Electronmicroscopic detection of the axonal coexistence of serotonin and substance P in B1-B2 raphé cells transplanted into the transected spinal cord of adult rats.

One week after a complete spinal cord transection at the thoracic (T8) level in adult rats, a suspension of rhombencephalic embryonic (day 14) cells containing the B1-B2 serotonergic groups was injected below the section. After a survival period of one month, the spinal cord was processed for an ultrastructural dual immunocytochemical detection of serotonin (5-HT) and substance P (SP). It was shown by ultrastructural dual immunolabeling that 5-HT and SP coexist in the same axon terminals of transplanted cells.