LAR peptide promoted sprouting of modulatoiy serotonergic axons within the PhMN pool. At 8 weeks after hemisection SCI, we assessed the density of serotonergic axon innervation of the PhMN pool on the side of injury by performing immunohistoehemistry for serotonin (5-HT) and quantifying the total length of 5-HT+ axons. Sagittal sections of the cervical spinal cord show that, compared to DMSO-only control (A), LAR peptide significantly increased 5-HT axon sprouting within the ipsilateral phrenic nucleus at C3 (B—C) at 8 weeks post-injury (n = 6 animals per group, *P = 0.02). However, LAR peptide did not affect the density of 5-HT axon innervation of the ipsilateral PhMN pool at C4 (D; P = 0.42) or C5 (E; P = 0.44). Scale bar: 100 μm. Arrowheads indicate 5-HT+ axons.