J Korean Pain Soc.  2001 Jun;14(1):1-6.

Molecular Biologic Study on the Role of Glutamate in Spinal Sensitization

• Kim HK
• Jung JS
• Baik SW

Abstract

BACKGROUND: Subcutaneous injection of 5% formalin into the hind paw of the rat produces a biphasic nociceptive response. The second phase depends on changes in the dorsal horn cell function that occur shortly after an initial C-fiber discharge, spinal sensitization, or windup phenomenon. This study was performed to investigate the role of glutamate during spinal sensitization.
METHODS
Sprague-Dawley rats weighing 200 to 250 g were used for this study. Under light anesthesia (0.5% isoflurane) the rats were segregated in a specially designed cage and 50microliter 0.5% formalin was injected subcutaneously in the foot dorsum of right hindlimb. Forty minutes after the formalin injection, the rat was quickly decapitated and spinal cord was removed. The spinal segments at the level of L3 (largest area) was collected and stored in a deep freezer (-70degrees C). The mRNA gene expression of N-methyl-D-aspartate receptor (NMDAR) and the metabotropic glutamate receptor subtype 5 (mGluR5) were determined by the polymerase chain reaction.
RESULTS
The number of flinches was 19.8+/-2.3/min. at one minute after formalin injection and decreased to zero after then. The second peak appeared at 35 and 40 minutes after formalin injection. The values were 17.8+/-2.2 and 17.2+/-3.0/min. The mRNA gene expressions of NMDAR and mGluR5 were increased by 459.0+/-46.8% (P < 0.01) and 111.1+/-4.8% (P > 0.05) respectively at 40 minutes after formalin injection. The increased rate of NMDAR was significantly higher than that of mGluR5 (P < 0.01).
CONCLUSION
From these results, it suggested that NMDAR partly contributed to the mechanism of central sensitization after the formalin test but mGluR5 did not.

Keyword

Central sensitization; Formalin test; mGluR5; NMDAR; Spinal cord

MeSH Terms

Anesthesia
Animals
Central Nervous System Sensitization
Foot
Formaldehyde
Gene Expression
Glutamic Acid*
Hindlimb
Injections, Subcutaneous
N-Methylaspartate
Pain Measurement
Polymerase Chain Reaction
Posterior Horn Cells
Rats
Rats, Sprague-Dawley
Receptors, Metabotropic Glutamate
RNA, Messenger
Spinal Cord
Formaldehyde
Glutamic Acid
N-Methylaspartate
RNA, Messenger
Receptors, Metabotropic Glutamate