COMPLEX CHANGES OF GABA(A) AND GABA(B) RECEPTOR-BINDING IN THE SPINAL-CORD DORSAL HORN FOLLOWING PERIPHERAL INFLAMMATION OR NEURECTOMY

Chronic peripheral inflammation or peripheral neurectomy cause changes in GABA levels and GABA immunoreactivity in the spinal cord dorsal ho rn. The present study aimed to investigate if such changes are accompa nied by alterations in GABA receptor binding. Neurectomy of the sciati c nerve caused an ipsilateral down-regulation of GABA(B) receptor bind ing in lamina II of the spinal cord 2-4 weeks after the nerve injury. Since approximately 50% of GABA(B) receptor binding in that region is located on primary afferent endings, degenerative changes of such endi ngs caused by the nerve lesion can explain the observed reduction. In contrast, GABA(A) binding was substantially enhanced following neurect omy, which may be due to an up-regulation of the receptors issued by t he concomitant decrease of endogenous GABA. In rats bearing unilateral chronic peripheral inflammation induced by intraarticular injection o f complete Freund's adjuvant we found a reduction of GABA(B) binding i n the superficial dorsal horn. This effect, which was maximal at 3-4 w eeks after adjuvant injection, was attributed to an enhanced release o f GABA by spinal interneurons. GABA(A) receptor binding was not change d in this experimental model. Together, these results suggest that the two receptor types may be located at different loci and are different ly affected by variations in sensory input.