Fig. 4
Reversal by daily lutein administration of SpVc WDR neuronal hyperactivity after CFA induction of inflammation. a-c General characteristics of spinal trigeminal nucleus caudalis (SpVc) wide-dynamic range (WDR) neuronal activity responses in orofacial skin. a Receptive field of whisker pad in the facial skin. b Distribution of SpVc WDR neurons responding to non-noxious and noxious mechanical stimulation of facial skin (n = 15). The number below each drawing indicates the frontal plane in relation to the obex. c Typical example of non-noxious and noxious mechanical stimulation-induced firing of SpVc WDR neurons. d Lutein administration reversed the hyperactivity of SpVc WDR neuronal activity after orofacial CFA inflammation. Example of non-noxious and noxious mechanical stimulation-induced discharge of SpVc WDR neurons in naïve, inflamed, and inflamed with lutein administration (10 mg/kg, i.p.) rats. Note that the decreased mechanical stimulation threshold needed to evoke neuronal firing, increased spontaneous discharges, increased size of receptive field, and occurrence of noxious pinch-evoked discharges in the inflamed rats were reversed to control levels following lutein administration. e Comparison of mean discharge frequency of SpVc WDR neurons evoked by mechanical stimulation (non-noxious and noxious) of whisker pad among three groups of rats. *, P < 0.05, naïve vs. inflamed rats and inflamed vs. inflamed with lutein *, P < 0.05, naïve vs. inflamed rats, inflamed vs. inflamed with lutein. f Comparison of mean mechanical thresholds of SpVc WDR neurons among three groups of rats. *, P < 0.05, naïve vs. inflamed rats and inflamed vs. inflamed with lutein. g Comparison of mean spontaneous discharges of SpVc WDR neurons among three groups of rats. *, P < 0.05, naïve vs. inflamed rats and inflamed vs. inflamed with lutein. h Comparison of mean noxious pinch-evoked after-discharge frequencies of SpVc WDR neurons among three groups of rats. *, P < 0.05, naïve vs. inflamed rats and inflamed vs. inflamed with lutein. i Comparison of mean receptive field size of SpVc WDR neurons among three groups of rats. *, P < 0.05, naïve vs. inflamed rats and inflamed vs. inflamed with lutein