Brain monoamines during carrageenan-induced acute paw inflammation in rats

Paw inflammation was induced in rats by sub-plantar administration of carrageenan. Significant inflammatory oedema was observed 1 h later and the peak effect was noted between 3-4 h. The oedema was markedly reduced after 12-24 h. Steady state levels of whole brain and hypothalamic monoamines were estimated spectrofluorometrically during the course of the carrageenan-induced paw inflammation. In addition, the rate of accumulation of the brain 5-hydroxytryptamine (5-HT) and noradrenaline (NA) was assessed in clorgyline-pretreated rats during the inflammation. The whole brain and hypothalamic concentrations of 5-HT and NA were augmented during the early phase of the inflammation, but fell below control values when peak inflammation was achieved. Thereafter, the monoamine levels tended to normalize by 24 h when the inflammation had virtually subsided. On the contrary, whole brain and hypothalamic dopamine levels remained largely unaffected. The rate of accumulation of brain 5-HT and NA were enhanced during carrageenan inflammation, indicating that the turnover of these monoamines is augmented during the inflammatory process. The results suggest that acute peripheral inflammation may significantly affect central 5-HT and noradrenergic activity in rats.