the behavioural test, with recovery 2 months after surgery. These results clearly show that the neuropathy produces abnormal pain-related disorders in the rat, which are reminiscent of those observed in some human neuropathies.

Bilateral behavioral and regional cerebral blood flow changes during painful peripheral mononeuropathy in the rat

“…The behaviors indicative of spontaneous chronic pain have been well characterized (Bennett and Xie, 1988;Attal et al, 1990;Kupers et al, 1992). Briefly, the CCI rats displayed prominent guarding of the affected hind paw, in a manner similar to that described by previous reports.…”

“…Resting paw posture-The resting paw posture of each hind paw of each animal was observed without intervention by the experimenter using the method from Attal et al (1990). Each animal was placed in clear rectangular Plexiglas cage (20 cm wide × 60 cm long × 20 cm high) and allowed to habituate for 15 min.…”

Soft Tissue Repair Capacity after Oxygen-Derived Free Radical-Induced Damage in One Hindlimb of the Rat

“…During a 5-min period, the time of different positions of the lesionedpaw was noted, according to the scale of Attal et al [21] which varied from 0 (the operated paw is pressed normally on the floor) to 5 (the animal licks the operated paw). The spontaneous pain was calculated by the formula t1 -f 21% 4-St3 + 4/4 + 5^/300 sec, where ti, t2, ia, tA, and ¿5 are the times (in sec) spent in categories 1, 2, 3, 4, or 5, respectively.…”

Increased Expression of Cutaneous α1-Adrenoceptors After Chronic Constriction Injury in Rats

“…Chronic constriction injury (CCI) of the rat sciatic nerve triggers signs of pain and hyperalgesia as early as 24 hours post-injury 3,5,9,18 , together with neurodegeneration of sensory nerve fibers in the injured sciatic nerve and the skin. The injured nerve fibers regenerate gradually in the weeks following injury, resulting in a de novo, spatially intimate association of sprouting sympathetic efferent fibers and sensory afferent fibers in the upper dermis 25-27, 37, 51 .…”