Fig. 2

Quantification of rostral–caudal tracer fluorescence (mean fluorescence intensity) per spinal level after grey (n = 10) and white (n = 10) matter injections at 20 min (a, left panel) and at 60 min (b, right panel). Each spinal cord level (“Level”) is expressed as the number of levels rostral (positive integers) or caudal (negative integers) to injection site. All error bars are expressed as ± SEM. In both white and grey matter injections at both time points, there was a sharp drop off of tracer fluorescence within 2 levels rostral and caudad to the injection. At the 20 min time point a, there was no difference in fluorescence intensity between white and grey matter injections, but on post hoc analysis a significant difference was reached at − 1 level caudal to the injection site (*p = 0.0341). At the 60 min time point b, fluorescence intensity was significantly higher in the white matter injections compared to the grey matter injections (p = 0.0026). On post hoc analysis significant differences were observed at + 1 and + 2 levels rostral to the injection point (*p = 0.0448 and 0.0259 respectively)