Models of Pain: Hot‐Plate and Formalin Test in Rodents

Anthony W. Bannon1

1 Amgen Inc., Thousand Oaks, California
Publication Name:  Current Protocols in Pharmacology
Unit Number:  Unit 5.7
DOI:  10.1002/0471141755.ph0507s00
Online Posting Date:  May, 2001
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Abstract

Experimental models of pain can be separated into three basic categories: acute, persistent, and neuropathic. Acute pain is modeled by the hot‐plate test, persistent pain by the formalin test, and neuropathic pain by nerve ligation. The neurotransmitters and neuromodulators that mediate the pain response in each of these models can differ. As a result, different drugs may be effective in attenuating pain for each model. A basic understanding of the mechanisms involved in the pain response can help investigators choose the model that would be most appropriate for testing the analgesic properties of specific compounds or classes of compounds. This unit presents protocols for both an acute model of pain using the hot‐plate test, and a persistent model of pain using the formalin test. Each protocol describes the preparation of animals (mice or rats) for the test, administration of a compound being tested for its analgesic properties, and data collection.

     
 
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Table of Contents

  • Basic Protocol 1: Measurement of Acute Pain Using the Hot‐Plate Test
  • Basic Protocol 2: Measurement of Persistent Pain Using the Formalin Test
  • Reagents and Solutions
  • Commentary
  • Literature Cited
  • Figures
  • Tables
     
 
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Materials

Basic Protocol 1: Measurement of Acute Pain Using the Hot‐Plate Test

  Materials
  • Animal: 30‐ to 35‐g male CD mice, group‐housed (e.g., Charles River Labs)
  • Test compounds in saline or other appropriate vehicle
  • Reference analgesic compound (e.g., morphine, to be given 10 mg/kg, i.p.)
  • 1‐ml syringes with 27‐G needles
  • Hot‐plate apparatus or metal plate in a controlled temperature water bath
  • Stopwatch or timer

Basic Protocol 2: Measurement of Persistent Pain Using the Formalin Test

  Materials
  • Animal: 250‐g male Sprague‐Dawley rats, group‐housed (e.g., Charles River Labs)
  • Test compounds in saline or appropriate vehicle
  • 5% formalin (see recipe)
  • Individual clear containers to hold animals (e.g., shoebox cages with tops; see Fig. )
  • Mirrors
  • 0.5‐ml syringes with 28.5‐G needles
  • 1‐ml syringes with 27‐G needles
  • Hand‐held counters (1 for each rat)
  • Clock or timer
  • Electronically controlled timing lights (optional)
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Figures

Videos

Literature Cited

Literature Cited
   Bannon, A.W., Gunther, K.L., and Decker, M.W. 1995. Is epibatidine really analgesic? Dissociation of the locomotor activity, temperature, and analgesic effects of (±)‐epibatidine. Pharmacol. Biochem. Behav. 51:693‐698.
   Dubuisson, D. and Dennis, S.G. 1977. The formalin test: A quantitative study of the analgesic effects of morphine, meperidine, and brain stem stimulation in rats and cats. Pain 4:161‐174.
   Hargreaves, K., Dubner, R., Brown, F., Flores, C., Jorrs, J. 1988. A new sensitive method for measuring thermal nociception in cutaneous hyperalgesia. Pain 32:77‐88.
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