Activation of spinal GABA receptors attenuates chronic central neuropathic pain after spinal cord injury.

Abstract

In this study, we investigated the role of the spinal GABAergic system in central neuropathic painlike outcomes following spinal cord injury (SCI) produced by a spinal hemitransection at T13 of the rat. After SCI, mechanical allodynia develops bilaterally in both hind paws of the rat, lasting longer than 40 days, as evidenced by an increase in paw withdrawal frequency in response to a weak von Frey filament. In naive rats, intrathecal (i.t.) administration in the lumbar spinal cord of GABAA and GABAB receptor antagonists, bicuculline (1-5 microg) and phaclofen (0.1-5 microg), respectively, causes a dose-dependent increase in the magnitude of mechanical allodynia. The SCI-induced mechanical allodynia in both hind-paws is attenuated by i.t. administration in the lumbar spinal cord of GABAA or GABAB receptor agonists, muscimol (1 microg) or baclofen (0.5 microg), respectively. In electrophysiological experiments, rats with SCI show a bilateral increase in hyperexcitability in response to natural stimuli in wide dynamic range (WDR) neurons in the lumbar spinal dorsal horn. The topical application of muscimol (1 microg) or baclofen (0.5 microg) onto the lumbar cord surface reduce the SCIinduced increased responsiveness of WDR neurons. Inhibitory effects of muscimol and baclofen on both the behavioral mechanical allodynia and the hyperexcitability in WDR neuron with SCI compared to controls, were antagonized by pre-treatment of bicuculline (10 microg) and phaclofen (5 microg), respectively. This study provides behavioral and electrophysiological evidence for the important role of the loss of spinal inhibitory tone, mediated by activation of both GABAA and GABAB receptors, in the development of central neuropathic pain following SCI.

• Authors: Young Seob Gwak, Huai Yu Tan, Taick Sang Nam, Kwang Se Paik, Claire E Hulsebosch, Joong Woo Leem
• Journal: Journal of neurotrauma (J Neurotrauma) Vol. 23 Issue 7 Pg. 1111-24 (Jul 2006) ISSN: 0897-7151 [Print] United States
• PMID: 16866624 (Publication Type: Comparative Study, Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)

Chemical References

• GABA Antagonists
• Receptors, GABA

Topics

• Animals
• GABA Antagonists (pharmacology)
• Male
• Pain (etiology, metabolism, prevention & control)
• Pain Measurement (drug effects, methods)
• Rats
• Rats, Sprague-Dawley
• Receptors, GABA (metabolism)
• Spinal Cord (drug effects, metabolism)
• Spinal Cord Injuries (complications, metabolism)