Figure 2

Distribution of GLP-1R- and GLP-1-immunoreactivity in the spinal cord. (a) Overview images of peroxidase immunohistochemistry (Ni-DAB) show the distribution of GLP-1R protein in cervical, thoracic, lumbar and sacral segments of the spinal cord. The arrows indicate the fiber bundles of CSF-contacting neurons in the ventral funiculus. High magnification images of the boxed areas are shown in (b–h). (b) GLP-1R labeling of small-sized perikarya (arrows) and processes in laminae II–III. (c) Beaded axons in lamina IX aggregate into dense patches in the tip of the ventral horn in the cervical enlargement. (d) GLP-1R perikarya in a dense network of varicose axons in the medial part of lamina V. (e) Intensely labeled perikarya and processes in lamina VIII of the thoracic segment. (f) GLP-1R labeling of a cell body and its long dendrites in lamina VII. (g) Perikarya and a network of dendrites in the sacral dorsal commissural nucleus. (h) Intense GLP-1R labeling of CSF-contacting neurons and their dendritic bulbs in the lumen of the central canal. (i) GLP-1 immunohistochemistry in a mid-thoracic segment of the spinal cord. Varicose GLP-1 axons provide moderate to dense innervation to the gray matter from the deep dorsal horn to the ventral horn, and the ventral funiculus. The more superficial layers of the dorsal horn (laminae I–III) receive only sparse GLP-1 fibers. (j) High magnification image of a varicose GLP-1 axon from the ventral horn. (k) Schematic drawings demonstrate the distribution density of GLP-1 fibers in cervical, thoracic, lumbar and sacral segments. Circles represent varicose GLP-1 axonal segments, lines represent some longer varicose segments. Abbreviations: cc, central canal; DH, dorsal horn; SDCom, sacral dorsal commissural nucleus; vf, ventral funiculus; VH, ventral horn.