Region-specific increase in glutamate release from dorsal horn of rats with adjuvant inflammation

Glutamate is considered an important pain transmitter and responsible for inflammatory hyperalgesia, but quantitative and topographical changes in glutamate release in the dorsal horn during peripheral inflammation have not been characterized. To address this issue, image analysis with a confocal laser scanning microscope was performed for quantitatively mapping capsaicin-evoked glutamate release from the lumbar cord slice of rats following unilateral adjuvant inoculation to the hind-paw. Capsaicin induced glutamate release from laminae I, II and X in the spinal cord of the adjuvant-treated and untreated sides, without apparent release from laminae III-V. The concentration of released glutamate in laminae I, II and X was higher on the adjuvant-treated side than on the untreated side. The results suggest that adjuvant inflammation increases glutamate release from capsaicin-sensitive primary afferents in laminae I, II and X.