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Abstract
Chronic peripheral inflammation or peripheral neurectomy cause changes in GABA levels
and GABA immunoreactivity in the spinal cord dorsal horn. The present study aimed
to investigate if such changes are accompanied by alterations in GABA receptor binding.
Neurectomy of the sciatic nerve caused an ipsilateral down-regulation of GABAB receptor
binding in lamina II of the spinal cord 2-4 weeks after the nerve injury. Since approximately
50% of GABAB receptor binding in that region is located on primary afferent endings,
degenerative changes of such endings caused by the nerve lesion can explain the observed
reduction. In contrast, GABAA binding was substantially enhanced following neurectomy,
which may be due to an up-regulation of the receptors issued by the concomitant decrease
of endogenous GABA. In rats bearing unilateral chronic peripheral inflammation induced
by intraarticular injection of complete Freund's adjuvant we found a reduction of
GABAB binding in the superficial dorsal horn. This effect, which was maximal at 3-4
weeks after adjuvant injection, was attributed to an enhanced release of GABA by spinal
interneurons. GABAA receptor binding was not changed in this experimental model. Together,
these results suggest that the two receptor types may be located at different loci
and are differently affected by variations in sensory input.