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Tryptophan hydroxylase and serotonin in spinal cord and brain stem before and after chronic transection

THE SPINAL cord of vertebrates contains appreciable amounts of serotonin (AMIN, CRAWFORD and GADDUM, 1954; CARLSSON, MAGNUSON and ROSENGREN, 1963; CARLSSON, FALCK, FUXE and HILLARP, 1964; ANDEN, 1965; ANDERSON and HOLGERSON, 1966). Serotonin in spinal cord is believed to be exclusively localized in descending axons from neurons whose cell bodies lie in the raphi nuclei of the brain stem (CARLSSON et al. 1964; DAHLSTROM and FUXE, 1964, 1965). However, recent neuropharmacological evidence indicates that there may be serotoninergic interneurons in the spinal cord (CLINESCHMIDT and ANDERSON, 1970). In another recent report, AZMITIA, ALGERI and COSTA (1970) have suggested that the brain stem level of tryptophan hydroxylase exceeds the amount required to maintain the steady-state level of serotonin, perhaps because the brain stem contains mostly cell bodies where the enzyme presumably is synthesized. The present study on tryptophan 5-hydroxylase (EC 1.99.1.4) and serotonin in brain stem and spinal cord of normal and transected animals was undertaken to obtain information pertaining to the possibility of serotonincontaining interneurons in spinal cord and to compare the ratios of the enzyme to the amine in an area rich in cell bodies with an area containing axons many cm removed from their cell bodies.