Growth of central substance P-containing neurons into superior cervical ganglia transplanted in the spinal cord of adult rats

Abstract

Superior cervical ganglia (SCG) contain substance P-like immunoreactive (SP-IR) fibers but not SP-IR neurons. In the present study, SCG were excised from adult rats and transplanted into the same animal's spinal thoracic cord (Th10). One or two weeks after the operation, SP-IR fibers from the host spinal cord or a higher level had grown and entered the transplanted SCG where they formed direct contacts with SCG neurons. However, these phenomena could not be observed when dorsal root ganglia (L4), which contained numerous SP-IR cells, were transplanted into their own spinal cord (Th10). This suggests that the SP-IR neuron system in the adult is able to grow ‘new axons’ to the grafted tissue to form a ‘new SP-IR’ neuronal circuit when the grafted tissue has lost its own SP-IR input.