Substance P and enkephalin containing fibers in the developing nucleus dorsalis of the human spinal cord

A peroxidase-antiperoxidase immunostaining method was employed to determine the initial stage of appearance and localization of substance P (SP) and e nkephalin (ENK) in the nucleus dorsalis of the developing human spinal cord . Both SP- and ENK-positive fibers started to appear from the 10th week of gestation in regions surrounding the nucleus dorsalis. SP-positive fibers t hen reached the nucleus at 13 weeks and from 26 weeks to term, three strand s of SP-positive fibers, which were predominantly originated from the super ficial layers of the dorsal horn, penetrated into the nucleus dorsalis from its medial, median and lateral aspects. From 26 weeks onwards, ENK-positiv e fibers, originated from the superficial and the adjacent layers of the sp inal cord, formed a thicker medial and a thinner lateral bundle projecting into the nucleus dorsalis. Our results show that both SP- and ENK-positive fibers started to appear at around 10 weeks and a consistent pattern of imm unoreactivity was established by around 26-30 weeks of gestation. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.