J Korean Pain Soc.  2002 Jun;15(1):48-57.

Involvement of Ionotropic, rather than Metabotropic, Glutamate Receptors in Hyperexcitability of Spinal orsal Neurons Induced after Spinal Cord Injury

• Gwak YS
• Shim B
• Yoon DM
• Nam TS
• Paik KS
• Leem JW

Abstract

BACKGROUND: Spinal cord injury (SCI) induces the development of central neuropathic pain which is characterized by symptoms such as allodynia, hyperalgesia, and spontaneous pain. However, the underlying mechanism is not fully understood. This study was conducted to see if activation of the glutamatergic system in the spinal dorsal horn is involved in the development of central pain following SCI.
METHODS
SCI was induced by a hemisection of the spinal cord at T13 in adult, male, Sprague-Dawley rats. Mechanical allodynia was tested by measuring paw withdrawal frequency in response to repeated applications of a von Frey hair to the plantar surface of the hind paw. Single neuronal activity of dorsal horn neurons (L4-L6) was recorded extracellularly using a carbon filament-filled glass microelectrode (2 4 M omega). The drugs were intrathecally and topically administrated on the spinal surface for behavioral and electrophysiological study, respectively.
RESULTS
After left spinal hemisection at T13, behavioral signs of mechanical allodynia developed on both hind limbs and the responsiveness of spinal dorsal horn neurons increased on both sides of the spinal dorsal horn. Ionotropic glutamate receptor antagonists including MK-801 (NMDA receptor antagonist) and NBQX (non-NMDA receptor antagonist) suppressed mechanical allodynia and increased responsiveness on both hind paws. Metabotropic glutamate receptor antagonist MCPG, however, had no significant effect.
CONCLUSIONS
These results indicate that activation of the ionotropic, but not metabotropic, glutamatergic system in the spinal cord plays a key role in the development of central pain following SCI.

Keyword

Central pain; MCPG; MK-801; NBQX; Spinal cord injury

MeSH Terms

Adult
Animals
Carbon
Dizocilpine Maleate
Excitatory Amino Acid Antagonists
Extremities
Glass
Glutamic Acid*
Hair
Horns
Humans
Hyperalgesia
Male
Microelectrodes
Neuralgia
Neurons*
Posterior Horn Cells
Rats, Sprague-Dawley
Receptors, Glutamate*
Receptors, Metabotropic Glutamate
Spinal Cord Injuries*
Spinal Cord*
Carbon
Dizocilpine Maleate
Excitatory Amino Acid Antagonists
Glutamic Acid
Receptors, Glutamate
Receptors, Metabotropic Glutamate