Figure 10. Exposure to green light emitting diode (GLED) reverses thermal hyperalgesia and mechanical allodynia induced in a model of neuropathic pain.

(A) Seven days following a spinal nerve ligation (SNL) surgery on their left hind paw, rats (n=6 per group for all groups throughout this figure) displayed a significant decrease in their paw withdrawal latencies (PWLs, seconds), which was completely reversed by daily eight hours exposure to GLED exposure (4 lux). #p<0.05 when comparing to BL, *p<0.05 when comparing to BL or SNL (one-way ANOVA followed by Student-Newman-Keuls test). (B) Bar graph of paw withdrawal thresholds (PWTs, grams) of rats after receiving a SNL injury and after GLED exposure for 3 days (4 lux, 8 hours per day). BL indicates the baseline PWT before GLED exposure. PWTs were completely reversed 3 days of GLED exposure compared to post-surgery (post-Sx) levels. #p<0.05 compared to BL (one-way ANOVA followed by Student-Newman-Keuls test). Time course of return to baseline for PWLs (C) and PWTs (D). Some error bars are smaller than the bars. (E) Quantitative RT-PCR for the indicated genes from spinal cords of naïve rats as well rats with SNL + GLED or Sham + GLED. The mRNA levels for each gene were normalized to L27 mRNA (a ribosomal internal control gene). The L27-normalized values for each condition were divided by the L27-normalized values for naïve and are expressed as fold change over naïve levels. Data represent mean fold change ± S.E.M. (n=3 for each). A robust upregulation of PENK mRNA was observed in SNL + GLED or Sham + GLED condition (*, p<0.05, Student’s t-test vs. control).