(A) Transverse section of an uninjured spinal cord at mid-thoracic region demonstrates normal innervation pattern of serotonergic pathway (5-HT positive fibers) within the spinal cord. (B) Higher magnification of the boxed area in A shows the presence of serotonergic fibers in the gray matter areas representing of the signal that was quantified in our assessments. (C–G) At 7 weeks post-injury, 5-HT positive fibers in all experimental groups show significant changes in their localization (images shown for 1.5 mm rostral). In contrast to uninjured spinal cord, 5-HT immunoreactive fibers were sprouting in different regions of white matter in all injured groups. (D) Higher magnification of the boxed area in C shows the presence of serotonergic fibers in the white matter areas representing of the signal that was quantified in our assessments (H) Quantification of 5-HT immunointensity in the entire cross section of the spinal cord (traced areas in images) at various rostral and caudal distances revealed significantly increased level of 5-HT immunoreactivity in ChABC+GFs/trained group compared to both vehicle treated group at all examined rostral and caudal distances (*p<0.05, Two-way ANOVA, Holm-Sidak post hoc, n = 3–6). Interestingly, at the epicenter and 1.5 mm rostral and caudal distances, the ChABC+GFs/untrained group also showed a significantly higher expression of 5-HT-immunoreactivity compared to the vehicle treated groups (*p<0.05, Two-way ANOVA, Holm-Sidak post hoc).