Chronic Post-Ischemia Pain Model for Complex Regional Pain Syndrome Type-I in Rats

Summary

Provided here is a protocol that details steps to establish an animal model of chronic post-ischemia pain (CPIP). This is a well-recognized model mimicking human complex regional pain syndrome type-I. Mechanical and thermal hypersensitivities are further evaluated, as well as capsaicin-induced nocifensive behaviors observed in the CPIP rat model.

Abstract

Complex regional pain syndrome type-I (CRPS-I) is a neurological disease that causes severe pain among patients and remains an unresolved medical condition. However, the underlying mechanisms of CRPS-I have yet to be revealed. It is known that ischemia/reperfusion is one of the leading factors that causes CRPS-I. By means of prolonged ischemia and reperfusion of the hind limb, the rat chronic post-ischemia pain (CPIP) model has been established to mimic CRPS-I. The CPIP model has become a well-recognized animal model for studying the mechanisms of CRPS-I. This protocol describes the detailed procedures involved in the establishment of the rat model of CPIP, including anesthesia, followed by ischemia/reperfusion of the hind limb. Characteristics of the rat CPIP model are further evaluated by measuring the mechanical and thermal hypersensitivities of the hind limb as well as the nocifensive responses to acute capsaicin injection. The rat CPIP model exhibits several CRPS-I-like manifestations, including hind limb edema and hyperemia in the early stage after establishment, persistent thermal and mechanical hypersensitivities, and increased nocifensive responses to acute capsaicin injection. These characteristics render it a suitable animal model for further investigation of the mechanisms involved in CRPS-I.

Introduction

Complex regional pain syndrome (CRPS) reprents complex and chronic pain symptoms resulting from fractures, trauma, surgery, ischemia or nerve injury^1,2,3. CRPS is classified into 2 subcategories: CRPS type-I and type-II (CRPS-I and CRPS-II)⁴. Epidemiological studies revealed that the prevalence of CRPS was approximately 1:2000⁵. CRPS-I, which shows no obvious nerve damage, can result in chronic pain and dramatically affects the life quality of the patients. Current available treatments show inadequate therapeutic effects. Theref....

Protocol

The animal protocols were approved by Zhejiang Chinese Medical University Animal Ethics Committee.

1. Animals

1. Obtain male Sprague-Dawley (SD) rats (280–320 g, 8-10 weeks of age) from Shanghai Laboratory Animal Center. House the animals in Zhejiang Chinese Medical University Laboratory Animal Center. Note that the breeding conditions should include 12 h/ 2h light/dark cycles and keep temperature constant at 24 °C. Provide water and food ad libitum. Note that a total of 48 rats are used in this study. One note, in this model, we need to observe the pain response during the whole process. If pain medication is a....

Results

After placing the O-ring on the ankle, the ipsilateral hind paw skin showed cyanosis, an indication of tissue hypoxia (Figure 1A). After cutting the O-ring, the ipsilateral hind paw began to fill with blood and showed robust swelling, which demonstrated an intense sign of hyperemia (Figure 1A). The paw swelling gradually diminished and returned to normal 48 h after the ischemic/reperfusion procedure (two-way ANOVA with Sidak pos.......

Discussion

This protocol describes the detailed methods for establishing a rat CPIP model by applying ischemia/reperfusion to hind limbs of the rats. It involves the evaluation of hind limb appearance, edema, mechanical/thermal hypersensitivities, and acute nocifensive behaviors in response to capsaicin injection.

Limb ischemia/reperfusion is a common factor contributing to CRPS-I in human patients¹². This protocol describes how to establish the rat CPIP model, which is a commonly.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1.5 ml Eppendorf tube	Eppendorf	22431021
DMSO	Sigma-Aldrich	D1435
Capsaicin	APEXBIO	A3278
Digital caliper	Meinaite	NA
O-ring	O-Rings West	Nitrile 70 Durometer	7/32 in. internal diameter
Plantar Test Apparatus	UGO Basile, Italy	37370
von Frey filaments	UGO Basile, Italy	NC12775