Brain research
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By using the microdialysis technique, the concentration of noradrenaline (NA) in the dorsal horn during unilateral hindpaw inflammation was compared between rats receiving bilateral lesions of the locus coeruleus (LC) and non-operated control rats. Bilateral lesions of the LC were made using an anodal current one week before testing. Unilateral hindpaw inflammation was produced by a subcutaneous injection of carrageenan (6 mg in 0.15 ml saline). ⋯ After carrageenan injection, in the non-operated rats, the NA level increased significantly compared to the baseline level only in the dorsal horn ipsilateral to the site of inflammation, but not in the dorsal horn contralateral to the site of inflammation. An increase of the NA level was not observed in the LC-lesioned rats and in rats receiving an injection of saline. The result suggests that unilateral hindpaw inflammation produces excitation of descending NA-containing neurons from the LC, resulting in an increase of the NA level in the dorsal horn ipsilateral to the site of inflammation.