Effect of lutein on the acute inflammation‐induced c‐Fos expression of rat trigeminal spinal nucleus caudalis and C1 dorsal horn neurons.

Although lutein is known to inhibit chronic inflammation, its effect on acute inflammation‐induced nociceptive processing in the trigeminal system remains to be determined. The aim of the present study was to investigate whether pretreatment with lutein attenuates acute inflammation‐induced sensitization of nociceptive processing in rat spinal trigeminal nucleus caudalis (SpVc) and upper cervical (C1) dorsal horn neurons, via c‐Fos immunoreactivity. Mustard oil, a transient receptor potential ankyrin‐1 channel agonist, was injected into the whisker pads to induce inflammation. Pretreatment of rats with lutein resulted in significant decreases in the inflammation‐induced mean times of face grooming and the thickness of inflammation‐induced edema in whisker pads relative to those features in inflamed rats (i.e., rats with no lutein pretreatment). In both the ipsilateral superficial and deep laminae of the SpVc and C1 dorsal horn, there were significantly larger numbers of c‐Fos‐positive neurons in inflamed rats than in naïve rats, and lutein pretreatment significantly decreased that number relative to inflamed rats. These results suggest that systemic administration of lutein attenuates acute inflammation‐induced nocifensive behavior and augmented nociceptive processing of SpVc and C1 neurons that send stimulus localization and intensity information to higher pain centers. These findings support lutein as a potential therapeutic agent for use as an alternative, complementary medicine to attenuate, or even prevent, acute inflammatory pain. [ABSTRACT FROM AUTHOR]