J Korean Pain Soc.  1998 May;11(1):23-29.

Suppression by Microinjection of Bicuculline into Brain Stem Nuclei of Dorsal Horn Neuron Responsiveness in Neuropathic Rats

• Leem JW
• Choi Y
• Lee JH
• Nam TS
• Paik KS

Abstract

BACKGROUND: The present study was conducted to investigate effects of mieroinjection of bicuculline, GABA-A receptor antagonist, into the brain stem nuclei on the dorsal horn neuron responsiveness in rats with an experimental peripheral neuropsthy.
METHODS
An experimental neuropathy was induced by a unilateral ligation of L5-L6 spinal nerves of rats. After 2-3 weeks after the surgery, single-unit recording was made from wide dynamic range (WDR) neurons in the spinal cord dorsal horn.
RESULTS
Responses of WDR neurons to both noxious and innocuous mechanical stimuli applied to the somatic reeeptive fields were enhanced on the nerve injured side. These enhanced responsiveness of WDR neurons were suppressed by microinjection of bicuculline into periaqueductal gray(PAG) or nucleus reticularis gigantocellularis(Gi). A similar suppression was also observed when morphine was microinjected into PAG or Gi. Suppressive actian by Gi-bicuculline was reversed by naloxonazine, p -opioid receptor antagonist, microinjected into PAG whereas PAG-bicuculline induced suppression was not affected by naloxonazine injection into Gi. Gi-bicuculline induced suppression were reversed by a transection of dorsolateral funiculus(DLF) of the spinal cord.
CONCLUSION
The results suggest that endogenous opioids, via acting on GABAergic interneurons in PAG and Gi, may be involved in the control of neuropathic pain by activating the descending inhibitory pathways that project to the spinal dorsal horn through DLF to inhibit the responsiveness of WDR neurons.

Keyword

Bicuculline; Descending inhibition; GABAergic system; Neuropathic pain

MeSH Terms

Analgesics, Opioid
Animals
Bicuculline*
Brain Stem*
Brain*
GABA-A Receptor Antagonists
Horns
Interneurons
Ligation
Microinjections*
Morphine
Neuralgia
Neurons
Posterior Horn Cells*
Rats*
Spinal Cord
Spinal Nerves
Analgesics, Opioid
Bicuculline
GABA-A Receptor Antagonists
Morphine